Page 219 - Anatomy and Physiology of Farm Animals, 8th Edition

204 / Anatomy and Physiology of Farm Animals

Proprioceptive
tracts
VetBooks.ir motor system
Dorsolateral

Spinocerebellar
tracts

Spinothalamic
tract Ventromedial motor
system

Figure 10-15. Cross‐section of cervical spinal cord with approximate locations of main sensory (blue)
and motor (red) pathways.

part of the vertebral column, the spinal (Fig. 10‐14). Not all sensation is sent to the
cord segments become shorter so that the cortex, however, as it may also be used to
cord terminates before the end of the ver- coordinate postural reflexes, mediate
tebral column (at vertebrae S1–S2 in horses reflexes, or to drive autonomic and emotional
and ruminants, S2–S3 in swine). As a behaviors.
result, the emerging spinal nerve roots of The dorsal funiculi contain afferent
the caudal cord become progressively tracts that carry information about body
longer as they course caudad within the position from joints, tendons, and muscles.
vertebral canal to reach their respective This type of sense is called proprioception.
intervertebral foramen. This means that Injury to this pathway produces uncoordi-
the vertebral canal caudal to the termina- nated, inaccurate movements, as the cortex
tion of the spinal cord contains the nerve lacks some of the information it needs to
roots of most of the sacral and all of the make ongoing adjustments in the planning
caudal spinal nerves. This bundle of nerve and execution of voluntary movements.
roots is called the cauda equina, after its Such incoordination is sensory ataxia.
resemblance to a horse’s tail (Fig. 10‐13). Proprioceptive information also ascends

Tracts of the Spinal Cord. A tract is a the spinal cord in several spinocerebellar
tracts, located in the lateral and ventral
bundle of functionally related axons in the funiculi. As the name suggests, these tracts
CNS. Tracts that carry sensory information are headed for the cerebellum, where the
are ascending tracts, whereas those carrying proprioceptive information is used to help
motor commands are descending tracts. shape voluntary movements so that they
The white matter of the spinal cord in which are accurate and smooth.
the tracts are found can be roughly divided Information about pain is carried by a
into three columns on each half of the cord: number of individual pathways, but these
a dorsal funiculus (often called the dorsal
are often grouped under the names spi-
column), a lateral funiculus, and a ventral
funiculus (Figs. 10‐12 and 10‐15). nothalamic tract or anterolateral sys-
tem. This large group of fibers is found in a
Sensory Tracts. Pathways that carry wide band through the lateral and ventral
sensory information for conscious funiculi. Some of these tracts terminate in
perception will ultimately terminate in the the brainstem, where they mediate certain
sensory regions of the cerebral cortex reflexes associated with painful stimuli.
after first relaying through the thalamus Others make connections that alert the