Muscles of the Body
Chapter 11
Interactions of Skeletal Muscles




The arrangement of body muscles
permits them to work either together or
in opposition to achieve a movement
As muscle contract they can only pull on
the skeleton; they can never push
If you are pushing an object it is the
contraction of some group of muscles in
the body that will accomplish it
Generally muscles are grouped to “undo”
an action done by another group
– Quadriceps / Hamstrings
Working out with Muscles

Muscle contraction causes shortening, not
lengthening of a muscle
– Concentric / shortening against resistance
– Eccentric / lengthening against resistance

Typically as a muscle contracts it moves
its insertion toward its origin
– Lat. bar pull down / Latissimus dorsi

However, some muscles can contract and
move its origin toward its insertion
– Pull ups / Latissiums dorsi
Functional Muscle Groups

Muscles can be classified into four
functional groups
–
–
–
–
Prime movers
Antagonists
Synergists
Fixators
Prime Movers


A muscle that
Origin of
provides the major Biceps Brachii
force for producing
a specific movement
is called a prime
mover or agonist
The biceps brachii is
the prime mover of
elbow flexion
Coracoid
Process
Antagonist



Muscles that oppose
a particular
movement are
called antagonist
When a prime
mover is active, the
antagonist muscles
are often stretched
and may be in a
relaxed state
Antagonists also
regulate the action
of prime mover
Synergist


Synergists aid
agonists by
promoting the same
movement and by
reducing extraneous
movements that
may be produced
when the prime
mover acts
In two joint muscles
synergists stabilize a
joint as the muscle
acts on the other
Synergist can also restrict rotary
movement at a joint so the muscle’s
full effort be applied to the desired
movement
Fixator



When a synergist
immobilize a
muscle’s origin they
are called fixators
Their action serves
to stabilize the bone
upon which a prime
mover acts
Serratus anterior
holds the scapula
against the thorax
while a prime mover
acts upon the arm
Naming Skeletal Muscles

Location of the muscle
– Intercostal, Temporalis

Shape of the muscle
– Deltoid; Trapezius

Relative size of the muscle
– Maximus; medius; minimus; brevis; longus

Direction of muscle fibers
– Rectus (straight) fibers run parallel to line of
pull
– Transverse; fibers run perpendicular to line
– Oblique; fibers are oblique to the line
Naming of Muscles

Number of origins
– Biceps; triceps; quadriceps

Location of muscle origin and/or
insertion
– Sterno (sternum); cleido (clavicle); mastoid
(mastoid process of temporal bone)

Action of the muscle
– Flexor; extensor; adductor, supinator
Arrangement of Fascicles



Arrangement of
fascicles within a
muscle vary
Arrangements result
in differing shapes and
capabilities
Common forms are
– Parallel
• fusiform
– Pennate
• Uni-, bi-, multi-
– Convergent
– Circular or sphincteral
Parallel Arrangement of Fascicles




In parallel arrangement the long axis
of the fascicles run
parallel to the long
axis of the muscle
Form long straplike
muscles that have
greatest potential
for shortening
Act over a long
excursion
Not very powerful
Pennate Arrangement of Fascicles



Pennate fascicles are
short and they
attach obliquely to a
central tendon
Occur as pennate,
bipennate and
multipennate forms
Pennate muscles
with the highest
concentration of
A) Pennate / Ext. digitorum longus
fibers, shorten little, B) Bipennate / Rectus Femoris
but are very
C) Multipennate / Deltoid
powerful
Convergent Arrangement of Fascicle




A convergent muscle
has a broad origin
and its fascicles
converge toward a
single tendon
Muscle has a broad
triangular shape
Muscle can act upon
the joint from a
variety of positions
Pectoralis major
Circular Arrangement of Fascicles



Fascicular pattern is
arranged in
concentric rings
Muscles with this
arrangement
surround external
body openings
which they close by
contracting
This type of muscles
are called sphincters
which literally
means squeezers
Lever Systems


