L24 Touch

Question 1

define stereognosis

Answer 1

ability to perceive the properties of a coherent object like its size, shape and texture by holding it in your hand i.e. key, coins

Question 2

define graphesthesia

Answer 2

the ability to distinguish letters drawn on the skin

Question 3

what does Brodmann’s areas tell us about the cerebral cortex?

Answer 3

histological characteristics
thickness of their layers
types of cells within them

Question 4

what Brodmann’s area is the primary somatosensory cortex?

Answer 4

areas 3,1and 2

Question 5

what are the 3 generalizations of the sensory cortex

Answer 5

topographical organization -
organization in columns
input layer 4

Question 6

what is topographical organization

Answer 6

quickly looking at a topographical map of S1 (primary somatosensory pathway) you can define where in S1 different parts of the body are referred = somatotopic map

Question 7

explain organization in columns

Answer 7

input processing neurons are organized in the cortex based on the speed of receptor that is sending the info
SA -RA-SA-RA-SA

Question 8

explain input layer 4

Answer 8

the cortex has 6 layers

layer 4 os S1 receieved input from the thalamus (VPL/VPM) where the 3rd order neurons are from

Question 9

what factors are responsible for contributing to high spatial resolution

Answer 9

high density of cutaneous mechanoreceptors
small receptive fields of the receptors
larger cortical area involved
special mechanisms - lateral inhibition etc.

Question 10

what special mechanism can increase resolution

Answer 10

lateral inhibition

Question 11

describe Tabes dorsalis

Answer 11

consequence of syphilitic infection
destruction of DRG and large myelinated fibers
TVP becomes very deficient but TP remain unaffected

Question 12

describe phantom limb sensation

Answer 12

person thinks they are feeling pain in a recently amputated limb
the pain is exacerbated when other parts of hte body are stimulated (hand and face example)

Question 13

what is responsible for phantom limb

Answer 13

rearrangement of the cortical input from an existing part of the body to the cortical area that once controlled this now missing limb (neurons in face region of cortex migrate to where the hand used to be)

Question 14

define lateral inhibition

Answer 14

the capacity of an excited neuron to reduce the activity of its neighbors.