370
UNIT 2
Covering, Support, and Movement of the Body
10
MUSCLE GALLERY
Table 10.15
Muscles of the Leg: Movements of the Ankle and Toes
(Figures 10.22 to 10.24)
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
PART I: MUSCLES
OF THE ANTERIOR
COMPARTMENT
(Figures 10.22 and 10.23)
All muscles of the anterior compartment dorsiflex the ankle and have a common innervation, the deep fibular
nerve. Paralysis of the anterior muscle group causes
foot drop
, which requires that the leg be lifted unusually
high during walking to prevent tripping over one’s toes. One cause of “shin splints,” also called anterior
compartment syndrome, is painful inflammation of the anterior compartment muscles.
Tibialis anterior
(tib
0
e-a
9
lis)
(
tibial
5
tibia;
anterior
5
toward the front)
Superficial muscle of
anterior leg; laterally
parallels sharp anterior
margin of tibia
O—lateral condyle and
upper 2/3 of tibial shaft;
interosseous membrane
I—by tendon into
inferior surface of medial
cuneiform and first
metatarsal bone
Prime mover of
dorsiflexion
; inverts foot;
helps support medial
longitudinal arch of foot
Deep fibular nerve
(L
4
and L
5
)
Extensor digitorum longus
(
extensor
5
increases angle
at a joint;
digit
5
finger or
toe;
longus
5
long)
Unipennate muscle on
anterolateral surface of leg;
lateral to tibialis anterior
muscle
O—lateral condyle of
tibia; proximal 3/4 of
fibula; interosseous
membrane
I—middle and distal
phalanges of toes 2–5 via
extensor expansion
Prime mover of toe
extension
(acts mainly
at metatarsophalangeal
joints); dorsiflexes foot
Deep fibular nerve
(L
5
and S
1
)
Fibularis (peroneus) tertius
(fib-u-lar
9
ris ter
9
shus)
(fibular
5
fibula;
tertius
5
third)
Small muscle; usually
continuous and fused with
distal part of extensor
digitorum longus; not
always present
O—distal anterior
surface of fibula and
interosseous membrane
I—tendon inserts
on dorsum of fifth
metatarsal
Dorsiflexes and everts
foot
Deep fibular nerve
(L
5
and S
1
)
Extensor hallucis longus
(hal
9
yu-kis)
(hallux
5
great toe)
Deep to extensor digitorum
longus and tibialis anterior;
narrow origin
O—anteromedial fibula
shaft and interosseous
membrane
I—tendon inserts on
distal phalanx of great
toe
Extends great toe
;
dorsiflexes foot
Deep fibular nerve
(L
5
and S
1
)
The deep fascia of the leg is continuous with the fascia lata that
ensheathes the thigh. Like a snug “knee sock” beneath the skin,
the leg fascia binds the leg muscles tightly, preventing excessive
muscle swelling during exercise and aiding venous return. Its
inward extensions segregate the leg muscles into
anterior
,
lateral
,
and
posterior compartments
(see Figure 10.26b), each with its own
nerve and blood supply. Distally the leg fascia thickens to form
the
flexor
,
extensor
, and
fibular
(or peroneal)
retinacula
, “ankle
brackets” that hold the tendons in place where they run to the
foot (Figures 10.22a, 10.23a).
The various muscles of the leg promote movements at the ankle
joint (dorsiflex and plantar flex), at the intertarsal joints (invert
and evert the foot), and/or at the toes (flex and extend). Muscles
in the
anterior extensor compartment of the leg
are primarily
toe extensors and ankle dorsiflexors. Although dorsiflexion is
not a powerful movement, it is important in preventing the toes
from dragging during walking. Lateral compartment muscles
are the
fibular
, formerly
peroneal
(
peron
5
fibula),
muscles
that
plantar flex and evert the foot. Muscles of the
posterior flexor
compartment
primarily plantar flex the foot and flex the toes
(Figure 10.24b–d). Plantar flexion is the most powerful movement
of the ankle (and foot) because it lifts the entire weight of our
body. It is essential for standing on tiptoe and provides the forward
thrust when walking and running. The
popliteus muscle
, which
crosses the knee, has a unique function. It “unlocks” the extended
knee in preparation for flexion (Figure 10.24b, f).
We consider the tiny intrinsic muscles of the sole of the foot
(lumbricals, interossei, and others) in Table 10.16.
Table 10.17 (Part II) summarizes the actions of the muscles in
this table.
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