Somatosensory System

Question 1

Review: What are 3 places where sensory info in the dorsal root ganglia ultimately go?

Answer 1

Reflexes
Cerebellum
Cerebral Cortex

Question 2

What is the difference between tonic and phasic signaling from sensory structures?

Answer 2

Tonic: slow-response, continued signaling in response to stimulus
Phasic: rapid-response, single signals for on-off

Question 3

Are small or large diameter axons more susceptible to anoxia?

Answer 3

Large diameter.

Question 4

Are small or large diameter axons more susceptible to local anesthetics?

Answer 4

Small are more susceptible. (Goal of epidural is to numb smaller pain fibers without numbing touch/pressure fibers)

Question 5

What is a receptive field?

Answer 5

Any area such that when you stimulate it, it affects the firing of a specific neuron.

Question 6

The difference between divergence and convergence, in the context of neuronal connections?

Answer 6

Divergence: neuron sends stimuli to many post-synaptic neurons
Convergence: neuron receives stimuli from many pre-synaptic neurons

Question 7

Briefly describe feedback inhibition (in the context of, say, cutaneous stimuli)? What is its effect?

Answer 7

Inhibitory interneurons inhibit signaling to relay neurons that are further from the site of the stimulus. Effect: Increased discrimination (a ring of neuron inhibition around the site of stimulation).

Question 8

Are our senses better at discriminating between intensities, or judging absolute values of intensity?

Answer 8

Discriminating between two. (recall Mach’s Bands, aka 7 Shades of Gray)

Question 9

Where is (and what is) S1 and which thalamic nuclei send connections to it?

Answer 9

S1 is for touch and proprioception. It’s in the postcentral gyrus (the somatosensory cortex). Sends connections to the VPl and VPm.

Question 10

On the primary motor cortex, where is the face/tongue/throat?

Answer 10

Lateral

Question 11

On the primary motor cortex, where is the upper limb?

Answer 11

Intermediate between lateral and dorsal areas.

Question 12

On the primary motor cortex, where are is the lower extremity (and genetalia) represented?

Answer 12

Dorsal.

Question 13

How are slow-adapting and rapid-adapting neurons organized into columns in the cortex?

Answer 13

Alternating columns….

Question 14

Is there just one “homunculus” in the somatosensory cortex? Why or why not?

Answer 14

No. Each one… has different information.

Question 15

If you lose afferent information to the somatosensory cortex (for example, by amputating a poor monkey’s finger), what happens eventually in the somatosensory cortex?

Answer 15

Surrounding areas become more heavily represented in the cortex.

Question 16

If you lose your leg at the knee, does your two-point discrimination in the thigh change?

Answer 16

Yes, you get a higher resolution two-point discrimination.

Question 17

Will using a digit more increase its representation in the somatosensory cortex?

Answer 17

Yup.

Question 18

What is a possible (but not really proven) mechanism for how remapping occurs?

Answer 18

Existing connections are “unmasked” when the more dominant connections are lost.

Question 19

Is the affective component of sensation (for example, pain) processed in the same place as the perceived intensity?

Answer 19

Nope. With hypnosis and weird things, people can feel intense pain but not be bothered by it.

Question 20

Review?: Which thalamic nucleus provides input to the anterior cingulate gyrus?

Answer 20

Anterior nucleus of the thalamus (this isn’t actually review… but it’s in the slide notes)

Question 21

Review?: What is a major input tot the anterior nucleus of the thalamus?

Answer 21

The mammillary bodies.