the somatosensory system: pain and thermal sensation Flashcards
how many forms can pain be classed as
3
what are the three forms of pain
nociceptive
inflammatory
pathological
how can nociceptive pain be described
acute - pin prick
how can inflammatory pain be described
prolonged pain - sunburn
how can pathological pain be described
damage to nerves or nervous system (no external stimulus)
pain sensation in the skin is ____ localised
and can be described as what
well localised
pricking, stabbing or burning
pain sensation in the muscle is _____ localised
and can be described as what
poorly localised
aching, soreness/tenderness, cramping, stabbing, burning
pain in the viscera is _____localised
and can be described as what
poorly localised (often referred to an area of skin)
dullness, fullness, nausea
nociceptive pain begins with the activation of what receptors
nociceptors
what type of neurons are nociceptors
specific peripheral primary sensory afferent neurons
nociceptors are specific peripheral primary sensory afferent neurons normally activated by _______
intense stimuli such as thermal, mechanical, chemical (noxious or damaging)
cell bodies of nociceptors are located where
dorsal root ganglia and trigeminal ganglia
what order of neurons are nociceptors
1st order neurons
nociceptors are first order neurons that relay info to _____ order neurons
second order neurons
nociceptors are first order neurons that relay info to second order neurons where and by what type of transmission
in the CNS and by chemical synaptic transmission
what kind of pain is adaptive
nociceptive pain
as nociceptive pain is adaptive, what does it serve as
an early warning system to detect and minimise contact with damaging stimuli
what pain is hight threshold
nociceptive
as nociceptive pain is high threshold, what does this entail
provoked only by intense stimuli that activate nociceptive
give 2 properties of nociceptive pain
adaptive
high threshold
nociceptive pain has the ability to _________ most other ongoing activites of the nervous system
override
what type of pain initiates a withdrawal reflex
nociceptive pain
what pain is said to be adaptive AND protective
inflammatory
why is inflammatory pain said to be adaptive and protective
caused by activation of the immune system in injury, or infection
inflammatory pain is caused by what system
immune system
what pain causes pain hypersensitivity
inflammatory pain
what pain is associated with allodynia (innocuous stimuli now elicit pain)
inflammatory pain
what are the 2 ways that inflammatory pain assists in healing of a damaged body part
discourages physical contact (wound)
discourages movement (inflamed joint)
what pain is said to be maladaptive with no protective function
pathological pain
what is pathological pain a result from
abnormal nervous system
how can pathological pain (route of) be described
neuropathic or dysfunctional
what happens in the absence of pain
gross damage to the body
what is the rare condition that doesn’t allow an individual to feel pain
congenital insensitivity to pain (CIP)
what is the mutation that causes CIP
loss of function (missense) in gene SCN9A
in CIP, the loss of function (missense) in the gene SCN9A encodes what kind of voltage channel
Na+ (Nav1.7)
a stimulus to nociceptors opens what type of channel
cation selective channel ion channel
stimulus (mechanical, thermal, or chemical) opens cation selective ion channel where
nerve terminal
stimulus (mechanical, thermal, or chemical) opens cation selective ion channels in nerve terminal to elicit what
a depolarising receptor potential
low threshold units respond to what
low intensity stimuli
low threshold mechanoreceptors (LTMs) mediate what (3)
touch, vibration, pressure
low threshold thermoreceptros mediate what (5)
cold, cool, indifferent, warm, and hot
give an example of high threshold units
nociceptors
high threshold units respond to what
high, but now low, intensity stimuli
(noxious, potentially damaging)
high threshold mechanoreceptors (mechanical nociceptors) respond to what
high mechanical stimuli
thermal nociceptors respond to what
extreme degrees of heat
>45C
<10-15C
chemical nociceptors respond to what
substances in tissue (as found in inflammation)
e.g. prostaglandins, bradykinin, serotonin, histamine
what do polymodal nociceptors respond to
at least 2 forms of painful stimuli
in primary sensory afferents what is the decreasing value in this value
Aalpa -> Abeta -> Adelta -> C
decreasing diameter
conduction velocity
Adelta and C fibres are what kind of nociceptors
mechanical/thermal
Adelta fibres are mechanical/thermal nociceptors that are _____ myelinated
thinly
A delta fibres mediate what kind of pain
first/fast
give a reason why C fibres have the lowest conductance rate
unmyelinated
C fibres respond to all noxious stimuli so they are said to be….
