MUSCUL AR
11
Axial
Muscles
SYSTEM
O U T L I N E
11.1 Muscles of the Head and Neck
11.1a
11.1b
11.1c
11.1d
11.1e
11.1f
11.1g
11.2
11.3
11.4
11.5
5
323
Muscles of Facial Expression 323
Extrinsic Eye Muscles 328
Muscles of Mastication 332
Muscles That Move the Tongue 332
Muscles of the Pharynx 334
Muscles of the Anterior Neck 335
Muscles That Move the Head and Neck
337
Muscles of the Vertebral Column 340
Muscles of Respiration 343
Muscles of the Abdominal Wall 345
Muscles of the Pelvic Floor 348
MODULE 6: MUSCUL AR SYSTEM
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Chapter Eleven
T
he artificial partitioning of the skeletal system into axial and
appendicular divisions provides a useful guideline for subdividing the muscular system as well. Axial muscles have both their
origins and insertions on parts of the axial skeleton. Axial muscles
support and move the head and spinal column, function in nonverbal communication by affecting facial features, move the lower
jaw during chewing, assist in food processing and swallowing, aid
breathing, and support and protect the abdominal and pelvic organs.
The axial muscles are not responsible for stabilizing or moving the
pectoral or pelvic girdles or their attached limbs; those are functions
of the appendicular muscles (see chapter 12). Some muscles of both
divisions are shown in figure 11.1.
Study Tip!
The following suggestions may help you learn the muscles, whether
axial or appendicular:
■
■
■
■
■
■
The axial muscles may be organized into groups based on their
location or function. Learning the muscles in groups is easiest.
When studying a particular muscle, try to palpate it on yourself.
Contract the muscle to sense its action and identify its regional
location.
Repeat the name of a muscle aloud to become familiar with its
name. It is easier to remember and spell terms that you can
pronounce.
Associate visual images from models, cadavers, a photographic
atlas, or dissected animals with muscle names. Connecting a
muscle name with direct observation will help you remember it.
Locate the origins and insertions of muscles on an articulated
skeleton. This helps you visualize the locations of muscles and
understand how they produce particular actions.
Learn the derivation of each muscle name because it usually
describes the muscle’s action, location, number of heads,
orientation of muscle fibers, shape, or size.
Refer to figure 10.14 for examples of how some muscles are named.
The axial muscles are organized into five groups based on
their location:
■
■
■
■
■
Muscles of the head and neck
Muscles of the vertebral column
Muscles of respiration
Muscles of the abdominal wall
Muscles of the pelvic floor
The discussion in this chapter has been organized according
to these specific groups. For each group, tables provide descriptions of the muscles as well as information about their action, origin, insertion, and innervation. (Note: The word innervation refers
to the nerve(s) that supplies a muscle and stimulates it to contract.
For further information about the nerves listed in the tables, see
chapters 15 and 16.)
11.1 Muscles of the Head and Neck
Learning Objectives:
1. Identify the major muscles involved in facial expression.
2. List the extrinsic muscles of the eye, and describe how
each affects eye movement.
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Axial Muscles
323
3. Name the muscles of mastication, and outline how each
affects mandibular movement.
4. Describe the movements of the tongue, and compare its
extrinsic and intrinsic muscles.
5. Identify the muscles of the pharynx, and explain their
function in swallowing.
6. Explain the organization and distribution of the muscles of
the anterior neck.
7. Detail the muscles involved in the major movements of the
head and neck.
The muscles of the head and neck are separated into several
specific groups, based on their location or general functions.
Almost all of these muscles (except for a few muscles of the
anterior neck) originate on either the skull or the hyoid bone.
11.1a Muscles of Facial Expression
The muscles of facial expression have their origin in the superficial fascia or on the skull bones (figure 11.2). These muscles
insert into the superficial fascia of the skin, so when they contract, they contort the skin, causing it to move. Most of these
muscles are innervated by the seventh cranial nerve (CN VII),
the facial nerve.
The epicranius is composed of the occipitofrontalis muscle
and a broad epicranial aponeurosis, also called the galea aponeurotica. The frontal belly of the occipitofrontalis is superficial to the
frontal bone on the forehead. When this muscle contracts, it raises
the eyebrows and wrinkles the skin of the forehead. The occipital
belly of the occipitofrontalis covers the posterior side of the head.
When this muscle contracts, it retracts the scalp slightly. Deep to
the frontal belly is the corrugator supercilii. This muscle draws
the eyebrows together and creates vertical wrinkle lines above the
nose. The orbicularis oculi consists of circular muscle fibers that
surround the orbit. When this muscle contracts, the eyelid closes,
as when you wink, blink, or squint. The levator palpebrae superioris (shown in figure 19.10) elevates the upper eyelid when you
open your eyes.
Several muscles of facial expression are associated with the
nose. The nasalis elevates the corners of the nostrils. When you
“flare your nostrils,” you are using the nasalis muscles. If you
wrinkle your nose in distaste after smelling a foul odor, you have
used your procerus muscle. This muscle is continuous with the
frontalis muscle, and it runs over the bridge of the nose, where it
produces transverse wrinkles when it contracts.
The mouth is the most expressive part of the face, and not
surprisingly the muscles in that area are very diverse. The orbicularis oris consists of muscle fibers that encircle the opening of
the mouth. When this muscle contracts, you close your mouth.
When you “pucker up for a kiss,” you are using this muscle. The
depressor labii inferioris does what its name suggests—it pulls
the lower lip inferiorly. The depressor anguli oris is considered
the “frown” muscle, because it pulls the corners of the mouth
inferiorly. (Note, however, that it takes more muscles than this
one to produce a frown!)
In contrast, some muscles of the mouth elevate part or all
of the upper lips. The levator labii superioris pulls the upper lip
superiorly, as if a person is sneering or snarling. The levator anguli
oris pulls the corners of the mouth superiorly and laterally. The
zygomaticus major and zygomaticus minor work with the levator
anguli oris muscles. You use these when you smile. The risorius
pulls the corner of the lips laterally; you use this muscle if you
make a closed-mouth smile.
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Chapter Eleven
Axial Muscles
Superficial
Deep
Frontal belly
of occipitofrontalis
Temporalis
Orbicularis oculi
Zygomaticus major
Masseter
Orbicularis oris
Platysma
Sternocleidomastoid
Sternohyoid
Trapezius
Pectoralis minor
Deltoid
Pectoralis major
Serratus anterior
Triceps brachii
External intercostal
Internal intercostal
Biceps brachii
Brachialis
External oblique
Rectus abdominis
Pronator teres
Transversus abdominis
Brachioradialis
Internal oblique (cut)
Flexor carpi radialis
External oblique (cut)
Palmaris longus
Iliopsoas
Tensor fasciae latae
Pectineus
Adductor longus
Sartorius
Gracilis
Rectus femoris
Quadriceps femoris
Vastus lateralis
Vastus medialis
Vastus intermedius
Figure 11.1
Selected Axial and Appendicular Muscles.
(a) Anterior view shows superficial muscles
on the right side of the body and some deeper
muscles on the left side. (b) Posterior view
shows superficial muscles on the left side of
the body and some deeper muscles on the
right side. Labels for the axial muscles are in
bold; not all muscles shown in the figure are
identified.
Fibularis longus
Tibialis anterior
Extensor digitorum longus
Extensor hallucis longus
(a) Anterior view
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Chapter Eleven
Superficial
Axial Muscles
325
Deep
Occipital belly of
occipitofrontalis
Semispinalis capitis
Sternocleidomastoid
Splenius capitis
Splenius cervicis
Levator scapulae
Trapezius
Teres minor
Teres major
Supraspinatus
Rhomboid minor
Rhomboid major
Infraspinatus
Teres minor
Teres major
Triceps brachii
Serratus anterior
Deltoid
Latissimus dorsi
Serratus posterior inferior
External oblique
Internal oblique
Erector spinae
Extensor digitorum
Extensor carpi ulnaris
Gluteus medius
Gluteus minimus
Gluteus maximus
Gluteus medius (cut)
Piriformis
Quadratus femoris
Adductor magnus
Biceps femoris
Hamstrings
Gracilis
Iliotibial tract
Semitendinosus
Semimembranosus
Gastrocnemius
Soleus
Calcaneal tendon
(b) Posterior view
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Chapter Eleven
Axial Muscles
Deep
Superficial
Epicranial aponeurosis
Figure 11.2
Epicranius
Muscles of Facial Expression.
(a) Illustration and cadaver photo,
anterior view. (b) Illustration and
cadaver photo, lateral view.
Frontal belly of
occipitofrontalis
Procerus
Orbicularis oculi
Nasalis
Levator labii superioris
Zygomaticus minor
Levator anguli oris (cut)
Zygomaticus major
Masseter
Buccinator
Risorius
Depressor anguli oris
Orbicularis oris
Depressor labii inferioris
Mentalis
Platysma
Sternocleidomastoid
Epicranial aponeurosis
Epicranius
Frontal belly of
occipitofrontalis
Corrugator supercilii
Procerus
Orbicularis oculi
Nasalis
Levator labii superioris
Zygomaticus minor
Levator anguli oris
Zygomaticus major
Masseter
Orbicularis oris
Depressor anguli oris
Mentalis
Depressor labii inferioris
Platysma
Sternocleidomastoid
(a) Anterior view
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Chapter Eleven
Axial Muscles
327
Epicranial
aponeurosis
Epicranius
Frontal belly
Temporalis
Occipital belly
Orbicularis oculi
Levator labii superioris
Zygomaticus minor
Levator anguli oris
Zygomaticus major
Masseter
Buccinator
Orbicularis oris
Sternocleidomastoid
Mentalis
Depressor labii inferioris
Depressor anguli oris
Platysma
Epicranial aponeurosis
Epicranius
Frontal belly of occipitofrontalis
Temporalis
Orbicularis oculi
Levator labii superioris
Zygomaticus minor
Levator anguli oris
Zygomaticus major
Orbicularis oris
Parotid gland
Parotid duct
Masseter
Buccinator
Sternocleidomastoid
Depressor labii inferioris
Depressor anguli oris
Platysma
(b) Lateral view
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Chapter Eleven
Axial Muscles
CLINICAL VIEW
Idiopathic Facial
Nerve Paralysis (Bell Palsy)
Unilateral paralysis of the muscles of facial expression is termed
facial nerve paralysis. This condition results from either disease
or injury to the facial nerve (CN VII). If the cause of the condition
is unknown, doctors refer to it as idiopathic (id ḗ -ō -path ́ ik; idios =
one’s own, pathos = suffering) facial nerve paralysis, or Bell palsy.
Recent studies indicate a frequent link between CN VII paralysis and
herpes simplex 1 viral infection. Facial nerve paralysis is also associated with exposure to cold temperatures, and is commonly seen
in individuals who sleep with one side of their head facing an open
window. Another possible cause of facial nerve paralysis is compression of the facial nerve by an adjacent blood vessel. Whatever the
underlying cause, the nerve becomes inflamed and compressed within
the narrow stylomastoid foramen.
to combat the symptoms of dry eye, and sometimes it’s necessary to
patch the affected eye to keep it closed while the patient is sleeping.
Like its underlying cause, recovery from idiopathic facial nerve
paralysis is mysterious. Over 50% of all patients experience a complete, spontaneous recovery within 30 days of their first symptoms.
