Page 217 - Anatomy and Physiology of Farm Animals, 8th Edition

202 / Anatomy and Physiology of Farm Animals

In some locations within the skull, the dura tracts, the white matter, surround this core
of gray matter. A spinal cord segment is
mater splits into two layers divided by
VetBooks.ir channels filled with blood. These dural defined by the presence of a pair of spinal
nerves. Spinal nerves are formed by the
sinuses receive blood from the veins of the
brain and empty into the jugular veins. conjoining of dorsal and ventral roots,
They are also the site of reabsorption of which come together as the nerve at the
CSF through the arachnoid granulations point where the axons pass through the
back into the circulation. intervertebral foramen. In the cervical
The pia mater and the arachnoid of the region, spinal nerves emerge at the
spinal meninges are much as they are intervertebral foramen cranial to the verte-
within the cranial vault. The dura mater of bra of the same number (e.g., C1 spinal
the spinal meninges, however, is separated nerve cranial to C1 vertebra). The eighth
from the periosteum of the vertebral canal cervical spinal nerve emerges between C7
by a fat‐filled space, the epidural space. and T1 vertebral bodies; thereafter, the spi-
Physicians and veterinarians intro- nal nerves exit at the intervertebral fora-
duce local anesthetics into the epidural men caudal to the vertebral body of the
space to produce anesthesia in the cau- same number (e.g., T1 spinal nerve caudal
dal parts of the body. This procedure, to T1 vertebra, L5 spinal nerve caudal to
epidural anesthesia, is often done for L5 vertebra, etc.) (Fig. 10‐13).
obstetric procedures. One common Sensory neuronal cell bodies are present
application is the injection of anesthetic in aggregates, called dorsal root ganglia
between the first and second caudal ver- (singular, ganglion), lateral to the spinal
tebrae of the ox as an aid to repairing cord. The neurons within these ganglia are
uterine, vaginal, or rectal prolapses. pseudounipolar, and they give rise to axons
that enter the dorsal horn of the spinal
cord and others that join with motor fibers
Spinal Cord from the ventral horn neurons to become
the spinal nerve extending into the periph-
The spinal cord (Figs. 10‐12, 10‐13, and ery. The processes that extend from the
10‐14) is the caudal continuation of the spinal nerve to the spinal cord constitute
medulla oblongata. Unlike that of the cer- the dorsal root, which is sensory in
ebrum, the spinal cord’s gray matter is function.
found at the center of the cord, forming a The ventral root of the spinal nerve
butterfly shape on cross‐section. Fiber consists of motor axons that arise from the

Dorsal funiculus Dorsal horn
Central canal
Sensory neuron Lateral horn
Dorsal root
Dorsal root
ganglion
Dorsal branch
of spinal nerve

Motor neuron
Spinal nerve
Lateral funiculus Ventral root
Ventral branch
Ventral funiculus Ventral horn of spinal nerve
Figure 10-12. Cross‐sectional anatomy of the spinal cord and spinal nerves.