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Saladin 5e Extended Outline
Chapter 10
The Muscular System
I. The Structural and Functional Organization of Muscles (pp. 320–327)
A. A muscle is an organ specialized to move a body part; muscle contraction serves at least four
overlapping functions (p. 320)
1. Movement. Muscles enable us to move from place to place, and muscle contraction
also moves body contents in the course of respiration, circulation, digestion, elimination,
and birth.
2. Stability. Muscles maintain posture and hold some joints in place by maintaining
tension on tendons; some are called antigravity muscles because they resist gravity.
3. Control of body openings and passages. Muscles encircle openings and passages in the
body, controlling flow of materials in, out, or through the body.
4. Heat production. Skeletal muscles produce as much as 85% of body heat.
B. In addition to muscular tissue, a skeletal muscle contains connective tissue, nervous tissue, and
blood vessels; a muscle contains four connective tissue components. (pp. 321–322) (Fig. 10.1)
1. The smallest and deepest of these is the endomysium, a thin sleeve of loose connective
tissue that surrounds each muscle fiber
a. The endomysium creates room for blood capillaries and nerve fibers to
nourish and stimulate the muscle fiber.
b. Excitation of a muscle fiber is based on ion exchange, which takes place
between the fluid of the endomysial tissue and the nerve and muscle fibers.
2. The perimysium is a thicker connective tissue sheath that wraps muscle fibers into
bundles called fascicles.
a. The perimysium carries larger nerves and blood vessels as well as stretch
receptors (muscle spindles).
3. The epimysium is a fibrous sheath that surrounds the entire muscle.
4. The fascia is a sheet of connective tissue that separates neighboring muscles or muscle
groups from each other and from subcutaneous tissue.
C. Fascicles determine in part the strength of a muscle and the direction of its pull; muscles can be
classified according to fascicle orientation into five categories (pp. 322–323) (Fig. 10.2)
1. Fusiform muscles are thick in the middle and tapered at each end, like the biceps
brachii.
2. Parallel muscles have a fairly uniform width and parallel fascicles.
a. Some are elongated straps, such as the rectus abdominis.
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b. Others are more squarish and are called quadrilateral muscles, such as the
masseter of the jaw.
c. Parallel muscles can span long distances but they have fewer muscle fibers
than a fusiform muscle of the same mass and produce less force.
3. Triangular (convergent) muscles are fan-shaped, broad at the origin and narrow at the
insertion; examples are the pectoralis major and the temporalis on the head.
4. Pennate muscles are feather shaped, with fascicles inserting obliquely on a tendon that
runs the length of the muscle; there are three types of pennate muscles.
a. Unipennate muscles have all fascicles approaching the tendon from one side;
an example is any of the palmar interosseous muscles of the hand.
b. Bipennate muscles have fascicles approaching the tendon from both sides; an
example is the rectus femoris of the thigh.
c. Multipennate muscles are shaped like a bunch of feathers with quills
converging on a single point; an example is the deltoid.
4. Circular muscles (sphincters) form rings around certain openings; examples are the
external urethral and anal sphincters.
a. Smooth muscle can also form sphincters, such as the pyloric valve and the
internal urethral and anal sphincters.
D. Skeletal muscles are attached to bones through extensions of their connective tissue
components in either indirect or direct attachments. (pp. 323–324)
1. In an indirect attachment, the muscle ends short of the bone, and the gap is bridged by
a fibrous band or sheet called a tendon. (Figs. 10.3, 10.32b, 10.38)
a. Collagen fibers of the muscle continue into the tendon and from there into the
periosteum and matrix of the bone.
b. In some cases, the tendon is a broad sheet called an aponeurosis, such as the
tendon located beneath the scalp, and the palmar aponeurosis beneath the skin of
the palm. (Fig. 10.29a)
c. In some places, groups of tendons from separate muscles pass under a band
of connective tissue called a retinaculum, such as the one that encircles the wrist
like a bracelet.
2. In a direct (fleshy) attachment, the red muscular tissue seems to emerge directly from
the bone as seen by the naked eye; for example, along the margins of the brachialis and
the lateral head of the triceps brachii. (Fig. 10.3)
a. At the microscopic level, the muscle fibers stop short of the bone, and the gap
is spanned by collagen fibers.
3. Some muscles insert not on bone but on the fascia or tendon of another muscle or on
collagen fibers of the dermis.
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4. Most skeletal muscles are attached to a different bone at each end, so the muscle or its
tendon spans at least one joint.
a. The bony site of attachment at the relatively stationary end is called the
muscle’s origin; the attachment site at the more mobile end is called the
insertion.
i. The biceps brachii has its origin on the scapula and its insertion on
the radius.
b. The thicker middle region of the muscle in between is called the belly of the
muscle.
c. The terminology of origin and insertion is imperfect and can be misleading,
since a muscle may have different action depending on the bone that is relatively
stationary; some anatomists refer to proximal/distal or superior/inferior
attachments instead.
E. Skeletal muscles function in groups whose combined action produces the coordinated motion of
a joint; muscles can be classified into four general categories according to actions. (p. 324) (Fig.
10.3)
1. The prime mover (agonist) is the muscle that produces most of the force in an action.
2. A synergist is a muscle that aids the prime mover; a synergist may stabilize a joint or
modify the direction of a movement.
3. An antagonist is a muscle that opposes the prime mover; often the antagonist maintains
some tension during movement limiting the speed or range of the movement to protect
injury.
a. The brachialis and triceps represent an antagonistic pair of muscles that act on
opposite sides of a joint.
i. In flexion of the elbow, the brachialis is the prime mover and the
triceps is the antagonist.
ii. In extension of the elbow, the triceps is the prime mover and the
brachialis is the antagonist.
b. Muscles can only pull, never push.
4. A fixator is a muscle that prevents a bone from moving; to fix a bone means to hold it
steady, allowing another muscle attached to it to pull on something else.
a. The biceps brachii originates on the scapula and inserts on the radius;
rhomboid muscles are fixator muscles that prevent the scapula from moving
when the biceps contracts to move the radius
F. An intrinsic muscle is entirely contained within a particular region, having both origin and
insertion there; an extrinsic muscle acts upon a certain region but has its origin elsewhere. The
forearm muscles that control the fingers are extrinsic muscles. (p. 324)
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G. The innervation of a muscle refers to the identity of the nerve that stimulates it; muscles are
innervated by two general groups of nerves. (p. 324–325)
1. Spinal nerves arise from the spinal cord, emerge through intervertebral foramina, and
innervate muscles below the neck. (Table 13.3–13.6)
a. Spinal nerves are identified by letters and numbers that refer to the adjacent
vertebrae, such as T6 for the sixth thoracic nerve and S2 for the second sacral
nerve.
b. Immediately after emerging from an intervertebral foramen, each spinal nerve
branches into a dorsal and ventral ramus.
c. The term plexus refers to weblike networks of spinal nerves adjacent to the
vertebral column.
2. Cranial nerves arise from the base of the brain, emerge through the skull foramina, and
innervate muscles of the head and neck. (Table 14.2)
a. Cranial nerves are identified by roman numerals, CN I to CN XII, although
not all 12 innervate skeletal muscles.
H. Muscles have Latin names that describe some distinctive aspects of the structure, location, or
action of a muscle; for example, flexor digiti minimi brevis is a short (brevis) muscle that flexes
(flexor) the smallest (minimi) finger (digit). (p. 325) (Fig. 10.4)
I. A rational strategy for learning the musculature system involves several tactics. (p. 325)
1. Examine models, cadavers, dissected animals, and photographic atlases to help you
remember the muscles.
2. Palpate the muscle on yourself if possible and see how its contraction works.
3. Located the origins and insertions of muscles on an articulated skeleton.
4. Study the derivation of each muscle name.
5. Say the name out loud to yourself or a study partner to help you remember and spell
them.
II. Muscles of the Head and Neck (pp. 328–338)
A. Muscles of the head and neck can be grouped as muscles of facial expression, muscles of
chewing and swallowing, and muscles that move the head as whole. (p. 328) (Fig. 10.5) (Tables
10.1, 10.2, 10.3)
B. Facial muscles are responsible for facial expressions; they also contribute to speech, chewing,
and other oral functions. (pp. 329–332) (Figs. 10.6, 10.7) (Table 10.1)
1. All but one of these muscles are innervated by the facial nerve (CN VII); the levator
palpebrae superioris that raises the upper eyelid is innervated by the oculomotor nerve
(CN III).
2. The two muscles of the scalp are connected to each other by the galea aponeurotica;
they are as follows:
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a. The frontalis raises the eyebrows.
i. Its origin is on the galea aponeurotica.
ii. Its insertion is on the subcutaneous tissue of eyebrows.
b. The occipitalis retracts the scalp.
i. Its origin is on the superior nuchal line.
ii. Its insertion is on the galea aponeurotica.
