Pain

Question 1

describe nociceptive nerves

Answer 1

free unspecialised nerve endings with pain channels in the membrane

Question 2

what is the most common pain receptor

Answer 2

transient receptor potential family of channels
sensitive to O2, pH, osmolarity, valinoids (capsicum), heat

allows calcium into the cell

Question 3

what substances can sensitise pain receptors

Answer 3

substance P, bradykinins, serotonin, pH, ATP, NO, other chemicals.

Question 4

what channels are opened when someone is exposed to extreme heat or cold

Answer 4

transient receptor potential vanilloid channels (TRPV)

Depolarises the cell by allowing sodium and calcium entry to give an action potential

can be regulated to change its sensitivity

Question 5

how are nociceptors activated when exposed to mechanical stimulation

Answer 5

unknown but presumed to be a form of insensitive mechanoreceptor which allows Na entry when activated

Question 6

what effect does histamine have on pain sensation

Answer 6

histamine causes hyperalgesia through its effects on blood vessels

(causes fluid to leave blood vessels)

Question 7

what effect does bradykinin have on pain fibres

Answer 7

activates pain fibres directly and causes an increase in prostaglandins

Question 8

what ion is produced by tissue damage

Answer 8

H+ ions which give muscle ache

Question 9

what enzyme is inhibited by NSAIDS

Answer 9

cyclooxegenase which makes prostaglandin E2

Question 10

what effect does calcitonin gene related peptide have on pain (vasodilator neuropeptide)

Answer 10

recruits silent receptors which increase summation in the dorsal horn

Question 11

describe A delta fibres

Answer 11

myelinated
sharp 1st pain
extreme temps
mechanical pinching

Question 12

describe C fibres

Answer 12

unmyelinated
secondary slow pain
mechanical pinching, temp and chemical pain

Question 13

what neurotransmitters are released by nociceptive fibres

Answer 13

glutamate, substance P, calcitonin gene release peptide

Question 14

what cause calor and rubor

Answer 14

hyperaemia

mediated by substance P and CGRP

Question 15

what causes tumour (swelling)

Answer 15

plasma extravasation

mediated by substance P and CGRP

Question 16

what is the anterolateral system

Answer 16

ascending pain system

Question 17

what is the function of periaqueductal gray

Answer 17

descending pain regulation

Question 18

what is the function of the reticular formation

Answer 18

motor response to pain and ascending arousal

Question 19

what is the neospinothalamic (anterior) route

Answer 19

fast/sharp pain to the VPL and primary somatosensory cortex

Question 20

what is the paleospinothalamic tract

Answer 20

slow burning pain to the limbic association cortices

Question 21

where do nociceptive fibres synapse

Answer 21

dorsal horn (quick to cross)

Question 22

what are nociceptive specific ascending axons

Answer 22

C and A delta only

Question 23

what are wide dynamic range neurons (WDR)

Answer 23

any sensory input can fire in a graded fashion based on C fibre frequency (higher pain = higher input)

Question 24

which pain fibres are polymodal

Answer 24

C fibres

Question 25

what are the 3 physiological signs of pain

Answer 25

heat, redness, swelling, mediated by histamine

Question 26

what is wind up (dorsal horn sensitisation)

Answer 26

long term sensitization of post synaptic neurons in the dorsal horn mediated by WDR neurons which open NMDA channels the inrush of calcium causes nuclear expression resulting n increased Na blockade of K channels the net result is a resting potential closer to the threshold and a more sensitive cell this amplifies the pain signal

Question 27

what is the function of wind up

Answer 27

priority salience in the cortex (you notice it more) protection from further injury memory- increased duration of stimulation increases the chance of consolidation

Question 28

what is the mechanism of wind up

Answer 28

based on the special characteristics of the NMDA receptor and Ca ion flow induces changes in nuclear expression and membrane channel activity the stronger the C fibre pain signal the more the dorsal horn post synaptic fibres become sensitive to input

Question 29

summarise wind up

Answer 29

the intensity of signal from the C fibres is translated through WDR neurons into variation in pain sensitivity

Question 30

what is the gate theory of pain

Answer 30

if you rub a painful area it activates A-beta fibres which inhibits pain similar theory behind TENS and capsaicin

Question 31

what do A-beta fibers detect

Answer 31

non painful stimuli

Question 32

name the endogenous opioids

Answer 32

endorphins, encephalins, and dinorphins sensitive to opiates and present at all levels of the pain pathway high efficacy for analgesia

Question 33

describe descending analgesia systems in the spinal cord

Answer 33

inhibition of incoming pain signals at the cord level and presence of encephalin secreting neurons that suppress pain signals in the cord this can be used by the CNS to increase or decrease salience of selected signals

Question 34

describe three methods of pain modulation

Answer 34

gate theory wind up descending analgesia and endogenous opioids

Question 35

describe the cortical pain matrix

Answer 35

there is no single pain centre in the brain somatosensory topographical discrimination limbic system including the cingulate gyrus saliency- relative potentiation of a specific input

Question 36

what areas of the brain are involved in pain

Answer 36

``` cortex brainstem (saliency) opioid PAG limbic system amygdala hypothalamus dorsal horn ```

Question 37

what happens if you electrically stimulate the PAG

Answer 37

strong analgesia but blocked by naloxone

Question 38

what is nociceptive pain

Answer 38

normal pain from injury, inflammation etc | will go away when the injury goes

Question 39

what is neuropathic pain

Answer 39

``` causalgia (peripheral nerve trauma) phantom limb pain entrapment neuropathy (carpal tunnel) peripheral neuropathy nociceptive pathway damage ``` pain persists beyond the healing process

Question 40

what is hyperalgesia

Answer 40

strong reaction to low intensity noxious stimuli

Question 41

what is allodynia

Answer 41

painful reaction to a non noxious stimuli

Question 42

what is summation

Answer 42

repeated low stimuli causes increasing intensity of response

Question 43

what is parasthesia

Answer 43

tingling without stimulation or dysthesia which is burning or shooting pain without stimulation which can sometimes be associated with thalamic syndrome

Question 44

why is persistent neuropathic pain hard to treat

Answer 44

caused by maladaptation of the dorsal horn wind up system

Question 45

what is central maladaptation

Answer 45

long term sensitisation in the structure of the synapses in the dorsal horn increased ionotropic glutamate receptors (NMDA) causes a sensitivity in second order neurons which then send more pain signals to the thalamus descending modulation of inhibitory interneurons becomes maladapted

Question 46

what are headaches caused by

Answer 46

irritation of venous sinuses, the dura at the base of the skull or meninges and blood capillaries dehydration causes low CSF causing the brain to settle onto the base of the skull causing deformation of the dura at the base of the skull and meninges

Question 47

what causes migranes

Answer 47

unknown but may be due to vasoconstriction and vasodilation

Question 48

what is the mechanism of referred pain

Answer 48

the brain localises pain by were is arises in the cortex skin and visceral sensory fibres travel together

Question 49

and finally

Answer 49

pain can not be re-experienced from memory the fear of pain is very important for patients

Question 50

describe a conceptual framework for pain

Answer 50

previous sensitising episodes (e.g. chlamydia) background factors mediators (sociocultural, family, economic) neurophysiology (e.g. central maladaption) pathology