The Spinal Cord

Question 1

cauda equina

Answer 1

literally means “horse’s tail”; term applied to the roots of the lumbar, sacral, and coccygeal nerves nerves, surrounding the conus medullaris and filum terminale, due to the collective resemblance of these structures to a horse’s tail; the cauda equina occupies the subarachnoid space within the vertebral canal

Question 2

cervical intumescence

Answer 2

from the Latin intumescentia, “a swelling”; the slight enlargement of the spinal cord from segments C6 to T2, corresponding to the spinal nerves that form the brachial plexus

Question 3

commissure

Answer 3

from the Latin commissura, “a joining together”; a site of union of corresponding parts; in the CNS, the term commissure is most often applied to bundles of axons connecting left and right sides (crossing the median plane)

Question 4

conus medullaris

Answer 4

the cone-shaped caudal end of the spinal cord; the tip of the conus medullaris is located between lumbar vertebrae 6 and 7 in the dog and between lumbar vertebrae 1 and 2 in humans

Question 5

fasiculus cuneatus

Answer 5

an ascending tract of axons which borders the dorsal median sulcus in the dorsal funiculus; this tract is composed of axons from cell bodies in the spinal (dorsal root) ganglia of spinal nerves innervating the cranial part of the trunk, the thoracic limb, and the neck; present only in the cranial portion of the spinal cord; axons that comprise it synapse in the medulla oblongata; seperated from the fasiculus gracilis on the surface of the spinal cord by the dorsal intermediate sulcus

Question 6

fasiculus gracilis

Answer 6

an ascending tract of axons wthat borders the dorsal median sulcus in the dorsal funiculus; extends the entire length of the spinal cord; composed of axons from cell bodies in the spinal (dorsal root) ganglia of spinal nerves innervating the caudal part of the trunk, the pelvic limb, and the tail; the axons that comprise it synapse in the medulla oblongata

Question 7

filum terminale

Answer 7

from the Latin filum, “a threadlike structure”; a slender threadlike extension of the pia mater from the conus medullaris to the sacral vertebrae or caudal vertebrae; surrounded by a similar extension of the dura mater called the filum durae matris spinalis

Question 8

fissure

Answer 8

meaning “cleft or groove” in Latin; in the CNS, a relatively deep groove

Question 9

gray matter

Answer 9

large collection of neruon cell bodies (cerebral cortex, cerebellar cortex, spinal cord gray matter, nuclei) in the CNS

Question 10

lower motor neurons (LMN’s)

Answer 10

somatic efferent (motor) neurons that have their cell bodies in the CNS and whose axons travel in spinal nerves and certain cranial nerves (all except I, II, and VIII) to innervate skeletal muscles; these include alpha and gamma motor neurons

Question 11

alpha motor neurons

Answer 11

lower motor neurons that innervate the main fibers (extrafusal fibers) of skeletal muscles

Question 12

gamma motor neurons

Answer 12

lower motor neurons that innervate the skeletal muscle fibers (intrafusal fibers) within muscle spindles (neuromuscular spindles)

Question 13

lumbar intumescense

Answer 13

the slight enlargement of the spinal cord from the segments L4 to S2, corresponding to the spinal nerves that form the lumbosacral plexus

Question 14

nerve fiber

Answer 14

a synonym for axon

Question 15

sulcus

Answer 15

means “a groove” in Latin; in the CNS, a relatively shallow groove

Question 16

tract (fasicle/fasiculus)

Answer 16

an organized bundle of axons in the CNS that have a common origin, termination, and function; tract names indicate the origin of the neuron cell bodies and the termination of the axons

Question 17

upper motor neurons (UMN’s)

Answer 17

CNS neurons whose cell bodies are located in the brain (cerebral cortex and brain stem nuclei); their axons descend to synapse with the lower motor neurons of spinal and cranial nerves

Question 18

white matter

Answer 18

large collections of axons, predominantly myelinated, in the CNS