3. The four muscles of the orbit and nasal regions are as follows:
a. The orbicularis oculi encircles the eye; it closes the eye in blinking, squinting,
and sleep.
i. Its origin is on the lacrimal bone and adjacent regions of the frontal
bone and maxilla and medial angle of eyelids.
ii. Its insertion is in the upper and lower eyelids and skin around the
margin of the orbit.
b. The levator palpebrae superioris elevates the upper eyelid to open the eye.
i. Its origin is on the lesser wing of the sphenoid in the posterior wall of
the orbit.
ii. Its insertion is in the upper eyelid.
c. The corrugator supercilii draws eyebrows together and downward in frowing
and reduces glare from light.
i. Its origin is at the medial end of the supraorbital margin.
ii. Its insertion is in the skin of the eyebrow.
d. The nasalis widens the nostrils and narrows the internal air passage.
i. Its origin is at the maxilla just lateral to the nose.
ii. Its insertion is at the bridge and alar cartilages of nose.
4. The oral region contains eight muscles; some of these insert into the modiolus, a
complex cord just lateral to each angle of the lips.(Fig. 10.6) They are as follows:
a. The orbicularis oris closes the mouth, purses and protrudes the lips, and is
involved in speech.
i. Its origin is at the modiolus.
ii. Its insertion is in the submucosa and dermis of lips.
b. The levator labii superioris elevates and everts the upper lip.
i. Its origin is on the zygomatic bone and maxilla.
ii. Its insertion is in the muscles of the upper lip.
c. The levator anguli oris elevates the angle of the mouth as in smiling.
i. Its origin is on the maxilla.
ii. Its insertion is in the muscles at the angle of the mouth.
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d. The zygomaticus major draws the angle of the mouth upward and laterally in
laughing.
i. Its origin is on the zygomatic bone.
ii. Its insertion is at the superolateral angle of the mouth.
e. The zygomaticus minor elevates the upper lip, exposing the upper teeth.
i. Its origin is on the zygomatic bone.
ii. Its insertion is in the muscles of the upper lip.
f. The risorius draws the angle of the mouth laterally.
i. Its origin is on the zygomatic arch and fascia near the ear.
ii. Its insertion is in the modiolus.
g. The depressor anguli oris draws the angle of the mouth laterally and
downward.
i. Its origin is on the inferior margin of the mandibular body.
ii. Its insertion is in the modiolus.
h. The depressor labii inferioris draws the lower lip downward and laterally.
i. Its origin is near the mental protuberance.
ii. Its insertion is in the skin and mucosa of the lower lip.
5. The two muscles of the mental region (chin) and buccal region (cheeks) are as follows:
a. The mentalis elevates and protrudes the lower lip in drinking, pouting, etc.
i. Its origin is in the mandible near the inferior incisors.
ii. Its insertion is in the skin of the chin at the mental protuberance.
b. The buccinator compresses the cheek against the teeth and gums and retracts
cheek from teeth when mouth is closed; also can expel air and liquid.
i. Its origins are in alveolar processes on the lateral surfaces of maxilla
and mandible.
ii. Its insertions are in the orbicularis oris and submucosa of cheek and
lips.
6. The platysma is a large sheet of muscle in the cervical and mental region.
a. The platysma draws the lower lip and angle of mouth downward in
expressions of horror or surprise and may aid in opening the mouth widely.
i. Its origins are in the fascia of the deltoid and pectoralis major.
ii. Its insertions are in the mandible and skin and subcutaneous tissue of
the lower face.
C. Muscles of chewing and swallowing may contribute to facial expression, but are primarily
concerned with the manipulation of food, including tongue movements. (pp. 333–336) (Figs. 10.8,
10.9, 10.10) (Table 10.2)
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1. The tongue has both intrinsic muscles and extrinsic muscles; the four extrinsic muscles
connect the tongue to the rest of the head. (Fig. 10.8)
2. Three of the extrinsic muscles are innervated by the hypoglossal nerve (CN XII); the
fourth, the palatoglossus, is innervated by the vagus nerve (CN X) and accessory nerve
(CN XI).
3. The four extrinsic muscles of the tongue are as follows:
a. The genioglossus can draw the tongue to one side or the other, and can
protrude the tongue.
i. Its origin is on the superior mental spine on the posterior surface of
the mental protuberance.
ii. Its insertion is on the ventral surface of the tongue.
b. The hyoglossus depresses the tongue.
i. Its origins are on the body and greater horn of the hyoid.
ii. Its insertions are on the lateral and ventral surfaces of the tongue.
c. The styloglossus draws the tongue upward and posteriorly.
i. Its origins are on the styloid process of temporal bone and ligament
from the styloid process to the mandible.
ii. Its insertion is on the dorsolateral surface of the tongue.
d. The palatoglossus elevates the root of the tongue and closes the oral cavity off
from the pharynx.
i. Its origin is in the soft palate.
ii. Its insertion is in the lateral surface of the tongue.
4. Four pairs of muscles produce the biting and chewing movements of the mandible; all
are innervated by the mandibular nerve, which is a branch of the trigeminal nerve (CN
V). The muscles are as follows:
a. The temporalis elevates, retracts, and produces lateral and medial excursion of
the mandible.
i. Its origins are on the temporal lines and temporal fossa of the
cranium.
ii. Its insertions are on the coronoid process and anterior border of
mandibular ramus.
b. The masseter elevates the mandible with smaller roles in protraction,
retraction, and excursion.
i. Its origin is on the zygomatic arch.
ii. Its insertion is at the lateral surface of the mandibular ramus and
angle.
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c. The medial pterygoid causes elevation, protraction, and excursion of the
mandible.
i. Its origins are on the medial surface of the lateral pteygoid plate,
palatine bone, and lateral surface of maxilla.
ii. Its insertion is on the medial surface of the mandibular ramus and
angle.
d. The lateral pterygoid depresses the mandible and also causes protraction and
excursion.
i. Its origins are at the lateral surfaces of the lateral pterygoid plate and
great wing of the sphenoid.
ii. Its insertions are on the neck of the mandible, and the articular disc
and capsule of the temporomandibular joint.
5. The suprahyoid group of hyoid muscles is composed of four pairs of muscles superior
to the hyoid that aid in chewing and swallowing; they are innervated by the trigeminal
(CN-V), facial (CN-VII), and hypoglossal (CN XII) nerves. (Fig. 10.10) The four
muscles are as follows:
a. The digastric, which has two bellies, elevates the hyoid when the mandible is
fixed.
i. Its origins are in the mastoid notch of the temporal bone and the
digastric fossa of the mandible.
ii. Its insertion is on the hyoid bone via a fascial sling.
b. The geniohyoid depresses the mandible when the hyoid is fixed and elevates
and protracts the hydoid when the mandible is fixed.
i. Its origin is on the inferior mental spine of the mandible.
ii. Its insertion is on the hyoid.
c. The mylohyoid spans the mandible from side to side and forms the floor of
the mouth, and it elevates the floor of the mouth in the initial stage of
swallowing.
i. Its origin is on the mylohyoid line near the inferior margin of the
mandible.
ii. Its insertion is on the hyoid.
d. The stylohyoid elevates and retraces the hyoid, elongating the floor of the
mouth.
i. Its origin is on the styloid process of the temporal bone.
ii. Its insertion is on the hyoid.
6. The infrahyoid group of hyoid muscles is composed of four pairs of muscles inferior to
the hyoid bone that aid in swallowing; the ansa cervicalis. a loop of nerve on the side of
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the neck formed by fibers of CN I–CN III, innervates three of these muscles, along with
the glossopharyngeal (CN IX), vagus (CN X), and hypoglossal nerves (CN XII). The four
muscles are as follows:
a. The omohyoid, which also has two bellies, depresses the hyoid after it has
been elevated.
i. Its origin is on the superior border of the scapula.
ii. Its insertion is on the hyoid.
b. The sternohyoid also depresses the hyoid after it has been elevated.
i. Its origin is on the manubrium of the sternum and the medial end of
the clavicle.
ii. Its insertion is on the hyoid.
c. The thyrohyoid depresses the hyoid, and with the hyoid fixed, it elevates the
larynx as in singing high notes.
i. Its origin is on the thyroid cartilage of the larynx.
ii. Its insertion is on the hyoid.
d. The sternothyroid depresses the larynx after it has been elevated in
swallowing and vocalization, and aids in singing low notes.
i. Its origin is on the manubrium of the sternum and costal cartilage 1.
ii. Its insertion is on the thyroid cartilage of the larynx.
7. The muscles of the pharynx consist of three pharyngeal constrictors.
a. During swallowing, the pharyngeal constrictors contract in order from
superior to middle to inferior to drive food into the esophagus.
i. Their origins are on the medial pterygoid plate, mandible, hyoid,
stylohyoid ligament, cricoid, and thyroid cartilages of larnynx.
ii. Their insertions are on the median pharyngeal raphe and basilar part
of the occipital bone.
