normal pain - ascending pathways Flashcards
what are nociceptors, what do they do and where are they found
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
what are the major types of nociceptors
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 `
which chemical mediators are released from damaged cells during transduction
prostaglandin, bradykinin, serotonin, histamine, ATP, potassium and H+
what do chemical mediators do
act as specific receptors on nociceptors and sensitise nociceptors or activate silent nociceptors
what can be released during nociceptors during axon reflex and what does this do
substance P + CGRP for histamine, vasodilation and bradykinin
these extend, amplify and broaden pain and are one mechanism for hyperalgesia and allodynia
describe nociceptive sensory afferent neurons
peripheral neurons of somatosensory ns capable of encoding noxious stimuli during conduction
t-shaped sensory neurons
conduct nociceptive signal to spinal cord dorsal horn
A delta fibred
stimuli, morphology, velocity, character, receptive field (localisation) ntsm @ spinal cord
noxious mechanical (and thermal) thin + myelinated 5-30m/s immediate sharp, pricking pain small + precise glutamate
C fibres stimuli, morphology, velocity, character, receptive field, localisation
noxious thermal, mechanical, chemical, silent nociceptors thin, unmeylinated, 0.3-2m/s long-lasting, dull, burning, aching pain large = diffuse glutamate + sub P
describe the excitatory ntsm in the spinal nociceptor synapse
glutamate - AMPA receptors
substance p - NK-1 receptors
what does it mean if a 1st order neurons is polysynaptic
one or more intervening excit/inhib interneurons to then synapse with projection neurons (second order)
describe the withdrawal reflex arc eg with touching hot object
thermal pain receptor in finger -> afferent pathway -> spindal cord -> ascending to brain and ALSO to efferent pathway to effector organs
what are the 3 ascending pain pathways
neospinal
paleospinal
archispinal
what are the 1st order neurons of the neospinal thalamic tract
a delta fibres
describe the 2nd order neurons of the n. thalamic tract
pain specific
all axons are decussate - ascend through anterior lateral part of the spinal cord to brainstem and terminate in the thalamus
describe the 3rd order neurons of n thalamic tract
to primary somatosensory cortex (somatotopic orientation)
responsible for immediate pain awareness and location of painful stimulus
describe the 1st order neurons of paleospinal and archispinal thalamic tracts
c fibres
describe the 2nd order neurons of p and a spinal tracts
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)
describe the synaptic connections of 2nd order neurons in p and a spinal tracts
periaqueductal great (PAG)for descending modulation reticular fornmation and hypothalamus for autonomic responses
describe the 3rd order neurons of the p and a thalamic tracts
secondary somatosensory cortex for recognising and remembering pain
insular, cingulate and frontal cortices for emotional components
what is referred pain
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
in the head and face and intraoral structures where are the 1st nociceptive neurons and where do they synapse and cross
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
is there a specific pain perception area in the brain
no we have a pain matrix
name 5 components of pain matrix
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