The operation of most skeletal muscles
involves the use of levers and lever systems
Lever
– A rigid bar that moves on a fixed point

Fulcrum
– A fixed point of leverage

Effort
– The forced applied to move a resistance

Load
– The resistance to me moved
Lever Systems


In the human body . . .
Levers
– The bones of the skeleton

Fulcrums
– The joints of the body

Effort
– Applied by the muscles of the body

Load
– Bone, overlying tissue, and other objects to
which your body applies force
Lever Systems


A lever allows a given effort to move a
heavier load or to move a load farther or
faster that it otherwise could
A small difference in the site of a muscle’s
insertion can translate into large
differences in the amount of force must
generate to move a given load
Mechanical Advantage


A small effort applied over a relatively long
distance can be used to move a large load over
a small distance
Such a lever operates at a mechanical
advantage and is commonly called a power
lever because it can lift heavy loads
Mechanical Disadvantage


When the load is far from the fulcrum and the force
is applied near the fulcrum, the force exerted by the
muscle must be greater than the load moved
These levers are useful because they allow the load
to move rapidly through a large distance and are
called speed levers
Lever Systems

Regardless of type, all levers follow the
same basic principle:
– Effort farther than load from fulcrum =
mechanical advantage
– Effort nearer than load to fulcrum =
mechanical disadvantage

Depending on the relative position of the
three elements (effort, fulcrum, load) a
lever is classified as either a first, second,
or third class lever
First Class Levers


In first class levers the effort is applied at one
end of the lever and the load is at the other end
with the fulcrum in between them (LFE)
Extension/flexion of the head, other exist but
usually operate at a mechanical disadvantage
Second Class Levers


In second class levers the effort is applied at one
end, the fulcrum is at the other, with the load
somewhere in between (FLE)
Plantar flexion of the foot
Third Class Levers



In third class levers, the effort is applied at a point
between the load and the fulcrum (LEF)
These levers operate with great speed and always at
a mechanical disadvantage
Most levers of the body are third class levers which
permit an insertion close to the joint and allow
rapid movement with little shortening of the muscle
Which Lever is it?

Fulcrum in the middle?
1st Class

Load in the middle?
2nd Class

Effort in the middle?
3rd Class
Lever Summary

Difference in the positioning of the three
elements modify muscle activity with respect to
– Speed on contraction
– Range of movement
– Weight of the load that can be lifted

Speed levers act at a mechanical disadvantage
– Force is lost, but speed is gained

Power levers act at a mechanical advantage
– Force is gained, but speed is lost
Major Skeletal Muscles





There are over 600 muscles in the body
Approximately 125 are presented in text
There will be 55 assigned to you to learn
As you learn these muscles try to relate to
its attachments and position and what
joint(s) it acts across
The best way to learn muscle actions is to
act them out in your body
Muscle of Head: Facial Expression
Table 10.1
Muscles of Head: Facial Expression




Promote facial expression and non-verbal
expression
Highly variable in shape and strength
Unusual in that they insert into skin or
other muscles and not bone
Innervated by Cranial nerve VII (facial)
Muscles of Head: Mastication
Muscles of Head: Mastication


Four pairs of muscles are involved with
mastication
Chewing and biting
– Masseter
– Temporalis

Grinding movements
– Pterygoid
– Buccinator

Trigeminal and Facial nerves
Muscles of Head: Tongue Movement
Table 10.2
Muscles of Head: Tongue Movement



The extrinsic muscles of the tongue serve
to anchor and move the tongue
These muscles serve to protrude, depress,
and retract the tongue
Innervated by the hypoglossal nerve
Muscle that Promote Swallowing
Table 10.8
Muscles that Promote Swallowing


Lateral view of the constrictor muscles of
the pharynx
These muscles are shown in their proper
anatomical relationship
Muscles of Anterior Neck & Throat
Table 10.3
Muscles of Anterior Neck & Throat