D. Muscles that move the head as a whole originate on the vertebral column, thoracic cage, and
pectoral girdle, and insert on the cranial bones; a particular muscle may cause a contralateral
movement of the head (toward the side opposite that of the muscle) or an ipsilateral movement
(toward the same side as that of the muscle) (pp. 337–338) (Table 10.3)
1. The flexors of the neck include four muscles, of which the prime mover is the
sternocleidomastoid; these muscles are innervated by the accessory nerve (CN XI) and
spinal nerves (C2–C8). (Fig. 10.10)
a. The sternocleidomastoid, when used unilaterally, turns the head from side to
side contralaterally; when used bilaterally, it draws the head forward and down.
i. Its origin is on the manubrium of the sternum and medial one-third of
the clavicle.
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ii. Its insertion is on the mastoid process and lateral half of the superior
nuchal line.
b. The three scalenes (anterior, middle, and posterior), when contracted
unilaterally, cause ipsilateral flexion (tilts head toward same shoulder) or
contralateral rotation (rotates face away); when contracted bilaterally, they flex
the neck.
i. Their origins are on the transverse processes of all cervical vertebrae.
ii. Their insertions are on ribs 1 and 2.
2. The extensors of the neck are located mainly in the nuchal region and tend to hold the
head erect or draw it back; they are innervated by the accessory nerve (CN XI) and by
cervical and thoracic nerve rami. (Fig. 10.12)
a. The trapezius holds up the head and neck.
i. Its origins are on the external occipital protuberance, medial one-third
of superior nuchal line, nuchal ligament, and spinous processes of
vertebrae C7–T3 or T4.
ii. Its insertions are on the acromion and spine of scapula and lateral
one-third of clavicle.
b. The splenius capitis and splenius cervicis produce ipsilateral flexion when
acting unilaterally and extend the head when acting bilaterally.
i. Their origins are on the inferior half of the nuchal ligament and
spinous processes of vertebrae C7–T6.
ii. Their insertions are insertions on the mastoid process and occipital
bone just inferior to the superior nuchal line, and on cervical vertebrae
C1–C2 or C3.
c. The semispinalis capitis and semispinalis cervicis extend and contralaterally
rotate the head.
i. Their origins are on the articular processes of vertebrae C4–C7 and
transverse processes of T1–T6.
ii. Their insertions are on the occipital bone between nuchal lines and
on spinous processes of vertebrae C2–C5.
III. Muscles of the Trunk (pp. 339–349)
A. The muscles of the trunk can be divided into three functional groups: those concerned with
respiration; with support of the abdominal wall and pelvic floor; and movement of the vertebral
column. (p. 339) (Tables 10.4, 10.5, 10.6, 10.7)
B. Some major muscles found in the trunk are not discussed in this section because they act upon
the limbs and limb girdles; they are discussed in the following section. (p. 339)
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C. Muscles of respiration include those that enclose the thoracic cavity: the diaphragm; external
intercostal muscles; and internal intercostal muscles, including the innermost intercostals. (pp.
339–340) (Fig. 10.13) (Table 10.4)
1. The diaphragm is a muscular dome between the thoracic and abdominal cavities,
bulging upward against the base of the lungs; it has openings for passage of the
esophagus, major blood and lymphatic vessels, and nerves; it is innervated by the phrenic
nerve.
a. The diaphragm is the prime mover of inspiration, responsible for two-thirds of
air intake.
i. Its origin includes the xiphoid process of the sternum; ribs and costal
cartilages 7–12; and the lumbar vertebrae.
ii. Its insertion is at the central tendon of the diaphragm.
2. The external intercostals slope downward and anteriorly from one rib to the next
inferior one; they are innervated by the intercostal nerves.
a. The 11 pairs of external intercostals muscles elevate and protract ribs 2–12
when the scalenes fix rib 1, and thereby expand the thoracic cavity.
i. The origins are on the inferior margins of ribs 1–11.
ii. The insertions are on the superior margin of the next lower rib.
3. The internal intercostals lie deep to the external intercostals; they slope downward and
posteriorly from each rib to the one below, at nearly right angles to the external
intercostals. They are also innervated by the intercostals nerves.
a. The 11 pairs of internal intercostals also elevate the ribs and expand the
thoracic cavity upon inspiration; during forceful expiration, they depress and
retract the ribs, expelling air.
i. The origins are on the superior margins and costal cartilates of ribs 2–
12 and the margin of the sternum.
ii. The insertions are on the inferior margin of the next higher rib.
4. The innermost intercostals muscles vary in number; their fibers run in the same
direction as the internal intercostals, and they are separated by a fascia from the internal
intercostals.
a. Their action is the same as that of the internal intercostals.
i. The origins are the superomedial surface of ribs 2–12, and they may
be absent from the upper ribs.
ii. The insertions are the medial edge of the costal groove of the next
higher rib.
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D. Muscles of the anterior abdominal wall include three muscle layers that enclose the lateral
abdominal region (two oblique and one transverse), and an anterior layer that runs vertically from
sternum to pubis (the rectus abdominis). (pp. 341–343) (Fig. 10.14) (Table 10.5)
1. The abdominal muscles are innervated by the ventral rami of spinal nerves ranging
from T6–L1, depending on the muscle.
2. The tendons of the oblique and transverse muscles are aponeuroses—broad fibrous
sheets. (Figs. 10.15, 10.16)
a. At the rectus abdominis, these sheets diverge and pass around its anterior and
posterior sides, enclosing the muscle in the rectus sheath.
b. These sheets meet again at a median line called the linea alba, between the
paired rectus muscles.
c. another line, the linea semilunaris, marks the lateral boundary whether the
rectus sheath meets the aponeurosis.
d. The aponeurosis of the external oblique also forms a cordlike inguinal
ligament at its inferior margin.
3. The three lateral abdominal muscles are as follows:
a. The external abdominal oblique supports the abdominal viscera against
gravity, stabilizes the vertebral column, maintains posture, and compresses
abdominal organs; unilateral contraction causes contralateral rotation of the
waist.
i. Its origins are on ribs 5–12.
ii. Its insertions are on the anterior half of the iliac crest, pubic
symphysis, and superior margin of the pubis.
b. The internal abdominal oblique has the same action as the external oblique
except that unilateral contraction causes ipsilateral rotation.
i. Its origins are on the inguinal ligament, iliac crest, and thoracolumbar
fascia.
ii. Its insertions are on ribs 10–12, costal cartilages 7–10, and the pubis.
c. The transverse abdominal compresses abdominal contents, but does not
contribute to movements of the vertebral column.
i. Its origins are on the inguinal ligament, iliac crest, thoracolumbar
fascia, and constal cartilages 7–12.
ii. Its insertions are on the linea alba, pubis, aponeurosis of internal
oblique.
4. The pair of rectus abdominis muscles are divided into segments by three transverse
tendinous segments that give the abdomen a “six pack” appearance in physically fit
individuals.
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a. The rectus abdominis flexes the lumbar region of the vertebral column,
producing forward bending at the waist.
i. Its origin includes the pubic symphysis and superior margin of the
pubis.
ii. Its insertions are the xyphoid process and costal cartilages 5–7.
E. Muscles of the back primarily extend, rotate, and laterally flex the vertebral column. (pp. 344–
346) (Figs. 10.17, 10.18, 10.19) (Table 10.6)
1. The most prominent superficial back muscles, the latissimus dorsi and trapezius, are
concerned with upper limb movements. (Tables 10.9, 10.10).
2. The deeper-lying serratus posterior superior and serratus posterior inferior, extending
from vertebrae to ribs, have unclear functions.
3. Deeper still is the erector spinae, which runs from cranium to sacrum; as it ascends, it
divides in the upper lumbar region into three parallel columns. (Figs. 10.18, 10.19)
a. The most lateral is the iliocostalis, which has lumbar, thoracic, and cervical
regions.
b. The next medial is the longissimus, which has thoracic, cervical, and cephalic
regions.
c. The most medial is the spinalis, which also has thoracic, cervical, and
cephalic reagions.
d. All these are similar in function and discussed collectively as the erector
spinae.
4. The major deep muscles are the semispinalis thoracis and the quadratus lumborum; the
latter is enclosed with the erector spinae in a fibrous sheath called the thoracolumbar
fascia.
5. The four major groups are summarized as follows:
a. The erector spinae provides extension and lateral flexion of the vertebral
column. The longissimus capitis also produces ipsilateral rotation of the head. It
is innervated by the dorsal rami of spinal nerves.
i. Its origins are at the nuchal ligament, ribs 3–12, thoracic and lumbar
vertebrae, median and lateral sacral crests, an thoracolumbar fascia.
ii. Its insertions are on the mastoid process, cervical and thoracic
vertebrae, and all ribs.
b. The semispinalis thoracis extends the spine and rotates it contralaterally. It is
also innervated by dorsal rami of spinal nerves.
i. Its origins are on vertebrae T6–T10.
ii. Its insertions are on vertebrae C6–T4.
