508
UNIT 3
Regulation and Integration of the Body
13
Superior
gluteal
Lumbosacral
trunk
Inferior
gluteal
Common
fibular
Tibial
Posterior
femoral
cutaneous
Pudendal
Sciatic
(a) Ventral rami and major branches of the sacral plexus
Superior
gluteal
Inferior
gluteal
Common
fibular
Deep
fibular
Superficial
fibular
Plantar
branches
Tibial
Sural (cut)
Posterior
femoral
cutaneous
Pudendal
Sciatic
(b) Distribution of the major nerves from
the sacral plexus to the lower limb
L
4
L
5
S
1
S
2
S
3
S
4
S
5
Co
1
Ventral rami
Ventral
rami:
Pudendal nerve
Gluteus maximus
Piriformis
Inferior gluteal
nerve
Common fibular
nerve
Tibial nerve
Sciatic nerve
Posterior femoral
cutaneous nerve
(c) Cadaver photo
Figure 13.12
The sacral plexus.
(Posterior view.)
Sacral Plexus
Te
sacral plexus
arises from spinal nerves
L
4
–S
4
and lies immediately caudal to the lumbar plexus
(Fig-
ure 13.12)
. Some fibers of the lumbar plexus contribute to the
sacral plexus via the
lumbosacral trunk
, as mentioned earlier.
Te sacral plexus has about a dozen named branches. About
half of these serve the buttock and lower limb; the others in-
nervate pelvic structures and the perineum. Here we describe
the most important branches.
Table 13.6
summarizes all but
the smallest ones.
Te largest branch of the sacral plexus is the
sciatic nerve
(si-
at
9
ik), the thickest and longest nerve in the body. It supplies the
entire lower limb, except the anteromedial thigh.
Te sciatic nerve is actually two nerves—the
tibial
and
common fibular
—wrapped in a common sheath. Te sciatic
nerve leaves the pelvis via the greater sciatic notch. It courses
deep to the gluteus maximus muscle and enters the poste-
rior thigh just medial to the hip joint (
sciatic
5
of the hip).
Tere it gives off motor branches to the hamstring muscles
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