Pain and thermosensation

Question 1

What is pain?

Answer 1

Sensory and emotional experience, associated with actual tissue damage or described in terms of such damage

Question 2

What are the 3 forms of pain?

Answer 2

Nociceptive; immediate, protective response. ADAPTIVE
Inflammatory; assists in healing, persists over days - weeks ADAPTIVE
Pathological; no physiological purpose, persists over months, years or a lifetime. MALADAPTIVE

Question 3

What are nociceptors?

Answer 3

Specific peripheral primary sensory afferent neurones which are normally activated preferentially by intense stimuli (thermal, mechanical and chemical)

Question 4

What fibres make up nociceptors?

Answer 4

A-delta

C fibres

Question 5

What noxious stimuli will A-delta fibres respond to?

Answer 5

Mechanical/ thermal

Question 6

What noxious stimuli will C fibres respond to?

Answer 6

Polymodal; all noxious stimulus

Question 7

Which pain will A-delta fibres mediate?

Answer 7

First; lancinating, stabbing, pricking

Question 8

Which pain will C-fibres mediate?

Answer 8

Second; burning, throbbing, cramping, aching

Question 9

What is the difference between A-delta and C fibres in terms of action potential conduction?

Answer 9

A-delta: thinly myelinated, quicker conduction velocity

C-fibres: unmyelinated, slower conduction velocity

Question 10

What receptors are utilized in thermal stimulus?

Answer 10

TRP family

Question 11

What receptors are common in chemical noxious stimulus?

Answer 11

H+ activates ASICs
ATP activates P2X and P2Y
Bradykinin activates B2

Question 12

What is the difference between type 1 and type 2 A-delta fibres?

Answer 12

Type 1 = very hot temperatures at 53 °C

Type 2 = less hot temperatures at 43 °C

Question 13

In which area will noxious axons enter the spinal cord?

Answer 13

Dorsal horn

Question 14

Which neurotransmitters are involved in afferent noxious information?

Answer 14

Glutamate

Peptides; substance P and neurokinin A

Question 15

What can noxious stimulation in the long term result in?

Answer 15

Hyperalgesia

Allodynia

Question 16

What can efferent noxious action potentials result in?

Answer 16

Pro-inflammatory mediator (CGRP, substance P) release from free nerve endings contributing to neurogenic inflammation

Question 17

What is the action of substance P?

Answer 17

Vasodilation and extravasation of plasma proteins
Promotes formation of bradykinin
Release of histamine from mast cells
Sensitizes surrounding nocicpetors

Question 18

What is the action of CGRP?

Answer 18

Induces vasodilation

Question 19

Is glutamate a slow or fast neurotransmitter?

Answer 19

Fast EPSP and neuronal excitation

Question 20

Which receptors will glutamate act on?

Answer 20

AMPA and then NMDA when afferent input is intense

Question 21

Describe the action of NMDA receptors

Answer 21

Usually silent as the pore is blocked by a magnesium
When the cell becomes depolarised via AMPA allowing Na+ inside the cell, the magnesium will be released and the NMDA will conduct calcium

Question 22

What is the impact of calcium entering the cell via NMDA receptors?

Answer 22

Changes in gene transcription resulting in increased sensitivity of post synaptic cells to glutamate

Question 23

What is the action of peptides in NMDA activation?

Answer 23

Cause a slow and prolonged EPSP that facilitates the activation of NMDA

Question 24

Which laminae of rexed do the cell bodies of noxious afferents lie in?

Answer 24

Laminae 1 and 2

5 for A-delta also

Question 25

With what cells will C and A-delta fibres synapse with in the laminae of rexed?

Answer 25

Nociceptive Specific (NS) cells

Question 26

Which cell is present in laminae 5 and what does it receive input from?

Answer 26

Wide Dynamic Range (WDR) which receives input from A-beta, A-delta and C fibres; NOXIOUS AND NON-NOXIOUS STIMULUS

Question 27

Which pathway will visceral pain afferents follow?

Answer 27

Symp pathways before entering the dorsal horn but do NOT synapse in the sympathetic ganglion

Question 28

How does referred pain occur?

Answer 28

Visceral and skin afferent converge upon the same spinothalamic neurones (all cells with a visceral receptive field also have a separate cutaneous RF)

Question 29

What is the segmental dermatomes for the heart?

Answer 29

T1-5

Question 30

What is the segmental dermatomes for gallbladder pain?

Answer 30

C4

Question 31

What is the gate control theory?

Answer 31

Pain evoked by nociceptors can be reduced by simultaneous activity in beta fibres via closing of the substantia gelatinosa

Question 32

Where will projection neurones from lamina 1 of the spinothalamic tract terminate?

Answer 32

Posterior nucleus of thalamus

Question 33

Where will projection neurons from the WDR nucleus of laminae 5 terminate?

Answer 33

Posterior and ventroposterior nucleus of the thalamus

Question 34

What is required for pain perception?

Answer 34

Simultaneous firing of WDR and laminae 1 neurons to allow for location and intensity

Question 35

Which fibres will the spinoreticular tract transmit?

Answer 35

Slow C-fibre pain

Question 36

With what nuclei will the spinoreticular tract communicate?

Answer 36

Reticular nuclei in the brain stem; periaqueductal grey and parabrachial nucleus

Question 37

What is the spinoreticular tract involved with?

Answer 37

Autonomic responses to pain, arousal, emotional responses and fear of pain

Question 38

What are thermoreceptors?

Answer 38

Neurones that are specialised to respond to small changes in temperature

Question 39

Do all thermoreceptors respond to all types of temperature?

Answer 39

NO - there are hot sensitive and cold sensitive spots which are innervated by different neurons