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c. The quadratus lumborum aids respiration by fixing rib 12 and stabilizing
inferior attachments of the diaphragm. Unilateral contraction causes ipsilateral
flexion of the lumbar region; bilateral contraction extends the lumbar region. It
is innervated by ventral rami of spinal nerves T12–L4.
i. Its origins are on the iliac crest and iliolumbar ligament.
ii. Its insertions are on rib 12 and vertebrae L1–L4.
d. The multifidus, a collective series of tiny muscles that connect adjacent
vertebrae, stabilizes adjacent vertebrae, maintains posture, and controls vertebral
movement. It is innervated by dorsal rami of spinal nerves.
i. Its origins are on vertebrae C4–L5, the posterior superior iliac spine,
sacrum, and aponeurosis of erector spinae.
ii. Its insertions are on the laminae and spinous processes of vertebrae
superior to the origins.
Insight 10.1 Heavy Lifting and Back Injuries
F. Muscles of the pelvic floor include three layers that span the pelvic outlet and support the
viscera. (pp. 347–349) (Fig. 10.20) (Table 10.7)
1. The floor of the pelvic cavity is penetrated by the anal canal, urethra, and vagina,
which open into a diamond-shaped region between the thighs called the perineum.
2. The perineum is bordered by four bony landmarks: the pubic symphysis (anterior), the
coccyx (posterior), and the two ischial tuberosities (lateral).
3. The anterior half of the perineum is the urogenital triangle, and the posterior half is the
anal triangle. (Fig. 10.20)
4. The pelvic floor is divided into three layers or compartments: The superficial perineal
space (Fig. 10.20a); the middle compartment (Fig. 10.20b); and the pelvic diaphragm
(Fig. 10.20c).
5. The superficial perineal space contains three muscles, which are innervated by the
pudendal nerve:
a. The ischiocavernosus maintains erection of the penis or clitoris by
compressing deep structures and forcing blood forward.
i. Its origin is on the ramus and tuberosity of the ischium.
ii. Its insertion ensheaths the deep structures of the penis or clitoris.
b. The bulbospongiosus expels remaining urine from the urethra after the
bladder has emptied, aids in erection of penis and clitoris, and performs
spasamodic contractions during orgasm and ejaculation.
i. Its origin is at the perineal body and median raphe.
ii. Its insertions ensheaths the root of the penis or clitoris
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c. The superficial transverse perineal muscle extends from the ischial
tuberosities to a strong median fibromuscular anchorage, the perineal body; it is
a weak muscle and not always present.
6. In the middle compartment, the urogenital triangle is spanned by a thin triangular sheet
called the urogenital diaphragm, which is composed of a fibrous membrane and two (or
in females, three) muscles; they are innervated by the pudendal nerve, spinal nerves S2–
S4, and the splanchnic nerve. They are as follows:
a. The external urethral sphincter retains urine in the bladder until voluntarily
voided.
i. The origin is on the right and left ischiopubic rami.
ii. It encircles the urethral orifice.
b. The compressor urethrae, found only in females, aids in urine retention.
i. The origin is on the right and left ischiopubic rami.
ii. They meet as a muscular sheet inferior to the external urethral
sphincter.
c. The deep transverse perineal muscle is weakly developed—it and the
superficial transverse perineal both anchor the perineal body, which in turn
anchors other pelvic muscles.
7. Also in the middle compartment, the anal triangle has a single muscle, which is also
innervated by the pudendal nerve, spinal nerves S2–S4, and the splanchnic nerve:
a. The external anal sphincter retains feces in the rectum until voluntarily
voided.
i. Its origins include the coccyx and the perineal body.
ii. It encircles the anal canal and orifice.
8. The deepest compartment, the pelvic diaphragm, consists of two muscle pairs, the
levator ani and the coccygeus. The levator ani is innervated by the pudendal nerve and
spinal nerves S2–S3; the coccygeus is innervated by S3–S4.
a. The levator ani is a composite of three muscles: the iliococcygeus, the
pubococcygeus, and the puborectalis; it compresses the anal canal, supports the
uterus and other pelvic visceral, and affects pressure differences internally to
support breathing.
i. Its origins are on the inner surface of the lesser pelvis from the pubis
through the tendinous arch of the obturator internus, to the spine of the
ischium.
ii. Its insertions are on the coccyx via the anococcygeal body and the
walls of the urethra, vagina, and anal canal.
b. The coccygeus aids the levator ani.
Saladin Outline Ch.10
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i. Its origin is on the spine of the ischium.
ii. Its insertion is on the coccyx and the adjacent border of the sacrum.
Insight 10.2 Hernias (Fig. 10.21)
IV. Muscles Acting on the Shoulder and Upper Limb (pp. 349–366)
A. The upper and lower limbs have numerous muscles that serve for movement and manipulation
of objects. (p. 349)
B. The limb muscles are organized into spaces called muscle compartments separated by fasciae
that contain one or more functionally related muscles along with nerve and blood supplies. (p.
349) (Figure 10.22)
1. The upper limb has anterior and posterior compartments, while the lower limb has
anterior, posterior, medial, and lateral compartments.
2. These compartments are separated by the interosseous membranes of the forearm and
leg and by thick fasciae called intermuscular septa.
3. Thinner fascia subdivide the muscle groups into superficial and deep layers.
4. Compartment syndrome is the result of injury to the muscles of blood vessels of a
compartment.
Insight 10.3 Compartment Syndrome
C. The upper limb is used for a broad range of actions and has a complex array of muscles that are
organized into logical groups. (pp. 349–350) (Tables 10.8, 10.9, 10.10, 10.11, 10.12)
D. Muscles acting on the pectoral girdle originate on the axial skeleton and insert on the clavicle
and scapula. (pp. 351–352) (Figure 10.23) (Table 10.8)
1. The major muscles of the anterior group are the pectoralis minor and serratus anterior.
(Fig. 10.24) (Fig. 10.15b).
a. The pectoralis minor draws the scapula laterally and forward around the chest
wall; it also, with other muscles, rotates the scapula and depresses the apex of
the shoulder. It is innervated by the medial and lateral pectoral nerves.
i. Its origin, with three heads, are on ribs 3–5 and overlying fascia.
ii. Its insertion is on the coracoid process of the scapula.
b. The serratus anterior, with the pectoralis minor, draws the scapula laterally
and forward around the chest wall; protracts the scapula and is the prime mover
in forward-reaching and pushing actions; aids ir rotating scapula to elevate the
apex of the shoulder; and fixes the scapula during abduction of the arm. It is
innervated by the long thoracic nerve.
i. Its origins includes nearly all ribs.
ii. Its insertion is on the medial border of the scapula.
2. The major muscles of the posterior group include the trapezius and three deep muscles:
the levator scapulae, rhomboideus minor, and rhomboideus major (the rhomboids).
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a. The trapezius stablizes the scapula and shoulder during arm movements;
elevates and depresses the apex of the shoulder, and acts with other muscles to
rotate and retract the scapula. It is innervated by the accessory nerve (CN XI)
and the ventral rami of C3–C4.
i. Its origins are on the external occipital protuberance, the medial onethird of the superior nuchal line, the nuchal ligament, and spinous
processes of vertebrae C7–T3 or T4.
ii. Its insertion includes the acromion and spine of the scapula and the
lateral one-third of the clavicle.
b. The levator scapulae elevates the scapula if cervical vertebrae are fixed; flexes
the neck laterally if scapula is fixed; retracts scapula and braces shoulder; and
rotates the scapula and depresses the apex of the shoulder. It is innervated by
C3–C4, and C5 via the dorsal scapular nerve.
i. Its origins are on the transverse processes of vertebrae C1–C4.
ii. Its insertion is from the superior angle to the medial border of the
scapula.
c. The rhomboideus minor ractracts the scapula and braces the shoulder; it fixes
the scapula during arm movements. It is innervated by the dorsal scapular nerve.
i. Its origin includes the spinous processes of vertebrae C7–T5 and the
nuchal ligament.
ii. Its insertion is on the medial border of the scapula.
d. The rhomboideus major has the same action as the rhomboideus minor and
has the same innervation.
i. Its origin includes the spinous processes of vertebrae T2–T5.
ii. Its’ insertion is on the medial border of the scapula.
E. Muscles acting on the arm consist of nine muscles that cross the shoulder joint and insert on the
humerus. (pp. 353–356) (Fig. 9.25) (Table 10.9)
1. Two of the nine are considered axial muscles because they originate on the axial
skeleton; the other seven comprise the scapular muscles with origins on the scapula.
