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The Muscular System-Gross Anatomy
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Over 600 Human skeletal muscles
Muscular terminology
Myology – the study of muscles
Kinesiology – the study of skeletal muscle action,
physiology and body mechanics (biomechanics)
• Nerve supply – part of the peripheral nervous system.
Either cranial nerves or spinal nerves.
Parts of a Skeletal Muscle
• Origin
– attachment to stationary
end of muscle
• Belly
– thicker, middle region of
muscle
• Insertion
– attachment to mobile end
of muscle
II. Coordinated Muscle Actions
A. Prime mover
– produces most of force
B. Synergist aids the prime mover
– stabilizes the nearby joint
– modifies the direction of movement that occurs
C. Antagonist
– opposes the prime mover
D. Fixator
– prevents movement of bone that prime mover is
attached to , joint stabilizer
Muscle Actions during Elbow Flexion
• Prime mover = brachialis
• Synergist = biceps brachii
• Antagonist = triceps brachii
• Fixator = muscle that holds
scapula firmly in place such as
rhomboids
III. How Muscles are Named
System of Latin names developed in 1895
– updated since then, last muscle- 1996
• English names for muscles are slight
modifications of the Latin names.
• Location
Size
• Action
Direction of Fibers
• Shape
• Number of heads
• Origin and Insertion
Skeletal Muscle Shapes
• Fusiform muscles
• Convergent muscle
• Parallel muscles
Skeletal Muscle Shapes (2)
• Circular muscles
• Pennate muscles
IV. Gross Anatomy of
Skeletal Muscleschapter 10
Major Skeletal Muscles: Anterior View
Major Skeletal Muscles: Posterior View
Muscles of Facial Expression
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Small muscles that insert into the dermis
Innervated by facial nerve (VII)
Paralysis causes face to sag
Found in scalp, forehead, around the eyes,
nose and mouth, and in the neck
Muscles of the Scalp and Forehead
Frontalis
Occipitalis
Occipitofrontalis is found in the
scalp. Frontalis raises the
eyebrows while Occipitalis fixes
the epicranial aponeuronesis
which is a CT covering of the
cephalic region
Muscles around the Eyes
Orbicularis Oculi
Nasalis
Orbicularis oculi closes the lid.
Nasalis widens nostrils,
wrinkles nose
Muscles around the Mouth
• Orbicularis oris encircles mouth called the “kissing muscle” because it is used to
pucker lips
• Zygomaticus group curl corner of mouth up in smile “smiling muscle”
• Risorius- syngerist to zygomaticus, “laughter muscle”
• Buccinator keeps food on top of teeth, blowing & sucking, “trumpeter’s muscle”,
used for facial expression and chewing
• Depressor Group (2)- draws angle of mouth downward
Levator labii
superioris
Zygomaticus major
Risorius
Depressor anguli oris
Depressor labii inferioris
Buccinator
Orbicularis oris
Some of the Muscles used in Facial Expression
Tenses neck
Muscles of Mastication
• Major muscles arise from
skull & insert on mandible
• Temporalis & Masseter
elevate the mandible
• Medial & Lateral
Pterygoids help elevate,
but produce excursion
movement, used to grind
• Buccinator- holds food in
mouth
Temporalis
Masseter
Lateral pterygoid
Medial pterygoid
Neck Muscles
Sternocleidomastoid
Turn head to look behind or
touch ear to shoulder
Platysma- tenses neck
Muscles of Respiration -- Diaphragm
• Muscular dome between
thoracic and abdominal
cavities
• Contraction flattens it
– increases the vertical dimension of the thorax drawing air
into the lungs
– raises the abdominal pressure to help expel urine, feces and
facilitating childbirth
Muscles of Respiration -- Intercostals
• External intercostals
– pull ribcage up & outward during
inspiration
• Internal intercostals