For others, recovery may take longer, while still others may never
recover. Current statistics indicate that the recovery rate for idiopathic facial nerve paralysis averages about 80%, and does not appear
to be related to its treatment.
The facial nerve innervates all but one of the muscles of facial expression,
so if its function becomes impaired, the muscles on the same side of the
face are paralyzed. The patient may be unable to wrinkle the forehead
(paralyzed occipitofrontalis muscle), pucker the lips (paralyzed orbicularis oris), or close the eyelid on the affected side (paralyzed orbicularis
oculi). These symptoms lead to other problems as well. For example, if
the affected individual cannot close his or her eye, the eye becomes dry,
possibly damaging the cornea. If unable to close the mouth, the person
drools, and the mucous membranes of the mouth become parched.
Treatment of facial nerve paralysis usually means alleviating the
symptoms. Doctors often use prednisone (a type of steroid) to reduce
the inflammation and swelling of the nerve. If herpes simplex infection is suspected, an antiviral medication called acyclovir (Zovirax)
is also given. Paralysis of the orbicularis oculi may require eyedrops
The mentalis attaches to the lower lip, and when it contracts, it protrudes the lower lip (as when a person “pouts”). The
platysma tenses the skin of the neck and pulls the lower lip inferiorly. If you stand in front of a mirror and tense the skin of your
neck, you can see these thin muscles bulging out.
The buccinator compresses the cheek against the teeth when
we chew (and is the reason our cheeks don’t bulge like a squirrel’s
cheeks when we eat). Infants use the buccinator when they suckle
at the breast. Some trumpet players (such as Dizzy Gillespie) have
stretched out their buccinator muscles, allowing their cheeks to be
“puffy” with air when they play the trumpet.
Table 11.1 summarizes the attachments and movements of the muscles of facial expression. Figure 11.3
illustrates how these muscles produce some of the more characteristic expressions.
W H AT D O Y O U T H I N K ?
1
●
What muscles of facial expression must contract for you to smile?
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Facial nerve (CN VII) paralysis on the left side of the face. Note the
drooping left side of the mouth (arrow) and the lack of contraction
by the left orbicularis oculi when the woman tries to smile.
11.1b Extrinsic Eye Muscles
The extrinsic eye muscles, often called extraocular muscles, move
the eyes. They are termed extrinsic because they originate within
the orbit and insert onto the white outer surface of the eye, called
the sclera. There are six extrinsic eye muscles: the rectus muscles
(medial, lateral, inferior, and superior) and the oblique muscles
(inferior and superior) (figure 11.4).
The rectus eye muscles have their origin from a common
tendinous ring in the orbit. These muscles insert on the anterior
part of the sclera of the eye, and are named according to which side
of the eye they are located at (medial, lateral, inferior, or superior).
The medial rectus attaches to the anteromedial surface
of the eye and pulls the eye medially (adducts the eye). It is
innervated by CN III (oculomotor nerve). The lateral rectus
attaches to the anterolateral surface of the eye and pulls the eye
laterally (abducts the eye). This muscle is innervated by CN VI
(abducens). (Note that this nerve’s name tells you what muscle
it innervates—the eye muscle that abducts the eye.) The inferior
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Chapter Eleven
Table 11.1
Muscles of Facial Expression
Region/Muscle
Action
Origin/Insertion
329
Axial Muscles
Innervation
SCALP
Epicranius (ep ́ı̆-krā ́nē-us)
epi = over
cran = skull
Composed of an epicranial
aponeurosis and the occipitofrontalis
muscle
Frontal belly of occipitofrontalis
(ok-sip ́i-tō-fron-tă ́lis)
front = forehead
Moves scalp, eyebrows; wrinkles
skin of forehead
O: Frontal bone
I: Epicranial aponeurosis
CN VII (facial nerve)
Occipital belly of
occipitofrontalis
occipito = base of skull
Retracts scalp
O: Superior nuchal line
I: Epicranial aponeurosis
CN VII (facial nerve)
Nasalis (nā ́ză-lis)
nasus = nose
Compresses bridge and depresses tip
of nose; elevates corners of nostrils
O: Maxillae and alar cartilage of nose
I: Dorsum of nose
CN VII (facial nerve)
Procerus (prō-sē ́rŭs)
procerus = long
Moves and wrinkles nose
O: Nasal bone and lateral nasal
cartilage
I: Aponeurosis at bridge of nose
and skin of forehead
CN VII (facial nerve)
Buccinator (buk ́sı̆-nā ́tōr)
bucco = cheek
Compresses cheek; holds food
between teeth during chewing
O: Alveolar processes of mandible
and maxillae
CN VII (facial nerve)
Depressor anguli oris (dē-pres ́ōr
ang ́ū-lı̄ ōr ́ŭs)
depressor = depresses
angul = angle
or = mouth
Draws corners of mouth inferiorly
and laterally (“frown” muscle)
O: Body of mandible
I: Skin at inferior corner (angle) of
mouth
CN VII (facial nerve)
Depressor labii inferioris
(dē-pres ́ōr lā ́bē-ı̄ in-fēr ́ē-ōr-is)
labi = lip
infer = below
Draws lower lip inferiorly
O: Body of mandible lateral to
midline
I: Skin at inferior lip
CN VII (facial nerve)
Levator anguli oris (lē-vā ́tor,
le-vā ́ter ang ́ū-lı̄ ōr ́ūs)
leva = raise
Draws corners of mouth superiorly
and laterally (“smile” muscle)
O: Lateral maxilla
I: Skin at superior corner of mouth
CN VII (facial nerve)
Levator labii superioris (lē-vā ́tor,
le-vā ́ter lā ́bē-ı̄ sū-pēr ḗ -ōr-is)
Opens lips; raises and furrows the
upper lip (“Elvis” lip snarl)
O: Zygomatic bone; maxilla
I: Skin and muscle of superior lip
CN VII (facial nerve)
Mentalis (men-tā ́lis)
ment = chin
Protrudes lower lip (“pout”);
wrinkles chin
O: Central mandible
I: Skin of chin
CN VII (facial nerve)
Orbicularis oris (ōr-bik ū
́ -lā ŕ is ōr í s)
orb = circular
or = mouth
Compresses and purses lips (“kiss”
muscle)
O: Maxilla and mandible; blend with
fibers from other facial muscles
I: Encircling mouth; skin and
muscles at angles to mouth
CN VII (facial nerve)
Risorius (ri-sōr ́ē-ŭs)
risor = laughter
Draws corner of lip laterally; tenses
lips; synergist of zygomaticus
O: Deep fascia associated with
masseter muscle
I: Skin at angle of mouth
CN VII (facial nerve)
Zygomaticus major (zı̄ g
́ ō-mat í -kŭs)
zygomatic = cheekbone
major = greater
Elevates corner of the mouth
(“smile” muscle)
O: Zygomatic bone
I: Skin at superolateral edge of
mouth
CN VII (facial nerve)
Zygomaticus minor (zı̄ g
́ ō-mat í -kŭs)
minor = lesser
Elevates corner of the mouth
(“smile” muscle)
O: Zygomatic bone
I: Skin of superior lip
CN VII (facial nerve)
NOSE
MOUTH
I: Orbicularis oris
(continued on next page)
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Chapter Eleven
Axial Muscles
Table 11.1
Muscles of Facial Expression (continued)
Region/Muscle
Action
Origin/Insertion
Innervation
Corrugator supercilii (kōr ́ŭ-gā-ter
soo ́per-sil ́ē-ı̄)
corrugo = to wrinkle
cilium = eyelid
Pulls eyebrows inferiorly and
medially; creates vertical wrinkles
above nose
O: Medial end of superciliary arch
I: Skin superior to supraorbital
margin and superciliary arch
CN VII (facial nerve)
Levator palpebrae superioris (see
figure 19.10) (le-vā ́ter pal-pē ́brā
soo-pēr ́ē-ōr-ı̆s)
levo = to lift
palpebra = eyelid
Elevates superior eyelid
O: Lesser wing of sphenoid bone
I: Superior tarsal plate and skin of
superior eyelid
CN III (oculomotor nerve)
Orbicularis oculi (ōr-bik ́ū-lā ́ris
ok ́ū-lı̄)
orb = circular
ocul = eye
Closes eye; produces winking,
blinking, squinting (“blink” muscle)
O: Medial wall or margin of orbit
I: Skin surrounding eyelids
CN VII (facial nerve)
Pulls lower lip inferiorly; tenses skin
of neck
O: Fascia of deltoid and pectoralis
major muscles and acromion of
scapula
I: Skin of cheek and mandible
CN VII (facial nerve)
EYE
NECK
Platysma (plă-tiz ́mă)
platy = flat
rectus attaches to the anteroinferior part of the sclera. The inferior rectus pulls the eye inferiorly (as when you look down) and
medially (as when you look at your nose). The superior rectus
is located superiorly and attaches to the anterosuperior part of
the sclera. The superior rectus pulls the eye superiorly (as when
you look up) and medially (as when you look at your nose). The
inferior and superior rectus muscles are innervated by CN III.
Figure 11.4d illustrates that the superior and inferior rectus muscles
do not pull directly parallel to the long axis of the eye; that is why
both muscles also move the eye slightly in the medial direction.
Figure 11.3
Depressor anguli oris
(frown)
The oblique eye muscles originate from within the orbit and
insert on the posterolateral part of the sclera of the eye. The inferior oblique elevates the eye and turns the eye laterally. Since this
muscle attaches to the inferior posterior part of the eye, contracting this muscle pulls the posterior part of the eye inferiorly (but
elevates the anterior part of the eye). This muscle is innervated by
CN III. The superior oblique depresses the eye and turns the eye
laterally. This muscle passes through a pulleylike loop, called the
trochlea, in the anteromedial orbit. This muscle attaches to the
superior posterior part of the eye, so contracting this muscle pulls
Orbicularis oculi
(blink/close eyes)
Zygomaticus major
(smile)
Surface Anatomy of Some
Muscles of Facial Expression.
These muscles permit complex
expressions that are often used
as a means of communication.
Orbicularis oris
(close mouth/kiss)
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Frontal belly of occipitofrontalis
(wrinkle forehead, raise eyebrows)
Platysma
(tense skin of neck)
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Chapter Eleven
Study Tip!
Remembering the innervation of the eye muscles can be difficult.
Use the following “chemical formula” to help you learn the eye muscle
innervation:
331
Axial Muscles
the posterior part of the eye superiorly (but depresses the anterior
surface of the eye). This muscle is innervated by CN IV (trochlear).
(Note that this nerve’s name is derived from the trochlea that
holds the superior oblique in place.)
Table 11.2 compares the extrinsic muscles of the eye.
[(S04)(LR6)]3
W H AT D I D Y O U L E A R N?
In other words, the superior oblique (SO) is innervated by cranial
nerve IV (4), the lateral rectus (LR) is innervated by cranial nerve VI (6),
and the rest of the eye muscles are innervated by cranial nerve III (3).
1
●
What are the origins for all the muscles of facial
expression?
2
●
List the extrinsic eye muscles, and describe the function of each
muscle.
3
●
The corners of the mouth are pulled inferiorly into a frown
position by the contraction of what muscle?