2. The axial muscles include the pectoralis major and the latissimus dorsi, which are the
prime movers of the shoulder joint. (Figs. 10.24, 10.25)
a. The pectoralis major, the thick, fleshy muscle of the mammary region, flexes,
adducts, and medially rotates the humerus and aids in deep inspiration. It is
innervated by the medial and lateral pectoral nerves.
i. Its origin is the medial half of the clavicle, costal cartilages 1–7, and
the aponeurosis of the external oblique.
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ii. Its insertion is the lateral lip of the intertubercular sulcus of the
humerus.
b. The latissimus dorsi adducts and medially rotates the humerus; extends the
shoulder joint; produces a backward swing of the arm; pulls the body forward
and upward as in climbing; aids in deep inspiration and sudden expiration; and
supports prolonged, forceful expiration as in singing or blowing a note on a
wind instrument. It is innervated by the thoracodorsal nerve.
i. Its origin includes vertebrae T7–L5, the lower three or four ribs, the
iliac crest, and the thoracolumbar fascia.
ii. Its insertion is the intertubercular sulcus of the humerus.
3. Three of the seven scapular muscles also contribute to large-scale movements of the
shoulder; the other four make up the rotator cuff.
a. The deltoid, which caps the shoulder, is the most conspicuous muscle; its
anterior fibers flex and medially rotate the arm; the lateral fibers abduct the arm;
and the posterior fibers extend and laterally rotate the arm. It is innervated by
the axillary nerve.
i. Its origin includes the acromion and spine of the scapula, and the
clavicle.
ii. Its insertion is on the deltoid tuberosity of the humerus.
b. The teres major extends and medially rotates the humerus; it is innervated by
the lower subscapular nerve.
i. Its origin is the inferior angle of the scapula.
ii. Its insertion is the medial lip of the intertubercular sulcus of the
humerus.
c. The coracobrachialis flexes and medially rotates the arm and resists deviation
of the arm from the frontal plane during abduction. It is innervated by the
musculocutaneous nerve.
i. Its origin is on the coracoid process.
ii. Its insertion is the medial aspect of the humeral shaft.
4. The tendons of the four remaining scapular muscles form the rotator cuff; they are
nicknamed the SITS muscles for the first letters of their names: supraspinatus,
infraspinatus, teres minor, and subscapularis. (Fig. 10.26)
5. The first three muscles lie on the posterior side of the scapula; the fourth, the
subscapularis, occupies the subscapular fossa on the anterior surface of the scapula. (Fig.
10.24)
a. The supraspinatus, which lies in the supraspinous fossa above the scapular
spine, aids the deltoid in abduction of the arm and resists downward slippage of
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the humeral head when the arm is relaxed or when carrying weight. It is
innervated by the suprascapular nerve.
i. Its origin is the supraspinous fossa.
ii. Its insertion is the greater tubercle of the humerus.
b. The infraspinatus, which lies in the infraspinous fossa below the scapular
spine, modulates the action of the deltoid, preventing the humeral head from
sliding upward, and rotates the humerus laterally. It also is innervated by the
suprascapular nerve.
i. Its origin is the infraspinous fossa.
ii. It insertion is the greater tubercle of the humerus.
c. The teres minor is inferior to the infraspinatus; it modulates the action of the
deltoid, preventing the humeral head from sliding upward during abduction, and
rotates the humerus laterally. It is innervated by the axillary nerve.
i. Its origin is on the lateral border and adjacent posterior surface of the
scapula.
ii. Its insertion is the greater tubercle of the humerus and the posterior
surface of the joint capsule.
d. The subscapularis occupies the subscapular fossa on the anterior surface of
the scapula, between the scapula and ribs; it modulates the action of the deltoid,
preventing the humeral head from sliding upward during abduction, and rotates
the humerus medially. It is innervated by the upper and lower subscapular
nerves.
i. Its origin is the subscapular fossa of the scapula.
ii. Its insertion is the lesser tubercle of the humerus and the anterior
surface of the joint capsule.
F. The muscles acting on the forearm have bellies found in both the arm and the forearm itself.
(pp. 357–358) (Table 10.10)
1. The elbow and forearm are capable of four motions: flexion, extension, pronation, and
supination.
2. Muscles with bellies in the arm (brachium) include the two elbow flexors in the
anterior compartment (brachialis and biceps brachii) and the elbow extender in the
posterior compartment (triceps brachii). (Fig. (10.24)
a. The brachialis is the prime mover of elbow flexion; it is innervated by the
musculocutaneous and radial nerves.
i. Its origin is the anterior surface of the distal half of the humerus.
ii. Its insertion is on the coronoid process and tuberosity of the ulna.
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b. The biceps brachii is so named because of its two heads. It is responsible for
rapid or forceful supination of the forearm; acts synergistically in elbow flexion;
flexes the shoulder slightly, and stabilizes the humeral head. It is innervated by
the musculocutaneous nerve.
i. The long head has its origin on the superior margin of the glenoid
cavity; the tendon then loops over the shoulder. The short head has its
origin on the coracoid process.
ii. The insertion is on the tuberosity of the radius and the fascia of the
forearm.
c. The triceps brachii is so named because of its three heads. It is the prime
mover of elbow extension and also adducts the humerus. It is innervated by the
radial nerve.
i. The long head has its origin on the inferior margin of the glenoid
cavity and joint capsule. The lateral head’s origin is on the posterior
surface of the proximal end of the humerus. The medial head’s origin is
the posterior surface of the entire humeral shaft.
ii. The insertion is at the olecranon and the fascia of the forearm.
3. Most muscles with bellies in the forearm (antebrachium) act on the wrist and hand, but
two are synergists in elbow flexion and three function in pronation and supination.
a. The brachioradialis flexes the elbow; it is innervated by the radial nerve.
(Figs. 10.24, 10.29a)
i. Its origin is the lateral supracondular ridge of the humerus.
ii. Its insertion is the lateral surface of the radius near the styloid
process.
b. The aconeus extends the elbow and may help to control ulnar movement
during pronation; it is innervated by the radial nerve. (Fig. 10.29d, e)
i. Its origin is the lateral epicondyle of the humerus.
ii. Its insertion is the olecranon and posterior surface of the ulna.
c. The pronator quadratus is the prime mover of forearm pronation and resists
separation of radius and ulna when force is applied; it is innervated by the
median nerve.
i. Its origin is on the anterior surface of the distal ulna.
ii. Its insertion is on the anterior surface of the distal radius.
d. The pronator teres assist the pronator quadratus in pronation, but only in rapid
or forceful action, and weakly flexes the elbow; it is innervated by the median
nerve.
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i. Its origin includes the humeral shaft near the medial epicondyle and
the coronoid process of the ulna.
ii. Its insertion is on the lateral surface of the radial shaft.
e. The supinator supinates the forearm; it is innervated by the posterior
interosseous nerve. (Fig. 10.27)
i. Its origin includes the lateral epicondyle of the humerus, the supinator
crest and fossa of the ulna distal to the radial notch, and the anular and
radial collateral ligaments of the elbow..
ii. Its insertion is the proximal one-third of the radius.
G. Muscles acting on the wrist and hand include extrinsic muscles in the forearm and intrinsic
muscles in the hand itself. (p. 359–363) (Table 10.11)
1. The action of the extrinsic muscles is mainly flexion of the wrist and digits, but also
radial and ulnar flexion, finger abduction and adduction, and thumb opposition.
2. Many of them act on the metacarpophalangeal joints and the interphalangeal joints;
some tendons cross multiple joints.
3. Most tendons of the extrinsic muscles pass under a fibrous sheath called the flexor
retinaculum on the anterior side of the wrist or the extensor retinaculum on the posterior
side; the carpal tunnel is a tight space between the flexor retinaculum and carpal bones.
4. Fascia divide the forearm muscles into anterior and posterior compartments, each of
which are further divided into superficial and deep layers. (Fig. 10.28)
5. The anterior (flexor) compartment, superficial layer, includes four muscles that are
wrist and finger flexors; these arise from a common tendon on the humerus.
a. The flexor carpi radialis flexes the wrist anteriorly and aids in radial flexion of
the wrist; it is innervated by the median nerve. It is a landmark for finding the
radial artery to take a pulse.
i. Its origin is the medial epicondyle of the humerus.
ii. Its insertion is the base of metacarpals II–III.
b. The flexor carpi ulnaris flexes the wrist anteriorly and aids in ulnar flexion of
the wrist; it is innervated by the ulnar nerve.
i. Its origin includes the medial epicondyle of the humerus, the medial
margin of the olecranon, and the posterior surface of the ulna.
ii. Its insertions are on the pisiform, hamate, and metacarpal V.
c. The flexor digitorum superficialis flexes the wrist, metacarpophalangeal, and
interphalangeal joints, depending on actions of other muscles; it is innervated by
the median nerve.
