220 Introduction to Anatomy and Physiology
Figure 6.20 Spinal Nerve Plexuses
Plexus Spinal nerves Exiting nerves Region supplied
Cervical
C1–C5 phrenic diaphragm, skin and muscles of neck and shoulder
Brachial C
5
–C
8
and T
1
axillary
radial
median
musculocutaneous
ulnar
skin and muscles of shoulder
skin and muscles of lateral and posterior arm and
forearm
skin and fl exor muscles of forearm, some hand muscles
skin of lateral forearm, elbow fl exor muscles
skin of hand, fl exor muscles of forearm, wrist and some
hand muscles
Lumbar L1–L4 femoral
obturator
saphenous
skin of medial and anterior thigh, anterior thigh muscles
skin and muscles of medial thigh and hip
skin of the medial thigh and medial lower leg
Sacral L4–L5 and
S1–S4
sciatic
tibial
common fi bular
superior and inferior
gluteal
posterior femoral
cutaneous
two of the hamstrings (semimembranosus,
semitendinosus), adductor magnus
muscles of knee fl exion, plantar fl exion, and toe fl exion;
skin of the posterior lower leg and sole of the foot
biceps femoris, tibialis anterior, muscles of toe extension,
skin of the anterior lower leg, superior surface of foot,
and lateral side of foot
gluteal muscles
skin of posterior thigh and posterior lower leg
Parasympathetic Nerves
In contrast to the sympathetic nervous
system, the parasympathetic nervous system
controls all of the automatic, day-in-and-day-
out functions of the circulatory, respiratory,
and digestive systems. For these reasons it is
sometimes called the “resting and digesting
system.” In addition, after a fi ght-or-fl ight
situation, the parasympathetic nervous system
produces a calming effect that returns the body
to a normal state.
Preganglionic parasympathetic neurons
originate in one of two separate regions—the
brain stem or the sacral (lowermost) region of the
spinal cord. For this reason, the parasympathetic
system is also known as the craniosacral (KRAY-
nee-oh-SAY-kral) division. Activation of both
preganglionic and postganglionic nerves in this
system triggers the release of the
neurotransmitter acetylcholine. Although
acetylcholine stimulates skeletal muscle, it also
inhibits activity in cardiac and smooth muscle.
1. How many pairs of cranial nerves does
the body have?
2. What kind of impulses do mixed nerves
carry?
3. How many pairs of spinal nerves does
the body have?
4. List the two divisions of the autonomic
nervous system.
5. Which nerves—the sympathetic or the
parasympathetic—activate the fi ght-or-
fl ight response?
Check Your Understanding