Trochlea
Trochlea
Superior rectus
Superior oblique
Frontal bone
Superior rectus
Superior oblique
Orbicularis
oculi
Medial rectus
Common tendinous ring
Optic nerve
Optic nerve
Lateral rectus
Inferior rectus
Inferior oblique
Common
tendinous ring
Inferior rectus
Maxilla
Inferior oblique
(a) Lateral view, right eye
(b) Medial view, right eye
Trochlea
Sagittal axis
Superior rectus
Coronal axis
Trochlea Center of eye
Inferior oblique
Superior oblique
Lateral rectus
Optic canal
Common
tendinous ring
Inferior oblique
Inferior rectus
Medial rectus
(c) Anterior view of right orbit, eye removed
Figure 11.4
Inferior rectus Lateral rectus Medial rectus
Superior rectus
Superior oblique
(d) Superior view
Extrinsic Muscles of the Eye. The extrinsic eye muscles control movements of the eye. (a) The insertions for the lateral, superior, and inferior
rectus, as well as both the inferior and superior oblique muscles, appear prominently in a lateral view of the right eye. (b) The medial rectus
muscle appears prominently in a medial view of the right eye. (c) Most of the eye muscles originate from a common tendinous ring, shown here
in an anterior view of the right orbit. (d) A superior view of the left and right orbits illustrates the insertion differences between the rectus and
oblique muscles, and how these differences affect their movement of the eye.
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Chapter Eleven
Axial Muscles
Table 11.2
Extrinsic Eye Muscles
Group/Muscle
Action
Origin/Insertion
Innervation
Medial rectus (mē´dē-ăl rek t́ us)
rectus = straight
Moves eye medially (adducts eye)
O: Common tendinous ring
I: Anteromedial surface of eye
CN III (oculomotor nerve)
Lateral rectus (lat é r-ăl rek t́ us)
Moves eye laterally (abducts eye)
O: Common tendinous ring
I: Anterolateral surface of eye
CN VI (abducens nerve)
Inferior rectus (in-fē´rē-ōr rek ́tus)
Moves eye inferiorly (depresses eye)
and medially (adducts eye)
O: Common tendinous ring
I: Anteroinferior surface of eye
CN III (oculomotor nerve)
Superior rectus (soo-pēr ́ē-ōr
rek ́tus)
Moves eye superiorly (elevates eye)
and medially (adducts eye)
O: Common tendinous ring
I: Anterosuperior surface of eye
CN III (oculomotor nerve)
Inferior oblique (in-fē ́rē-ōr
ob-lēk ́)
obliquus = slanting
Moves eye superiorly (elevates eye)
and laterally (abducts eye)
O: Anterior orbital surface of maxilla
I: Posteroinferior, lateral surface
of eye
CN III (oculomotor nerve)
Superior oblique (soo-pēr ́ē-ōr
ob-lēk ́)
Moves eye inferiorly (depresses eye)
and laterally (abducts eye)
O: Sphenoid bone
I: Posterosuperior, lateral surface
of eye
CN IV (trochlear nerve)
RECTUS MUSCLES
OBLIQUE MUSCLES
CLINICAL VIEW
Strabismus
When the eyes are improperly aligned, the condition is called
strabismus (stra-biz m
́ ŭs; strabismos = a squinting). The misalignment means the eyes are not working synchronously to transmit a
stereoscopic view to the brain. With each eye sending a slightly
different image, the brain becomes confused and ignores one of
the images. The ignored eye becomes weaker and weaker over
time, resulting in a condition termed “lazy eye.” If uncorrected,
the lazy eye loses visual acuity, a condition termed strabismic
amblyopia (amblē-ō ṕ ē-ă; amblys = dull, ops = eye).
Causes of strabismus include birth injuries, diseases localized to
the eye or its bony orbit, improper attachment of the extrinsic
eye muscles, and heredity. Two forms of strabismus are recognized. External strabismus occurs when the oculomotor nerve
(CN III) is injured, so that the affected eye moves laterally while at
rest but cannot move medially and inferiorly. Conversely, internal
strabismus occurs when the abducens nerve (CN VI) is injured. The
affected eye moves medially but cannot move laterally.
11.1c Muscles of Mastication
The term mastication (mas-ti-kā ś hŭn; masticatus = to chew)
refers to the process of chewing. These muscles move the mandible at the temporomandibular joint. There are four paired
muscles of mastication: the temporalis, the masseter, and the
lateral and medial pterygoids (figure 11.5). The muscles of
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mastication are innervated by the mandibular division of CN V
(trigeminal nerve).
The temporalis (or temporal muscle) is a broad, fan-shaped
muscle that extends from the temporal lines of the skull and
inserts on the coronoid process of the mandible. It elevates and
retracts (pulls posteriorly) the mandible. You can palpate the temporalis by placing your fingers along your temple (lateral skull
at same level of orbits) as you open and close your mouth. The
muscle you feel contracting is the temporalis.
The masseter elevates and protracts (pulls anteriorly)
the mandible. It is the most powerful and important of the
masticatory muscles. This short, thick muscle is superficial to
the temporalis. You can feel the contraction of the masseter by
palpating near the angle of the mandible as you open and close
your mouth.
The lateral and medial pterygoid muscles arise from the
lateral pterygoid plates of the sphenoid bone and insert on the
mandible. Both pterygoids protract the mandible and move it
from side to side during chewing. These movements maximize
the efficiency of the teeth while chewing or grinding foods of
various consistencies. The medial pterygoid also elevates the
mandible.
Table 11.3 summarizes the characteristics of the muscles
of mastication.
11.1d Muscles That Move the Tongue
The tongue is an agile, highly mobile organ. It consists of
intrinsic muscles that curl, squeeze, and fold the tongue during chewing and speaking. Thus, the tongue itself acts like a
big muscle.
The extrinsic muscles of the tongue have their origin on
other head and neck structures and insert on the tongue. The
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Axial Muscles
Temporalis (cut)
Temporalis
Lateral pterygoid
Medial pterygoid
Masseter
Buccinator
Buccinator
Orbicularis oris
Orbicularis oris
(a) Superficial lateral view
(b) Deep lateral view
Figure 11.5
Muscles of Mastication.
(a) Superficial and (b) deep lateral views of the muscles of mastication (shown in bold), which move the mandible.
extrinsic muscles end in the suffix -glossus, meaning “tongue”
(figure 11.6). These extrinsic tongue muscles are used in various combinations to accomplish the precise, complex, and delicate tongue movements required for proper speech. Additionally,
they manipulate food within the mouth in preparation for swallowing. Most of these muscles are innervated by CN XII, the
hypoglossal nerve.
The left and right genioglossus muscles have their origin on the mandible and protract the tongue. You use these
muscles when you stick out your tongue. The left and right
styloglossus muscles originate on the styloid processes of the
temporal bone. These muscles elevate and retract the tongue
(pull the tongue posteriorly, back into the mouth). The left
and right hyoglossus muscles originate at the hyoid bone and
insert on the sides of the tongue. These muscles depress and
retract the tongue. The left and right palatoglossus muscles
originate on the soft palate and elevate the posterior portion of
the tongue.
Table 11.3
Muscles of Mastication
Muscle
Action
Origin/Insertion
Innervation
Temporalis (tem-pō-rā ́lis)
tempora = pertaining to temporal
bone
Elevates and retracts mandible
O: Superior and inferior temporal
lines
I: Coronoid process of mandible
CN V3 (trigeminal nerve, mandibular
division)
Masseter (ma ś e-ter)
maseter = chewer
Elevates and protracts mandible;
prime mover of jaw closure
O: Zygomatic arch
I: Coronoid process, lateral surface
and angle of mandible
CN V3 (trigeminal nerve, mandibular
division)
Medial pterygoid (mē ́dē-ăl ter í goyd)
Elevates and protracts mandible;
produces side-to-side movement
of mandible
O: Maxilla, palatine, and medial
surface of lateral pterygoid plate
I: Medial surface of mandibular
ramus
CN V3 (trigeminal nerve, mandibular
division)
Lateral pterygoid (lat ́er-ăl ter ́igoyd)
pterygoid = winglike
Protracts mandible; produces side-toside movement of mandible
O: Greater wing of sphenoid and
lateral surface of lateral pterygoid
plate
I: Condylar process of mandible
CN V3 (trigeminal nerve, mandibular
division)
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Figure 11.6
Muscles That Move the Tongue. Extrinsic tongue muscles
(shown in bold) originate on structures other than the tongue
and insert onto it to allow gross tongue movement.
Styloid
process
Tongue
Palatoglossus
Styloglossus
Genioglossus
Stylohyoid
Mandible (cut)
Hyoglossus
Geniohyoid
Hyoid bone
Thyroid cartilage
Right lateral view
Table 11.4 summarizes the characteristics of the muscles
that move the tongue.
11.1e Muscles of the Pharynx
The pharynx, commonly called the “throat,” is a funnelshaped tube that lies posterior to and extends inferiorly from
both the oral and nasal cavities. Several muscles help form
this muscular tube or attach to it and aid in swallowing
(figure 11.7). Most pharyngeal muscles are innervated by
CN X (vagus nerve).
The primary pharyngeal muscles are the pharyngeal constrictors (superior, middle, and inferior). When a bolus of food
enters the pharynx, these muscles contract sequentially to initiate
swallowing and force the bolus inferiorly into the esophagus.
Other pharyngeal muscles help elevate or tense the palate when
swallowing. These muscles are summarized in table 11.5.
Table 11.4
Muscles That Move the Tongue
Muscle
Action
Origin/Insertion
Innervation
Genioglossus (jē ́nı̄-ō-glos ́ŭs)
geni = chin
glossus = tongue
Protracts tongue
O: Mental spines of mandible
I: Inferior region of tongue; hyoid
bone
CN XII (hypoglossal nerve)
Styloglossus (stı̄ ́lō-glos ́ŭs)
stylo = pertaining to styloid process
of temporal bone
Elevates and retracts tongue
O: Styloid process of temporal bone
I: Sides and inferior aspect of
tongue
CN XII (hypoglossal nerve)
Hyoglossus (hı̄ ́ō-glos ́ŭs)
hyo = pertaining to hyoid bone
Depresses and retracts tongue
O: Hyoid bone
I: Inferolateral side of tongue
CN XII (hypoglossal nerve)
Palatoglossus (pal-ā-tō-glos ́ŭs)
palato = palate
Elevates posterior part of tongue
O: Anterior surface of soft palate
I: Side and posterior aspect of
tongue
CN X (vagus nerve) via pharyngeal
plexus of nerves
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335
Figure 11.7
Pharyngeal Constrictors, Palate Muscles, and Laryngeal Elevators.
A right lateral view reveals some of the muscles that constrict the
pharynx when swallowing, move the palate, and elevate the larynx
(palatopharyngeus and salpingopharyngeus not shown).
Tensor veli
palatini
Levator veli
palatini
Superior constrictor
11.1f Muscles of the Anterior Neck
Stylopharyngeus
The muscles of the anterior neck are divided into the suprahyoid
muscles, which are superior to the hyoid bone, and the infrahyoid
muscles, which are inferior to the hyoid bone (figure 11.8). The
suprahyoid muscles are associated with the floor of the mouth.