Most of these muscles are involved with
the coordinated action of swallowing
which have the following sequence
– Widening the pharynx and closing the larynx
– Closing the superior nasal cavity
– Propulsion of food through the pharynx into
the esophagus
– Return of musculature to normal positioning
Muscles of Neck



Sternocleidomastoid is a head flexor
Scalenes contribute to lateral flexion of the neck
Splenius is a head extensor
Muscles of Neck

The head is moved by muscles originating
from the axial skeleton which include
– Sternocleidomastoid / head flexors
– Scalenes / lateral head flexion
– Splenius / head extension
Muscles of Vertebral Column
Muscle of the Vertebral Column


Trunk extension is effected by the deep
muscles of the back
The erector spinae is the largest of the
group and consists of three bands
– Iliocostalis
– Longissimus
– Spinalis

Other muscles of the vertebral column
include
– Semispinalis / extends head
– Quadratus lumborum / Lateral flexion
Muscle of the Thorax: Breathing
External
Intercostals



O - Inferior border of
rib above
I - Superior border of
rib below
A - Pulls ribs upward to
aid in respiration
Internal
intercostals



O - Superior border
of rib below
I - Inferior border of
rib above
Draws ribs together;
aids in expiration
Muscles of the Thorax: Breathing
Diaphragm



O - Inferior
border of rib
cage, costal
cartilages of last
6 ribs, and
lumber vertabrae
I - Central
tendon
A - Inspiration
Muscles of the Abdominal Wall
Muscles of Abdominal Wall



The anterior and lateral abdominal wall
has no bony reinforcement
It is composed of four paired muscles,
their investing fasciae and their
aponeuroses
The muscles of the abdominal wall include
–
–
–
–
Rectus abdominis
External oblique
Internal oblique
Transverse abdominis
Muscles of the Abdominal Wall
Muscles of the Abdominal Wall



Illustration of how the aponeuroses of the
lateral abdominal muscles contribute to the
rectus abdominis sheath
Enclosure of the Rectus abdominis within the
aponeuroses prevents anterior protrusion or
bowstringing of the muscle
The Linea alba represents the central fusion of
the aponeurses along the midline
Rectus
abdominis



O - Pubic crest
and symphasis
I - xiphoid
process and
costal cartilages
of ribs 5 - 7
A - Flex and
rotate lumbar
region of the
vertebral
column
External
oblique



O - by fleshy
strips from outer
surfaces of ribs
5-7
I - Linea alba;
pubic crest and
tubercle via
aponeurosis
A - flexing
vertebral
column
Internal
oblique



O -Lumbodorsal
fasica, iliac crest
and inguinal
ligament
I - Linea alba,
pubic crest and
last 3 ribs
A - Flex
vertebral
column
Transverse
abdominis



O - inguinal
ligament, lumbodorsal fascia,
cartilages of last
6 ribs, iliac crest
I - Linea alba,
pubic crest
A - compresses
abdominal
contents
Muscles of the Pelvic Floor
Muscles of the Pelvic Floor


Stretching between the two sides of the pelvic
arch is the urogenital diaphram
The Sphinter urethrae surrounds the urethra
and allow voluntary urination
Muscles of the Pelvic Floor


Superficial space contains muscles (Ischocavernosus,
Bulbospongiosus) that help maintain erection of the
penis and clitoris
The external anal sphinter encircles the anus and
allows for voluntary control of defectation
Muscles of the Anterior Thorax
Pectoralis
minor



O - anterior
surfaces of ribs
3-5
I - coracoid
process of
scapula
A - ribs fixed
draws scapula
forward and
downward
Serratus
anterior



O - ribs 1-9
I - entire
anterior surface
of vertebral
border of
scapula
A - Protract the
scapula; rotates
scapula
Muscles of the Posterior Thorax
Trapezius



