Kenyon: Somatosensory

Question 1

Sensory information can take two pathways into the thalamus and cortex. What are they?

Answer 1

1. TVP: receptors for fine touch, vibration, proprioception

2. receptors for pain and temp

Question 2

What is the difference between receptor/generator potentials and action potentials?

Answer 2

receptor potentials are small, graded, and not conducted; action potentials are large, all-or-none, and conducted

Question 3

Where are the receptors of primary afferent neurons? What are they often found within?

Answer 3

in the periphery (skin, muscle, blood vessels, etc); often inserted into a specialized capsule that can be important in encoding the stimulus

Question 4

Where are the cell bodies of primary afferent neurons located?

Answer 4

in the DRG or brainstem ganglia

Question 5

Are primary afferent neurons like autonomic neurons?

Answer 5

No; they have no dendrites, no synaptic input to the cell body in the ganglion; no synapses at the DRG; action potentials pass right through

Question 6

Where are the terminal ends of primary afferent neurons located?

Answer 6

in the spinal cord; some connections in the cord at the level of entry, some branches go up, some go down, synapse, etc

Question 7

Which fibers are LARGE in diameter and conduct rapidly?

Answer 7

A fibers

Question 8

Which fibers are SMALL in diameter and conduct less rapidly?

Answer 8

C fibers

Question 9

Which fibers are faster, A-alpha or A-delta?

Answer 9

A-alpha

Question 10

Which fibers are the slowest?

Answer 10

C fibers and A delta

Question 11

Which fibers are the fastest?

Answer 11

A-beta and TVP

Question 12

the area of skin within which a tactile stimulus evokes a sensory response

Answer 12

the receptive field

Question 13

the ability to distinguish one or two tactile stimuli varies over the body.

Answer 13

2 point discrimination

Question 14

As two points are moved apart on the skin, AP frequency from neuron (blank) fall as AP frequencies in neurons (blank) rise

Answer 14

B; A and C

Question 15

Where does information from the body and the back of the head go to?

Answer 15

Information from the body and back of the head is collected by neurons with cell bodies in the dorsal root ganglia. Enter cord via the dorsal roots

Question 16

Where does information about TVP and pain and temperature from the face go to?

Answer 16

Information from the face (and teeth) is collected by neurons with cell bodies in trigeminal ganglion. Enter brainstem via trigeminal (V)

Question 17

What is this?
branches enter the spinal cord at multiple levels and synapse in Rexed’s laminae. Important in spinal reflexes (ex: knee jerk, somatosomatic, viscerosomatic, etc)

Answer 17

pathway B

Question 18

What is this?
forms the dorsal columns of the spinal cord. Lower limbs are medial gracile tracts. Upper limbs, trunk and neck are lateral cuneate tracts.

Answer 18

Pathway A

Question 19

Lesions of the dorsal columns have modest effects on ability to perform simple tactile tasks. Loss of some proprioception and ability to detect direction and speed of a stimulus. What does this imply?

Answer 19

this implies that although the dorsal columns are a major pathway for TVP, they are not the only pathway

Question 20

The foot/leg (lower body) uses what tract/nucleus? The neck and occiput (upper body) uses what tract?

Answer 20

gracile tract (midline); cuneate tract (lateral)

Question 21

In the dorsal column/medial lemniscus pathway, what happens to the axons in the dorsal columns?

Answer 21

they synapse with second order relay neurons in the lower medulla

• gracile nucleus
• cuneate nucleus

Question 22

In which tract do the axons go ventral and cross over forming the Medial Lemniscus?

Answer 22

internal arcuate tract

Question 23

What do axons in the medial lemniscus synapse with? Where do these neurons project to?

Answer 23

third order neurons in the ventral posterior lateral nucleus of the thalamus; project to the primary sensory cortex;

Question 24

T/F: The ventral posterior complex contains a complete representation of the somatic sensory periphery.

Answer 24

True

Question 25

Somatic sensation from the face and mouth is innervated by the sensory component of which nerve?

Answer 25

CN 5

Question 26

Where do primary afferent axons synapse in the trigeminal pathway?

Answer 26

on the chief nucleus of the trigeminal complex

Question 27

The secondary sensory axons in the trigeminal pathway cross over and join the (blank). Where do they synapse? Where do they project?

Answer 27

medial lemniscus; synapse in the ventral posterior medial nucleus of the thalamus; project to the cortex

Question 28

As you go across the primary somatosensory cortex, what do you find?

Answer 28

4 areas, each of which contains a separate and complete representation of the body, but differ in function.

Question 29

If you damage the anterior cerebral artery, you will lose TVP to what body parts?

Answer 29

trunk, legs

Question 30

If you damage the middle cerebral artery, you will lose TVP to what body parts?

Answer 30

arms, face

Question 31

What happens once neurons reach the primary sensory cortex?

Answer 31

they project to the adjacent secondary somatosensory cortex and then to the limbic structures, amygdala, and hippocampus. these projections mediate functions

Question 32

What are descending pathways? Are there more descending or ascending axons?

Answer 32

projections from the sensory cortex down to the thalamus, brainstem, and spinal cord, which modulate the flow of sensory information; more descending axons