Pain and Nociception Flashcards
what is pain?
an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
what is nociceptive pain?
the day to day pain that we have all felt
what nerve fibres sense nociceptive pain?
A delta and C fibres
what are the two types of pain?
nociceptive and clinical chronic pain
when is nociceptive pain elicited?
when intense/noxious stimuli threaten to damage normal tissue
what is the adaptive/biological role of nociceptive pain?
it serves as a protective function
what is nociceptive pain characterised by?
a high threshold and limited duration
what are the two types of clinical pain?
acute and chronic
what does acute clinical pain come from?
tissue injury or inflammation
what is the protective function of acute pain?
makes you guard the area so no further pain
what is chronic clinical pain?
a sustained sensory abnormality >3 months, resistant to treatment
what is chronic clinical pain the result of?
ongoing peripheral pathology e.g. chronic inflammation, peripheral nerve injury
what type of pain is chronic pain?
maladaptive - offers no survival advantage
comment on the pain induction of chronic pain
it can either be spontaneous or evoked
what are the attributes to pain?
location, quality, intensity, frequency/duration, provoking/relieving events
what are the segments of the spinal cord?
cervical (8), thoracic (12), lumbar (5), sacral (5), coccygeal (1)
how many segments of the spinal cord are there in total?
31
what body region does the cervical nerves supply?
back of head, neck and arms
what body region does the thoracic nerves supply?
trunk and forearm
what body region does the lumbar nerves supply?
hips and front of legs and feet
what body region does the sacral nerves supply?
bum, back of legs
what is referred pain?
pain that is felt in one part of the body but the pathology is elsewhere
why is makes pain referred?
the convergence of inputs in the CNS
where does pain tend to be referred to?
sites of common embryological origin or from an internal organ to a superficial area e.g. skin
what branches of the trigeminal nerve are for sensory only?
ophthalmic and maxillary
what branch of the trigeminal nerve has mixed sensory and motor function?
mandibular division
what is the structure of a sensory nerve cell?
receptor, axon, cell body
name the cutaneous and subcutaneous receptors
meissners corpuscle, merkel disc, hair follicle receptor, pacinian corpuscle, ruffini ending
what type of endings are nociceptor endings?
free endings
comment on the threshold of activation of nociceptor endings
they have a high threshold of activation
what type of stimuli do A delta fibres respond to?
noxious mechanical/heat
what type of stimuli do C fibres respond to?
polymodal (respond to numerous stimuli but eventually lead to the dull aching pain)
what is the advantage of nociceptor endings carrying several types of receptor proteins?
they are responsive to different noxious stimuli
what happens when a nerve is stimulated?
all the axons conduct action potentials
on a graph, what does the first recorded peak represent?
the activation of the fast conducting afferents (A alpha and beta)
on a graph, what does the second peak represent?
activation of thinly myelinated A delta fibres
on a graph, what does the third peak represent?
activation of the C fibres
in the spinothalamic pathway where does the primary sensory neuron go?
to the spinal cord and then changes to the secondary neuron
in the spinothalamic pathway where does the secondary neuron pass through?
spinothalamic tract - spinal lemniscus (medulla, pons, midbrain, thalamus)
in the spinothalamic pathway where does the tertiary neuron pass through?
the internal capsule and then the sensory cortex
in the tooth where do the nociceptive nerve endings extend to?
into the dentine
in the anterior trigeminothalamic pathway where does the primary neuron go to instead of the spinal dorsal horn?
the spinal trigeminal nucleus
what are the receeptors of the pain pathway?
nociceptors
what afferent nerves are involved in the pain pathway?
A delta and C fibres
what are the CNS relay cells of the pain pathway
spinal dorsal horn and spinal trigeminal nucleus
what are the CNS pathways of the pain pathway
spinothalamic and anterior trigeminothalamic tract
what areas of the forebrain are involved in the pain pathway?
primary sensory cortex and subcortical areas
what factors affect pain perception?
genetic, molecular, cellular, anatomical, physiological, psychological, social
what contributes to the molecular basis of pain?
SCN9A - gene that encodes the alpha subunit of voltage-gated sodium channels Na 1.7 is strongly expressed in nociceptive afferents, if the SCN9A gene is mutated there is loss of Na channel function and inability to experience pain
what psychological factors contribute to pain?
sex, age, cognitive level, previous pains, family, culture
what situational factors contribute to pain?
expectation, control, relevance
what emotional factors contribute to pain?
fear, anger, frustration
what is the gate control theory of pain?
by rubbing the place where you feel pain it makes you feel better, the A beta fibres activate the inhibitory INs which blocks the primary neuron entering the spinothalamic tract and pain is not felt
what is wheal?
white bit around the site of pain
what is flare?
red mottled appearance surrounding wheal
what is CGRP
calcitonin gene related peptide
what does CGRP do?
cause dilation of blood vessels so skin regions occur redder (flare)
what is the triple response?
local mast cells degranulate and release histamine which acts on receptive endings to reinforce there is trauma in the region, plasma extravasation and oedema correspond to wheal region, CGRP causes dilation of blood vessels so skin regions occur redder (flare region)
