somatosensation and pain L3 Flashcards
(38 cards)
Signals about touch travel from the thalamus to the ….
Signals about touch travel from the thalamus to the primary somatosensory cortex (S-I) located in the post-central gyrus
The post-central gyrus is located …….
The post-central gyrus is located immediately posterior of the central sulcus.
describe how the cortex is organised into layers and columns
The cortex is organised in a series of vertical columns, 300-600 μm wide, spanning all six layers from the cortical surface to the white matter
All neurons within a column receive input from the same area of skin,
why is this important?
All neurons within a column receive input from the same area of skin, thus preserving stimulus location.
do neureons also only respond to a single modality?
yes
does a column also preserve modality?
as well as stimulus location?
yes
Thalamic afferents terminate in layer …
Thalamic afferents terminate in layer IV.
Layer __ projects back to the thalamus.
Layer VI projects back to the thalamus.
Layers II and III project to ……
while layer V projects to ….
Layers II and III project to other cortical regions while layer V projects to subcortical structures.
what is the homunculus?
much os the cortical area is devoted to hadns and face
describe Direction or motion selectivity in somatosensory cortex
Cortical neurons can respond in a highly selective manner to stimulus features. The figure (right) below shows the response of a neuron in area 2 of S-I that responds strongly to movement from the ulnar side of the wrist (UW) to the radial fingers (RF). Moving the stimulus in the opposite direction (RW to UF) produced the smallest response. The neuron could be described as direction-sensitive
what can explain a units sensitivity to direction?
The spatial arrangement of excitatory and inhibitory inputs can explain a unit’s sensitivity to direction.
describe
(A) a neuron in area 3b has overlapping inhibitory and excitatory zones. A simple convergence of three of these neurons in area 2 shows how downward motion of a horizontal bar produces a strong excitatory response whereas movement in upward direction is inhibitory.
In B2 a vertical bar produces a weak output as the bar crosses the excitatory and inhibitory areas simultaneously.
Attention enhances the responses of neurons in S-II
The responses from neurons in S-I can largely be predicted by the bottom-up input from the periphery.
In contrast the responses of neurons in area S-II are influenced by top-down processes such as attention.
T or F
Context (memory) can alter the responses of single units in S2
T
memory altering S2 firing rates:
the response to the second stimulus, f2, was determined by the frequency of f1.
The response was _-_____ when f2 > f1.
The response was greater when f2 > f1.
describe active touch
move out fingers over things to gain different information about its surface
whats going on here?
he activity of cortical areas was examined following passive stroking of the right hand with a sponge, or active touching of the sponge. In both conditions, areas 3b and 1 were activated in the left hemisphere.
In active touch, however, areas M1 (primary motor cortex) and ACC (anterior cingulate cortex) were also engaged.
describe how the cortex is plastic
is you use a particular part of the touch system for long periods of time - its representation in the cortex will expand. \
a monkey was trained to maintain contact with a rotating disc in order to get a reward. The cortical hand representation of the same monkey, following 20 weeks of daily training, showed a marked expansion of the representations of the distal aspects of digits 2 and 3
describe th concept of phantom limbs?
eg: arm amputation:
There is a complete map of the fingers on both the face and upper arm. The hypothesis is that the sensory input from these areas is now innervating the hand area of the somatosensory thalamus or cortex.
a recent study has shown that the greater the reorganisation the greater the amount of pain felt!
tinnitus is a phantom auditory sensation with many similarities to phantom limbs. - auditory system comparison
D: pain
Pain can be defined as
“an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage”
where do pain afferents terminate?
insula,
anterior cingulate nucleus
sensory 1
Termination sites in the dorsal horn of nociceptive afferents
describe:
(this is in the spinal cord)
Projection neurons in lamina I receive input from myelinated Aδ nociceptive fibres and both direct and indirect input from ‘C’ fibres
Lamina V neurons receive input from both large diameter fibres (Aβ) from mechanoreceptors as well as input from other nociceptors
Lamina V neurons therefore respond to innocuous stimuli at low intensity and noxious stimuli at high intensities and they are known as wide-dynamic range neurons (see below).
describe how lamina V neurones are wide dynamic range neurones
Lamina V neurons receive input from both large diameter fibres (Aβ) from mechanoreceptors as well as input from other nociceptors.
Lamina V neurons therefore respond to innocuous stimuli at low intensity and noxious stimuli at high intensities and they are known as wide-dynamic range neurons (see below).