In general, these muscles act as a group to elevate the hyoid bone
during swallowing or speaking. Some of these muscles perform
additional functions: The digastric has two bellies, anterior and
posterior. One belly extends from the mental protuberance to the
hyoid, and the other continues from the hyoid to the mastoid portion of the temporal bone. The two bellies are united by an intermediate tendon that is held in position by a fascia sling (fibrous
loop). In addition to elevating the hyoid bone, this muscle can also
Middle constrictor
Inferior constrictor
Esophagus
Right lateral view
Table 11.5
Muscles of the Pharynx1
Region/Muscle
Action
Origin/Insertion
Innervation
Levator veli palatini (lē-vā ́tor,
le-vā ́ter vel ı̄́ pal ́ă-tē ́nı̄)
levator = elevates
velum = veil
Elevates soft palate when swallowing
O: Petrous part of temporal bone
I: Soft palate
CN X (vagus nerve)
Tensor veli palatini (ten ́sōr vel ı̄́
pal ́ă-tē ́nı̄)
tensus = to stretch
Tenses soft palate and opens auditory
tube when swallowing or yawning
O: Sphenoid bone; region around
auditory tube
I: Soft palate
CN V3 (trigeminal nerve, mandibular
division)
Superior constrictor
(kon-strik ́ter, -tor)
constringo = to draw together
Constricts pharynx in sequence to
force bolus into esophagus; superior
is innermost
O: Pterygoid process of sphenoid
bone; medial surface of mandible
I: Posterior median raphe (muscle
fiber union from both sides)
CN X (vagus nerve) via branches of
pharyngeal plexus
Middle constrictor
Constricts pharynx in sequence
O: Hyoid bone
I: Posterior median raphe
CN X (vagus nerve) via branches of
pharyngeal plexus
Inferior constrictor
Constricts pharynx in sequence;
inferior is outermost
O: Thyroid and cricoid cartilage
I: Posterior median raphe
CN X (vagus nerve) via branches of
pharyngeal plexus
PALATE MUSCLES
PHARYNGEAL CONSTRICTORS
LARYNGEAL (VOICE BOX) ELEVATORS
1
Palatopharyngeus
(păl ắ -tō-far-in -́ jē-ŭs)
pharynx = pharynx
Elevates pharynx and larynx
O: Soft palate
I: Side of pharynx and thyroid
cartilage of larynx
CN X (vagus nerve) via branches of
pharyngeal plexus
Salpingopharyngeus
(sal-ping ́gō-făr-in ́jē-ŭs)
salpinx = trumpet
Elevates pharynx and larynx
O: Auditory tube
I: Blends with palatopharyngeus on
lateral wall of pharynx
CN X (vagus nerve) via branches of
pharyngeal plexus
Stylopharyngeus (stı̄ ́lō-far-in j́ ē-ŭs)
stylo = styloid process
Elevates pharynx and larynx
O: Styloid process of temporal bone
I: Side of pharynx and thyroid
cartilage of larynx
CN IX (glossopharyngeal nerve) via
branches of pharyngeal plexus
Only the pharyngeal constrictors are discussed in the text.
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Deep
Superficial
Mylohyoid
Suprahyoid
muscles
Genioglossus
Stylohyoid
Digastric:
Anterior belly
Posterior belly
Geniohyoid
Hyoglossus
Suprahyoid
muscles
Hyoid bone
Omohyoid
Infrahyoid
muscles
Omohyoid
Thyrohyoid
Sternohyoid
Sternothyroid
Infrahyoid
muscles
Sternocleidomastoid
Scalene
muscles
Trapezius
Clavicle
Mylohyoid
Stylohyoid
Suprahyoid
muscles
Digastric:
Anterior belly
Posterior belly
Hyoid bone
Infrahyoid
muscles
Omohyoid
Thyrohyoid
Omohyoid
Sternohyoid
Sternocleidomastoid
Sternothyroid
Infrahyoid
muscles
Scalene
muscles
Trapezius
Clavicle
Anterior view
Figure 11.8
Muscles of the Anterior Neck. An illustration and a cadaver photo show the anterior neck muscles, which move the hyoid bone and the thyroid
cartilage. Superficial muscles are shown on the right side, while deeper muscles are shown on the left side.
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Chapter Eleven
depress the mandible. The geniohyoid originates from the mental
spines of the mandible and inserts on the hyoid bone. This muscle
elevates the hyoid bone. The broad, flat mylohyoid provides a muscular floor to the mouth. When this muscle contracts, it both elevates the hyoid bone and raises the floor of the mouth. The muscle
fibers of the left and right mylohyoid are aligned in a V shape.
The stylohyoid originates from the styloid process of the skull and
inserts on the hyoid. Upon contraction, it elevates the hyoid bone,
causing the floor of the oral cavity to elongate during swallowing.
As swallowing ends, the infrahyoid muscles contract to
influence the position of the hyoid bone and the larynx. In general, these muscles either depress the hyoid bone or depress the
thyroid cartilage of the larynx. The omohyoid contains two thin
muscle bellies anchored in place by a connective tissue “sling.”
This muscle is lateral to the sternohyoid and extends from the
superior border of the scapula and inserts on the hyoid, where it
depresses the hyoid bone. The sternohyoid extends from the sternum to the hyoid, where it depresses the hyoid bone. The sternothyroid is deep to the sternohyoid. It extends from the sternum
to the thyroid cartilage of the larynx. It depresses the thyroid
cartilage to return it to its original position after swallowing. The
thyrohyoid extends from the thyroid cartilage of the larynx to
the hyoid. It depresses the hyoid bone and elevates the thyroid
cartilage to close off the larynx during swallowing. In addition,
the omohyoid, sternohyoid, and thyrohyoid help anchor the hyoid
so the digastric can depress the mandible.
Table 11.6 summarizes the characteristics of the muscles of
the anterior neck.
W H AT D O Y O U T H I N K ?
2
●
Since muscles frequently are named for their attachment sites,
what do you think the prefix -omo in “omohyoid” means?
Axial Muscles
337
11.1g Muscles That Move the Head and Neck
Muscles that move the head and neck originate on the vertebral
column, the thoracic cage, and the pectoral girdle, and insert on
bones of the cranium (figure 11.9; see figure 11.8).
Anterolateral Neck Muscles
The anterolateral neck muscles flex the head and/or neck. The
main muscles in this group are the sternocleidomastoid and the
three scalenes.
The sternocleidomastoid is a thick, cordlike muscle that
extends from the sternum and clavicle to the mastoid process
posterior to the ear. Contraction of both sternocleidomastoid muscles (called bilateral contraction) flexes the neck. Contraction of
just one sternocleidomastoid muscle (called unilateral contraction) results in lateral flexion of the neck and rotation of the head
to the opposite side. Thus, if the left sternocleidomastoid muscle
contracts, it rotates the head to the right side of the body. The
three scalene muscles (anterior, middle, and posterior) work
with the sternocleidomastoid to flex the neck. In addition, the
scalene muscles elevate the first and second ribs during forced
inhalation.
Posterior Neck Muscles
Several muscles work together to extend the head and/or neck
(figure 11.10). The trapezius attaches to the skull and helps
extend the head and/or neck. The primary function of the trapezius is to help move the pectoral girdle, so it is discussed in
greater detail in chapter 12. When the left and right splenius
capitis, splenius cervicis, semispinalis capitis, and longissimus capitis muscles bilaterally contract, they extend the neck.
Unilateral contraction turns the head and neck to the same side.
A group of muscles called the suboccipital muscles includes the
Table 11.6
Muscles of the Anterior Neck
Region/Muscle
Action
Origin/Insertion
Innervation
Digastric (dı̄-gas t́ rik)
di = two
gaster = belly
Depresses mandible; elevates hyoid
bone
O: Anterior belly, mandible near
mental protuberance; posterior
belly, mastoid process
I: Hyoid bone via fascia sling
Anterior belly: CN V3 (trigeminal
nerve, mandibular division)
Posterior belly: CN VII (facial nerve)
Geniohyoid (jĕ ́nı̄-ō-hı̄ ́-oyd)
hyoid = hyoid bone
Elevates hyoid bone
O: Mental spines of mandible
I: Hyoid bone
First cervical spinal nerve (C1) via
CN XII (hypoglossal nerve)
Mylohyoid (mı̄ ́lō-hı̄ ́oyd)
myle = molar
Elevates hyoid bone; elevates floor
of mouth
O: Mylohyoid line of mandible
I: Hyoid bone
CN V3 (trigeminal nerve, mandibular
division)
Stylohyoid (stı̄ ́lō-hı̄ ́oyd)
Elevates hyoid bone
O: Styloid process of temporal bone
I: Hyoid bone
CN VII (facial nerve)
Omohyoid (ō ́mō-hı̄ ́oyd)
omo = shoulder
Depresses hyoid bone; fixes hyoid
during opening of mouth
O: Superior border of scapula
I: Hyoid bone
Cervical spinal nerves C1–C3
through ansa cervicalis (from
cervical plexus)
Sternohyoid (ster n
́ ō-hı̄ ́oyd)
sterno = sternum
Depresses hyoid bone
O: Manubrium of sternum and
medial end of clavicle
I: Hyoid bone
Cervical spinal nerves C1–C3
through ansa cervicalis (from
cervical plexus)
Sternothyroid (ster n
́ ō-thı̄ ́royd)
thyro = thyroid cartilage
Depresses thyroid cartilage of larynx
O: Posterior surface of manubrium
of sternum
I: Thyroid cartilage of larynx
Cervical spinal nerves C1–C3
through ansa cervicalis (from
cervical plexus)
Thyrohyoid (thı̄ ́rō-hı̄ ́oyd)
Depresses hyoid bone and elevates
thyroid cartilage of larynx
O: Thyroid cartilage of larynx
I: Hyoid bone
First cervical spinal nerve C1 via
CN XII (hypoglossal nerve)
SUPRAHYOID MUSCLES
INFRAHYOID MUSCLES
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Stylohyoid
Posterior belly of digastric
Semispinalis capitis
Mylohyoid
Splenius capitis
Levator scapulae
Anterior belly of digastric
Thyrohyoid
Inferior constrictor
Sternocleidomastoid
Sternothyroid
Superior belly of omohyoid
Scalene muscles
Sternohyoid
Trapezius
Inferior belly of omohyoid
Platysma (cut)
Anterolateral view
Figure 11.9
Muscles That Move the Head and Neck.
and/or neck.
Anterolateral muscles collectively flex the neck, while posterior neck muscles extend the head
CLINICAL VIEW
Congenital Muscular Torticollis
Congenital muscular torticollis (CMT), often known as wryneck, is a
condition where a newborn presents with a shortened and tightened
sternocleidomastoid muscle. CMT is relatively common with estimates
between 0.4% and 2% of births. It is thought to be a result of trauma
resulting from either a difficult birth or prenatal position of the fetus.
The trauma causes a hematoma and fibrosing of the muscle tissue.
Pediatricians also have seen an increase in acquired muscular torticollis among newborns who are kept in their infant seats for extended
periods of time outside of the car. Infants and children with CMT often
tilt their heads to the affected side and their chins to the unaffected
side. Since the infant favors a particular head position, plagiocephaly
(flattening of the head) often accompanies CMT.
CMT treatment typically involves repeated daily stretching of the
affected muscle, changing sleeping positions, and making the child
use the affected side while playing and interacting with others. More
severe cases may require surgery. A newer approach to treatment of
CMT is the use of botulinum toxin (Botox) combined with stretching.