– pull ribcage downward during
forced expiration
Muscles of the Abdomen
• 4 Pairs of sheetlike muscles
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external oblique
internal oblique
transverse abdominis
rectus abdominis
Rectus Abdominis & External Oblique
• External oblique
Superficial,
Downward
anteriorly
Compresses
abdomen
Rotates trunk
laterally
External oblique
• Rectus abdominis
– vertical, straplike
– Six pack abs
– linea alba (CT)
Compresses abdomen
Rectus abdominis
Internal Oblique -Transverse Abdominis
• Internal oblique
– anteriorly
– Upwards deeper
Compresses abdomen
Internal oblique
• Transverse abdominis
– horizontal fiber orientation
– deepest layer
Compresses abdominal
contents
Transverse
abdominis
Anterior Scapular Muscle Group
• Pectoralis Minor
– protracts & depresses
scapula
– lifts ribs during forced
expiration
• Serratus Anterior
– abducts & rotates or
depresses scapula
– Throwing and pushing
muscle
– “boxer’s muscle”
Posterior Scapular Muscle Group
• Rhomboids
– Retracts and rotates
scapula, fixator of
scapula
Trapezius
Raises and lowers
Shoulders
“shrugs shoulders”
• Levator scapulae
Elevates and retracts
scapula
Muscles Acting on the Humerus
• Muscles cross the shoulder joint to the humerus
– Pectoralis major – prime mover of arm flexion
adduction against resistance
– Latissimus dorsi-prime mover of arm extension,
powerful arm adductor (power stroke)
Pectoralis major
Latissimus dorsi
Flexes
upper arm
Major chest muscle
Extends and
Adducts humerus
Swimmer’s muscle
Muscles Acting on the Humerus
Deltoid is prime mover of arm
abduction, antagnostic to
pectoralis major
“shoulder pad muscle”
4 form the rotator cuff muscles
that reinforce the shoulder
joint capsule
(supraspinatus, teres minor,
infraspinatus, subscapularis)
Muscles Acting on the Elbow
• Principal flexors
– biceps brachii
• Inserts on radius
– brachialis
• inserts on ulna, prime mover
• Synergistic flexor
– Brachioradialis
• Flexors in order of strengthbrachialis, biceps brachii,
brachioradialis
• Extensor
– triceps brachii
• inserts onto ulna
Muscles of the wrist and handexamples
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Flex/extend wrist and fingers, adduct/abduct wrist
Digitorum = inserts into fingers
Carpi = inserts onto carpal bones
Pollicis = inserts into thumb
Muscles of the wrist and handexamples
• Extension of wrist and fingers, Adduct/abduct wrist
• Extension and abduction of thumb (pollicis)
• Brevis = short, Ulnaris = on ulna side of forearm
Extensors
Muscles of Posterior Thigh
Prime mover of
Knee flexion
Hamstring group
(Biceps fermoris,
semitendinosus,
semimembranosus)
Muscles of the Anterior Thigh
Tensor fasciae
latae- abducts
Sartorius
Gracilis- adducts
thigh
Tailor’s musclecrossing legs
Quadriceps femoris- prime mover of knee extension and
hip flexion
(Rectus femoris, vastus lateralis, vastus medialis, vastus intermedialis)
Posterior Muscles Acting on the Hip
• Gluteus maximus
– forms mass of the
buttock
– prime hip extensor
– provides most of lift
when you climb stairs
Gluteus medius and
gluteus minimusabducts thigh and
stabilizes pelvic girdle
for walking
Gluteus medius
Gluteus maximus
Iliotibial
band(tensor
fascia
latae)abducts
thigh
Adductors of the Hip Joint
• 5 muscles act for adduction of
the thigh
• Adductor magnus is also an
Adductor
extensor of hip joint
brevis
Adductor brevis and
Adductor longus adduct the
Adductor
femur
longus
Adductor magnus
Anterior Compartment of the Leg
Tibialis
anterior
• Tibialis anterior = dorsiflexes and inverts foot
Posterior Compartment of the Leg
Superficial Group of Plantar Flexors
Gastrocnemius
• Gastrocnemius = flexes knee and plantar flexes ankle