Somatosensation Part 2

Question 1

What is referred pain and how does it happen?

Answer 1

Pain from internal organs can be perceived as a cutaneous pain instead, this can happen because internal pain (visceral pain) is conveyed centrally via dorsal horn neurons that may also convey cutaneous pain

Question 2

What is the gate control theory?

Answer 2

A type of central pain modulation, the theory states that transmission of pain signals can be modulated in two ways: non-painful inputs from type 2 (A-beta) fibers or descending signals from the brain

Question 3

Where is the “nerve gate” located and what does it do in terms of central pain modulation?

Answer 3

The nerve gate is located in the substantia gelatinosa in the dorsal horn of the spinal cord, it controls passage of pain signals to the brain through interneurons that inhibit second order neurons from sending the pain signal to the brain

Question 4

Describe how the gate control theory works in terms of type 2 (A-beta) axons

Answer 4

Non-painful inputs “close the gate” to painful inputs to reduce pain, inputs from A-beta axons reduce the transmission of pain through the dorsal horn. These axons synapse on inhibitory interneurons to reduce the intensity of the pain onto the second order neuron
(Ex. pain stimulus from stubbed toe reduced with the noxious/non-painful stimulus of rubbing the area)

Question 5

Describe how the gate control theory works in terms of descending modulation

Answer 5

Two areas of the brainstem become activated when the brain perceives pain: the periaqueductal gray in the midbrain and the raphe nucleus in the rostral ventral medulla. The PAG and raphe nucleus activate descending tracts that inhibit pain by releasing serotonin to activate inhibitory interneurons. The interneurons will inhibit the second order neuron from sending pain signals

Question 6

How many tracts will spinocerebellar fibers travel in?

Answer 6

Fibers will travel in 4 tracts
- Dorsal spinocerebellar tract
- Cuneocerebellar tract
- Ventral spinocerebellar tract
- Rostral spinocerebellar tract

Question 7

The cerebellum will receive input from what other areas of the nervous system?

Answer 7

• All areas of the cerebral cortex
• Sensory modalities of vision, vestibular, auditory, and somatosensory
• Brainstem nuclei
• Spinal cord

Question 8

What are the three functional divisions of the cerebellum?

Answer 8

Spinocerebellum
Cerebrocerebellum
Vestibulocerebellum

Question 9

Where does the spinocerebellum receive input from, send output to, and what is its function?

Answer 9

Input: directly from the spinal cord (somatosensory and interneurons) and visual, auditory, and vestibular system
Output: to lateral and medial motor tracts
Function: movement of distal and proximal muscle function (walking and postural control)

Question 10

What two types of information are provided to the cerebellum via the spinocerebellar pathway?

Answer 10

Afferent information from peripheral receptors about limb movement (dorsal spinocerebellar tract send info from LE, cuneocerebellar tract send info from UE)

Internal feedback tracts send information from spinal interneurons and descending motor pathways to the cerebellum (ventral spinocerebellar tract send info from LE, rostral spinocerebellar tract send info from UE)

Question 11

Describe the first order neuron of the dorsal spinocerebellar tract

Answer 11

Carries proprioceptive, touch, and pressure information from LEs and enters the spinal cord at the dorsal horn. It’s axon travels to an area between L2 and C8 in the fasciculus gracilis of the dorsal column to synapse with the second order neuron on the nucleus dorsalis of Clarke.

Question 12

Describe the second order neuron of the dorsal spinocerebellar tract

Answer 12

After synapsing with the first order neuron on the nucleus dorsalis of Clarke, the axon will ascend ipsilaterally in the dorsolateral funiculus near the surface of the spinal cord. It will then project to the cerebellar cortex via the ipsilateral inferior cerebellar peduncle

Question 13

Describe the first order neuron of the cuneocerebellar tract

Answer 13

Carry proprioceptive, touch, and pressure information from the upper extremities and neck and enters the spinal cord at the dorsal horn. It ascends in the dorsal column in the ipsilateral fasciculus cuneatus and will synapse with the second order neuron on the cuneate nucleus which is positioned laterally in the caudal medulla

Question 14

Describe the second order neuron of the cuneocerebellar tract

Answer 14

After synapsing with the the first order neuron at the cuneate nucleus, the axon will travel ipsilaterally in the tract and enter the inferior cerebellar peduncle to terminate in the cerebellar cortex

Question 15

Describe the ventral spinocerebellar tract

Answer 15

One neuron that communicates interneuron info from the LEs arises from cells in the central gray of the spinal cord and crosses over to the contralateral side in the ventral commissure. It will then ascend in the contralateral tract to the midbrain, it will join the superior cerebellar peduncle and crosses over again to the ipsilateral cerebellar hemisphere

Has “double crossed” fibers

Question 16

Describe the rostral spinocerebellar tract

Answer 16

This pathway is less clearly understood, it is similar to the ventral spinocerebellar tract but relays info from UEs instead. It enters both superior and inferior cerebellar peduncles and fibers can be either ipsilateral or “double crossed”

Question 17

The cerebellum coordinates motor function for the ipsilateral side of the body, so tracts that send feedback information to the cerebellum must travel __________ or be ________

Answer 17

Ipsilateral

Double-crossed