somatosensation and pain L3 Flashcards
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).
describe referred pain
Pain from internal organs is often felt as pain in a more superficial region
Signals from an inflamed visceral organ converge on projection neurons at the dorsal horn of the spinal cord.
Sensory input from a distant somatic structure converges on the same neurones.
The CNS cannot distinguish between superficial and deep pain and this failure results in the incorrect assignment of pain to the healthy somatic area.
whats the most well known refered pain?
The most well-known referred pain is that of Angina Pectoris. This is triggered by an inadequate supply of blood to the heart and is experienced as referred pain in the chest and left arm.
Neurons in several regions of the cerebral cortex respond to pain.
what ar ethe main areas?
The main areas are located in S-I, the anterior cingulate cortex (ACC) and insula.
whats the anterior cingulate’s role in pain?
The anterior cingulate is part of the limbic system and is thought to be responsible for the emotional element of pain.
role of the insula in pain?
The insular cortex processes information on the internal state of the body and thus contributes to the autonomic component of the overall pain response.
describe narrow vs wide dynamic range neureons
Interestingly both types of neural response are observed in the spinal cord; nociceptors are prominent in lamina I while WDR neurons are found in lamina V.
T ro F
Pain is a heavily modulated sensation.
T
The descending systems that modulate pain are located in …….
The descending systems that modulate pain are located in the periaqueductal gray (PAG) matter of the mid-brain, the raphe nuclei, and other nuclei of the rostral medulla.
significance of the the periaqueductal gray (PAG) matter of the mid-brain
Electrical stimulation of the PAG can produce sufficient analgesia to perform abdominal surgery without the need for anaesthesia.
Other, non-painful, sensations were left intact.
The PAG is thought to control the ‘nociceptive’ gate in the dorsal horn by integrating inputs from the cortex, thalamus and hypothalamus.
Morphine induced analgesia is blocked by injection of ______ (an opiate antagonist) into the PAG.
Morphine induced analgesia is blocked by injection of naloxone (an opiate antagonist) into the PAG.
T or F
Bilateral transection of the dorsolateral funiculus blocks both this stimulation- and morphine-induced analgesia.
t
describe placebo analgesia
Placebo analgesia refers to the situation where administration of a substance known to be non-analgesic produces an analgesic response when the subject is told that it is a pain killer.
It should be noted that the placebo effect also works for asthma, cough, diabetes, ulcers, multiple sclerosis and Parkinsonism.
Volunteers (!!) had capsaicin applied to the distal region of all four limbs and were then asked to report the magnitude of pain felt at each site.
explain this experiment
This spatially specific placebo response was abolished with the intravenous infusion of naloxone (an opioid antagonist) suggesting that it was mediated by one of the endogenous opioid systems.
fat
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