Pain

Question 1

What are the 4 stages linking pain stimulus to response?

Answer 1

1. Pain sensing by Nociceptors
2. Signals from nociceptors transmitted from dorsal horn to periphery via afferent nerves, first order synapse with second order neuron in dorsal horn.
3. Signal transmitted through spinal cord to brain via ascending tracts. Decussation occurs, then ascent in spinothalamic tract through medulla.
4. Synapse with 3rd order neuron in thalamus. 3rd order neuron transmits signal to cortex where somatosensory pain is consciously perceived, connected with prefrontal cortex where cognitive and motor responses occur.

Question 2

What is the significance of the dorsal horn in pain signalling pathways?

Answer 2

Enables signals transmitted to the brain to be amplified or inhibited and for spinal level reflexes to initiate protective motor responses.

Question 3

How can the way other types of stimulus make a painful stimulus seem less painful be explained?

Answer 3

Due to reduced transmission cell activity less pain is felt when there is more activity in the large diameter fibres such as touch, pressure and vibration, Relative to activity in the small diameter fibres for pain transmission.

Question 4

What are 3 examples of excitatory neurotransmitters?

Answer 4

glutamate, substance P and CGRP

CGRP= Calcitonin Gene-related peptide

Question 5

What are 5 examples of inhibitory neurotransmitters?

Answer 5

enkephalins, B-endorphin, GABA, glycine and cannabinoids.

Question 6

How can descending inhibitory neuron pathway inhibit neurotransmission at the dorsal horn?

Answer 6

By releasing noradrenaline (NA) and 5-hydroxytryptamine (5-HT)

Question 7

Explain the gate control theory of pain

Answer 7

The dorsal horn synapse is a gate through which afferent pain signals have to pass to be transmitted to the brain.

The degree to which the gate is open can be influences by factors such as descending inhibitory nerve impulses and other local sensory afferent inputs.

Question 8

Where are the cell bodies of afferent neurons contained?

Answer 8

cell bodies are contained in the dorsal root ganglion.

Question 9

What does unilateral spinal cord damage result in and how can you explain this?

Answer 9

results in loss of pain sensation on one side of the body and loss of fine touch on the other side.

It can be explained because the afferents for pain decussate to the contralateral spinal cord whereas the afferents for touch and vibration remain in the ipsilateral.

Question 10

What are the two subtypes of nociceptor afferents?

Answer 10

• Slower unmyelinated C fibres for sustained dull pain (majority)
• Faster myelinated A fibres for rapid sharp pain sensation.

Question 11

How are nociceptive nerve endings activated?

(and how is this faciltated?)

Answer 11

• Sufficient influx of Na+ ions to depolarize beyond threshold.
• Generation also facilitated by increased availability of Ca2+ ions.

Question 12

What effect does cellular damage have on Na+ conductance?

Answer 12

increases availability of H+ ions, ATP, and reactive partially reduced derivatives of Oxygen which all increase Na+ conductance.

Question 13

How do Potassium ions generate pain in tissues?

Answer 13

Potassium ions reduce the transmembrane gradient hence favourising depolarisation at nociceptors.

Question 14

What are 2 ways in which products of inflammation increases activation of nociceptive nerve endings?

Answer 14

• Prostaglandins, prostacyclin and leukotrienes are agonists at g-protein coupled receptors linked to adenylate cyclase which indirectly up-regulate Na+ influx hence depolarisation at nociceptive nerve endings.
• Histamine, serotonin, bradykinin and noradrenaline are agonists at G-protein coupled receptors linked to enzyme phospholipase C which initiates a cascade of phosphorylation reactions leading to the production of inositol triphosphate which indirectly increases intracellular Ca2+ concentration.

Question 15

What is the function of adenylate cyclase?

Answer 15

An enzyme that generates 2nd messenger CAMP (cyclic AMP) from ATP.

Question 16

What are 2 inhibitory mediators at nocicpetors?

Answer 16

• Endogenous opioids are antagonists at G-protein coupled receptors linked to adenylate cyclase indirectly down-regulating Na+ Influx
• Nitric oxide (NO) diffuses into nociceptors activating guanylate cyclase, generating cyclic CMP which reduces the availability of Ca+ ions.

Question 17

What are the 3 subtypes of pain ?

Answer 17

Nociceptive, inflammatory and neuropathic.

Question 18

What are the 2 types of nociceptive pain?

Answer 18

Somatic pain and visceral pain

Question 19

Describe somatic pain:

Answer 19

• Can be superficial from skin
• Can be deep pain from muscles/joints/bones
• Well localised.

Question 20

describe visceral pain:

Answer 20

• From internal organs
• Poorly located and may be referred pain
• Autonomic activation.

Question 21

Describe inflammatory pain

Answer 21

• When inflammation is the main driver in the activation of the pain pathway
• Can be chronic or acute.

Question 22

What is allodynia?

Answer 22

Pain from a stimulus that doesnt usually provoke pain.

Question 23

What Is hyperalgesia?

Answer 23

Increased pain from a stimulus that usually provokes pain.

Question 24

Describe neuropathic pain/

Answer 24

Damage to nerves in the peripheral or central nervous system, described as burning, shooting and stabbing.