O - Occipital
bone,
ligamentum
nuchae, spines
of C7 & all
thoracic vert.
I - Acromium
and spine of
scapula and
lateral 1/3 of
clavicle
A - elevate and
rotate scapula
Levator
scapulae



O - transverse
processes of
C1 - C4
I - superior
angle of
scapula
A - elevates
and adducts
scapula
Rhomboid
major



O - spinous
processes of
T2 - T5
I - medial
border of
scapula
A - retract;
rotate; and
stabilize
scapula
Rhomboid
minor



O - spinous
processes of
C7 and T1
I - medial
border of
scapula
A - retract;
rotate; and
stabilize
scapula
Muscles Crossing the Shoulder Joint


A total of nine muscles cross the shoulder
joint to insert on the humerus
The three prime movers of the shoulder
joint are
– Pectoralis major
– Lastissimus dorsi
– Deltoid


The remaining six muscles are synergists
and fixators
Four of these six are muscles of the
rotator cuff
Muscles Crossing the Shoulder Joint
Pectoralis
major



O - clavicle,
sternum, and
cartilages of
ribs 1 - 6
I - greater
tubercle of
humerus
A - arm flexion,
medial arm
rotation, arm
adduction
Latissimus
dorsi



O - spines of
T6 - T12 and
L1 - L5 etc
I - Intertubicular
groove of
humerus
A - arm
extension,
adduction and
med. rotation
Deltoid



O - Lateral 1/3
of clavicle,
acromium, and
spine of scapula
I - Deltoid
tuberosity of
humerus
A - arm
abduction; flex/
ext. arm; med./
lat. rotate arm
Subscapularis



O - subscapular
fossa of scapula
I - lesser
tubercle of
humerus
A - medial
rotator of arm
Supraspinatus



O - supra
spinatus fossa
of scapula
I - superior
part of greater
tubercle of
humerus
A - holds head
of humerus in
glenoid fossa
to stabilize
shoulder joint
Infraspinatus



O - infra
spinatus fossa
of scapula
I - greater
tubercle of
humerus
A - laterally
rotates scapula
Teres minor



O - lateral
border of dorsal
scapular surface
I - greater
tubercle of
humerus
A - laterally
rotates scapula
Teres major



O - posterior
surface of
scapula at
inferior angle
I - lesser
tubercle of
humerus
A - extends,
medially
rotates and
adducts
humerus
Coracobrachialis



O - coracoid
process of
scapula
I - medial
surface of
shaft of
humerus
A - flexion and
adduction of
humerus
Muscles Crossing the Elbow Joint


Since the elbow is a hinge joint the
movement promoted by these muscles are
limited almost to flexion and extension of
the forearm
There are three muscles anteriorly
– Biceps brachii
– Brachialis
– Brachioradialis

There is one muscle posteriorly
– Triceps brachii
Muscles Crossing the Elbow Joint
Triceps
brachii



O - long head/
infraglenoid
tubercle; lat. and
medial heads /
posterior
humerus;
I - Olecranon
process of ulna
A - forearm
extensor; long
head assist in
adduction
Biceps
brachii



O - short head/
coracoid process
of scapula; long
head / supra
glendoid tubercle
I - radial
tuberosity
A - flexes arm
and forearm;
supinates
Brachialis



O - anterior,
distal humerus
I - coracoid
process of ulna
A - forearm
flexor
Brachio
radialis



O - lateral
supracondylar
ridge
I - styloid
process of radius
A - forearm
flexion; a semi
pronated
position gives it
its best
mechanical
advantage
Muscles of
Forearm

Muscles of the
forearm are
divided equally
into flexors and
extensors
– Flexors on the
medial epicondyle
– Extensors on the
lateral epicondyle
Pronator
teres



O - medial
epicondyle of
humerus
I - lateral radius
at midshaft
A - pronates
forearm; weak
elbow flexor
Flexor carpi
radialis



O - medial
epicondyle of
humerus
I - base of
second and third
metacarpals
A - powerful
wrist flexor;
Palmaris
longus



