Part 6
Head Muscles
 Grouped into two large categories:
1. Facial Muscles – Permit us to frown, smile, deliver a
kiss, pout, etc…
2. Chewing Muscles –
Begin the breakdown
of food
Head Muscles- Facial Muscles
1. Orbicularis Oculi – Run in circles around the eye;
Allows you to close your eyes, squint, blink, and wink
2. Orbicularis Oris – Circular muscle of the lips; It
closes the mouth and protrudes the lips; Often called
the “kissing” muscle
Head Muscles – Facial Muscles
3. Buccinator – Fleshy muscle that runs horizontally across the
cheek and inserts into the orbicularis oris; It flattens the cheek
(as in whistling or blowing) and compresses the cheek to hold
the food between the teeth during chewing
4. Zygomaticus – Extends from the corner of the mouth to the
cheek bone; It raises the corners of the mouth upward; Often
referred to as the “smiling” muscle
Head Muscles – Chewing Muscles
1. Buccinator - Discussed with the facial muscles
2. Masseter – Covers the angle of the lower jaw as it
runs from the temporal bone to the mandible; Closes
the jaw by elevating the mandible
3. Temporalis – Fan-shaped muscle overlying the
temporal bone and inserts into the mandible; Acts as
a synergist of the masseter in closing the jaw
Neck Muscles
 The neck muscles move the head and shoulder
girdle; They are small and strap-like
Platysma – Single, sheetlike muscle that covers the
anterolateral neck
1.


Originates from the chest muscles and inserts into the
area around the mouth
Its action is to pull the
corners of the mouth
inferiorly, which
produces a downward
sag of the mouth
Neck Muscles
2. Sternocleidomastoid – Paired muscles that are two-
headed (one found on each side of the neck)


Of the two heads of each muscle, one arises from the
sternum and the other arises from the clavicle. The
heads fuse before inserting into the temporal bone
Action:
 When both muscles contract together,
they flex the neck
 If just one muscle contracts, the head
is rotated toward the opposite side
Trunk Muscles
 Include :
Those that move the
vertebral column
1.

Most are posterior antigravity muscles
2. Anterior thorax muscles
 Move the ribs, head, and arms
3. Muscles of the abdominal wall
 Help to move the vertebral column and form the muscular
“natural girdle” of the abdominal body wall
Trunk Muscles - Anterior
 Pectoralis Major – Large
fan-shaped muscle
covering the upper part
of the chest; Acts to
adduct and flex the arm
Trunk Muscles - Anterior
 Intercostal Muscles –
Deep muscles found
between the ribs
 Action

External Intercostals –
Important in breathing
because they help to raise
the rib cage for breathing
air in
Internal Intercostals Depress the rib cage,
which helps to move air
out of the lungs when you
exhale forcibly
Trunk Muscles - Anterior
 Muscles of the Abdominal Girdle include 1. Rectus abdominis
2. External oblique
3. Internal oblique
4. Transversus abdominis
 These muscle together form a natural “girdle” that
reinforces the body trunk. Taken together they resemble
the structure of plywood.
 The fibers of each muscle run in a different direction
 The abdominal muscles form a muscular wall that is well
suited for its job of containing and protecting the
abdominal contents
Trunk Muscles – Anterior
 Abdominal Girdle Muscles
1. Rectus Abdominis – Paired
and straplike; Most superficial
muscles of the abdomen


Run from the pubis to the
ribcage
Action – Flex the vertebral
column, also compress the
abdominal contents during
defecation and childbirth, are
involved in forced breathing
Trunk Muscles – Anterior
 Abdominal Girdle Muscles
2. External Oblique – Paired
superficial muscles that
make up the lateral walls
of the abdomen

Action – Flex the vertebral
column , rotate the trunk,
and bend it laterally
Internal Oblique – Paired
muscles deep to the external obliques
3.


Their fibers run at right angles to those of the external
obliques
Action – Same as those of the external obliques
Trunk Muscles – Anterior
 Abdominal Girdle
Muscles
4. Transversus Abdominis
– Deepest muscle of
the abdominal wall and
has fibers that run
horizontally across the
abdomen

Action – Compresses
the abdominal contents
Trunk Muscles – Posterior
Trapezius – Are the most
superficial muscles of
the posterior neck and
upper trunk
1.


