Sensory Physiology Flashcards
How are peripheral nerves classified?
Contribution to compound AP
Fiber diameter, myelin thickness, and conduction velocity
What does conduction velocity determine?
Fiber’s contribution to the ocmound AP
How can you you test for peripheral nerve disease ?
Conduction velocity and compound AP
What is the correlation of fiber diameter and conduction velocity?
Large diameter correlates to faster conduction velocity
What kind of receptor is
Meissner Corpuscle?
RA or SA?
In what kind of skin?
Sensation type?RA in glabrous skin
Touch and vibration. Flutter and tapping
What kind of receptor is
Pacinian Corpuscle?
RA or SA?
In what kind of skin?
Sensation type?RA
Both hairy and glabrous
Rapid indentation of skin - vibration
What kind of receptor is
RUffini Corpuscle?
RA or SA?
In what kind of skin?
Sensation type?SA
Both hairy and glabrous
Stretch, touch, pressure and proprioception
What kind of receptor is
Merkel Corpuscle?
RA or SA?
In what kind of skin?
Sensation type?SA
Glabrous skin
Pressure sensation
What kind of receptor is
Hair follicle receptor?
RA or SA?
In what kind of skin?
Sensation type?RA and SA
Motion across skin and directionality of motion
What kind of receptor is
Tactile free nerve endings?
RA or SA?
In what kind of skin?
Sensation type?(High threshold)
SA
Pain and temperature
What are receptive fields?
Areas of innervation where individual mechanoreceptors fibers convey info from a limited area of skin
What part of the body have a high density of small receptive fields?
What does this allow for?
High density of small receptive field
Allows for fine discrimination of sensory inputs
Where is tactile acuity lowest?
Calf, back and thigh
What is S1 involved in?
Integration of info for position sense, size and shape discrimination
What is S2 responsible for?
Comparison b/w objects, different tactile sensations, determining whether not something becomes a memory
What is the parietal temporal occipital association area responsible for?
High level interpretation of sensory inputs
Analysis rs sptial coordinates of self in environments
What is phantom limb pain?
Describes pain in a body part that is no longer present
What is the Law of Projection?
Sensation along an afferent pathway (no matter where it is stimulated) will always go back to the origin
What is nociceptin?
Neural process of encoding noxious stimuli
What is hypersensitivity caused by?
Increased RESPONSIVENESS of nociceptive neurons to NORMAL INPUT
What is hyperaesthesia?
Increased sensitivity to stimulation
What is hyperalgeisa?
Increased pain from a painful stimulus
What is allodynia?
Pain due to stimulus that does NOT normally provoke pain
What are the characterizations of A-delta fibers?
What info does it carry?
Myelinated
Faster conduction velocity than C fibers
Carries pain info from MECHANICAL Rs.
Small receptive fields
What are the characterizations of the C fibers?
Unmyelinated
Slow conduction velocity
Activated by CHEMICAL and thermal stimulation
Larger receptive field
What do C fibers release upon receiving chemical or thermal stimuli?
Release: Substanc P Glutamate Aspartate CGRP VIP NO
What kind of pain is elicited by A fibers?
C Fibers?
What do these two responses comprise?
A fibers: Sharp and localized
C fibers: dull, throbbing, and less localized
Bi-phasic response to pain
What can nociceptors be activated by?
Mechanical (pressure)
Thermal (noxious heat and cold)
Chemical (endogenous or exogenous compounds)
What is TRPV1?
What expresses it?
What is it sensitive to?
What can it be activated by?
Ligand gated non-selective cation channel
C fibers
Vallinoid compounds
Activated by inflammatory mediators, bradykinin and heat
What does activating TRPV1 do?
Leading to what?
AP firing
Release of Neuropeptide like CGRP, Neurokinins, Substance
Leads to vasodilation and activation of immune and other cell types
What does the release of pro-inflammatory mediator release by TRPV1 cause?
Potentiation of TRPV1 channel (a positive feedback loop)
What kind of pain is TRPV1 involved w/?
Migraine Dental pain Cancer pain Inflammatory pain Neuropathic pain Visceral pain OA
How is TRPA1 activated?
What can act thru TRPA1?
Alkyl isothicyanate in mustard oil, wasabi, and horseradish
Anesthetics act thru TRPA
(A1 sauce - has wasabi in it)
What is TRPM8 activated by?
Innocuous cooling
Noxious cold
Cooling agents
(TRMP8 = Temper8)
What happens when the Gate is closed in the Theory of Pain?
Inhibitory interneuron is blocking nociceptive pathway
Not allowing nociceptive signal to move forward
According to the gate control theory of pain, what happens if
Pain is sensed?
Gate opens during strong c-fiber activation
Allows strong signal to be sent to the brain
According to the Gate control theory of pain, How is pain modulated?
Rubbing that spot, activates an A beta fiber
To dorsal horn and synapses on an inhibitory interneuron, releases EAA
Inhibitory interneuron activated and releases glycine
INHIBITS secondary sensory neuron of pain path
NO MORE PAIN
How do opiates, EAA and cannibinoid work?
Opiates, EAA, canniboid —> PAG —> Locus Ceruleus RAphe NUclei —> NE and 5HT to dorsal horn —> Activated inhibitory interneurons —> Local inhibitory interneurons release opiates —> Mu receptors of C Fibers —> Reduction of AP from C fibers —> Reduction of nociception
What is central sensitization?
Generates post injury pain hypersensitivity via cellular and molecular mechanisms
By reducing threshold of dorsal horn neurons to noxious stimulation
What is peripheral sensitization?
Neuroplastic changes of PNS
What is a key phenomenon of peripheral sensitization?
PGE2 sensitizes peripheral nociceptors, reduces firing threshold, and increases responsiveness
What are peptidergic nociceptors?
What are they responsive to?
What are peptidergic afferents?
Express Neuropeptides like Substance P and CGRP
Responsive to nerve growth factors
Most are visceral
1/2 of cutaneous are peptidergic
What upregulates the neuropeptides released by peptidergic nociceptors?
Chronic inflammation
What are non-peptidergic nociceptors?
What are its associated afferents?
Do not express neuropeptides
Responds to GDNF
1/2 of cutaneous afferents
Very few are visceral afferents
Where are non-peptidergic nociceptors seen?
Diabetic neuropathy
What is S1 and S2 role in pain?
Receive input from nociceptors
Play role in localization of pain
What is the insular cortex in regards to pain?
What does damage to this cortex cause?
Important for interpretation of nociception
And processes info about internal state of body
Damage = asymbolia
What is the amygdala in the pain pathway?
Emotional component to pain
What is the hypothalamus and medulla’s role in the pain pathway?
Visceral input travels w/ autonomic nerves to here
Integrates physiological changes associated w/ visceral pain
