pain Flashcards
define pain
An unpleasant sensory & emotional experience associated with actual
potential tissue damage, or described in terms of such damage
does pain require actual tissue damage
no
it is not the same as nociception
and is not proportional to damage
define acute pain
Short term pain of less than 12 weeks
can usually be explained and treated
define chronic pain
Continuous long term pain of more than 12 weeks
medical investigations may not provide diagnosis
treatment aimed at relieving pain not curing it
widespread effect on life
define Nociceptive pain
Pain that arises from actual or threatened damage to nonneuronal tissue and is due to the activation of nociceptors
define Neuropathic pain
Pain initiated or caused by a primary lesion/dysfunction of the nervous system e.g. due to spinal nerve root compression
what are the neurones within the pain pathway
Within the pain pathway there are 3 orders of neurones that carry action potentials signalling pain:
first order neurones
second order neurones
third order neurones
where are the 3 pain neurones
between the sensory receptor
located in the periphery and the perception of sensation at the level of the cerebral cortex
course of first order/primary afferent neurone
Enters the spinal cord through a spinal nerve, or the brainstem
through the trigeminal nerve, on the same side of the body
(ipsilaterally) as the peripheral receptor is located
* Remains ipsilateral and synapses with a second order neurone
within the CNS
course of second order neurone
Cell body is located in the spinal cord/brainstem (exact location
depends where sensory receptor is, i.e. brainstem if the face etc.)
* Its axons CROSS over (decussates) to the other side of the CNS and
ascends to the thalamus where it terminates
course of third order neurone
Cell body is located within the thalamus and its axon projects to the
somatosensory cortex - located in the post central gyrus of the
parietal lobe of the cerebral hemisphere
what are nociceptors
Sensory neurons that are found in any area of the body that can sense pain
either externally or internally:
* Externally: skin, cornea, mucosa
* Internally: viscera, joints, muscles & connective tissue etc
where do cell bodies of nociceptors reside
in dorsal root ganglion (body)
or
trigeminal ganglion (face/head/neck)
what happens when there is tissue damage
bradykinin & prostaglandin E2 - both reduce the nociceptive action potential threshold thereby
increasing their sensitivity to stimuli - known as hyperalgesia
why are most nociceptors polymodal
they contain multiple receptors and thus respond to various combinations of the stimuli - thermal/chemical/mechanical pain
what are the types of afferent fibres
- Alpha delta fibres
- C fibres
describe alpha delta fibres
- Thinly myelinated
- Carries; touch, pressure, temperature & FAST pain information
- Small diameter (1-5 micrometers)
- Conduction speed is medium (5-40m/s)
describe C fibres
- Unmyelinated
- Carries; SLOW pain, temperature, touch, pressure, itch,
postganglionic autonomic fibres information - Smallest diameter (0.2-1.5 micrometers)
- Conduction speed is the slowest (0.5-2m/s)
where do Nociceptors (A delta & C fibres - first-order neurones) synapse with secondary afferent neurones (second order)
in the GREY MATTER of the
DORSAL HORN of the spinal cord (which is divided up into Rexed laminae)
what do the A delta (primary afferent neurone) terminals release
they release GLUTAMATE (FAST ACTING) as their neurotransmitter
what do the C fibres (primary afferent neurone) terminals release
GLUTAMATE &
SUBSTANCE P (SLOW ACTING - involved in the mediation of dull aching
pain) as their neurotransmitters
where do first order/primary afferent neurones transmit information into
into the dorsal root ganglion where they synapse with second order neurones at the substantia gelatinosa
where do second order neurones transmit the pain impulse up
- SPINOTHALAMIC TRACT (carries pain,temperature & crude touch
information from the BODY) - enters the spinal cord at LISSAUER’S
FASCICULUS - Trigemino-thlamic tract (carries pain, temperature & crude touch
information from the face/head/neck):
- First order neurones enter at the pons and then descend to the
medulla forming the spinal trigeminal tract
- Receives contributions from the trigeminal, facial, vagus &
glossopharyngeal nerves
where do spinothalmic tract and trigemino thalmic tract terminate
at the thalamus (ventral posterior lateral nucleus)
