Spinal Cord

Question 1

Understand the divergence and convergence patterns of sensory afferent neurons and motor neurons and their role in spinal reflexes.

Answer 1

Divergence: One presynaptic neuron may have connections with multiple postsynaptic neurons or multiple connections with one postsynaptic neuron
Convergence: One postsynaptic neuron may receive connections from many presynaptic neurons

Question 2

Understand the difference between a withdrawal reflex and pain response and how these can be used to determine the site of a spinal cord injury.

Answer 2

Withdrawal reflex: Nociception; occurs all in the spinal cord, doesn’t need the brain
Pain reflex: Requires intact cerebral cortes; pain receptors called nociceptors

lack of pain reflex indicative of poor prognosis, fact that the nerves are unable to regenerate/heal

Question 3

Central Canal

Answer 3

Filled with CSF and lined with ependymal cells

Gray matter surrounds ependymal layer (neuronal and glial cell bodies)

Question 4

Dorsal horn

Answer 4

Upper arm of gray matter “butterfly” shape

Contains interneurons and central terminations of sensory afferent fibers

Question 5

Dorsal root

Answer 5

Edge of dorsal horn

Entry point of sensory axons

Question 6

Cutaneous areas

Answer 6

Smaller than dermatomes; name given to a particular peripheral nerve

Question 7

Cutaneous trunci relfex

Answer 7

Lesion location determination; skin twitch

Question 8

Major of info sent to CNS from sensory afferents is either:

Answer 8

Not perceived at that moment because of cortical pathway inhibition
OR
Can never perceived because a pathway to the cortex doesn’t exist

Question 9

Dermatome

Answer 9

Skin area innervated by one segment of the spinal cord (one nerve and all of its peripheral branches)

Question 10

Number of spinal vertebral segments in dogs

Answer 10

8 cervical, 13 thoracic, 7 lumbar, 3 sacral, and ~5 caudal
Cervical region has one more spinal cord segment than cervical vertebrae because the spinal cod and vertebral column grow at different rates after birth, spinal cord also ends quite cranial to the sacrum

Question 11

White matter

Answer 11

Surrounds gray matter
Contains myelinated and unmyelinated axons of both ascending and descending nerve fibers
Divided into dorsal, lateral, and ventral funiculus
Amount increased from caudal to cranial

Question 12

Lower motor neurons

Answer 12

Utilized when only going to spinal cord

Question 13

Upper motor neurons

Answer 13

Utilized when under command of the brain

Question 14

Injury to brachial enlargement

Answer 14

Forelimbs: paralysis, areflexia, atonia, denervation atrophy, sensory disturbance
Hindlimbs: paralysis, hyperreflexia, hypertonia, disuse atrophy, sensory disturbance

Question 15

Injury to thoracolumbar region

Answer 15

Forelimbs: mostly normal plus Schiff-Sherrington (increase extension of forelimb)
Hindlimbs: paralysis, hyperreflexia, hypertonia, disuse atrophy, sensory disturbance

Question 16

Injury to lumbosacral region

Answer 16

Forelimbs: normal
Hindlimbs: Paralysis, areflexia, atonia, denervation atrophy, sensory disturbance

Question 17

Cauda equina

Answer 17

Spinal nerves that descend caudal to the conus modulars and contain only the dorsal and ventral roots

Question 18

Conus medullaris

Answer 18

Termination of spinal cord; dogs at L6/L7

Question 19

Cervical enlargement

Answer 19

Exit site of spinal nerves of brachial plexus -> supply forelimbs

Question 20

Lumbar enlargement

Answer 20

Exit site of nerves of lumbosacral plexus -> supply hindlimbs

Question 21

Destinations of sensory primary afferent fibers

Answer 21

Local spinal reflex interneurons
2nd order interneurons projecting cranially to a supraspinal site
Propriospinal interneurons projecting cranially or caudally to other spinal cord segments
Monosynaptic to lower motor neurons

Question 22

Motor neuron destinations

Answer 22

Send axons out through ventral roots, into spinal/peripheral nerve, and innervate a skeletal muscle at a neuromuscular junction
Cell bodies for each muscle grouped in motor neuron pool that spans several segments

Question 23

Convergence

Answer 23

One postsynaptic neuron may receive connections from many presynaptic neurons

Question 24

Withdrawal reflex

Answer 24

Nociception; occurs all in the spinal cord, doesn’t need the brain

Question 25

Pain response

Answer 25

Requires intact cerebral cortes; pain receptors called nociceptors

Question 26

Divergence

Answer 26

One presynaptic neuron may have connections with multiple postsynaptic neurons or multiple connections with one postsynaptic neuron

Question 27

Ventral horn

Answer 27

Lower arm of gray matter “butterfly” shape

Contains interneurons and somatic motor neurons

Question 28

Ventral root

Answer 28

Motor axons exit cord at bottom of ventral horn

Question 29

Intermediate zone

Answer 29

Between dorsal and ventral horn; extends laterally as lateral horn
Contains interneurons and visceral motoneurons associated with autonomic function

Question 30

Central gray

Answer 30

Surrounds central canal and contains the dorsal and ventral gray commissures
Contains interneurons and visceral motoneurons associated with autonomic function