Muscular Anatomy
University of Washington PMT
Muscular Anatomy

Muscle Organization and Function

Muscle organization affects power, range
and speed of muscle movement

Fascicles
• Muscle cells (fibers) are organized into bundles

Classification of Skeletal Muscles

By the way fascicles are organized

By relationships of fascicles to tendons
Fascicle Arrangement

Organization of Skeletal Muscle Fibers

Four patterns of fascicle organization
• Parallel
• Convergent
• Pennate
• Circular
Levers

Levers

Mechanically, each bone is a lever (a
rigid, moving structure)
• And each joint a fulcrum (a fixed point)

Muscles provide applied force (AF)
• Required to overcome resistance (R)
Levers


Function of a lever is to change

Direction of an AF

Distance and speed of movement produced by an AF

Effective strength of an AF
The Three Classes of Levers

Depend on the relationship between applied force,
fulcrum, and resistance
• First class, second class, and third class
First Class Lever
Second Class Lever
Third Class Lever
Types of Muscle--Actions




Prime mover (Agonist) – muscle with the
major responsibility for a certain movement
Antagonist – muscle that opposes or
reverses a prime mover
Synergist – muscle that aids a prime mover
in a movement and helps prevent rotation
Fixator – stabilizes the origin of a prime
mover
Naming Skeletal Muscles
Direction of
Muscle
Fibers
Location
Action
Skeletal
Muscle
Origin
&
Insertion
Size
Shape
Number
Of
Origins
Direction of Muscle Fibers


Relative to the Midline
RECTUS = parallel to the
midline


TRANSVERSE =
perpendicular to midline


Rectus Abdominus
Transverse Abdominus
OBLIQUE = diagonal to
midline

External Oblique
Location

Structure near
which muscle is
found


FRONTALIS =
near FRONTAL
bone
OCCIPITALIS =
near OCCIPITAL
bone
Size


Relative Size of Muscle
MAXIMUS = largest


MEDIUS = middle


Fibularis Longus
BREVIS = short


Gluteus Minimus
LONGUS = longest


Gluteus Medius
MINIMUS = smallest


Gluteus Maximus
Fibularis Brevis
TERTIUS = shortest

Fibularis Tertius
Number of Origins


Number of tendons of
origin
BICEPS = Two



TRICEPS = Three


Biceps Brachii
Biceps Femoris
Triceps Brachii
QUADRICEPS = Four

Quadriceps Femoris
Shape





Relative Shape of
the Muscle
DELTOID =
triangular shape Δ
TRAPEZIUS =
trapezoid shape 
SERRATUS = sawtoothed ♒
RHOMBOIDEUS =
rhomboid shape 
TERES = round ○
Origin & Insertion



Origin – attachment
to an immoveable
bone
Insertion –
attachment to a
movable bone
ILIO COSTALIS=
attaches to the
ilium & ribs (costal
= ribs)
Action
NAME
FLEXOR
EXTENSOR
ACTION
EXAMPLE
Decrease angle at a joint
Flexor Carpi Radialis
Increase angle at a joint
Extensor Carpi Ulnaris
ABDUCTOR
Move bone away from
midline
Abductor Pollicis Longus
ADDUCTOR
LEVATOR
Move bone toward midline
Adductor Longus
Produce upward movement
Levator Scapulae
DEPRESSOR
Produce downward
movement
Depressor Labii Inferioris
SUPINATOR
Turn palm upward/anterior
Supinator
PRONATOR
Turn palm
downward/posterior
Pronator Teres
Head & Neck Muscles
Muscles of the Axial Skeleton
Muscles of the Axial Skeleton

Intrinsic Muscles

Erector Spinae:
maintain posture of
back/extension
• Spinalis
• Longissimus
• Iliocostalis


Oblique Muscles:
rotation of the
vertebrae
Muscles of Quiet
Respiration




Abdominal Muscles


• Semispinalis
• Multifidus
• Rotatores



Diaphragm
External Intercostals
Internal Intercostals—
deep breaths
External Obliques
Internal Obliques
Transverse
Abdominus
Rectus Abdominus
(flexes vertebral
column)
Quadratus Lumborum
Muscles of Scapular
Stabilization

Trapezius:








Retraction
Elevation
Depression
Upward Rotation
Rhomboid—retraction
Levator Scapular—Elevation
Pectoralis Major—Protraction
Serratus Anterior—Protraction
Anterior Muscles of Shoulder

Deltoid




Pectoralis Major




Whole muscle: Abduction @
shoulder
Anterior part: flexion / medial
rotation
Posterior part: extension /
lateral rotation
Flexion
Adduction
Medial Rotation
Biceps Brachii—Flexion
Posterior Muscles of Shoulder

Teres Major




Latissimus Dorsi




Adduction
Extension
Medial Rotation
Adduction
Extension
Medial Rotation
Triceps Brachii

Extension
Muscles of the
Elbow/Forearm


Triceps Brachii—
Extension
Bicep Brachii—




Brachialis—Flexion
Brachioradialis—





Flexion
Supination
Flexion
Pronation
Pronator Teres
Pronator Quadratus
Supinator Longus
Muscles of the Wrist & Hand






Flexor Carpi
Ulnaris
Flexor Carpi
Radialis
Flexor Digitorum
Extensor Carpi
Ulnaris
Extensor Carpi
Radialis
Extensor Digitorum
Anterior (Palmar) View
Posterior (Dorsal) View
Muscles Of Hip:
Anterior Muscles
Muscles of Hip:
Anterior Muscles

Medial/Adductor
Muscles:




Adductor Magnus
Adductor Longus
Adductor Brevis
Gracilis

Anterior Muscles


Iliopsoas—Flexion
Pectineus—
• Flexion

Sartorius—
• Flexion (knee)
• Lateral Rotation
(hip)
Muscles of Hip:
Gluteal Muscles




** Gluteus Minimus is under the
Gluteus Medius
Gluteus Maximus—
Extension
Gluteus Medius—
Abduction
Gluteus Minimus—
Abduction
Tensor Fasciae
Latae—


Flexion
Abduction
Muscles of Anterior Thigh

“Quadriceps”

Rectus Femoris—
• Hip flexion
• Knee extension




Vastus Lateralis—
knee extension
Vastus Medialis—
knee extension
Vastus Intermedius—
knee extension
Sartorius—
• Hip & Knee Flexion
• Lateral Hip Rotation
**Vastus Intermedius is
beneath Rectus Femoris
Muscles of Posterior Thigh

“Hamstrings”





Responsible for
Knee Flexion & Hip
Extension
Semimembranosus
Semitendinosus
Biceps Femoris
Gastrocnemius

Knee Flexion
Muscles of the Lower Leg

Anterior Compartment




Posterior Compartment



Tibialis Anterior—Dorsiflexion &
inversion
Extensor Digitorum Longus
Fibularis Tertius—dorsiflexion &
eversion
Gastrocnemius—plantarflexion,
knee flexion
Soleus—plantarflexion
Lateral Compartment


Fibularis Longus—plantarflexion
& eversion
Fibularis Brevis—plantarflexion &
eversion