O - medial
epicondyle of
humerus
I - palmer
aponeurosis
A - weak wrist
flexor; tenses
palmer
aponeurosis
Flexor carpi
ulnaris



O - medial
epicondyle of
humerus
I - pisiform bone
and base of 5th
metacarpal
A - flexor of
wrist
Muscles Crossing the Hip and Knee

Muscles crossing the hip and knee can be
grouped into
–
–
–
–
–
–
Hip flexors (4)
Gluteal muscles (3)
Medial compartment (5 adductors)
Anterior compartment (4 knee extensors)
Posterior compartment (3 knee flexors)
Lateral rotators (5)
Muscles
Crossing
the Hip
and Knee
Iliacus



O - iliac fossa
I - lesser
trochanter of
femur
A - hip flexion
Psoas major



O - transverse
processes and
bodies of T12
and all lumbar
vertebrae
I - lesser
trochanter of
femur
A - hip flexion
and lateral hip
flexion
Psoas minor



O - Transverse
processes and
bodies of T12
and L1
I - Rim of
acetabulum
A - flexes lumbar
vertebrae
Sartorius



O - anterior
superior iliac
spine
I - medial aspect
of proximal tibia
A - Flexes and
laterally rotates
thigh; flexes
knee
Adductors

Adductors
–
–
–
–
–
Adductor magnus
Adductor longus
Adductor brevis
Pectineus
Gracilis
Adductor
magnus



O - ischial and
pubic rami and
ischial tuberosity
I - linea aspera
and adductor
tubercle
A - adducts and
laterally rotates
thigh
Adductor
longus



O - pubis near
pubic symphysis
I - linea aspera
A - adducts,
flexes and
laterally rotates
thigh
Adductor
brevis



O - body and
inferior ramus
of pubis
I - linea aspera
A - adducts and
laterally rotates
thigh
Pectineus



O - pectineal line
of pubis
I - lesser
trochanter of
femur
A - adducts,
flexes, and
laterally rotates
thigh
Gracilis



O - inferior
ramus and body
of pubis
I - medial
surface of tibia
just inferior to
media condyle
A - adducts
thigh, flexes and
medially rotates
thigh
Quadriceps
femoris

Muscles include
–
–
–
–
Rectus femoris
Vastus lateralis
Vastus medialis
Vastus intermedius
Rectus
femoris



O - anterior
inferior iliac
spine
I - patella and
tibial tuberosity
A - extends knee
and flexes thigh
at hip
Vastus
lateralis



O - greater
trochanter,
intertrochanteric
line
I - patella and
tibial tuberosity
A - extends knee
Vastus
medialis



O - linea aspera,
intertrochanteric
line
I - patella and
tibial tuberosity
A - extends knee
Vastus
intermedius



O - anterior and
lateral surfaces
of proximal
shaft of femur
I - patella and
tibial tuberosity
A - extend knee
Tensor
fascia latae



O - anterior
aspect of iliac
crest
I - iliotibial tract
A - flexes and
abducts thigh
Gluteal
Muscles
Gluteus
maximus



O - dorsal ilium,
sacrum and
coccyx
I - gluteal
tuberosity of
femur
A - thigh
extension
Gluteus
medius



O - between
anterior and
posterior gluteal
lines on lateral
surface of ilium
I - greater
trochanter of
femur
A - abducts and
medially rotates
thigh
Gluteus
minimus



O - between
anterior and
inferior gluteal
lines on external
surface of femur
I - greater
trochanter of
femur
A - abducts and
medially rotates
thigh
Lateral
rotators

In this view
cutting the
gluteal
muscles
reveals the
lateral
rotators of
the thigh
Lateral
rotators

In this view
cutting the
gluteal
muscles
reveals the
lateral
rotators of
the thigh
Biceps
femoris