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i. Its origin includes the medial epicondyle of the humerus, the ulnar
collateral ligament, the coronoid process, and the superior half of the
radius.
ii. Its insertions are on middle phalanges II–V.
d. The palmaris longus anchors the skin and fascia of the palmar region and
resists shearing forces when climbing or using tools; it is innervated by the
median nerve. It is weakly developed and absent in some individuals.
i. Its origin is on the medial epicondyle of the humerus.
ii. Its insertion is the flexor retinaculum and palmar aponeurosis.
6. The anterior (flexor) compartment includes two flexors. (Fig. 10.29c)
a. The flexor digitorum profundus flexes the wrist, metacarpophalangeal, and
interphalangeal joints and is the sole flexor of the distal interphalangeal joints; it
is innervated by the median and ulnar nerves.
i. Its origin includes the proximal three-quarters of the ulna, the
coronoid process, and the interosseous membrane.
ii. Its insertions are on digital phalanges II–V.
b. The flexor pollicis longus flexes the phalanges of the thumb; it is innervated
by the median nerve.
i. Its origins are on the radius and the interosseous membrane.
ii. Its insertion is on distal phalanx I.
7. The posterior (extensor) compartment, superficial layer, includes five muscles that are
wrist and finger extensors; they arise from a common tendon on the humerus. (Fig.
10.30a)
a. The extensor carpi radialis longus extends the wrist and aids in radial flexion
of the wrist; it is innervated by the radial nerve.
i. Its origin is on the lateral supracondylar ridge of the humerus.
ii. Its insertion is on the base of metacarpal II.
b. The extensor carpi radialis brevis also extends the wrist and aids in radial
flexion of the wrist; it is innervated by the posterior interosseous nerve.
i. Its origin is on the lateral epicondyle of the humerus.
ii. Its insertion is on the base of metacarpal III.
c. The extensor digitorum extends the wrist, metacarpophalangeal, and
interphalangeal joints and tends to spread digits apart when extending
metacarpophalageal joints; it is innervated by the posterior interosseous nerve.
i. Its origin is on the lateral epicondyle of the humerus.
ii. Its insertions are on the dorsal surfaces of phalanges II–V.
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d. The extensor digiti minimi extends the wrist and all joints of the little finger;
it is innervated by the posterior interosseous nerve.
i. Its origin is on the lateral epicondyle of the humerus.
ii. Its insertion is the proximal phalanx V.
c. The extensor carpi unlaris extends and fixes the wrist when the fist is
clenched or the hand grips and aids in ulnar flexion of the wrist; it is innervated
by the posterior interosseous nerve.
i. Its origin includes the lateral epicondyle of the humerus and posterior
surface of the ulnar shaft.
ii. Its insertion is on the base of metacarpal V.
8. The posterior (extensor) compartment, deep layer, includes four muscles that serve
only the thumb and index finger; all are innervated by the posterior interosseous nerve.
(Fig. 10.30b)
a. The abductor pollicis longus abducts the thumb in the frontal (palmar) plane
(radial abduction) and extends the thumb at the carpometacarpal joint.
i. Its origin includes the posterior surfaces of the radius and ulna and
the interosseous membrane.
ii. Its insertion includes the trapezium and base of metacarpal I.
b. The extensor pollicis brevis extends metacarpal I and the proximal phalanx of
the thumb.
i. Its origin includes the shaft of the radius and the interosseous
membrane.
ii. Its insertion is on proximal phalanx I.
c. The extensor pollicis longus extends distal phalanx I, aids in extending
proximal phalanx I and metacarpal I, and adducts and laterally rotates the
thumb.
i. Its origin includes the posterior surface of the ulna and the
interosseous membrane.
ii. Its insertion is on distal phalanx I.
d. The extensor indicis extends the wrist and index finger.
i. Its origin includes the posterior surface of the ulna and the
interosseous membrane.
ii. Its insertion is on the middle and distal phalanges of the index finger.
Insight 10.4 Carpal Tunnel Syndrome (Fig. 10.31)
H. The actions of the intrinsic muscles of the hand are mainly to assist the flexors and extensors in
the forearm to make finger movements more precise. They are divided into three groups: The
Saladin Outline Ch.10
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thenar group, the hypothenar group, and the midpalmar group. (pp. 364–365) (Fig. 10.32) (Table
10.12)
1. The thenar group of muscles form the thick, fleshy mass as the base of the thumb; all
four muscles in this group are concerned with thumb movement.
a. The adductor pollicis draws the thumb toward the palm as in gripping a tool;
it is innervated by the ulnar nerve.
i. Its origin includes the capitate, bases of metacarpals II–III, anterior
ligaments of the wrist, and the tendon sheath of the flexor carpi radialis.
ii. Its insertion is the medial surface of proximal phalanx I.
b. The abductor poliicis brevis abducts the thumb in the sagittal plane; it is
innervated by the median nerve.
i. Its origin is mainly on the flexor retinaculum; also the scaphoid,
trapezium, and abductor pollicis longus tendon.
ii. Its insertion is on the lateral surface of proximal phalanx I.
c. The flexor pollicis brevis flexes the metacarpophalangeal joint of the thumb;
it is innervated by the median and ulnar nerves.
i. Its origin includes the trapezium, trapezoid, capitate, anterior
ligaments of the wrist, and the flexor retinaculum.
ii. Its insertion is on proximal phalanx I.
d. The opponens pollicis flexes metacarpal I to oppose thumb to finger tips; it is
innervated by the median nerve.
i. Its origin is on the trapezium and flexor retinaculum.
ii. Its insertion is on metacarpal I.
2. The hypothenar group of muscles form the fleshy mass at the base of the little finger;
all three muscles are concerned with movement of the little finger. They are innervated
by the ulnar nerve.
a. The abductor digiti minimi abducts the little finger as in spreading fingers
apart.
i. Its origin is on the pisiform and the tendon of the flexor carpi ulnaris.
ii. Its insertion is on the medial surface of proximal phalanx V.
b. The flexor digiti minimi brevis flexes the little finger at the
metacarpophalangeal joint.
i. Its origin is on the hamulus of the hamate bone and the flexor
retinaculum.
ii. Its insertion is on the medial surface of proximal phalanx V.
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c. The opponens digiti minimi flexes metacarpal V and the carpoteacarpal joint
when the little finger is moved into opposition with the tip of the thumb and
deepens the palm of the hand.
i. Its origin is on the hamulus of the hamate bone and flexor
retinaculum.
ii. Its insertion is on the medial surface of metacarpal V.
3. The midpalmar group of muscles occupies the hollow of the palm; it has 11 small
muscles divided into three groups.
a. The dorsal interosseous muscles (four muscles) abducts the fingers and
strongly flex the metacarpophalangeal joints, but extend the interphalangeal
joints, depending on actions of other muscles; they are important for grip
strength. They are innervated by the ulnar nerve.
i. Their origins, each with two heads, arise from facing surfaces of
adjacent metacarpals.
ii. Their insertions are on proximal phalanges II–IV.
b. The palmar interosseous muscles (three muscles) adduct the fingers and have
other actions similar to the dorsal interosseous muscles; they are innervated by
the ulnar nerve.
i. Their origins are on metacarpals I, II, IV, and V.
ii. Their insertions are on proximal phalanges II–V.
c. The lumbricals (four muscles) extend the interphalangeal joints and contribute
to the ability to pinch objects between the fleshy pads of the digits; they are
innervated by the median and ulnar nerves.
i. Their origins are the tendons of the flexor digitorum profundus.
ii. Their insertions are on proximal phalanges II–V.
V. Muscles Acting on the Hip and Lower Limb (pp. 366–381)
A. The largest muscles are found in the lower limb; they can be grouped into those that act on the
femur and hip joint, those that act on the leg and knee joint, extrinsic (leg)muscles that act on the
foot and ankle joint, and intrinsic (foot) muscles that act on the arches and toes (p. 366) (Tables
10.13, 10.14, 10.15, 10.16)
B. Muscles acting on the hip and femur mostly originate on the hip bone. (pp. 367–369) (Fig.
10.33) (Table 10.13)
1. The anterior muscles of the hip are the iliacus and the psoas major, collectively termed
the iliopsoas. They share a common tendon to the femur.
a. The iliacus flexes the thigh at the hip when the trunk is fixed and flexes the
trunk when the thigh is fixed; it balances the trunk during sitting. It is innervated
by the femoral nerve.
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i. Its origin includes the iliac crest and fossa, superolateral region of the
sacrum, and anterior sacroiliac and iliolumbar ligaments.
ii. Its insertion is on the lesser trochanter and nearby shaft of the femur.
b. The psoas major has the same action as the iliacus; it is innervated by the
ventral rami of lumbar spinal nerves.
i. Its origin includes the bodies and intervertebral discs of vertebrae
T12–L5 and transverse processes of the lumbar vertebrae.
ii. Its insertion is on the lesser trochanter and nearby shaft of the femur.
