Chapter 10
The Muscular System
373
10
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
PART II: MUSCLES OF THE LATERAL COMPARTMENT
(Figures 10.23 and 10.24)
These muscles have a common innervation, the superficial
fibular nerve. Besides plantar flexion and foot eversion, these muscles stabilize the lateral ankle and lateral longitudinal arch of the foot.
Fibularis (peroneus) longus
(See also Figure 10.22)
Superficial lateral muscle;
overlies fibula
O—head and upper
portion of lateral fibula
I—by long tendon that
curves under foot to first
metatarsal and medial
cuneiform
Plantar flexes and everts
foot
; may help keep foot
flat on ground
Superficial fibular
nerve (L
5
–S
2
)
Fibularis (peroneus) brevis
(
brevis
5
short)
Smaller muscle; deep to
fibularis longus; enclosed in
a common sheath
O—distal fibula shaft
I—by tendon running
behind lateral malleolus
to insert on proximal end
of fifth metatarsal
Plantar flexes and everts
foot
Superficial fibular
nerve
PART III: MUSCLES OF THE POSTERIOR COMPARTMENT
(Figure 10.24)
The muscles of the posterior compartment have a common
innervation, the tibial nerve. They act in concert to plantar flex the ankle.
Superficial Muscles
Triceps surae
(tri
0
seps sur
9
e)
(See also Figure 10.23)
Refers to muscle pair (gastrocnemius and soleus) that shapes the posterior calf and inserts via a common tendon
into the calcaneus of the heel; this
calcaneal
or
Achilles tendon
is the largest tendon in the body. Prime movers
of ankle plantar flexion.
Gastrocnemius
(gas
0
truk-ne
9
me-us)
(
gaster
5
belly;
kneme
5
leg)
Superficial muscle of pair;
two prominent bellies that
form proximal curve of calf
O—by two heads from
medial and lateral
condyles of femur
I—posterior calcaneus via
calcaneal tendon
Plantar flexes foot
when
knee is extended; because
it also crosses knee joint,
it can flex knee when
foot is dorsiflexed
Tibial nerve (S
1
, S
2
)
Soleus
(so
9
le-us)
(
soleus
5
fish)
Broad, flat muscle, deep to
gastrocnemius on posterior
surface of calf
O—extensive origin from
superior tibia, fibula, and
interosseous membrane
I—as for gastrocnemius
Plantar flexes foot
; impor-
tant locomotor and pos-
tural muscle during walk-
ing, running, and dancing
Tibial nerve
Plantaris
(plan-tar
9
is)
(
planta
5
sole of foot)
Generally a small, feeble
muscle, but varies in size
and extent; may be absent
O—posterior femur
above lateral condyle
I—via a long, thin tendon
into calcaneus or its tendon
Helps to flex knee and
plantar flex foot
Tibial nerve
Deep Muscles
(Figure 10.24c–f)
Popliteus
(pop-lit
9
e-us)
(
poplit
5
back of knee)
Thin, triangular muscle
at posterior knee; passes
inferomedially to tibial
surface
O—lateral condyle
of femur and lateral
meniscus of knee
I—proximal tibia
Flexes and rotates leg
medially to unlock
extended knee when
flexion begins
; with
tibia fixed, rotates thigh
laterally
Tibial nerve (L
4
–S
1
)
Flexor digitorum longus
(
flexor
5
decreases angle at
a joint)
Long, narrow muscle; runs
medial to and partially
overlies tibialis posterior
O—extensive origin on
the posterior tibia
I—tendon runs behind
medial malleolus and
inserts into distal
phalanges of toes 2–5
Plantar flexes and inverts
foot; flexes toes
; helps
foot “grip” ground
Tibial nerve (L
5
–S
2
)
Flexor hallucis longus
(See also Figure 10.23)
Bipennate muscle; lies
lateral to inferior aspect of
tibialis posterior
O—midshaft of fibula;
interosseous membrane
I—tendon runs under
foot to distal phalanx of
great toe
Plantar flexes and inverts
foot; flexes great toe
at all joints
; “push off”
muscle during walking
Tibial nerve (L
5
–S
2
)
Tibialis posterior
(
posterior
5
toward the
back)
Thick, flat muscle deep to
soleus; placed between
posterior flexors
O—superior tibia and
fibula and interosseous
membrane
I—tendon passes behind
medial malleolus and
under arch of foot; inserts
into several tarsals and
metatarsals II–IV
Prime mover of foot
inversion
; plantar flexes
foot; stabilizes medial
longitudinal arch of foot
(as during ice skating)
Tibial nerve (L
4
and L
5
)
MUSCLE GALLERY
Table 10.15
(continued)
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