The Somatosensory System

Question 1

What is a two-point discrimination test?

Answer 1

informs receptive field density, receptive field size, computing power, special neural mechanisms

Question 2

What is receptive field size and adaptation dynamics for Meissner’s corpuscle

Answer 2

Small and rapidly adapting - fine touch and vibration

Question 3

What is receptive field sizes and adaptation dynamics for Pacinian corpuscle

Answer 3

Large and rapidly adapting - deep pressure and vibration

Question 4

What is receptive field size and adaptation dynamics for Merkel’s disk

Answer 4

Small and slowly adapting - touching texture

Question 5

What is receptive field size and adaptation dynamics for Ruffini’s ending

Answer 5

Large and slowly adapting - skin stretch, movement, position

Question 6

What are the four types of primary sensory afferent axons and their main functions?

Answer 6

A alpha - proprioception of skeletal muscle
A beta - mechanoreceptors of skin
A delta - pain and temperature
C - pain, temp,and itch

Question 7

What are dermatomes?

Answer 7

an area of the skin corresponding to a single spinal nerve

Question 8

How do shingles highlight dermatomes?

Answer 8

a shingles rash appears in a certain dermatome, highlighting it

Question 9

How is somatic sensory information from the face area is being processed?

Answer 9

large mechanoreceptors axons from the face -> principal sensory trigeminal nucleus (pons) -> crosses over -> thalamus - > S1 (face area)

Question 10

Which cranial nerve is involved in processing from the face?

Answer 10

Trigeminal nerve (CN5)

Question 11

What is homunculus?

Answer 11

cortical somatotopy

Question 12

What is ‘barrel cortex’?

Answer 12

areas in S1 region which directly correlate to whisker

Question 13

How can one demonstrate that blocking glutamate transmission can stop activation of one of the barrels?

Answer 13

using CNQX and AP5 can block glutamate transmission of a single barrel without affecting the others

Question 14

Can somatic sensory cortical map get reorganized with a loss of a digit or an overly extensive use of a digit?

Answer 14

yes, adjusted use of digits leads to reorganization of somatosensory cortex

Question 15

What are some of the chemicals that mediate pain?

Answer 15

substance P

Question 16

What are first and second pains?

Answer 16

First pain activates A delta fiber which is myelinated and very fast.
Second pain activates C fiber which is much slower

Question 17

What is hyperalgesia?

Answer 17

extreme sensitivity to pain.
primary - substance P release lowers pain threshold
secondary - convergence facilitation

Question 18

What is the major difference between the ascending spinothalamic and dorsal lemniscal pathways?

Answer 18

They’re used for different sensations.
dorsal lemniscal pathway decussates in the thalamus. spinothalamic decussates in the spinal cord

Question 19

What is a top-down modulation of pain?

Answer 19

neurons of PAG send signal to raphe nuclei to dorsal horns of spinal cord to depress the activity of nociceptive neurons

Question 20

What areas of the brain are involved in top-down modulation?

Answer 20

Midbrain (PAG) -> Medulla (Raphe Nuclei) -> Spinal Cord (Dorsal Horn)

Question 21

What receptors are responsible for thermal sensations?

Answer 21

Thermoreceptor TRP channels of varying sensitivity
Ad and C fibers coupled to cold receptors.
C fibers coupled to hot receptors

Question 22

Is temperature pathway similar to pain pathway?

Answer 22

yes, the organization is the same. use A delta and C fibers. decussate in spinal cord.

Question 23

How can we distinguish between temperature and pain pathways?

Answer 23

both are spinothalamic

Question 24

what senses use the spinothalamic pathway?

Answer 24

some touch, temperature, pain

Question 25

what senses use the dorsal column- medial lemniscal pathway?

Answer 25

touch, vibration, two-point discrimination, proprioception