2. The lateral and posterior muscles of the hip include the tensor fasciae latae and three
gluteal muscles, along with important fascia and tendons. (Figs. 10.34, 10.35)
a. The fascia lata is a fibrous sheath that encircles the thigh and binds its
muscles; it combines with tendons of the gluteus maximus and tensor fasciae
latae to form the iliotibial band, which extends from iliac crest to lateral condyl
of the tibia and braces the knee. (Fig. 10.35) (Table 10.14)
b. The tensor fasciae latae extends the knee, laterally rotates the tibia, aids in
abduction and medial rotation of the femur, and steadies the pelvis and femur
during standing. It is innervated by the superior gluteal nerve.
i. Its origin includes the iliac crest, anterior superior spine, and deep
surface of the fascia lata.
ii. Its insertion is on the lateral condyl of the tibia via the iliotibial band.
c. The gluteus maximus extends the thigh at the hip as in stair climbing or
running and walking, adducts the thigh, elevates the trunk after stooping, holds
the trunk erect, and helps stabilize the femur on the tibia. It is innervated by the
inferior gluteal nerve.
i. Its origins include the posterior gluteal line of the ilium on the
posterolateral surface from iliac crest to posterior superior spine, and
coccyx, the posterior surface of the lower sacrum, and the apneurosis of
the erector spinae.
ii. Its insertion includes the gluteal tuberosity of the femur and lateral
condyle of the tibia via the iliotibial band.
d. The gluteus medius and gluteus minimus abduct and medially rotate the thigh;
during walking, they shift the weight of the trunk toward the planted limb as the
other foot is lifted. They are innervated by the superior gluteal nerve.
i. Their origins include most of the lateral surface of the ilium between
crest and acetabulum.
ii. Their insertions are on the greater trochanter of the femur.
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3. The six lateral rotators lie inferior to the gluteus minimus and deep to the other two
gluteal muscles. They are named for their action on the femur. They oppose medial
rotation by the gluteus medius and minimus and are responsible for shifting the body
weight when walking. (Fig. 10.34)
a. The gemellus superior laterally rotates the extended thigh and abducts the
flexed thigh; it is sometimes absent. It is innervated by the nerve to the obturator
internus.
i. Its origin is on the ischial spine.
ii. Its insertion is on the greater trochanter of the femur.
b. The gemellus inferior has the same actions as the gemellus superior; it is
innervated by the nerve to the quadratus femoris.
i. Its origin is on the ischial tuberosity.
ii. Its insertion is on the greater trochanter of the femur.
c. The obturator externus is not well understood but is thought to laterally rotate
the thigh in climbing; it is innervated by the obturator nerve.
i. Its origins include the external surface of the obturator membrane and
the pubic and ischial rami.
ii. Its insertion is on the femur between the head and greater trochanter.
d. The obturator internus is also not well understood, but is thought to laterally
rotate the extended thigh and abduct the flexed thigh; it is innervated by the
nerve to the obturator internus.
i. Its origins include the ramus of the ischium, inferior ramus of the
pubis, and the anteromedial surface of the lesser pelvis.
ii. Its insertion is on the greater trochanter of the femur.
e. The piriformis laterally rotates the extended thigh and abducts the flexed
thigh; it is innervated by spinal nerves L5–S2.
i. Its origins include the anterior surface of the sacrum, the gluteal
surface of the ilium, and the capsule of the sacroiliac joint.
ii. Its insertion is on the greater trochanter of the femur.
f. The quadratus femoris laterally rotates the thigh; it is innervated by the nerve
to the quadratus femoris.
i. Its origin is on the ischial tuberosity..
ii. Its insertion is on the intertrochanteric crest of the femur.
4. The medial (adductor) compartment of the thigh includes five muscles that act as
adductors, but some cross both the hip and knee joints. (Fig. 10.33)
a. The adductor brevis adducts the thigh; it is innervated by the obturator nerve.
i. Its origin is on the body and inferior ramus of the pubis.
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ii. Its insertion is on the linea aspera and spiral line of the femur.
b. The adductor longus adducts and medially rotates the thigh, and flexes the
thigh at the hip; it is innervated by the obturator nerve.
i. Its origin is on the body and inferior ramus of the pubis.
ii. Its insertion is on the linea aspera of the femur.
c. The adductor magnus adducts and medially rotates the thigh, and extends the
thigh at the hip; it is innervated y the obturator nerve and the tibial nerve.
i. Its origin includes the inferior ramus of the pubix, and the ramus and
tuberosity of the ischium.
ii. Its insertion includes the linea aspera, gluteal tuberosity, and medial
supracondylar line of the femur.
d. The gracilis flexes and medially rotates the tibia at the knee; it is innervated
by the obturator nerve.
i. Its origin includes body and inferior ramus of the pubis and the ramus
of the ischium.
ii. Its insertion is on the medial surface of the tibia just below the
condyle.
e. The pectineus flexes and adducts the thigh; it is innervated by the femoral
nerve.
i. Its origin is on the superior ramus of the pubis.
ii. Its insertion is on the spiral line of the femur.
C. Muscles acting on the knee and leg form most of the mass of the thigh and produce actions on
the knee joint; some cross both the hip and knee joints. (pp. 370–372) (Table 10.14)
1. The anterior (extensor) compartment of the thigh contains the quadriceps femoris,
which is the prime mover of knee extension and the most powerful muscle in the body.
(Figs. 10.35, 10.36)
2. This compartment also includes the sartorius (tailor’s muscle), the longest muscle in
the body.
3. The four heads of the quadriceps converge on the quadriceps (patellar) tendon that
extends to the patella and then continues as the patellar ligament that inserts on the tibial
tuberosity. All are innervated by the femoral nerve.
a. The rectus femoris extends the knee, flexes the thigh at the hip, and flexes the
trunk on the hip if the thigh is fixed.
i. Its origin includes the ilium at the anterior inferior spine and superior
margin of the acetabulum, and the capsule of the hip joint.
ii. Its insertion is on the patella, tibial tuberosity, and lateral and medial
condyles of the tibia.
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b. The vastus lateralis extends the knee and retains the patella in the groove on
the femur during knee movements.
i. Its origin includes the femur at the greater trochanter and
intertrochanteric line, the gluteal tuberosity, and the linea aspera.
ii. Its insertion is the same as the rectus femoris.
c. The vastus medialis has the same action as the vastus lateralis.
i. Its origin includes the femur at the intertrochanteric line, the spiral
line, linea aspera, and medial supracondylar line.
ii. Its insertion is the same as the rectus femoris
d. The vastus intermedius extends the knee.
i. Its origin includes the anterior and lateral surfaces of the femoral
shaft.
ii. Its insertion is the same as the rectus femoris.
e. The sartorius aids in knee and hip flexion, as in sitting or climbing; it abducts
and laterally rotates the thigh. It is innervated by the femoral nerve.
i. Its origin is on and near the anterior superior spine of the ilium.
ii. Its insertion is on the medial surface of the proximal end of the tibia.
4. The posterior (flexor) compartment of the thigh contains three muscles colloquially
known as the hamstring muscles. (Fig. 10.37) (Table 10.14)
a. The biceps femoris flexes the knee, extends the hip, elevates the trunk from a
stooping posture, laterally rotates the tibia on the femur when the knee is flexed,
laterally rotates the femur when the hip is extended, and counteracts forward
bending at the hips. It is innervated by the tibial nerve and common fibular
nerve.
i. The origin of the long head is on the ischial tuberosity; the origin of
the short head includes the linea aspera and lateral supracondylar line
of the femur.
ii. Its insertion is on the head of the fibula.
b. The semitendinosus flexes the knee, medially rotates tibia on the femur when
the knee is flexed, medially rotates the femur when the hip is extended, and
counteracts forward bending at the hips. It innervated by the tibial nerve.
i. Its origin is on the ischial tuberosity.
ii. Its insertion is on the medial surface of the upper tibia.
a. The semimembranosus has the same action as the semitendinosus.
i. Its origin is on the ischial tuberosity.
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ii. Its insertion includes the medial condyl and nearby margin of the
tibia, the intercondylar line and lateral condyle of the femur, and the
ligament of the politeal region.
5. The posterior compartment of the leg contains one muscle that acts on the knee, the
popliteus; the others act on the ankle and foot. (Fig. 10.37) (Table 10.14)
a. The popliteus rotates the tibia medially on the femur if the femur is fixed
(sitting down), or rotates the femur laterally on the tibia if the tibia is fixed
(standing up; it unlocks the knee to allow flexion, and may prevent forward
dislocation of the femur during crouching. It is innervated by the tibial nerve.
i. Its origin includes the lateral condyle of the femur, lateral meniscus,
and joint capsule.
ii. Its insertion is on the posterior surface of the upper tibia.