When seen together
they form a diamond or
kite-shaped muscle
Actions – Extend the
head, can also elevate,
depress, adduct, and
stabilize the scapula
Trunk Muscles – Posterior
2. Latissimus Dorsi – Large,
flat muscle pair that covers
the lower back


Action - Extends and
adducts the humerus
Very important muscles
when the arm must be
brought down in a power
stroke (such as swimming
or striking a blow)
Trunk Muscles – Posterior
3. Erector Spinae – Group of
deep muscles that are a prime
mover of back extension


Action – Powerful back
entensors and also provide
resistance that helps control
the action of bending over at
the waist
Following injury to back
structures, these muscles go
into spasms, a common
source of lower back pain
Trunk Muscles – Posterior
4. Deltoid – Fleshy, triangle-
shaped muscles that form the
rounded shape of your
shoulders


Action – Prime movers of
arm abduction
Because they are so bulky,
they are a favorite injection
site when relatively small
amounts of medication must
be given intramuscularly
Muscles of the Upper Limb
 All anterior arm muscles
cause elbow flexion.
1. Biceps Brachii – The
powerful prime mover for
flexion of the forearm and
acts to supinate the forearm

Most familiar muscle of the
arm because it bulges when the
elbow is flexed
Muscles of the Upper Limb
2. Brachialis – Lies deep to the biceps
muscle; Is as important as the
biceps in elbow flexion
3. Brachioradialis – Fairly weak
muscle; Resides mainly in the
forearm
Muscles of the Upper Limb
4. Triceps Brachii – The powerful
prime mover of elbow extension



The only muscle fleshing out of
the posterior humerus
It contains three heads
It is the antagonist of the biceps
brachii
Muscles of the Lower Limb
Gluteus Maximus –
Superficial muscle of the hip
that forms most of the flesh
of the buttock
1.


It is a powerful hip extensor
that acts to bring the thigh
in a straight line with the
pelvis
It is the most important
muscle for extending the
hip when power is needed
(as when climbing stairs or
jumping)
Muscles of the
Lower Limb
2. Gluteus Medius – Runs beneath
the gluteus maximus beneath for
most of its length


Action - Is a hip abductor and is
important in steadying the pelvis
during walking
Important site for giving
intramuscular injections when
more than 5 ml is administered
Muscles of the
Lower Limb
3. Iliopsoas – Fused muscle
composed of two muscles
(iliacus and the psoas
major)

Action – Prime mover of
hip flexion and acts to keep
the upper body from falling
backward when we are
standing erect
Muscles of the
Lower Limb
4. Adductor Muscles – The muscles
of the adductor group form the
muscle mass at the medial side of
each thigh


Action – Adduct or press the
thighs together
Since gravity does most of their
work for them, they tend to
become flabby very easily. Special
exercises are usually needed to
keep them toned.
Muscles of the Lower Limb
5. Hamstring Group –
The muscles forming
the muscle mass of the
posterior thigh
Action: Extends the
thigh and flexes the
knee
Consists of three
muscles:


1.
2.
3.
Biceps Femoris
Semimembranosus
Semitendinosus
Muscles of the
Lower Limb
6. Sartorius – Thin, straplike
muscle that is the most
superficial muscle of the
thigh

Action – Weak thigh
flexor
Muscles of the
Lower Limb
Quadriceps Group – The
group as a whole acts to
extend the knee
powerfully (as when
kicking a football)
7.
Consists of four muscles
that flesh out the anterior
thigh:

1.
2.
Rectus Femoris
Three Vastus Muscles
Muscles of the
Lower Limb
Tibialis Anterior – Superficial
muscle on the anterior lower
leg; Acts to dorsiflex and
invert the foot
9. Extensor Digitorum Longus –
Lateral to the tibialis
anterior; Prime mover of toe
extension and a dorsiflexor of
the foot
8.
Muscles of the
Lower Limb
10. Fibularis Muscles – Found on
the lateral part of the leg;
Group as a whole plantar
flexes and everts the foot

Consists of three fibularis
muscles – the longus, brevis,
and tertius
Muscles of the
Lower Limb
11. Gastrocnemius – Two-bellied
muscle that forms the curved calf of
the posterior leg



Arises by two heads (one from each
side of the distal femur) and inserts
through the Achilles tendon into the
heel of the foot
Action – Prime mover for plantar
flexion of the foot
If its insertion tendon is cut, walking
is very difficult (the foot drags
because the heel cannot be lifted)
Muscles of the
Lower Limb
12. Soleus – Located deep to the
gastocnemius

Action – Strong plantar flexor
of the foot
Self Assessment-Muscle Questions
A) What are the muscles of:






anterior body trunk?
posterior body trunk?
Anterior upper leg?
Posterior upper leg?
Anterior lower leg?
Posterior lower leg?
B) What is their prime
action?