Cutaneous Testing

Question 0

where are the receptors for touch sensation localised ?

Answer 0

in the dermis and epidermis

Question 1

when is our ability to discriminate between 2 points greatest ?

Answer 1

when there is a low level of convergence 1st order sensory neurons onto 2nd order neurons in the spinal cord

Question 2

what is used to assess touch thresholds ?

Answer 2

using von frey aesthesiometer

Question 3

what fibres are activated for touch sensation in human skin ?

Answer 3

reliant exclusively on activation of myelinated sensory afferent fibres

Question 4

what channels can capsaicin activate ?

Answer 4

activate ion channels that are linked to thermal heat perception

Question 5

what is the Trpv1 channel permeable to ?

Answer 5

calcium ion s

Question 6

what is the threshold for thermal pain sensitivity ?

Answer 6

> 40 degrees

Question 7

what is the Trpv2 channel activated by ?

Answer 7

activated by nociceptive heat stimuli

Question 8

what pathway carries innocuous mechanical sensations to the brain and how does it ascend to the brain ?

Answer 8

dorsal column-medial lemniscus pathway

ascends to the brain in the ipsilateral spinal cord

Question 9

where does the somatosensory cortex receive inputs from ?

Answer 9

ventro-basal complex within the thalamus

Question 10

what does the 2-pt discrimination test tell us ?

Answer 10

it tells us that the 2-pt discrimination thresholds are different at different body surface locations

Question 11

what factors influence human 2 point discrimination ?

Answer 11

• density of mechanoreceptors innervating an area of skin = if an area is more densely innervated by mechanoreceptors then the discrimination i smaller
• size of receptive field = area of skin contains many receptors with small receptive fields then the 2 point discrimination is smaller because the receptors are able to pack together more closely but still activate 2 different CNS neurons 2 enable 2 different points to be distinguished
• amount of cortical tissue deciphering the info= greater cortical representation means greater processing of mechanical activity

Question 12

what is the firing adaptation, receptive field and physiological role of merkels disks?

Answer 12

• slow adaptation firing rates
• small receptive field
• detects form, shape, texture, rough edges of objects

Question 13

what is the firing adaptation, receptive field and physiological role of ruffini’s endings ?

Answer 13

• slow adaptation firing rates
• large receptive field
• detects lateral movements of the skin, indentation and stretching of the skin

Question 14

what are the firing adaptations, receptive field and physiological role of meissners corpuscles ?

Answer 14

• fast adaptation firing rates
• small receptive field
• detects low frequency states ranging from 30-50Hz and rough textures and movements

Question 15

what are the firing adaptations, receptive field and physiological role of pacinians corpuscles ?

Answer 15

• fast adaptation firing rates
• large receptive field
• detects high frequency vibrations within the range of 250-350Hz and fine textures and movements

Question 16

explain the pathway involved in ascending non-painful touch to the brain ?

Answer 16

dorsal column medial lemniscus pathway

• primary afferents enter into the spinal cord via the dorsal roots and ascend to the medulla on the ipsilateral side
• 2 dorsal column pathways= fasiculus gracilis and fasiculus cuneatus
• in the medulla the first order neurons synapse with the 2nd order neurons which then decussate onto the contralateral side to ascend to the thalamus
• at the thalamus the 2nd order neurons synapse with the 3rd order neurons which then ascend to various areas in the cerebral cortex

Question 17

what primary afferents are involved in innocuous touch sensation pathways ?

Answer 17

A alpha
A beta
A delta

Question 18

what information does the fasiculus gracilis transmit ?

Answer 18

information caudal to T6

Question 19

what information does fasiculus cuneatus transmit ?

Answer 19

information rostral to T6

Question 20

if a correlation coefficient is close to 1 what does this tell you ?

Answer 20

indicates strong positive linear correlation
because it is a positive value it indicates a direct relationship whereas if it was close to -1 it would indicate an indirect relationship

Question 21

why is the representation of mechanical stimuli greater than thermal stimuli ?

Answer 21

because there is a greater density of mechanoreceptors in the somatic nervous system and also the density of thermal receptors throughout the skin is not evenly spread out

Question 22

what is the main receptor for hot thermal stimuli ?

Answer 22

Trpv1

Question 23

what is the main receptor for thermal cold stimuli ?

Answer 23

Trpm8

Question 24

what receptor is activated by capsaicin ?

Answer 24

the vanilloid receptor Trpv1

Question 25

what happens to the sensitivity to thermal hot stimuli after capsaicin application to the skin and why ?

Answer 25

human sensitivity to thermal hot stimuli is more sensitive after capsaicin application because it inccreases the sensitivity of the VR1 receptors
- it causes increased sensitivity by causing the Trpv1 receptors to open at lower temperatures

Question 26

what endogenous substances can increase the sensitivity of Trpv1 receptors and why does this occur ?

Answer 26

e.g. substance P and bradykinin

they increase the sensitivity of nociceptors by reducing the pain threshold and this is known as primary hyperalgesia

Question 27

what should happen to the von frey tests after capsaicin application ?

Answer 27

it should cause the pain threshold to occur using a small diameter von frey hair because the Trpv1 receptors are thermal nociceptors and therefore it would be expected that they would become more sensitive to mechanical stimuli as nociceptors can be polymodal permitting their activation by mechanical stimulation

Question 28

define magnification factor:

Answer 28

it is the amount by which a point on the skin is expanded in a central representation

Question 29

what does an area containing cels with small receptive fields need ?

Answer 29

it needs a large number of cels to represent a given surface area

Question 30

what does an area with cells that have large receptive fields need?

Answer 30

it requires only a few cells to represent the given area

Question 31

what does an area of the body with smaller receptive fields occupy ?

Answer 31

occupies a larger cortical area and provides greater acuity