Botox is injected into the muscle to impair contraction in response to
nerve stimulation, and thus the muscle responds better to stretching.
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Photo of a 7-year-old boy with CMT. Notice the prominence of the
sternocleidomastoid on the left (affected) side.
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Chapter Eleven
Deep
Axial Muscles
339
Deeper
Rectus capitis
posterior minor
Rectus capitis
posterior major
Semispinalis capitis
Obliquus capitis superior
Sternocleidomastoid
Obliquus capitis inferior
Longissimus capitis
Splenius capitis
Semispinalis capitis (cut)
Levator scapulae
Splenius capitis (cut)
Splenius cervicis
Scalene (posterior)
Rectus capitis
posterior minor
Rectus capitis
posterior major
Semispinalis capitis
Obliquus capitis superior
Sternocleidomastoid
Obliquus capitis inferior
Longissimus capitis
Splenius capitis (cut)
Splenius capitis
Semispinalis capitis (cut)
Splenius cervicis (cut)
Levator scapulae
Splenius cervicis
Posterior view
Figure 11.10
Posterior Neck Muscles.
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An illustration and a cadaver photo show the deep and deeper muscles that extend and rotate the head and neck.
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Chapter Eleven
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Table 11.7
Muscles That Move the Head and Neck
Muscle
Action
Origin/Insertion
Innervation
Sternocleidomastoid (ster ́nō-klı̄ ́dōmăs ́toyd)
sterno = sternum
cleido = clavicle
masto = mastoid process
Unilateral action : Lateral flexion,
rotation of head to opposite side
Bilateral action2: Flexes neck
O: Manubrium and sternal end of
clavicle
I: Mastoid process
CN XI (accessory nerve)
Scalene muscles (anterior, middle,
posterior) (see also table 11.9)
(skā ́lēnz)
scalene = uneven
Flex neck (when 1st rib is fixed);
elevate 1st and 2nd ribs during
forced inhalation when neck is fixed
O: Transverse processes of cervical
vertebrae
I: Superior surface of 1st and 2nd
ribs
Cervical spinal nerves
Splenius capitis and cervicis
(splē ́nē-ŭs ka p
́ ı̆-tis) (ser v
́ i-sis)
splenion = bandage
Unilateral action: Turns head to same
side
Bilateral action: Extends head/neck
O: Ligamentum nuchae
I: Occipital bone and mastoid
process of temporal bone
Cervical spinal nerves
Longissimus capitis
(lon-jis ́i-mŭs ka p
́ ı̆-tis)
longissimus = longest
caput = head
Unilateral action: Turns (rotates)
head toward same side
Bilateral action: Extends head/neck
O: Transverse process of T1–T4 and
articular processes of C4–C7
vertebrae
I: Mastoid process
Cervical and thoracic spinal nerves
Obliquus capitis superior
(ob-lı̄ ́kŭs ka p
́ ı̆-tis soo-pēr ́ē-ōr)
Turns head to same side
O: Transverse process of atlas
I: Inferior nuchal line
Suboccipital nerve (posterior ramus
of 1st cervical spinal nerve)
Obliquus capitis inferior
(ob-lı̄ ́kŭs ka p
́ ı̆-tis in-fē ́rē-ōr)
obliquus = slanting
Turns head to same side
O: Spinous process of axis
I: Transverse process of atlas
Suboccipital nerve (posterior ramus
of 1st cervical spinal nerve)
Rectus capitis posterior major
(rek ́tŭs ka ́pı̆-tis pos-tēr ḗ -ŏr)
Extends head/neck
O: Spinous process of axis
I: Inferior nuchal line of occipital
bone
Suboccipital nerve (posterior ramus
of 1st cervical spinal nerve)
Rectus capitis posterior minor
Extends head/neck
O: Posterior tubercle of atlas
I: Inferior nuchal line of occipital
bone
Suboccipital nerve (posterior ramus
of 1st cervical spinal nerve)
1
1
Unilateral action means only one muscle (either the left or right muscle) is contracting.
2
Bilateral action means both the left and right muscles are contracting together.
obliquus capitus superior, obliquus capitus inferior, rectus
capitis posterior major, and rectus capitis posterior minor. The
obliquus muscles turn the head to the same side, while the rectus
muscles extend the head and neck.
Table 11.7 summarizes the characteristics of the muscles of
the head and neck.
W H AT D I D Y O U L E A R N?
4
●
5
●
6
●
7
●
What movements do the medial and lateral pterygoids perform?
Which muscle protracts the tongue?
List the suprahyoid muscles. What is their common function?
The unilateral contraction of which muscle causes lateral flexion of
the neck and rotation of the head to the opposite side?
11.2 Muscles of the Vertebral Column
Learning Objective:
1. Detail the muscles involved in the movements of the
vertebral column.
The muscles of the vertebral column are very complex; they
have multiple origins and insertions, and they exhibit extensive
overlap (figure 11.11). All of these muscles are covered by the
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most superficial back muscles, which actually move the upper
limb, including the trapezius and the latissimus dorsi.
Note that the “neck” is actually the cervical portion of the
vertebral column. Thus, the muscles discussed previously in connection with neck extension (splenius cervicis, splenius capitis,
longissimus capitis, semispinalis capitis) extend the cervical
portion of the vertebral column.
The erector spinae function to maintain posture and to help
an individual stand erect. When the left and right erector spinae
muscles contract together, they extend the vertebral column. If
the erector spinae muscles on only one side contract, the vertebral
column flexes laterally toward that same side.
The erector spinae muscles are organized into three groups;
a series of multipart, overlapping muscles compose each of these
groups. These muscles share a common tendinous insertion from
the posterior part of the iliac crest, posterior sacrum, and spinous
processes of the lumbar vertebrae. The muscles are named based
on the body region with which they are associated.
■
■
The iliocostalis group is the most laterally placed of the
three erector spinae components. It is composed of three
parts: cervical, thoracic, and lumbar.
The longissimus group is medial to the iliocostalis group.
The longissimus muscle group inserts on the transverse
processes of the vertebrae. The longissimus group is
composed of three parts: capitis, cervical, and thoracic.
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341
Axial Muscles
Deeper
Deep
Semispinalis capitis
Longissimus capitis
Semispinalis cervicis
Splenius capitis
Serratus posterior superior
External intercostals
Splenius cervicis
Transversospinalis
Iliocostalis group
Erector spinae
Semispinalis thoracis
Longissimus group
Spinalis group
Serratus posterior inferior
Internal oblique (cut)
Multifidus
Quadratus lumborum
External oblique (cut)
Semispinalis cervicis
Splenius capitis
Serratus posterior superior
Splenius cervicis
Iliocostalis group
Erector spinae
Semispinalis thoracis
Longissimus group
Transversospinalis
Spinalis group
Multifidus
Serratus posterior inferior
Internal oblique
Quadratus lumborum
External oblique (cut)
Figure 11.11
Deep Muscles of the Vertebral Column.
the vertebral column, neck, and ribs.
mck78097_ch11_322-353.indd 341
Posterior view
An illustration and a cadaver photo show the muscles that affect, modify, and stabilize the positions of
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342
■
Chapter Eleven
Axial Muscles
The spinalis group is the most medially placed of the
erector spinae muscles. The spinalis muscle fibers insert
on the spinous processes of the vertebrae (hence, the name
of this muscle group). The spinalis group is composed of
cervical and thoracic parts. The cervical part originates
from the C7 spinous process.
Deep to the erector spinae, a group of muscles collectively
called the transversospinalis muscles connect and stabilize the
vertebrae (figure 11.12). There are several specific muscles in this
group (table 11.8). In addition, minor deep back muscles called
interspinales and intertransversarii assist the transversospinalis
muscles with moving the vertebral column.
A final pair of muscles helps move the vertebral column.
The quadratus lumborum muscles are located primarily in the
lumbar region (see figure 11.11). When the left and right quadratus
lumborum muscles bilaterally contract, they extend the vertebral
column. When either the left or right quadratus lumborum muscle
unilaterally contracts, it laterally flexes the vertebral column.
Table 11.8 summarizes the characteristics of the muscles of
the vertebral column.
Intertransversarius
Rotatores thoracis
Transverse process
of vertebra
Interspinales
Spinous process
of vertebra
W H AT D I D Y O U L E A R N?
8
●
Figure 11.12
Describe the erector spinae, and briefly discuss their function.
Transversospinalis Muscles and Minor Deep Back Muscles.
These muscles affect and modify the positions of the vertebral
column.
Table 11.8
Muscles of the Vertebral Column
Group/Muscle
Action
Origin/Insertion
Innervation
Iliocostalis group (il-ē-ō-kos-tā ́lis)
ilio = ilium
cost = rib
Extends neck and vertebral column;
maintains posture
O: Tendon from posterior part of
iliac crest, posterior sacrum, and
lumbar spinous processes
I: Angles of ribs; transverse
processes of cervical vertebrae
Cervical, thoracic, and lumbar spinal
nerves
Longissimus group (lon-jis í -mŭs)
longissimus = longest
Extends neck and vertebral column
and rotates head; maintains posture
O: Tendon from posterior part of
iliac crest, posterior sacrum,
and lumbar spinous processes
I: Mastoid process of temporal
bone and transverse processes of
cervical and thoracic vertebrae
Cervical and thoracic spinal nerves
Spinalis group (spı̄-nā ́lis)
spin = spine
Extends neck and vertebral column;
maintains posture
O: Lumbar spinous processes
(thoracic part) and C7 spinous
process (cervical part)
I: Spinous process of axis and
thoracic vertebrae
Cervical and thoracic spinal nerves
Multifidus (mul-tif í -dŭs)
multus = much
findo = to cleave
Extends vertebral column; rotates
vertebral column toward opposite
side
O: Sacrum and transverse processes
of each vertebra
I: Spinous processes of vertebrae
located 2–4 segments superior to
origin
Cervical, thoracic, and lumbar spinal
nerves
Rotatores (rō-tā ́tōrz)
rotatus = to revolve
Extends vertebral column; rotates
vertebral column toward opposite
side
O: Transverse processes of each
vertebra
I: Spinous process of immediately
superior vertebra
Cervical, thoracic, and lumbar spinal
nerves
Semispinalis group (sem ́ē-spı̄nā ́lis)
Bilateral action: Extends vertebral
column/neck
Unilateral action: Laterally flexes
vertebral column/neck
O: Transverse processes of C4–T12
vertebrae
I: Occipital bone and spinous
processes of cervical and thoracic
vertebrae
Cervical and thoracic spinal nerves
ERECTOR SPINAE
TRANSVERSOSPINALIS GROUP
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343
Table 11.8
Muscles of the Vertebral Column (continued)
Group/Muscle
Action
Origin/Insertion
Innervation
Interspinales (in-ter-spı̄-nā ́lēz)
inter = between
Extends vertebral column; rotates
vertebral column to opposite side
O: Spinous processes of each
vertebra
I: Spinous processes of more
superior vertebrae
Cervical, thoracic, and lumbar spinal
nerves
Intertransversarii (in-ter-trans v
́ ersăr ́ē-ı̄)
Lateral flexion of vertebral column
O: Transverse processes of each
vertebra
I: Transverse process of more
superior vertebrae
Cervical, thoracic, and lumbar spinal
nerves
O: Iliac crest and iliolumbar
ligament
I: Last rib; transverse processes of
lumbar vertebrae
Thoracic and lumbar spinal nerves
MINOR DEEP BACK MUSCLES
SPINAL EXTENSORS AND LATERAL FLEXORS
Quadratus lumborum (kwah-drā ́tūs
lŭm-bōr ́ŭm)
quad = four-sided
lumb = lumbar region
Bilateral action: Extends vertebral
column
Unilateral action: Laterally flexes
vertebral column
11.3 Muscles of Respiration
Learning Objective:
1. Name the muscles of respiration, and explain their
functions.
