mechanisms of pain perception

Question 1

what is pain?

Answer 1

an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

Question 2

what are the 3 components of pain perception?

Answer 2

-sensory component - eg location, intensity and quality of pain
-motivational component - unpleasantness
-cognitive component - distraction, emotional response etc

Question 3

describe the duration & characteristics of acute pain?

Answer 3

-duration - seconds
-characteristics - associated with the detection of potentially tissue damaging noxious stimuli eg hot surface or pin prick

Question 4

describe the duration and characteristics of sub acute pain?

Answer 4

-duration - hours to days
-characteristics - associated w/ tissue damage and the infiltration of immune cells; resolves on recovery eg wound inflammation

Question 5

describe the duration and characteristics of chronic pain

Answer 5

-duration - months - years
-characteristics- pain exceeds resolution of damage, pain may become pathological and then is often chronic eg damage to nervous system

Question 6

what is dysfunctional chronic pain?

Answer 6

pain that has no known pathophysiology
-hard to treat

Question 7

what is nociception?

Answer 7

refers to the detection of noxious stimuli by nociceptors followed by the transduction and transmission of the sensory info from the periphery to the brain

Question 8

describe the characteristics of nociceptors

Answer 8

-located at free nerve endings of primary afferent sensory neurons
-found in skin, muscle joints etc
-respond to mechanical, thermal or chemical stimuli
-info re actual tissue damage or the potential for such damage is relayed to the brain

Question 9

what are the 4 types of nociceptors?

Answer 9

• mechanical
• chemical
  -thermal
  -polymodal

Question 10

what do mechanical nociceptors detect?

Answer 10

-stretch of skin
-pressure on skin
-sharp, prickling pain eg cutting or pinching

Question 11

what do chemical nociceptors detect?

Answer 11

-noxious chemicals
-factors eg bradykinins, prostaglandins etc

Question 12

what do thermal nociceptors detect?

Answer 12

-thermal sensations eg slow and burning or cold and sharp

Question 13

what do polymodal nociceptors detect?

Answer 13

-detect high intensity mechanical, thermal, and chemical stimuli

Question 14

describe a delta pain fibres - info carried, speed and response

Answer 14

• permit the localisation of pain and form the afferent pathway for the reflexes elicited b y pain
  info carried - acute pain eg sharp, well localised
  -speed - fast, small myelinated fibres
  -response - trigger immediate withdrawal and allow localisation of pain

Question 15

describe C pain fibres - info carried, speed, response

Answer 15

-C fibres are considered polymodal - they can react to various stimuli
-info carried - dull aching, diffuse pain , temp etc
-speed - slow unmyelinated fibres
-response - suffering, emotional

Question 16

what is the 3 order neuron system for pain pathway?

Answer 16

-primary pain afferent to spinal cord
-spinothalamic tract to thalamus
-thalamus to sensory cortex

Question 17

where do the 1st order neurons synapse with the 2nd order neurons?

Answer 17

in the dorsal horn of the spinal cord

Question 18

describe the pathway of the 2nd order neurons in the pain pathway

Answer 18

-2nd order neurons cross over to opposite side of spinal cord and enter spinal tract
-they ascend the contralateral spinothalamic tract and terminate in the thalamus where they synapse with the 3rd order neurons

Question 19

through which cranial nerve do 1st order neurons travel with to send information to the brain about pain in the face?

Answer 19

via the trigeminal nerve

Question 20

what neurotransmitters are released in the ascending nociceptive pain pathway?

Answer 20

-glutamate
-substance P

Question 21

what is substance P?

Answer 21

small peptide neurotransmitter that is important for the transmission of pain signals from the periphery to the brain

Question 22

what important NT’s are involved in the modulation descending nociceptive pathway?

Answer 22

-GABA
-Opiates

these act on 1st and 2nd order neurons to modulate pain perception

Question 23

what are the effects of the NT’s involved in the descending / pain modulation pathway?

Answer 23

-inhibit NT please from 1st order neuron ie substance P and glutamate
-hyperpolarisation of 2nd order neuron, reducing cell excitability
-reduces firing of AP in the 2nd order neuron which blocks the transmission of the pain signal

Question 24

what happens if opioids bind to the endogenous opioid receptors at the level of the spinal cord in the pain pathway?

Answer 24

-they exert analgesic effects by reducing neurotransmission of substance P and glutamate in the spinal cord both the at the presynaptic and postsynaptic locations

Question 25

what effects do opioids have @ the presynpatic and postsynaptic neurons in the pain pathway?

Answer 25

-presynaptic = reduce synaptic release of substance P and glutamate by inhibiting Ca2+ influx
-post synaptic - antagonise depolarising effects of substance P & glutamate

Question 26

what is the gate theory of pain?

Answer 26

Somatic non noxious stimuli can inhibit the transmission of pain signals in the spinal cord

Question 27

describe the gate theory

Answer 27

-gate is located in the substantial gelatinosa in the dorsal horn of the spinal cod through which pain information must pass on its way to the brain
-large diamater A beta fibres carrying touch pressure vibration etc synapse with interneurons in the dorsal horn and inhibit transmission of info
-interneurons inhibit the transmission of pain from C fibres at the synapse between 1st and 2nd order neurons using GABA etc

Question 28

what is somatic pain ?

Answer 28

pain felt from skin, muscles & joints

Question 29

what is visceral pain?

Answer 29

-pain from internal organs
-poorly localised felt in areas removed from site of stimulus
-often perceived in a different location (referred pain)

Question 30

what is referred pain?

Answer 30

-pain is felt in a location other than the actual source of the pain stimulus
-This occurs because sensory nerves from different parts of the body may converge on the same neural pathways in the spinal cord and brain, leading to confusion in the brain about the origin of the pain signal.

Question 31

what is allodynia?

Answer 31

a sensation of pain experienced in response to a non-nociceptive stimulus eg something brushing against the skin

Question 32

what is hyperalgesia?

Answer 32

-phenomenon when there is an enhanced sensation of pain at normal threshold stimulation

Question 33

what is neuropathic pain?

Answer 33

pain as a result of a disease or injury to the peripheral or central nervous system

Question 34

what are the causes of neuropathic pain - CNS vs PNS?

Answer 34

• CNS - stroke, spinal cord injury, neurodegenerative diseases
  -PNS - diabetic neuropathy, inflammatory disorders