normal pain - ascending pathways

Question 1

what are nociceptors, what do they do and where are they found

Answer 1

high threshold sensory receptors of peripheral somatosensory nervous system
capable of transducing and encoding noxious stimuli (mechanical, thermal, chemical)
found at free nerve endings
electrically silent at baseline but produce all-or-none aps when stimulated

Question 2

what are the major types of nociceptors

Answer 2

mecahno, chemical, mechano-thermal, polymodal, silent
silent = low threshold when activated, dont respond to threshold of stimulus unless there is actual injury - respond to inflammation of tissues `

Question 3

which chemical mediators are released from damaged cells during transduction

Answer 3

prostaglandin, bradykinin, serotonin, histamine, ATP, potassium and H+

Question 4

what do chemical mediators do

Answer 4

act as specific receptors on nociceptors and sensitise nociceptors or activate silent nociceptors

Question 5

what can be released during nociceptors during axon reflex and what does this do

Answer 5

substance P + CGRP for histamine, vasodilation and bradykinin
these extend, amplify and broaden pain and are one mechanism for hyperalgesia and allodynia

Question 6

describe nociceptive sensory afferent neurons

Answer 6

peripheral neurons of somatosensory ns capable of encoding noxious stimuli during conduction
t-shaped sensory neurons
conduct nociceptive signal to spinal cord dorsal horn

Question 7

A delta fibred

stimuli, morphology, velocity, character, receptive field (localisation) ntsm @ spinal cord

Answer 7

noxious mechanical (and thermal)
thin + myelinated
5-30m/s
immediate sharp, pricking pain
small + precise
glutamate

Question 8

C fibres stimuli, morphology, velocity, character, receptive field, localisation

Answer 8

noxious thermal, mechanical, chemical, silent nociceptors
thin, unmeylinated, 0.3-2m/s
long-lasting, dull, burning, aching pain
large = diffuse 
glutamate + sub P

Question 9

describe the excitatory ntsm in the spinal nociceptor synapse

Answer 9

glutamate - AMPA receptors

substance p - NK-1 receptors

Question 10

what does it mean if a 1st order neurons is polysynaptic

Answer 10

one or more intervening excit/inhib interneurons to then synapse with projection neurons (second order)

Question 11

describe the withdrawal reflex arc eg with touching hot object

Answer 11

thermal pain receptor in finger -> afferent pathway -> spindal cord -> ascending to brain and ALSO to efferent pathway to effector organs

Question 12

what are the 3 ascending pain pathways

Answer 12

neospinal
paleospinal
archispinal

Question 13

what are the 1st order neurons of the neospinal thalamic tract

Answer 13

a delta fibres

Question 14

describe the 2nd order neurons of the n. thalamic tract

Answer 14

pain specific
all axons are decussate - ascend through anterior lateral part of the spinal cord to brainstem and terminate in the thalamus

Question 15

describe the 3rd order neurons of n thalamic tract

Answer 15

to primary somatosensory cortex (somatotopic orientation)

responsible for immediate pain awareness and location of painful stimulus

Question 16

describe the 1st order neurons of paleospinal and archispinal thalamic tracts

Answer 16

c fibres

Question 17

describe the 2nd order neurons of p and a spinal tracts

Answer 17

non-specific, wide dynamic range
act by fibres with non-nociceptive mech stimuli
encode intensity
winf up with rep. stim
larger receptive field than pain specific ones
not all axons decussate (cross over)

Question 18

describe the synaptic connections of 2nd order neurons in p and a spinal tracts

Answer 18

periaqueductal great (PAG)for descending modulation 
reticular fornmation and hypothalamus for autonomic responses

Question 19

describe the 3rd order neurons of the p and a thalamic tracts

Answer 19

secondary somatosensory cortex for recognising and remembering pain
insular, cingulate and frontal cortices for emotional components

Question 20

what is referred pain

Answer 20

superficial somatic and visceral primary afferents converging onto the same 2nr order neurons of the p thalamic tract.
visceral nociceptive signa; perceived as pain at the site of the superficial somatic primary affernet receptive field

Question 21

in the head and face and intraoral structures where are the 1st nociceptive neurons and where do they synapse and cross

Answer 21

body in trigeminal ganglion = enter pons, descend to medulla and synapse at spinal trigeminal nucleus
cross midline and ascend as trigeminothalamic tract terminating in the thalamus

Question 22

is there a specific pain perception area in the brain

Answer 22

no we have a pain matrix

Question 23

name 5 components of pain matrix

Answer 23

reticular formation, hypothalamus (autonomic responses)
1st somatosensory cortex for locating pain and assessing intensity
2nd somatosensory cortex for recognising and remembering past pain
limbic system, insular, cingulate and frontal cortices - emotional components
motor cortical area - motor responses