The process of respiration involves inhalation and exhalation. When an individual inhales, several muscles contract to
increase the dimensions of the thoracic cavity to allow the lungs to
fill with air. When an individual exhales, some respiratory muscles
contract and others relax, collectively decreasing the dimensions of
the thoracic cavity and forcing air out of the lungs.
The muscles of respiration are on the anterior and posterior surfaces of the thorax. These muscles are covered by more
superficial muscles (such as the pectoral muscles, trapezius, and
latissimus dorsi) that move the upper limb. Two posterior thorax
muscles assist with respiration. These muscles are located deep
to the trapezius and latissimus dorsi, but superficial to the erector spinae muscles. The serratus posterior superior attaches to
ribs 2–5 (see figure 11.11) and elevates these ribs during inspiration, thereby increasing the lateral dimensions of the thoracic
cavity. The serratus posterior inferior attaches to ribs 8–12 and
depresses those ribs during expiration.
Several groups of anterior thorax muscles change the dimensions of the thorax during respiration (figure 11.13). The scalene
muscles (discussed previously with other neck muscles) help
elevate the first and second ribs during forced inspiration, thereby
increasing the dimensions of the thoracic cavity.
The external intercostals extend inferomedially from the
superior rib to the adjacent inferior rib. The external intercostals
assist in expanding the thoracic cavity by elevating the ribs during
inhalation. This movement is like lifting a bucket handle—that is, as
CLINICAL VIEW
Paralysis of the Diaphragm
Injury to critical parts of the brain, spinal cord, or phrenic nerves can
result in the loss of diaphragmatic innervation and cause paralysis.
When the diaphragm becomes paralyzed, it cannot contract, and thus
no air is exchanged in the lungs. The patient cannot breathe, and death
is inevitable unless artificial breathing measures are implemented.
The most common cause of diaphragmatic paralysis today is spinal
cord injury at or superior to the fourth cervical vertebra, where the
motor neurons that innervate the diaphragm are located. In years
past, infection with the poliovirus was a common cause of diaphragmatic paralysis, as the viral infection destroyed brain and spinal cord
motor neurons. Prior to the development of the modern ventilator (a
device to help the patient breathe) and other respiratory assistance
techniques, the polio patient with diaphragmatic paralysis was placed
in a device known as an iron lung. This was a chamber in which the air
pressure surrounding the patient was cyclically decreased to facilitate
inhalation and then increased to facilitate exhalation. Lying prone,
mck78097_ch11_322-353.indd 343
with only the head extending from this large, tubular apparatus, a
patient spent weeks or even months while the iron lung supplied the
needed respiratory assistance.
A patient in an iron lung due to diaphragm paralysis.
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Chapter Eleven
Axial Muscles
Scalene muscles
Scalene muscles
Sternum
External
intercostals
Serratus
anterior
Internal
intercostals
Internal
intercostals
Transversus
thoracis
External
intercostals
Ribs (cut)
Diaphragm
Lung
Diaphragm
(a) Anterior view
(b) Anterolateral view
Sternum
Xiphoid process
Costal cartilage
Sternum
Caval opening
Central tendon
of diaphragm
Sternum
Esophageal
opening
External intercostals
Internal intercostals
(c) Lateral view
Aortic opening
(hiatus)
12th rib
Right crus
L2
Left crus
L3
L4
Quadratus lumborum
muscle (cut)
Psoas major
muscle (cut)
(d) Diaphragm, inferior view
Figure 11.13
Muscles of Respiration. These skeletal muscles contract rhythmically to alter the size of the thoracic cavity and facilitate respiration.
(a) Anterior view. (b) A cadaver photo provides an anterolateral view, with the inferior ribs cut to expose the thoracic cavity and the superior
surface of the diaphragm. (c) Lateral views demonstrate fiber directions of the external and internal intercostals. (d) Inferior view of the
diaphragm.
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Chapter Eleven
Axial Muscles
Table 11.9
Muscles of Respiration
Muscle
Action
Description
Origin/Insertion
Innervation
Serratus posterior superior
(sĕr-ā ́tŭs pos-tēr-ē-ōr
soo-pēr ́ē-ōr)
serratus = a saw
Elevates ribs during
inhalation
Thin, superior intermediate
back muscle; splits into four
separate muscle segments
O: Spinous processes of
C7–T3 vertebrae
I: Lateral borders of
ribs 2–5
Thoracic spinal nerves
Serratus posterior inferior
(sĕr-ā ́tŭs pos-tēr ḗ -ōr
infē ́rē-ōr)
Depresses ribs during
exhalation
Thin, inferior intermediate
back muscle; splits into four
separate muscle segments
O: Spinous processes of
T11–L2 vertebrae
I: Inferior borders of
ribs 8–12
Thoracic spinal nerves
External intercostals
(eks-ter n
́ ăl in t́ er-kos t́ alz)
inter = between
cost = rib
Elevates ribs during
inhalation
11 pairs of oblique fibers
between ribs; project
anteroinferiorly
O: Inferior border of
superior rib
I: Superior border of
inferior rib
Thoracic spinal nerves
Internal intercostals
(in-ter ́nal in ́ter-kos t́ alz)
Depresses ribs during forced
exhalation; antagonistic to
external intercostals
11 pairs of oblique fibers
between ribs; project
posteroinferiorly
O: Superior border of
inferior rib
I: Inferior border of
superior rib
Thoracic spinal nerves
Transversus thoracis
(trans-ver ś ŭs thō-ra ́sis)
Depresses ribs during
exhalation
Assist in decreasing
diameter of thoracic cavity
O: Posterior surface of
xiphoid process and
inferior region of sternum
I: Costal cartilages 2–6
Thoracic spinal nerves
Diaphragm (dı̄ ́ă-fram)
dia = across
phragm = partition
Contraction causes
flattening of diaphragm
(moves inferiorly), and
thus expansion of thoracic
cavity; increases pressure in
abdominopelvic cavity
Dome-shaped, broad muscle;
separates thoracic and
abdominopelvic cavities
O: Inferior internal surface
of ribs 7–12; xiphoid
process of sternum
and costal cartilages of
inferior 6 ribs; lumbar
vertebrae
I: Central tendon
Phrenic nerves (C3–C5)
345
Scalene muscles (anterior,
middle, posterior) (see
table 11.7 for description)
the bucket handle (rib) is elevated, its distance from the center of the
bucket (thorax) increases. Thus, contraction of the external intercostals increases the transverse dimensions of the thoracic cavity. The
internal intercostals lie deep to the external intercostals, and their
muscle fibers are at right angles to the external intercostals. The
internal intercostals depress the ribs, but only during forced exhalation; normal exhalation takes no active muscular effort.
A small transversus thoracis extends across the inner surface of the thoracic cage and inserts on ribs 2–6. It helps depress
the ribs.
Finally, the diaphragm is an internally placed, domeshaped muscle that forms a partition between the thoracic and
abdominopelvic cavities. It is the most important muscle associated with breathing. The muscle fibers of the diaphragm converge from its margins toward a fibrous central tendon, a strong
aponeurosis that is the insertion tendon for all peripheral muscle
fibers of the diaphragm. When the diaphragm contracts, the central tendon is pulled inferiorly toward the abdominopelvic cavity,
thereby increasing the vertical dimensions of the thoracic cavity.
As it compresses the abdominopelvic cavity, it also increases
intra-abdominal pressure, an event that is necessary for urination, defecation, and childbirth. Beyond respiration, diaphragm
movements are also important in helping return venous blood to
the heart from the inferior half of the body.
Table 11.9 summarizes the characteristics of the muscles of
respiration.
mck78097_ch11_322-353.indd 345
W H AT D O Y O U T H I N K ?
3
●
After you’ve eaten a very large meal, it is sometimes difficult to
take a big, deep breath. Why is it more difficult to breathe deeply
with a full GI tract?
W H AT D I D Y O U L E A R N?
9
●
Compare the functions of the external intercostals and the internal
intercostals.
10
●
Identify the muscle of respiration that partitions the thoracic and
abdominopelvic cavities. What is the name of the structure to
which all fibers of this muscle converge?
11.4 Muscles of the Abdominal Wall
Learning Objective:
1. Illustrate the organization and function of the muscles of
the abdominal wall.
The anterolateral wall of the abdomen is reinforced by four
pairs of muscles that collectively compress and hold the abdominal
organs in place: the external oblique, internal oblique, transversus abdominis, and rectus abdominis (figure 11.14). These muscles also work together to flex and stabilize the vertebral column.
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Chapter Eleven
Axial Muscles
Superficial
Deep
Pectoralis
minor
Pectoralis major
Serratus anterior
External oblique
Tendinous intersections
Rectus sheath
Rectus abdominis
Umbilicus
Transversus abdominis
Internal oblique (cut)
Linea alba
External oblique (cut)
Aponeurosis of
external oblique
Inguinal ligament
Internal oblique
and
rectus abdominis
(a) Anterior view
External
intercostal
Tendinous intersections
Internal
intercostal
Inguinal
ligament
Rectus
abdominis
Rectus sheath
Transversus
abdominis
Umbilicus
(c)
Linea alba
Transversus abdominis
Internal oblique (cut)
Aponeurosis of
external oblique
External oblique (cut)
Inguinal ligament
(b) Anterolateral view
mck78097_ch11_322-353.indd 346
Figure 11.14
Muscles of the Abdominal Wall.
The abdominal muscles compress abdominal
contents and flex the vertebral column. (a) An
illustration provides an anterior view of some
superficial and deep muscles. (b) A cadaver
photo provides an anterolateral view of the
muscles of the abdominal wall. (c) Diagrams
show some individual abdominal muscles,
ranging from superficial to deep.
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Chapter Eleven
Table 11.10
Muscles of the Abdominal Wall
Muscle
Action
1
347
Axial Muscles
Description
Origin/Insertion
Innervation
External oblique
(eks-ter n
́ ăl ob-lēk ́)
Unilateral action : Lateral
flexion of vertebral column;
rotation of vertebral column
to opposite side
Bilateral action2: Flexes
vertebral column and
compresses abdominal wall
Large superficial muscle
sheet; fibers project
inferomedially; forms
inguinal ligament
O: External and inferior
borders of the inferior
8 ribs
I: Linea alba by a broad
aponeurosis; some to
iliac crest
Spinal nerves T8–T12, L1
Internal oblique
(in-ter n
́ al ob-lēk ́)
Unilateral action: Lateral
flexion of vertebral column;
rotation of vertebral column
to opposite side
Bilateral action: Flexes
vertebral column and
compresses abdominal wall
Middle muscle sheet, deep
to external oblique and
superficial to transversus
abdominis; fibers primarily
project superomedially
O: Lumbar fascia, inguinal
ligament, and iliac crest
I: Linea alba, pubic crest,
inferior rib surfaces (last
4 ribs); costal cartilages
of ribs 8–10
Spinal nerves T8–T12, L1
Transversus abdominis
(trans-ver ́sŭs ab-dom í -nis)
Unilateral action: Lateral
flexion of vertebral column
Bilateral action: Flexes
vertebral column;
compresses abdominal wall
Deepest of the three muscle
sheets; fibers project
horizontally
O: Iliac crest, cartilages of
inferior 6 ribs; lumbar
fascia; inguinal ligament
I: Linea alba and pubic
crest
Spinal nerves T8–T12, L1
Rectus abdominis
(rek t́ ŭs ab-dom í -nis)
Flexes vertebral column;
compresses abdominal wall
Paired anterior and medial
surface muscles; extend
from thoracic cage to pubis;
wrapped by aponeuroses of
lateral muscles; segmented
by three perpendicular
tendinous intersections
O: Superior surface of pubis
near symphysis
I: Xiphoid process of
sternum; inferior surfaces
of ribs 5–7
Spinal nerves T7–T12
1
Unilateral action means only one muscle (either the left or right muscle) is contracting.
