Lab Quiz 4

Question 1

what is the basic spinal reflex arc?

Answer 1

receptors detect stimuli and send an afferent (sensory) signal to the dorsal/posterior horn, this signal is transmitted to the ventral/anterior horn where an efferent (motor) signal is sent to effectors that respond to the stimuli

Question 2

how can you distinguish between cervical, thoracic, and lumbar sections of the spinal cord from axial sections?

Answer 2

cervical: larger anterior/ventral horns, lots of white matter
thoracic: anterior/ventral horn is small, lateral horns are present, clarks nucleus is present
lumbar: less gray matter and more white matter than cervical, slightly smaller anterior/ventral horns

Question 3

what are the major divisions of the spinal cord on an axial slice?

Answer 3

intermediate gray, posterior/dorsal horn, anterior/ventral horn, anterior funiculus, posterior funiculus, lateral funiculus, gracile fasicle, cuneate fasicle, Lissauer’s tract, posterior median sulcus, ventral median fissure, posterior (dorsal) column, anterior (ventral) column, posterior intermediate sulcus, posterolateral sulcus, central canal, anterior white commissure, gray commissure
(diagram on lab quiz 4 practice note)

Question 4

where are the major sensory and motor tracts located on an axial spinal cord slice?

Answer 4

lateral corticospinal tract: located in the white matter between the posterior and anterior horns
anterior spinocerebellar tracts: located surrounding the lateral corticospinal tract on the lower sider
posterior spinocerebellar tracts: located surrounding the lateral corticospinal tract on the upper sider
anterolateral system (spinothalamic tract): surrounds the bottom of the anterior horn

Question 5

how is information transmitted in the posterior column/medial lemniscus pathway?

Answer 5

• impulses are transmitted from mechanoreceptors in the periphery along large-diameter fibers
• cell bodies of these 1st order neurons are located in the dorsal root ganglia and their centrally projecting axons ascend in either the fasciculus gracilis (leg) or fasciculus cuneatus (arm) of the spinal cord
• the 1st order axons ascend and synapse in the gracile and cuneate nuclei (2nd order neurons) located in the caudal medulla
• neurons projecting from the gracile and cuneate nuclei then decussate in the caudal medulla and ascend on the contralateral side in a bundle of fibers known as the medial lemniscus
• the fibers of the medial lemniscus synapse on 3rd order neurons in the thalamus (ventral posterolateral nucleus; VPL) and these 3rd order neurons then send axons to the postcentral gyrus via the posterior limb of the internal capsule

Question 6

what are some clinical tests for posterior column/medial lemniscal system function?

Answer 6

position sense (move fingers/toes with patients eyes closed and ask about direction of movement), two-point discrimination, vibration, stereognosis (coin in hand)

Question 7

how is information transmitted in the anterolateral (spinothalamic) system?

Answer 7

• sensory impulses travel toward the central nervous via small diameter axons that have their cell bodies in the dorsal root ganglion (1st order neurons) and central processes that branch in Lissauer’s tract and synapse in the substantia gelatinosa (Rexed lamina 1 and 2 in the gray matter of the spinal cord)
• axons of 2nd order neurons cross the midline (near the spinal cord level of entry) in the ventral white commissure and ascend through the anterolateral region of white matter in the spinal cord and reticular formation of the brain stem
• most fibers ascend as the spinothalamic tract (STT) to the VPL of the thalamus
• from the VPL, the 3rd order neurons send axons through the internal capsule to the postcentral gyrus for stimulus localization

Question 8

what are some clinical tests for anterolateral system function?

Answer 8

pain (prick skin with needle) and temperature (touch skin with vial of warm or cold water)

Question 9

how is information transmitted in the spinocerebellar system?

Answer 9

two major spinocerebellar tracts:
1. dorsal (posterior) spinocerebellar tract:
- 1st order neurons terminate in Clarke’s nucleus in the spinal cord
- this nucleus sends projection axons into the lateral funiculus of the same side
- once these fibers reach the brain stem they ascend through the inferior cerebellar peduncle to the cerebellum
2. ventral (anterior) spinocerebellar tract:
- 1st order neurons that terminate on cells found on the periphery of the spinal cord gray matter (spinal border cells)
- these cells send axons rostrally in the peripheral part of the lateral funiculus after crossing
- fibers in this tract reach the cerebellum by crossing again and ascending in the superior cerebellar peduncle

Question 10

what is each pathway/system responsible for detecting?

Answer 10

posterior column medial leminiscus: involved in transmission of discriminative touch as well as positional and vibrational sense from the trunk and limbs
anterolateral (spinothalamic): transmit impules for pain, temperature, and light touch from trunk and limbs
spinocerebellar system: carries impulses from muscle spindles, golgi tendon organs, and skin receptors to the cerebellum for unconscious proprioceptive monitoring and controlling posture