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Spinal cord pathways and pain
Terms in this set (39)
grey matter is made up of
neuronal cell bodies and dendrites
white matter is made up of
tracts comprising axons
gracilis (from leg) and cuneate (from arm)
posterior and anterior
what do spinocerebellar tracts do
transmit muscle and skin afferent signals to cerebellum, which in turn projects through thalamus to motor cortex
Poppele hypothesis about spinocerebellar tracts
spinocerebellar tract neurons integrate inputs from ensembles of skin and muscle afferents to encode limb end-point position.
pain and temp afferents synapse on ____ interneurons that cross _____ to form the _____ tracts. These synapse onto ____ neutrons.
2nd order; within 2 segments; spinothalamic; thalamocortical.
mechanoreceptive afferents form _____, which project to brainstem ______, thalamus and somatosensory cortex.
dorsal columns; dorsal column nuclei.
first-order afferents synapse on the ____ neurons in the ______
second order; dorsal column nucleus.
spinothalamic tracts mediate
pain and temperature sensation
_______ nociceptive and thermoreceptive afferents synapse on projection neurons in substantia gelantinosa of _____
C and A gamma; dorsal horn
projection neurons cross _______, project to the ____ and _____ via spinothalamic tracts
within one or two segments; thalamus and sensory cortex
when you have a right leg transection
lose pain and temp in right leg, but keep in left; lose touch and pressure in left but keep in right
pain and temperature crosses over _____, so it isn't blocked on the opposite side of the body
within a segment or two
- central canal enlarges and destroys crossing axon of projection neurons
- pain and temp abolished bilaterally in body areas innervated by the spinal segments over which the cavity extends (usually about 2-4)
thresholds to further painful or mechanical stimuli are reduced in the injured area
over time, there's inflammation around the site and whole area becomes very sensitive
4 mechanisms of hyperalgesia:
1) K+, bradykinin and prostaglandins sensitize nociceptors, and aspirin inhibits synthesis of prostaglandins.
2) the axo-axonic reflex
3) substance P causes vasodilation, releasing more bradykinin.
4) central sensitization of synapses in pain pathways.
nociceptor firing releases substance P, histamine release from mast cells, sensitizing nociceptors (positive FB).
referred pain definition
- sharing of projection neurons
examples of referred pain
- cardiac pain perceived in left arm and chest
- liver, gall bladder, lung and diaphragm pain perceived in neck and shoulders
Gate theory of pain was developed by _____
Melzack and Wall (1965)
- Inhibitory neurons in the substantial gelantinosa of dorsal horn suppress nociceptive transmission in projection neurons.
- activated by large mechanoreceptor afferents from skin and muscle
- net inhibition of projection neurons
- explains analgesic effects of acupuncture, skin rubbing, TENS, and spinal dorsal column stimulators.
absence of pain
- descending aminergic pathways
- interneurons release endogenous opiates such as enkephalins, which inhibit projection neurons
opiates ____ the duration of APs in nociceptive afferents in the dorsal horn, ____ excitatory transmitter release on projection neurons
____ and _____ activate K channels, ______ projection neurons and making them less responsive to nociceptive input
enkephalins and opiates; hyperpolarize
naloxone (narcan) blocks ____ receptors, _____ effects of opiates including side effects
side effects of opiates
sedation, respiratory depression, constipation
aspirin inhibits ____ synthesis and release from ____
prostaglandin; damaged tissues
opioids (eg morphine) block _____ release at synapses on projection neurons
activity in the analgesic system in the brainstem can suppress pain by
- releasing endogenous opiate neurotransmitters onto pain fibre endings in the spinal cord (fight/flight)
gabapentin blocks conduction in
3 dimensions of pain was proposed by
Melzack and Casey
3 dimensions of pain are
analgesic pathways originate in the ____
peri-aqueductal grey (PAG) matter
electrical stimulation in PAG can:
- reduce intractable pain of central origin
- eg: caused by spinal cord or brainstem tumours or limb amputation
analgesic pathways are active in ____ situations, where pain is ____
_____ abolishes some forms of stress-induced analgesia, but not others, indicating that there are _____ descending analgesic pathways as well.
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