2
Bilateral action means both the left and right muscles are contracting together.
When these muscles unilaterally contract, they laterally flex the
vertebral column.
The muscle fibers of the superficial external oblique are
directed inferomedially. The external oblique is muscular along the
lateral abdominal wall and forms an aponeurosis as it projects anteriorly. Inferiorly, the aponeurosis of the external oblique forms a strong,
cordlike inguinal ligament that extends from the anterior superior
iliac spine to the pubic tubercle. Immediately deep to the external
oblique is the internal oblique. Its muscle fibers project superomedially, which is at right angles to the external oblique. Like the external
oblique, this muscle forms an aponeurosis as it projects anteriorly.
Unilaterally, the external and internal oblique also rotate the vertebral
column to the opposite side of the contracting muscle.
The deepest muscle is the transversus abdominis, whose
fibers project transversely across the abdomen. The rectus
abdominis is a long, straplike muscle that extends vertically the
entire length of the anteromedial abdominal wall between the sternum and the pubic symphysis. It is partitioned into four segments
by three fibrous tendinous intersections, which form the traditional “six-pack” of a muscular, toned abdominal wall. The rectus
abdominis is enclosed within a fibrous sleeve called the rectus
sheath, which is formed from the aponeuroses of the external
oblique, internal oblique, and transversus abdominis muscles. The
left and right rectus sheaths are connected by a vertical fibrous
strip termed the linea alba.
Table 11.10 summarizes the characteristics of the muscles
of the abdominal wall.
mck78097_ch11_322-353.indd 347
Study Tip!
Knowing the direction of the oblique and intercostal muscle fibers
can help you identify these specific muscles on models and cadavers:
■
The fibers of the external intercostals and external oblique
muscles run in the same direction—inferomedially. This is the
same direction that you put your hands in your pockets.
■
The fibers of the internal intercostals and internal oblique
muscles run perpendicular (in the opposite direction) to the
external muscles—superomedially.
We have seen that multiple muscles may work together to
perform a common function. For example, several neck muscles
and back muscles work together to extend the vertebral column. Learning muscles in groups according to common function helps most students assimilate the anatomy information.
Table 11.11 summarizes the actions of various axial muscles
and groups them according to common function. Note that a
muscle that has multiple functions is listed in more than one
group.
W H AT D I D Y O U L E A R N?
11
●
Identify the muscles of the abdominal wall.
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Chapter Eleven
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Table 11.11
Muscle Actions on the Axial Skeleton
Extend the Head,
Neck, and/or
Vertebral Column
Flex the Head,
Neck, and/or
Vertebral Column
Laterally Flex the
Vertebral Column
Rotate the Head
and/or Neck to One
Side
Elevate the Ribs
Depress the Ribs
Splenius muscles2
Sternocleidomastoid2
Quadratus lumborum1
Sternocleidomastoid1
Serratus posterior
superior
Serratus posterior
inferior
Erector spinae2
(iliocostalis,
longissimus, spinalis)
Scalenes2
External oblique1
Splenius muscles1
External intercostals
Internal intercostals
Quadratus lumborum2
External oblique2
Internal oblique1
Longissimus capitis1
Scalene muscles (ribs
1 and 2 only)
Transversus thoracis
Transversospinalis
group2
Internal oblique2
Transversus abdominis1
Obliquus capitis
inferior1
Minor deep back
muscles2
Transversus abdominis2
Rectus capitis posterior
major and minor2
Rectus abdominis2
1
Unilateral action of muscles
2
Bilateral action
Obliquus capitis
superior1
11.5 Muscles of the Pelvic Floor
Learning Objective:
1. Identify the muscles that form the pelvic floor and perineum.
The floor of the pelvic cavity is formed by three layers of
muscles and associated fasciae, collectively known as the pelvic
diaphragm. (The term diaphragm refers to a muscle or group
CLINICAL VIEW:
In Depth
Hernias
The condition in which a portion of the viscera protrudes through a
weakened point of the muscular wall of the abdominopelvic cavity is
called a hernia (her ń ē -ă; rupture). A significant medical problem may
develop if the herniated portion of the intestine swells, becoming
trapped. Blood flow to the trapped segment may diminish, causing
that portion of the intestine to die. This condition, called a strangulated intestinal hernia, is very painful and can be life-threatening
if not treated promptly.
Two common types of hernias are inguinal hernias and femoral hernias.
An inguinal hernia is the most common type of hernia to require
treatment. The inguinal region is one of the weakest areas of the
abdominal wall. Within this region is a canal (inguinal canal) that
allows the passage of the spermatic cord in males, and a smaller structure in females called the round ligament of the uterus. The inguinal
canal, or the superficial inguinal ring associated with it, is often
the site of a rupture or separation of the abdominal wall. Males are
more likely to develop inguinal hernias than females, because their
inguinal canals and superficial inguinal rings are larger to allow room
for the spermatic cord. Rising pressure in the abdominopelvic cavity,
as might develop while straining to lift a heavy object, provides the
mck78097_ch11_322-353.indd 348
of muscles that covers or partitions an opening.) The pelvic
diaphragm extends from the ischium and pubis of the ossa coxae
across the pelvic outlet to the sacrum and coccyx. These muscles
collectively form the pelvic floor and support the pelvic viscera
(figure 11.15).
The most superior(deepest) layer of the pelvic diaphram consists of the coccygeus and the levator ani. The coccygeus pulls the
coccyx anteriorly after its posterior deflection during defecation or
force to push a segment of the small intestine into the canal. There
are two types of inguinal hernia:
■
■
In a direct inguinal hernia, the loop of small intestine protrudes
directly through the superficial inguinal ring, but not through
the entire length of the inguinal canal, and creates a bulge
in the lower anterior abdominal wall. This type of hernia is
typically seen in middle-aged males with poorly developed
abdominal muscles and protruding abdomens.
In an indirect inguinal hernia, the herniation travels through
the entire inguinal canal and may even extend all the way into
the scrotum, since the path of the herniation follows the path
of the spermatic cord. This type of hernia tends to occur in
younger males or male children who have a congenital anomaly
called patent process vaginalis, in which the embryonic path
taken by the testis into the scrotum fails to regress.
A femoral hernia occurs in the upper thigh, just inferior to the inguinal
ligament, originating in a region called the femoral triangle. The medial
part of the femoral triangle is relatively weak and prone to stress injury,
thus allowing a loop of small intestine to protrude. Women more commonly
develop femoral hernias because of the greater width of their femoral
triangle, which equates to the wider hip span of the female anatomy.
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349
Figure 11.15
Muscles of the Pelvic Floor.
The pelvic cavity floor is composed of
muscle layers that form the urogenital
and anal triangles, extend across the
pelvic outlet, and support the organs
in the pelvic cavity (puborectalis not
shown). (a) Superior view of the female
pelvic cavity. (b, c) Inferior views show
male and female perineal regions,
respectively.
Sacrum
Sacroiliac articulation
Ilium
Coccyx
Piriformis
Coccygeus
Ischial spine
Obturator internus
Anal canal
Iliococcygeus
Levator
Pubococcygeus ani
Obturator canal
Vagina
Urethra
Urogenital diaphragm
Pubic symphysis
(a) Female, superior view
Pubic symphysis
Pubic ramus
External urethral
sphincter
Urethra
Deep transverse
perineal muscle
Raphe
Bulbospongiosus
Urogenital
triangle
Ischiocavernosus
Superficial transverse
perineal muscle
Perineal body
Anus
External anal
sphincter
Levator ani
Anal
triangle
Gluteus maximus
Superficial
Deep
(b) Male, inferior view
Pubic symphysis
Pubic ramus
External urethral
sphincter
Urethra
Vagina
Deep transverse
perineal muscle
Perineal body
Anus
External anal
sphincter
Urethra
Vagina
Urogenital
triangle
Bulbospongiosus
Ischiocavernosus
Superficial transverse
perineal muscle
Levator ani
Anal
triangle
Gluteus maximus
Superficial
Deep
(c) Female, inferior view
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childbirth. The external anal sphincter (located within a region
called the anal triangle) assists in defecation. The largest and most
important collection of muscles in the pelvic floor is the levator ani.
It supports the pelvic viscera and functions as a sphincter at the
anorectal junction, urethra, and vagina. The levator ani is formed
by the iliococcygeus, the pubococcygeus, and the puborectalis (not
shown in figures). The puborectalis muscle forms a circular “sling”
around the anorectal junction. When this muscle is contracted, it
increases the bend or angle of the anorectal junction. When an
individual wishes to defecate, the puborectalis muscle must be consciously relaxed to decrease the bend of the anorectal junction and
allow for the easy passage of feces through the rectum.
The diamond-shaped region between the lower appendages is
called the perineum. The perineum has four significant bony landmarks: the pubic symphysis anteriorly, the coccyx posteriorly, and
both ischial tuberosities laterally. A transverse line drawn between
the ischial tuberosities partitions the perineum into an anterior urogenital triangle that contains the external genitalia and urethra, and
a posterior anal triangle that contains the anus (figure 11.15b, c).
The urogenital triangle is subdivided into a superficial layer
and a deep layer. The superficial layer of the urogenital triangle is
composed of three muscles: bulbospongiosus, ischiocavernosus,
and superficial transverse perineal (table 11.12). The ischiocavernosus inserts on the pubic symphysis, while the bulbospongiosus
and superficial transverse perineal muscles insert on a tendinous
central structure called the perineal body (or central tendon of the
perineum). The deep layer of the urogenital triangle is composed
of two muscles: the deep transverse perineal and the external
CLINICAL VIEW
Episiotomy
An episiotomy (e-piz-ē-ot ṓ -mē; epicios = vulvar, otomy = to cut) is a
surgical incision made in the perineal skin and soft tissues between
the vagina and the anus during childbirth to prevent tearing of the
mother’s tissues and to minimize fetal injury. It was long believed
that a clean surgical incision heals more rapidly and effectively than
a laceration or tear, but lately its routine use has come into question.
Large studies have indicated that serious perineal lacerations may be
more common in women who have had an episiotomy. Furthermore,
in some European countries where the procedure is rarely done, no
significant increase in serious maternal or fetal complications has
been seen. Medical studies now indicate that, at most, 25–30% of
women would benefit from the procedure, and that the selective use
of episiotomy may be a better health-care option. Women approaching childbirth are advised to talk in advance with their health-care
provider about the necessity of having an episiotomy.
urethral sphincter. These muscles are collectively referred to as
the urogenital diaphragm, because they serve as a partition for
the urogenital portion of the pelvic floor.
