Somatosensory System Part 2

Front 1

Relay Nuclei
1. what are they the homes of?
2. what are their receptor fields like? why?

Back 1

1. secondary and tertiary neurons
2. larger and more complex than those of primary sensory neurons (b/c they receive input from more than one primary neuron)

Front 2

Inhibitory interneurons
1. feedback inhibition
2. feedforward inhibition

Back 2

1. send signals back to relay neurons to modify their output
2. send signals to thalamus modifying its output

Front 3

How does the complexity of receptors fields change amongst relay nuclei?
-where are they most complex?

Back 3

complexity increases which each successive relay nucleus
-primary sensory cortex is most complex

Front 4

Ventrobasal complex consists of severeal nuclear subdivision that project to both S1 and S2
-what are they and what do they receive?

Back 4

1. VPL: ALS (pain/temp), DCMLS (vib), a little prop
2. VPM: ventral trigeminothalamic tract (face pain/temp), a little prop
3. VPS: most propriception from both face and body
4. VPI: mixed sensations projectin gto S2

Front 5

What does these primary sensory areas receive from the thalamus?
1. 3a
2. 3b
3. 1
4. 2

Back 5

1. prop from deep muscle receptors
2. highly conserved projections from skin mechanoreceptors (both RA and SA); ex: reading braile
3. RA skin receptors
4. deep pressure and joint position receptors

Front 6

In terms of complexity, what type of stimuli do areas 3a and 3b respond to?
areas 1 and 2?

Back 6

3a/3b: point stimuli (most focused of cortical sensory neurons)
1/2: stimulus moving across skin, different textures (more abstract)

Front 7

Primary Sensory Cortex
1. brodmann's areas
2. location
3. lesions

Back 7

1. 3, 1, 2
2. postcentral gyrus, posterior paracentral lobule
3. impair finer aspect of somatic sensations (judging location/intensity) and senses of body position; little or no impact on pain

Front 8

Secondary Sensory Cortex
1. receives input from...
2. location
3. receptor fields
4. plays a role in..

Back 8

1. S1 and a little from VPI
2. parietal operculum (upper border of lateral fissure), extends onto insula
3. bilateral receptive fields
4. pain perception and memory/recall of somatosensory events

Front 9

Most of the cerebral cortex contains 6 layers, known as (1)...more primitive areas consisit of fewer than six layers (ex: hippocampus) and are called (2)...or (3)...

Back 9

1. neocortex
2. archicortex
3. paleocortex

Front 10

What two fiber types convey pain to CNS? What type of pain does each of them carry? to where? Via what tract?

Back 10

1. A delta fibers: rapid, transient pain to thalmus via spinothalamic tract of ALS
2. C fibers: longer lasting, deep pain to brainstem via spinoreticular tract of ALS

Front 11

What pathways make up the ALS?
-which is the smallest?
-where do most pain and temp pathways project?

Back 11

1. spinothalamic (smallest)
2. spinoreticular
3. spinotectal
4. spinohypothalamic
5. spinoreticulothalamic
-subcortical structures

Front 12

What is an alternative pain pathway?
-what problems does it cause

Back 12

the dorsolateral tract
-can frustrate attempts to abolish pain by tractotomy of ALS

Front 13

What else enters the dorsal horn along with A-delta and C pain fibers?

Back 13

A-beta fibers: large-diameter nonpain sensory axons

Front 14

Chronic Pain
1. what does it usually accompany?
2. usually the result of...

Back 14

1. inflammation
2. temporary changes in peripheral receptors (increase #) or central tract neuron (begin to fire at tonic rates due to removal of Mg++ that usually block NMDA receptors)

Front 15

6 pathways leading to feedback inhibition of pain

Back 15

1. ALS
2. PAG (periaqueductal gray)
3. ENK (enkephalinergic)
4. 5-HT (serotonin)
5. NRM (nucleus raphe magnus)
6. NRPG (nucleus reticularis paragigantocellularis)

Front 16

3 pathways leading to feedback inhibition of pain at level of dorsal horn

Back 16

1. NA (noradrenergic)
2. SER (serotonergic)
3. ENK (enkephalinergic)

Front 17

Neuropathic pain
1. caused by...
2. what is allodynia?

Back 17

1. permanent changes in architecture of central neural paths
2. after neuronal damage, small fibers (pain) less likely to regenerate, so large fibers (touch) synapse on the vacated relay nuclei (touch is now transmitted as pain)

Front 18

Neuropathic pain
1. peripheral nerve injury
2. central lesions

Back 18

1. entrapment, neurotmesis, amputation (if amputation leads to allodynia = phantom pain)
2. occlusion of thalamogeniculate branch of PCA causing thalamic pain (constant, agonizing pain with no sensory input)