Tutorial 2- Somatosensation

Question 1

In the skin, sensation of touch is mediated by

Answer 1

cutaneous mechanoreceptors

Question 2

maintained skin stretch is mediated by

Answer 2

ruffini endings

Question 3

continuous pressure is sensed by

Answer 3

merkel disk receptors

Question 4

vibration is sensed by

Answer 4

pacinian corpuscles

Question 5

the nerve fibres that transmit touch info are mainly

Answer 5

A beta fibres

Question 6

are there different thermoreceptors for each level of temperature?

Answer 6

yes

Question 7

painful stimuli are mediated by

Answer 7

nociceptors

Question 8

temperature and painful stimuli are transmitted by axons of

Answer 8

A delta and C fibres

Question 9

pain is not a stimulus, rather

Answer 9

ex extreme cold is a stimulus

Question 10

c fibres can respond to many simuli, such as

Answer 10

chemicals, temperature (warmth and cooling) and itch - it is therefore polymodal

Question 11

sensory nerves respond to increasing stimulus intensity by

Answer 11

increasing firing frequency proportionately with strength of stimulus

Question 12

nerves that are stimulated by inflammation/mechanical damage:

Answer 12

nociceptors

Question 13

A alpha receptors are not involved in cutaneous touch, rather in

Answer 13

deep joint proprioception- therefore only present in DRGs involved in deep joint proprioception

Question 14

are c fibres myelinated or unmyelinated?

Answer 14

unmyelinated

Question 15

diameter, speed and detectable stimuli for c fibres:

Answer 15

0.2-1.5 microm, 0.5-2 m/s, pain+temp.+itch

Question 16

diameter, speed and detectable stimuli for A delta fibres:

Answer 16

1-5 microm, 5-35 m/s, pain+temp.

Question 17

diameter, speed and detectable stimuli for A beta fibres:

Answer 17

6-12 microm, 35-75 m/s, touch

Question 18

diameter, speed and detectable stimuli for A alpha fibres:

Answer 18

13-20 microm, 8-120 m/s, proprioception

Question 19

which NT do C, A delta and A beta fibres use?

Answer 19

glutamate

Question 20

in addition to glutamate, which other NTs can C fibres use?

Answer 20

peptidergic transmitters such as substance P and CGRP

Question 21

what do the differences in NT of c fibres do?

Answer 21

create 2 classes of c fibre, one which only uses glutamate and the other that uses both glutamate and peptidergic transmitters

Question 22

the touch pathway can also be referred to as the

Answer 22

medial lemniscal, dorsal column pathway

Question 23

where does the touch pathway cross the midline?

Answer 23

at the dorsal column nuclei in the medulla

Question 24

the nociceptive pathway is also referred to as the

Answer 24

spinothalamic/ anterolateral tract

Question 25

the nociceptive pathway crosses the midline

Answer 25

at the level of the spinal cord that it enters via a projection neuron, then doesn’t synapse again until the thalamus

Question 26

the touch and nociceptive pathways travel from the thalamus to the cerebral cortex via the

Answer 26

internal capsule

Question 27

does the brain receive both touch and nociceptive signals from the opposite side of the body?

Answer 27

yes

Question 28

do the touch, temp. and nociceptive pathways from body have equivalent pathways subserving the head and neck/

Answer 28

yes

Question 29

what are the names of the 3 pathways subserving the head and neck?

Answer 29

1. Spinothalamic
2. Trigeminal nerve
3. Dorsal column/medial lemniscus—> divided into fasciculus gracilus and fasiculus cuneatus

Question 30

what does the spinothalamic transmit?

Answer 30

body pain

Question 31

what does the trigeminal nerve transmit?

Answer 31

face and neck pain

Question 32

where are the cell bodies of trigeminal nerve?

Answer 32

the trigeminal ganglion, which is analogous to the DRG

Question 33

how many branches are in the DRG?

Answer 33

2, 1 to organ and one to spinal cord

Question 34

which DRG is the fasciculus gracilus from?

Answer 34

the lumbar DRG

Question 35

which DRG is the fasciculus cuneatus from?

Answer 35

the cervical DRG

Question 36

which DRG does the trigeminal go via?

Answer 36

the rostral DRG

Question 37

which stimuli does the trigeminal nerve transmit?

Answer 37

all senses, so both nociception and touch

Question 38

what are local anaesthetics and how do they work/

Answer 38

membrane stabilising drugs, work by blocking sodium channels so no influx of sodium so no pain

Question 39

how do opioid painkillers work?

Answer 39

by acting on opioid receptors: delta, kappa and most importantly mew.

Question 40

what are the 3 main side effects of opioids?

Answer 40

constipation, decreased respiration, addiction

Question 41

how do NSAIDs work as painkillers?

Answer 41

they inhibit COX enzymes, which would normally produce prostaglandins which sensitize nociceptors

Question 42

TENS can be used to control certain chronic pain states by:

Answer 42

inhibiting interneurons and therefore utilising the gate theory, although mechanism is debatable

Question 43

what is the main theory of why electrodes permanently implanted into the PAG work? (ex in parkinsonian pain)

Answer 43

PAG is the pain centre, so this would stimulate descending pathways and signal to projection neurons in the spine, therefore “dumping” he NTs serotonin and NA onto the projection neurons which act as inhibitors and stop pain signals from c fibres reaching the brain.