Table 11.12 summarizes the characteristics of the muscles of
the pelvic floor.
Table 11.12
Muscles of the Pelvic Floor
Group/Muscle
Action
Origin/Insertion
Innervation
Coccygeus (kok-si ́jē-ŭs)
coccy = coccyx
Forms pelvic floor and supports
pelvic viscera
O: Ischial spine
I: Lateral and inferior borders of
sacrum
Spinal nerves (S4–S5)
External anal sphincter (eks-ter ́năl
ā ́năl sfingk ́ter)
anal = referring to anus
sphin = squeeze
Closes anal opening; must relax to
defecate
O: Perineal body
I: Encircles anal opening
Pudendal nerve (S2–S4)
ANAL TRIANGLE
Levator ani (lē-vā ́tor, le-vā ́-ter ā ́nı̄)
levator = raises
ani = anus
Iliococcygeus (il ́ē-ō-kok-si j́ ē-ŭs)
ilio = ilium
Pubococcygeus (pū ́bō-kok-si ́
jē-ŭs)
pubes = pubis
Puborectalis (pū ́-bō-rek t́ ăl-is)
rectal = rectum
Group of muscles that form the
anterior and lateral parts of the
pelvic diaphragm
Forms pelvic floor and supports
pelvic viscera
Pubis and ischial spine
Coccyx and median raphe
Pubis and ischial spine
Coccyx and median raphe
Pudendal nerve (S2–S4)
Forms pelvic floor and supports
pelvic viscera
O:
I:
O:
I:
Supports anorectal junction; must
relax to defecate
O: Pubis and ischial spine
I: Coccyx and median raphe
Pudendal nerve (S2–S4)
Bulbospongiosus (female)
(bul ́bō-spŭn j́ ē-ō ́sŭs)
bulbon = bulb
spongio = sponge
Narrows vaginal opening;
compresses and stiffens clitoris
O: Sheath of collagen fibers at base
of clitoris
I: Perineal body
Pudendal nerve (S2–S4)
Bulbospongiosus (male)
Ejects urine or semen; compresses
base of penis; stiffens penis
O: Sheath of collagen fibers at base
of penis
I: Median raphe and perineal body
Pudendal nerve (S2–S4)
Pudendal nerve (S2–S4)
UROGENITAL TRIANGLE
SUPERFICIAL LAYER
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Chapter Eleven
Table 11.12
Muscles of the Pelvic Floor (continued)
Group/Muscle
Action
Axial Muscles
Origin/Insertion
Innervation
351
UROGENITAL TRIANGLE (continued)
SUPERFICIAL LAYER
Ischiocavernosus (ish ́ē-ō-kav ́ernō ́sŭs)
ischi = hip
caverna = hollow chamber
Assists erection of penis or clitoris
O: Ischial tuberosities and ischial
ramus
I: Pubic symphysis
Pudendal nerve (S2–S4)
Superficial transverse perineal
muscle (soo-per-fish ́ăl trans-vers ́
per-i-nē ́-ăl)
Supports pelvic organs
O: Ramus of ischium
I: Perineal body
Pudendal nerve (S2–S4)
DEEP LAYER (UROGENITAL DIAPHRAGM)
Deep transverse perineal muscle
(dēp trans-vers ́ per-i-nē ́ăl)
Supports pelvic organs
O: Ischial ramus
I: Median raphe of urogenital
diaphragm
Pudendal nerve (S2–S4)
External urethral sphincter
(eks-ter n
́ ăl ū-rē ́thrăl sfingk t́ er)
sphin = squeeze
Constricts urethra to voluntarily
inhibit urination
O: Rami of ischium and pubis
I: Median raphe of urogenital
diaphragm
Pudendal nerve (S2–S4)
Clinical Terms
linea nigra Condition sometimes seen in pregnant females. The
linea alba of the rectus sheath darkens (hence the term
“nigra”), forming a line that extends along the midline of the
abdomen.
rectus sheath separation Separation of the left and right rectus
muscles/sheaths due to great expansion of the abdomen (as
occurs in some pregnancies). If severe, the separation may
have to be repaired surgically.
Chapter Summary
11.1 Muscles of
the Head and
Neck 323
■
The axial muscles attach to components of the axial skeleton, whereas the appendicular muscles stabilize or move
components of the appendicular skeleton.
■
Axial musculature functions include supporting and positioning the head, vertebral column, and thoracic cage; controlling
movements associated with respiration; and forming part of the floor of the pelvic cavity.
■
Muscles of the head and neck are separated into groups based on their specific activities.
11.1a Muscles of Facial Expression
■
11.1b Extrinsic Eye Muscles
■
328
The six extrinsic eye muscles attach to the eye and control the movements and position of the eyes.
11.1c Muscles of Mastication
■
323
The muscles of facial expression arise from the skull and often attach to the skin.
332
The muscles of mastication move the mandible during chewing.
11.1d Muscles That Move the Tongue
■
11.1e Muscles of the Pharynx
■
334
Muscles of the pharynx function in swallowing.
11.1f Muscles of the Anterior Neck
■
332
The muscles of the tongue are divided into intrinsic muscles, which function during chewing and speaking, and extrinsic
muscles, which function during food manipulation, swallowing, and some speech-related activities.
335
Anterior neck muscles are the suprahyoid muscles, superior to the hyoid bone, and the infrahyoid muscles, inferior to the
hyoid bone. These move the hyoid bone or thyroid cartilage during swallowing or speaking.
11.1g Muscles That Move the Head and Neck
11.2 Muscles of
the Vertebral
Column 340
337
■
Muscles that move the head and neck originate on the vertebral column, the thoracic cage, and the pectoral girdle, and
insert on bones of the cranium.
■
Deep back muscles extend the vertebral column.
(continued on next page)
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352
Chapter Eleven
Axial Muscles
Chapter Summary (continued)
11.3 Muscles of
Respiration 343
11.4 Muscles of
the Abdominal
Wall 345
11.5 Muscles of the
Pelvic Floor 348
■
The muscles of respiration are located on the anterior and posterior surfaces of the thorax and are covered by more
superficial muscles. Their contraction either increases or decreases the size of the thoracic cavity.
■
The muscles of the abdominal wall compress the abdomen, help hold the abdominal organs in place, and assist the
stabilization and lateral flexion of the vertebral column.
■
The muscles of the pelvic floor extend from the pubis and ischium anteriorly to the sacrum and coccyx posteriorly.
They support the pelvic cavity organs and control the evacuation of waste materials from the digestive and urinary
systems.
Challenge Yourself
Matching
Match each numbered item with the most closely related lettered
item.
______ 1. platysma
a. moves eye laterally
______ 2. buccinator
b. elevates and retracts tongue
______ 3. lateral rectus
c. elevates and retracts
mandible
______ 4. temporalis
______ 5. levator ani
______ 6. digastric
______ 7. external intercostal
______ 8. styloglossus
______ 9. zygomaticus major
______ 10. spinalis group
d. tenses skin of neck
e. extends vertebral column
f. elevates angles of mouth
g. compresses cheeks
h. supports pelvic floor
and viscera
i. depresses mandible
j. elevates ribs
Multiple Choice
Select the best answer from the four choices provided.
______ 1. The geniohyoid muscle
a. depresses the hyoid bone and larynx.
b. elevates the floor of the mouth.
c. elevates the hyoid bone.
d. depresses the larynx.
______ 2. When the left and right ______ contract, they flex
the neck.
a. sternocleidomastoid
b. longissimus group
c. splenius
d. rectus abdominis
______ 3. When this large muscle contracts, the vertical
dimensions of the thoracic cavity increase.
a. external intercostal
b. internal intercostal
c. diaphragm
d. transversus thoracis
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______ 4. Which of the following is not a muscle within the
urogenital triangle?
a. bulbospongiosus
b. coccygeus
c. superficial transverse perineal
d. ischiocavernosus
______ 5. The muscle that does not cause some lateral
movement in the eye is the
a. inferior rectus.
b. inferior oblique.
c. lateral rectus.
d. superior oblique.
______ 6. Which muscle allows you to stick out your tongue?
a. palatoglossus
b. genioglossus
c. lateral pterygoid
d. hyoglossus
______ 7. Each of these muscles can laterally flex the vertebral
column, except the
a. external oblique.
b. transversus abdominis.
c. spinalis.
d. internal oblique.
______ 8. Which muscle is not involved in extending the head
or neck?
a. rectus capitis posterior major
b. longissimus capitis
c. sternocleidomastoid
d. splenius cervicis
______ 9. One function of the transversus abdominis muscle is
to
a. elevate the ribs.
b. compress the abdominal wall.
c. extend the vertebral column.
d. increase the dimensions of the thoracic cavity.
______ 10. Which muscle protrudes the lower lip (as when you
“pout”)?
a. risorius
b. levator labii superioris
c. mentalis
d. zygomaticus major
2/14/11 3:06 PM
Chapter Eleven
Content Review
1. Describe which muscles of facial expression you use to
(a) smile and (b) frown.
2. Compare and contrast the functions of the extrinsic muscles
of the tongue.
3. Discuss why the eye moves slightly medially during the
contraction of either the superior or inferior rectus muscle.
4. Discuss the effect of contracting the three pharyngeal
constrictors during swallowing.
5. Distinguish between suprahyoid and infrahyoid muscles,
and describe the functions of each group.
6. Describe the differences in action between bilateral and
unilateral contraction of the splenius muscles.
7. Describe the functions of the thoracic diaphragm.
8. What is the effect of contracting the abdominal oblique
muscles?
9. What structures form the rectus sheaths, and how do the
left and right rectus sheaths relate to the linea alba?
Axial Muscles
353
10. What are the general functions of the pelvic diaphragm
muscles, and what specific muscles form the pelvic
diaphragm?
Developing Critical Reasoning
1. Albon is a 45-year-old male who characterizes himself as a
“couch potato.” He exercises infrequently and has a rounded
abdomen (“beer belly”). While helping a friend move
some heavy furniture, he felt a sharp pain deep within his
abdominopelvic cavity. An emergency room resident told
Albon that he had suffered an inguinal hernia. What is
this injury, how did it occur, and how might Albon’s poorly
developed abdominal musculature have contributed to it?
2. While training on the balance beam, Pat slipped during
her landing from a back flip and fell, straddling the beam.
Although only slightly sore from the fall, she became
concerned when she suddenly lost the ability to completely
control her urination. What might have happened to Pat’s
pelvic floor structures during the fall?
Answers to “What Do You Think?”
1. The zygomaticus major, zygomaticus minor, levator anguli
oris, risorius, and levator labii superioris all contract when
you smile.
2. Since the omohyoid attaches to the scapula, the prefix -omo
means “shoulder.”
3. When you breathe deeply, the diaphragm contracts and
pushes down on the GI tract (abdominal viscera). If these
viscera are bulging with food, the diaphragm has difficulty
contracting fully, making it hard to take deep breaths.
www.mhhe.com/mckinley3 Enhance your study with practice tests and activities to
assess your understanding. Your instructor may also recommend the interactive eBook,
individualized learning tools, and more.
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