O - (long) ischial
tuberosity,
(short) linea
aspera
I - head of fibula
and lateral
condyle of tibia
A - extends thigh
and flexes knee,
laterally rotates
leg
Semitendinosus



O - ischial
tuberosity
I - medial aspect
of upper tibial
shaft
A - extends thigh
at hip; flexes
knee, medially
rotates leg
Semimembranosus



O - ischial
tuberosity
I - medial
condyle of tibia
A - extends thigh
and flexes knee,
medially rotates
leg
Muscles -Anterior
Compartment

Muscles of the anterior
compartment are
primarily toes extensors
and dorsiflexors
–
–
–
–

Tibialis anterior
Extensor digitorum longus
Extensor hallucis longus
Peroneus tertius
Important in walking
during the recovery phase
of gait
Tibialis
anterior



O - lateral
condyle and
upper 2/3 of tibia
I - inferior medial
surface of medial
cuneiform and 1st
metatarsal bone
A - dorsiflexion,
inverts foot
Extensor
digitorum
longus



O - lateral
condyle of tibia,
proximal 3/4 of
fibula
I - 2nd & 3rd
phalanges of toes
2-5 via extensor
expansion
A - Dorsiflexion,
toe extension
Peroneus
tertius



O - distal surface
of fibula and
interosseous
membrane
I - dorsum of
fifth metatarsal
A - dorsiflexes
and everts foot
Extensor
hallucis



O - anteriomedial
fibula shaft and
interosseous
membrane
I - distal phalanx
of great toe
A - extends great
toe, dorsiflexes
foot
Muscles - Lateral Compartment

Muscles of the
lateral
compartment
are primarily
plantar flex
and evert the
foot
– Peroneus
longus
– Peroneus
brevis
Peroneus
longus



O - head and
upper portion of
fibula
I - under the foot
to first metatarsal
and medial
cuneiform
A - plantar flexes
and everts foot
Peroneus
brevis



O - distal shaft
of fibula
I - proximal end
of the 5th
metatarsal
A - Plantar
flexes and everts
foot
Muscles of Posterior Compartment

Muscles of the
posterior
compartment are
primarily plantar
flexors and flex the
toes
–
–
–
–
Gastrocnemius
Soleus
Tibialis posterior
Flexor digitorum
longus
– Flexor hallucis
longus
Gastrocnemius



O - from medial
and lateral
condyles of
femur
I - calcaneus via
calcaneal tendon
A - plantar flexes
foot, flexes knee
Soleus



O - superior
tibia, fibula and
interosseus
membrane
I - calcaneus via
calcaneal tendon
A - plantar flexes
ankle
Plantaris



O - posterior
femur above
lateral condyle
I - calcaneus
A - plantar
flexion, knee
flexion
Popliteus



O - lateral
condyle of femur
I - proximal tibia
A - flexes and
rotates knee
medially to
unlock knee
from full
extension
Flexor
digitorum
longus



O - posterior
tibia
I - distal
phalanges of toes
2-5
A - plantar flexes
and flexes toes
Flexor
hallicus
longus



O - medial part
of shaft of fibula,
interosseous
membrane
I - distal phalanx
of great toe
A - plantar flexes
and inverts foot,
flexes great toe
Tibialis
posterior



O - superior
tibia and fibula
and interosseous
membrane
I - tarsals and
metatarsals 2-4
A - inversion,
plantar flexion
Intrinsic Muscles of the Foot



The intrinsic muscles of
the foot help to flex,
extend, abduct, and
adduct the toes
Collectively the muscles
support the arches of the
foot assisted by some
tendons of leg muscles
The muscles occur in
four layers from
superficial to deep
Intrinsic Muscles of the Foot


Muscles of the second
layer flex, adduct, and
abduct the toes
Muscles include
– Flexor digitorum brevis
– Abductor hallucis
– Abductor digiti minimi
Intrinsic Muscles of the Foot
Intrinsic Muscles of the Foot
Intrinsic Muscles of the Foot