somatosensation and pain L3

Question 1

Signals about touch travel from the thalamus to the ….

Answer 1

Signals about touch travel from the thalamus to the primary somatosensory cortex (S-I) located in the post-central gyrus

Question 2

The post-central gyrus is located …….

Answer 2

The post-central gyrus is located immediately posterior of the central sulcus.

Question 3

describe how the cortex is organised into layers and columns

Answer 3

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

Question 4

All neurons within a column receive input from the same area of skin,

why is this important?

Answer 4

All neurons within a column receive input from the same area of skin, thus preserving stimulus location.

Question 5

do neureons also only respond to a single modality?

Answer 5

yes

Question 6

does a column also preserve modality?

as well as stimulus location?

Answer 6

yes

Question 7

Thalamic afferents terminate in layer …

Answer 7

Thalamic afferents terminate in layer IV.

Question 8

Layer __ projects back to the thalamus.

Answer 8

Layer VI projects back to the thalamus.

Question 9

Layers II and III project to ……

while layer V projects to ….

Answer 9

Layers II and III project to other cortical regions while layer V projects to subcortical structures.

Question 10

what is the homunculus?

Answer 10

much os the cortical area is devoted to hadns and face

Question 11

describe Direction or motion selectivity in somatosensory cortex

Answer 11

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

Question 12

what can explain a units sensitivity to direction?

Answer 12

The spatial arrangement of excitatory and inhibitory inputs can explain a unit’s sensitivity to direction.

Question 13

describe

Answer 13

(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.

Question 14

Attention enhances the responses of neurons in S-II

Answer 14

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.

Question 15

T or F

Context (memory) can alter the responses of single units in S2

Answer 15

T

Question 16

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.

Answer 16

The response was greater when f2 > f1.

Question 17

describe active touch

Answer 17

move out fingers over things to gain different information about its surface

Question 18

whats going on here?

Answer 18

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.

Question 19

describe how the cortex is plastic

Answer 19

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

Question 20

describe th concept of phantom limbs?

Answer 20

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

Question 21

D: pain

Answer 21

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”

Question 22

where do pain afferents terminate?

Answer 22

insula,

anterior cingulate nucleus

sensory 1

Question 23

Termination sites in the dorsal horn of nociceptive afferents

describe:

(this is in the spinal cord)

Answer 23

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).

Question 24

describe how lamina V neurones are wide dynamic range neurones

Answer 24

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).

Question 25

describe referred pain

Answer 25

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.

Question 26

whats the most well known refered pain?

Answer 26

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.

Question 27

Neurons in several regions of the cerebral cortex respond to pain.

what ar ethe main areas?

Answer 27

The main areas are located in S-I, the anterior cingulate cortex (ACC) and insula.

Question 28

whats the anterior cingulate’s role in pain?

Answer 28

The anterior cingulate is part of the limbic system and is thought to be responsible for the emotional element of pain.

Question 29

role of the insula in pain?

Answer 29

The insular cortex processes information on the internal state of the body and thus contributes to the autonomic component of the overall pain response.

Question 30

describe narrow vs wide dynamic range neureons

Answer 30

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.

Question 31

T ro F

Pain is a heavily modulated sensation.

Answer 31

T

Question 32

The descending systems that modulate pain are located in …….

Answer 32

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.

Question 33

significance of the the periaqueductal gray (PAG) matter of the mid-brain

Answer 33

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.

Question 34

Morphine induced analgesia is blocked by injection of ______ (an opiate antagonist) into the PAG.

Answer 34

Morphine induced analgesia is blocked by injection of naloxone (an opiate antagonist) into the PAG.

Question 35

T or F

Bilateral transection of the dorsolateral funiculus blocks both this stimulation- and morphine-induced analgesia.

Answer 35

t

Question 36

describe placebo analgesia

Answer 36

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.

Question 37

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

Answer 37

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.

Question 38

fat

Answer 38

mamba