Page 221 - Anatomy and Physiology of Farm Animals, 8th Edition

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column. The limbs, however, are supplied (A) C6 C7 (B)
with sensory and motor fibers within tan-
VetBooks.ir gled arrangements of spinal nerves known a C8 T1 d a L4 L5 L6 S1 S2 S3/4 e d

as plexuses. The regions of the spinal cord
supplying the plexuses are visibly greater e b
in diameter because they have more sen- b f
sory and motor neurons supplying the f c
mass of the limbs. These enlargements are g
called intumescences. c
Brachial Plexus. Each thoracic limb is
supplied by a brachial plexus, a network g h
of nerves derived from the last three
cervical and first one or two thoracic g
nerves (Figs. 10‐1 and 10‐16A). The spinal
cord associated with the brachial plexus is g i
greater in diameter than adjacent parts of
the cord and lies primarily within the
caudal cervical vertebrae; consequently it
is described as the cervical enlargement.
The brachial plexus gives rise to specific
named nerves that innervate the muscles Figure 10-16. (A) Nerve (n., nn.) supply of tho-
of the thoracic limb and supply sensation racic limb of the horse. a, suprascapular n.; b, mus-
to the same general regions of the skin. culocutaneous n.; c, median n.; d, axillary n.; e,
radial n.; f, ulnar n.; g, medial and lateral palmar
Table 10‐2 lists the nerves arising from the nn. (B) Nerve supply of pelvic limb of the horse. a,
brachial plexus and the region and muscles femoral n.; b, obturator n.; c, saphenous n.; d,
supplied by each. pudendal n.; e, gluteal n.; f, sciatic n.; g, common

Lumbosacral Plexus. The right and left peroneal n.; g’, superficial peroneal n.; g”, deep per-
lumbosacral plexuses supply nerves to oneal n.; h, tibial n.; i, medial and lateral plantar nn.
the respective pelvic limbs (Figs. 10‐1 and
10‐16B). The lumbosacral plexuses are do not, however, have discernible dorsal
made up of the ventral branches of the and ventral roots, and some are strictly
last few lumbar and first two or three motor or sensory (as opposed to spinal
sacral nerves. The visible spinal cord nerves, which are all mixed nerves).
enlargement here is called the lumbar Cranial nerve II, the optic nerve, only
enlargement. The nerves derived from superficially resembles an actual nerve of
the lumbosacral plexus are described in the PNS. Its axons are actually a tract of the
Table 10‐3.
CNS, invested with meninges and with
myelin provided by oligodendrocytes.
Cranial Nerves Features and functions of the 12 cranial
nerves are outlined in Table 10‐4.
Classically, 12 pairs of cranial nerves
arising from the brain are described
(Fig. 10‐17). They are designated by roman Autonomic Nervous System
numerals, numbered from most rostral (I)
to most caudal (XII). With the exception of The ANS is the part of the nervous system
cranial nerves I (olfactory) and II (optic), that regulates activity in viscera and other
the cranial nerves arise from the midbrain, structures not normally under voluntary
pons, and medulla oblongata and in gen- control (Fig. 10‐18). The common repre-
eral resemble ordinary spinal nerves. They sentation of the ANS as a motor subdivision