Somatosensory systems

Question 1

What things are sensed by the somatosensory system?

Answer 1

pain
touch 
proprioception
itch
visceral (nonpainful stimulus i.e bladder)

Question 2

What are the 4 stages of sensation

Answer 2

transduction
transmission
perception
modulation

Question 3

What are the classes of neurons that mediate modulation of somatic sensations?

Answer 3

dorsal root ganglion neurons

trigeminal sensory neurons

Question 4

What are the types of neurons in the dorsal root ganglion

Answer 4

type A (beta or delta)
type C

Question 5

Describe type A beta dorsal root ganglionic neurons

Answer 5

large, myelinated

Question 6

Describe type A delta dorsal root ganglionic neurons

Answer 6

small, unmyelinated

Question 7

Describe type C dorsal root ganglionic neurons

Answer 7

have schwann cells that just bundle C cells together, not myelinating

Question 8

What type of dorsal root ganglionic neuron is responsible for pain, temp, itch sensation

Answer 8

type C dorsal root ganglionic neuron

Question 9

What is the difference between slowly adapting and fast adapting neurons?

Answer 9

Slow adapting neurons give information on intensity and duration of stimuli by mediating its firing rate (slow = weak stim. fast = strong stim.); fast adapting neurons only transmit when there is a change in strength of stimulus

Question 10

What is the purpose of two pt discrimination

Answer 10

touch your lip with two fingers and touch your thigh with two fingers; it is easier to discriminate between the feeling of each finger on the lips than the thigh

Question 11

What are the kinds of mechanoreceptors responsible for touch

Answer 11

Meissner corpuscle
Merkel cells
Pacinian Corpuscle
Ruffini endings

Phoebe mainly makes rice

Question 12

What are the superficial mechanoreceptors responsible for touch

Answer 12

Meissner corpuscle

Merkel cells

Question 13

What are the deep mechanoreceptors responsible for touch

Answer 13

pacinian corpuscle

ruffini endings

Question 14

What are the rapidly adapting mechanoreptors

Answer 14

Meissner corpuscle

Pacinian corpuscle

Question 15

What are the slowly adapting mechanoreceptors

Answer 15

Merkel cells

Ruffini endings

Question 16

What are the means of proprioception

Answer 16

Joint receptors (sensory receptors in joint + in joint capsule which transduce tension) and muscle receptors (muscle spindles lie parallel to the muscle fibre transducing length + Golgi tendons transduce tension)

Question 17

What neurons transduce hot stimuli

Answer 17

A delta axons neurons

Question 18

What neurons transduce cold stimuli

Answer 18

C axons (unmyelinated)

Question 19

What neurons transduce dangerous stimuli

Answer 19

nociceptors

Question 20

What are the modalities of nociceptors

Answer 20

Thermal
Mechanical 
(both A delta fibres)
Polymodal (C fibres)
Silent

Question 21

What determines nociceptor diversity

Answer 21

transduction molecule expression on the surface

Question 22

What type of nociceptor causes sensitivity in an area following injury

Answer 22

silent nociceptors

Question 23

Describe how A beta fibres bring action potentials to the somatosensory cortex

Answer 23

A beta fibres enter the dorsal coloums/medial lemniscal system. Ascending ipsilaterally in the spinal cord and conveys mechanosensory information from the limbs and trunk to the cortex via VPL to the thalamus. Then the second order neuron in the medulla dessucates to the contralateral side and ascends to the thalamus where the third order neuron is located and goes to the somatosensory system.

Question 24

Describe how nociceptors signal the brain

Answer 24

through contralateral anterolateral system.

Question 25

What are the divisions of the somatic sensory cortex

Answer 25

S1 - primary
S2 - secondary
+ posterior parietal cortex

Question 26

What are the cytoarchitectonic divisions of S1

Answer 26

Brodmanns areas 3a, 3b, 1 and 2