D. Muscles acting on the foot include the crural muscles, which are tightly bound by deep fasciae
that compress them and aid in the return of blood from the legs. (pp. 373–378) (Fig. 10.38) (Table
10.15)
1. The fasciae separate the crural muscles into anterior, lateral, and posterior
compartments; the posterior compartment has superficial and deep groups. (Fig. 10.42b)
2. The anterior (extensor) compartment of the leg contains four muscles that dorsiflex the
ankle; their tendons are held tightly against the ankle by two extensores retinacula similar
to those at the wrist. All four are innervated by the deep fibular (peroneal) nerve.
a. The fibularis (peroneus) tertius dorsiflexes and everts the foot during walking,
helping toes clear the ground during forward swing.
i. Its origin includes the medial surface of the lower one-third of the
fibula and the interosseus membrane.
ii. Its insertion is on metatarsal V.
b. The extensor digitorum longus extends the toes, dorsiflexes the foot, and
tightens the plantar aponeurosis.
i. Its origin includes the lateral condyle of the tibia, the shaft of the
fibula, and the interosseous membrane.
ii. Its insertions are on the middle and distal phalanges II–V.
a. The extensor hallucis longus extends the great toe and dorsiflexes the foot.
i. Its origin includes the anterior surface of the middle of the fibula and
the interosseous membrane.
ii. Its insertion is on distal phalanx I.
a. The tibialis anterior dorsiflexes and inverts the foot, resists backward tipping
of the body, and helps support the medial longitudinal arch of the foot.
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i. Its origin includes the lateral condyle and lateral margin of the
proximal half of the tibia and the interosseous membrane.
ii. Its insertion includes the medial cuneiform and metatarsal I.
3. The posterior (flexor) compartment of the leg, superficial group, includes three plantar
flexors; all are innervated by the tibial nerve.
a. The first two, the gastrocnemius and the soleus, are collectively known as the
triceps surae and insert on the calcaneus via the calcaneal (Achilles) tendon.
b. The gastrocnemius plantar flexes the foot, flexes the knee, and is active in
walking, running, and jumping.
i. Its origin includes the the condyles and popliteal surface of the femur,
lateral supracondylar line, and capsule of the knee joint.
ii. Its insertion is on the calcaneus.
c. The soleus also plantar flexes the foot and steadies the leg on the ankle during
standing.
i. Its origin includes the posterior surface of the head and proximal onefourth of the fibula, the middle one-third of the tibia, and the
interosseous membrane.
ii. Its insertion is on the calcaneus.
a. The plantaris is a weak synergist of the triceps surae; it is absent in many
people. Its long tendon is often used for tendon grafts if needed in other parts of
the body.
4. The posterior (flexor) compartment of the leg, deep group, contains four muscles, one
of which, the popliteus, is described in Table 10.14 because it acts on the knee. All are
innervated by the tibial nerve. (Fig. 10.41)
a. The flexor digitorum longus flexes phalanges II–V as the foot is raised from
the ground, stabilizes metatarsal heads, and keeps distal pads of the toes in
contact with the ground in toe-off and tiptoe movements.
i. Its origin is on the posterior surface of the tibial shaft.
ii. Its insertions are on distal phalanges II–V.
b. The flexor hallucis longus has the same actions as the flexor digitorum
longus, but for the great toe (digit I).
i. Its origin includes the inferior two-thirds of the fibula and
interosseous membrane.
ii. Its insertion is on distal phalanx I.
c. The tibialis posterior inverts the foot and may assist in strong plantar flexion
or control pronation of the foot during walking.
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i. Its origin includes the posterior surface of the proximal half of the
tibia, fibula, and interosseous membrane.
ii. Its insertions are on the navicular, medial cuneiform, and metatarsals
II–IV.
5. The lateral (fibular) compartment of the leg includes two muscles; they are innervated
by the superficial fibular (peroneal) nerve. (Figs. 10.38a, 10.39a, 10.42a)
a. The fibularis (peroneus) brevis maintains the concavity of the sole during toeoff and tiptoeing, and may evert the foot and limit inversion and help to steady
the leg on the foot.
i. Its origin is on the lateral surface of the distal two-thirds of the fibula.
ii. Its insertion is on the base of metatarsal V.
b. The fibularis (peroneus) longus also maintains concavity of the sole during
toe-off and tiptoeing, and everts and plantar flexes the foot.
i. Its origin is the head and lateral surface of the proximal two-thirds of
the fibula.
ii. Its insertion includes the medial cuneiform and metatarsal I.
E. The many intrinsic muscles of the foot help to support the arches and act on the toes; several are
similar in name and location to the intrinsic muscles of the hand; all remaining muscles are on the
ventral aspect and are grouped into four layers. (p. 379–381) (Fig. 10.43) (Table 10.16)
1. The dorsal aspect of the foot has only one muscle, the extensor digitorum brevis; the
medial slip of this muscle is sometimes called the extensor hallucis brevis.
a. The extensor digitorum brevis extends proximal phalanx I and all phalanges
of digits II–IV; it is innervated by the deep fibular (peroneal) nerve.
i. Its origin includes the calcaneus and the inferior extensor retinaculum
of the ankle.
ii. Its insertion includes proximal phalanx I and tendons of extensor
digitorum longus to II–IV.
2. Ventral layer 1 (most superficial) is the first muscle layer encountered beneath the
plantar aponeurosis, a tough fibrous sheet between the skin and the muscles that serves as
an origin for several ventral muscles.
a. The flexor digitorum brevis is a stout muscle on the midline that flexes digits
II–IV and supports the arches; it is innervated by the medial plantar nerve.
i. Its origin includes the calcaneus and the plantar aponeurosis.
ii. Its insertions are middle phalanges II–V.
a. The abductor digiti minimi, lateral to the flexor digitorum brevis, abducts and
flexes the little tow and supports the arches of the foot; it is innervated by the
lateral plantar nerve.
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i. Its origin includes the calcaneus and the plantar aponeurosis.
ii. Its insertion is on proximal phalanx V.
c. The abductor hallucis, medial to the flexor digitorum brevis, abducts the great
toe and supports the arches of the foot; it is innervated by the medial plantar
nerve.
i. Its origin includes the calcaneus, plantar aponeurosis, and flexor
retinaculum.
ii. Its insertion is on proximal phalanx I.
3. Ventral layer 2, the next deeper layer, contains one thick muscle, the quadratus plantae,
and the four lumbrical muscles.
a. The quadratus plantae has the same action as the flexor digitorum longus
(Table 10.15) and also flexes digits II–V. It is innervated by the lateral plantar
nerve.
i. It has two heads with origins on the medial and lateral sides of the
calcaneus.
ii. Its insertions are on distal phalanges II–V via the flexor digitorum
longus tendons.
a. The four lumbricals flex toes II–V; they are innervated by the lateral and
medial plantar nerves.
i. Their insertions are the tendon of the flexor digitorum longus.
ii. Its insertions are on proximal phalanges II–V.
4. Ventral layer 3, next deepest, contains three muscles that serve only the great and little
toes.
a. The flexor digiti minimi brevis flexes the little toe; it is innervated by the
lateral plantar nerve.
i. Its origins include metatarsal V and the sheath of the fibularis longis.
ii. Its insertion is on proximal phalanx V.
b. The flexor hallucis brevis flexes the great toe; it is innervated by the medial
plantar nerve.
i. Its origins include the cuboid, lateral cuneiform, and tibilais posterior
tendon.
ii. Its insertion is on proximal phalanx I.
c. The adductor hallucis, with an oblique head and a transverse head, adducts the
great toe; it is innervated by the lateral plantar nerve.
i. The two heads have origins on metatarsals II–IV, the fibularis longus
tendon, and ligaments at the bases of digit III–V.
ii. Its insertion is on proximal phalanx I.
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5. Ventral layer 4, the deepest layer, consists of only the small interosseous muscles
between the metatarsal bones—four dorsal and three plantar. All are innervated by the
lateral plantar nerve.
a. The dorsal interosseous muscles are bipennate and abduct toes II–IV.
i. Each has two heads with origins on facing surfaces of two adjacent
metatarsals.
ii. Their insertion are on proximal phalanges II–IV.
b. The plantar interosseous muscles are unipennate and adduct toes III–V.
i. Their origins are the medial aspect of metatarsals III–V.
ii. Their insertions are on the proximal phalanges III–V.
Insight 10.5 Athletic Injuries
Connective Issues: Muscular System Interactions
Cross References
Additional information on topics mentioned in Chapter 10 can be found in the chapters listed below.
Chapter 11: The length–tension relationship
Chapters 13 & 14: The peripheral nervous system
Chapter 22: Respiration