Physiology and Pathophysiology of Pain

Question 1

what is pain?

Answer 1

an unpleasant sensory and emotional experience associated with or resembling that associated with actual or potential tissue damage

Question 2

what is nociception?

Answer 2

physiologic process in which noxious stimulation is communicated through the peripheral and central nervous system and may or may not result in pain

Question 3

what is pain?

Answer 3

subjective experience, perception occurs in the somatosensory cortex and can be triggered without tissue damage if brain or spinal cord malfunction

Question 4

what are the neural pathways?

Answer 4

periphery- detection of tissue damage by nociceptors and are transuded to the spinal cord through the 1st order/primary afferent neurones - spinal cord processing and spinal is transmitted to the brain (thalamus) by the 2nd order neurones- brain= various centres receive input- perception, learning and response - modulation= descending tracts - avoid or dampen stimuli

Question 5

what fibres are involved in nociception?

Answer 5

A delta= lightly myelinated and transmits the fast pain whereas C fibres are unmyelinated and transmit slow pain

Question 6

what happens to nociception in the spinal cord?

Answer 6

the 1st order neurones synapse in the dorsal horn of the spinal cord and the 2nd order neurones continue as tracts

Question 7

what ascending tracts carries nociceptive information?

Answer 7

spinothalamic tract which raised in the rexed lamina 1,2 and 5 which is mainly lateral but also small amount anterior - spinoreticular tract in the medulla, spinomesencephalic tract in the brainstem, spinohyopthalamic tract in the hypotahalmus

Question 8

what is the function of thalamus?

Answer 8

secondary centre which is in the brain - depending on where they project to in the thalamus from the spinal cord, they are divided into the lateral and medial systems

Question 9

what is the medial system?

Answer 9

VMpo and Mdvc mainly receive primarily lamina I and they project to the insulation and ACC and they are involved in evaluating the pain

Question 10

what are the descending pathways involved in nociception?

Answer 10

periaquductal grey (PAG) in the midbrain which assimilates the information and is effective via the rostroventral medulla which is noradrenergic system and have on and off cells and usually decreases pain signal (diffuse noxious inhibitory control - DNIC= normal tone) - normally on= inhibitory but if on= more signals sent to the higher centres

Question 11

what is pain modulation?

Answer 11

at each stage in the nociception pathway can be subject to modulation and can become independent on their own giving rise to chronic pain

Question 12

how do nociceptors?

Answer 12

to create a signal sodium channels must close to allow the cells to depolarise

Question 13

how does inflammation influence nociception?

Answer 13

inflammatio will cause most cells, macrophages etc to congregate which will release mediators wg histamine, NGF etc which will influence the sodium channels by either keeping them open for longer or inhibit

Question 14

what effect with inhibition of sodium channels have?

Answer 14

peripheral sensation -lower intensity of stimulus will give rise to greater pain sensation

Question 15

what is allodynia?

Answer 15

perception of non-painful stimuli due to decreased threshold for response

Question 16

what is hyperalgesia?

Answer 16

exaggerated response to normal and supranoraml stimuli

Question 17

what is spontaneous pain?

Answer 17

spontaneous (without pain) activity in nerve fibres

Question 18

what is central sensitisation?

Answer 18

response of 2nd order neurones in the CNS to both noxious and non-noxious stimuli and have 3 main components= wind-up, classical and long-term potential

Question 19

what is wind-up?

Answer 19

involves only the activated synapses- homosynaptic activity dependent on progressive increase in response of the neurones, it manifests over the course of stimuli and terminated with stimuli and the neurotransmitters involved are substance P and CGRP

Question 20

what is classical?

Answer 20

involves opening up of new synapses (silent nocicpetors), heterosynaptic activity dependent plasticity with intermediate onset with appropriate stimuli and can outlast the initial stimuli duration and can be maintained even at low levels of ongoing stimulus

Question 21

what is long-term potentiation?

Answer 21

involves mainly the activated synapses and occurs primarily for very intense stimuli

Question 22

what are the different possible durations of pain?

Answer 22

acute or chronic

Question 23

what are the different mechanisms of pain?

Answer 23

nociceptive, neuropathic or nopciplastic

Question 24

what is acute pain?

Answer 24

physiological and needs the presence of noxious stimuli, served protective function and is usually nociceptive

Question 25

what is chronic pain?

Answer 25

pathological and presence of noxious stimuli is not essential, does not serve any purpose and cab be nociceptive, neuropathic or nociplastic

Question 26

what is nociceptive pain?

Answer 26

a sensory experience that occurs when specific peripheral sensory neurones (nociceptors) respond to noxious stimuli - painful region is typically localised to the site of injury, usually resolves when the damaged tissue heals

Question 27

what is neuropathic pain?

Answer 27

pain caused by a lesion or disease of the somato-sensory nervous system - pain occurs in the neurological territory of the affected structure, predominantly a chronic condition and responds poorly to conventional analgesics

Question 28

what is nociplastic pain?

Answer 28

pain that arises from altered nociception despite no clear evidence of actual or theatened tissue damage causing the activation of peripheral nociceptors or evidence of disease or lesion of the somatosensory system causing pain - pathological pain