polymodal
C fibres mediate what kind of pain
second or slow
what is frequency coding
the rate of an action potential discharge correlates with the intensity of the applied stimulus
signalling by nociceptors can be described as what (direction)
bidirectional
in the nociceptor, what does the central terminal do
no responsive to environmental stimuli
site of Ca2+ dependant transmitter release (glutamate , neuropeptides)
targeted by endogenous molecules that regulate activity
in the nociceptor, what does the soma allow
major site of protein synthesis - these are delivered to both the central and peripheral terminal
in the nociceptor, what does the peripheral terminal do
responds to environmental stimuli
site of release of molecules that influence local tissue environment
what is a subset of C fibres
peptidergic polymodal nociceptors
peptidergic polymodal nociceptors (a subset of C fibres) have what 2 functions
afferent and efferent functions
peptidergic polymodal nociceptors (a subset of C fibres) have afferent and efferent functions
explain the afferent function
transmit nociceptive info to the CNS
via
release of glutamate and peptides
with the dorsal horn
peptidergic polymodal nociceptors (a subset of C fibres) have afferent and efferent functions
explain the efferent function
release pro inflammatory mediators
from peripheral terminals
contributes to neurogenic inflammation
what is SP
a peptide
what does SP (a type of peptide) cause in neurogenic inflammation
vasodilation and extravasation of plasma proteins
release of histamine from mast cells
sensitisation of surrounding nociceptors
what is CGRP
a peptide
what does CGRP induce
vasodilation
(neurogenic inflammation)
once CGRP induces vasodilation what ensues
hyperalgesia and allodynia ensue
neurotransmission in the dorsal horn of the spinal cord
what receptors are exhibited in the synaptic cleft during the movement of glutamate, Na, and Ca
NMDA and AMPA
what does visecral pain originate from
nociceptors covering tissues
visceral pain is perceived at a distance from the ….
affected organ
how many neurons are there in the somatic sensory pathway
3
first order, second, third
when you feel pressure, or a vibration, when do does the first neuron decussate to the contralateral side
brain stem
what 3 structures make up the brain stem
medulla, pons, and mid brain
what rout in the spine occurs when activation of the somatic pathway by touch/vibration
dorsal column
when there is pain, what pathway do the neurons take
spinothalamic
when there is a painful stimulus, where do they neruons decussate
close to the point of entry on the spinal cord
where do the second and third order neurons synapse
thalamus
where does the third order neuron synapse
point of the brain where the pain is perceived - somatopically mapped
what 3 tracts make up the anterolateral system
spinothalamic
spinoreticular
spinomesencephalic
what is the main tract in the anterolateral system for transmitting pain to the cerebral cortex
spinothalamic
pain begins where through noxious stimuli (extreme heat etc…)
nociceptors
when nociceptors are activated they send a signal through the sinal cord and then to the brain through what system
anterolateral
what tract is responsible for the emotional compinent of pain
spinoreticular
where does the spinoreticular tract originate
reticular formation
where foes the spinomesencephalic tract synapse
periaqueductal grey
when the periaqueductal grey is stimulated they can activate a natural what
pain suppression system
when they periaqueductal grey is stimulated they can activate a natural pain suppression system through release of what
endogenous opioids
-> inhibition of pain signal
where is the periaqueductal grey located
in the midbrain of the brainstem
what is analgesia
pain reduction
what receptors in the PAG rich in
opioid receptors
once PAG is activated what structure do they activate in the medulla
raphe nuclei
the raphe nuclei is responsible for producing what nurotransmitter
serotonin
where does the serotonin go after it is produced from the raphe nuclei
dorsal horn of the spinal cord
what occurs once the raphe nuceli send the serotonin to the ventral horn of the spinal cord
inhibits the neurons responsible for transmitting pain signals
GATE CONTROL THEORY
what neuron is responsible for inhibiting the inhibitory interneuron
a branch off the first order cell body
what is responsible for being able to inhibit the neuron that inhibits the inhibitory interneuron to stop it from inhibiting the pain signal
mechanoreceptor Abeta
“closes the gate+
where does the gate theory occur
think about agate to an ice cream shop
substantia gelatinosa
