366
UNIT 2
Covering, Support, and Movement of the Body
10
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
Vastus intermedius
(in
0
ter-me
9
de-us)
(
intermedius
5
inter-
mediate)
Obscured by rectus femoris;
lies between vastus lateralis
and vastus medialis on
anterior thigh
O—anterior and lateral
surfaces of proximal
femur shaft
I—as for rectus femoris
Extends knee
Femoral nerve
Tensor fasciae latae
(ten
9
sor fa
˘
9
she-e la
9
te)
(
tensor
5
to make tense;
fascia
5
band;
lata
5
wide)
Enclosed between fascia
layers of anterolateral
aspect of thigh;
functionally associated with
medial rotators and flexors
of thigh
O—anterior aspect of
iliac crest and anterior
superior iliac spine
I—iliotibial tract*
Steadies the knee and
trunk on thigh by making
iliotibial tract taut
; flexes
and abducts thigh; rotates
thigh medially
Superior gluteal nerve
(L
4
and L
5
)
PART II: POSTERIOR MUSCLES
(Figure 10.21)
Gluteal Muscles—Origin on Pelvis
Gluteus maximus
(gloo
9
te-us mak
9
sı˘-mus)
(
glutos
5
buttock;
maximus
5
largest)
Largest and most
superficial gluteus muscle;
forms bulk of buttock
mass; fibers are thick and
coarse; important site of
intramuscular injection
(dorsal gluteal site); overlies
large sciatic nerve; covers
ischial tuberosity only when
standing; when sitting,
moves superiorly, leaving
ischial tuberosity exposed
in the subcutaneous
position
O—dorsal ilium, sacrum,
and coccyx
I—gluteal tuberosity of
femur; iliotibial tract
Major extensor of thigh
;
complex, powerful, and
most effective when
thigh is flexed and force
is necessary, as in rising
from a forward flexed
position and in thrusting
the thigh posteriorly
in climbing stairs and
running; generally
inactive during standing
and walking; laterally
rotates and abducts thigh
Inferior gluteal nerve
(L
5
, S
1
, and S
2
)
Gluteus medius
(me
9
de-us)
(
medius
5
middle)
Thick muscle largely
covered by gluteus
maximus; important site
for intramuscular injections
(ventral gluteal site);
considered safer than
dorsal gluteal site because
less chance of injuring
sciatic nerve
O—between anterior
and posterior gluteal
lines on lateral surface
of ilium
I—by short tendon into
lateral aspect of greater
trochanter of femur
Abducts and medially
rotates thigh
; steadies
pelvis; its action is
extremely important in
walking; e.g., muscle of
limb planted on ground
tilts or holds pelvis in
abduction so that pelvis
on side of swinging limb
does not sag and foot of
swinging limb can clear
the ground
Superior gluteal nerve
(L
5
, S
1
)
Gluteus minimus
(mı˘
9
nı˘-mus)
(minimus
5
smallest)
Smallest and deepest
gluteal muscle
O—between anterior
and inferior gluteal lines
on external surface of
ilium
I—anterior border of
greater trochanter of
femur
As for gluteus medius
Superior gluteal nerve
(L
5
, S
1
)
Lateral Rotators
Piriformis
(pir
9
ı˘-form-is)
(
piri
5
pear;
forma
5
shape)
Pyramidal muscle located
on posterior aspect of hip
joint; inferior to gluteus
minimus; issues from pelvis
via greater sciatic notch
O—anterolateral surface
of sacrum (opposite
greater sciatic notch)
I—superior border of
greater trochanter of
femur
Rotates extended thigh
laterally
; because inserted
above head of femur,
can also help abduct
thigh when hip is flexed;
stabilizes hip joint
S
1
and S
2
, L
5
*The iliotibial tract is a thickened lateral portion of the
fascia lata
(the fascia that ensheathes all the muscles of the thigh). It extends as a tendinous band
from the iliac crest to the knee (see Figure 10.21a).
MUSCLE GALLERY
Table 10.14
Muscles Crossing the Hip and Knee Joints: Movements of the Thigh and Leg
(Figures 10.20 and 10.21)
(continued)
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