Sensory physiology Flashcards
What are the two schemes by which peripheral nerves are classified?
their contribution to a compound action potential and based on fiber diameter
What are the different electrophysiologic classifications of peripheral sensory afferent fibers?
A-alpha, a-beta, a-delta, C
What is the class and group of afferent fibers associated with A alpha fibers?
Ia and Ib
What is the class and group of afferent fibers associated with Abeta fiebrs?
II
What is the class and group of afferent fibers associated with Adelta fibers?
III
What is the class and group of afferent fibers associated with C fibers?
IV
What is the fiber diameter of Aalpha fibers?
large
what is the fiber diameter of C fibers?
small
what is the conduction velocity of Aalpha fibers?
80-120 m/s (fast)
what is the conduction velocity of C fibers?
.5-2 m/s (slow)
what do Aalpha afferent fibers innervate?
primary muscle spindles and golgi tendon organ
what do Abeta afferent fibers innervate?
secondary muscle spindles and skin mechanoreceptors
what do Adelta afferent fibers innervate?
skin mechanoreceptors, thermal receptors and nociceptors
what do C afferent fibers innervate?
skin mechanoreceptors, thermal receptors, and nociceptors
What do Aalpha efferent fibers innervate?
extrafusal skeletal muscle fiebrs
what do Agamma efferent fibers innervate?
intrafusal muscle fibers
What do B efferent fibers innervate?
preganglionic autonomic fibers
what do C efferent fibers innervate?
postganglionic autonomic fibers
What are the two types of skin?
hairy and glabrous (hairless)
what are receptors that respond to prolonged and constant stimulation?
slowly adapting receptors
what are receptors that respond only at the beginning or end of a stimulus and they are only active when the stimulus intensity increases or decreases?
rapidly adapting receptors
What receptor is responsible for touch and vibration less than 100 Hz. Flutter and tapping?
meissner corpuscle
What receptor is responsible for rapid indentation of the skin such as that during high-frequency vibration (100-400 Hz)
pacinian corpuscle
what receptor is responsible for magnitude and direction of stretch. Touch and pressure and proprioception?
ruffini corpuscle
what receptor is responsible for pressure?
merkel cell
what receptor is responsible for motion across the skin and directionality of that motion?
hair-follicle receptor
what receptor is responsible for pain and temperature?
tactile free nerve ending
what is the only high threshold receptor?
tactile free nerve endings
what are the rapidly adapting receptors?
meissner corpuscle and pacinian corpuscle and hair follicle receptor
what are the slowly adapting receptors?
ruffini corpuscle, merkel cell, hair follicle receptor and tactile free-nerve endings
where are meissner corpuscles found?
glaborous skin
where are pacinian corpuscles found?
both hairy and glaborous skin
where are ruffini corpuscles found?
both hairy and glaborous skin
where are merkel cells found?
glaborous skin
where is tactile acuity the highest?
in the fingertips and lips
where is tactile acuity the lowest?
on the calf, back, and thigh
where is the primary somatosensory cortex located?
in the post central gyrus
what is the primary somatosensory cortex responsible for?
the integration of the information for position sense as well as size and shape discrimination
where is the secondary somatosensory cortex found?
in the wall of the sylvian fissure
what is the secondary somatosensory cortex responsible for?
comparisons between objects, different tactile sensations, and determining whether something becomes a memory
where does the highest level of interpretation of sensory inputs occur?
parieto-temporal-occipital association cortex
what is the primary role of the parieto-temporal-occipital association cortex?
identification of objects and analyzing coordination of your environment
what is the most basic principal that is thought to contribute to the pathophysiology of phantom limb pain?
law of projection
what does the law of projection state?
no matter where along the afferent pathway a stimulation is applied, the perceived sensation arises from the origin of the sensation
what is the term for increased responsiveness of nociceptive neurons to their normal input and/or recruitment of a response to normally subthreshold inputs?
hypersensitivity
what is increased sensitivity to stimulation, excluding the special senses?
hyperaesthesia
what is increased pain from a stimulus that normally provokes pain
hyperalgesia
what is pain due to a stimulus that does not normally provoke pain?
allodynia
What does it mean when it is said that we have a biphasic response to pain?
there is a combination of both a and Adelta fibers; initially you have a big quick peak in amplitude being transmitted by the Adelta fibers; then the response is from the C fiber, which is slower to respond
Are A delta fibers myelinated or unmyelinated?
myelinated
are C fibers myelinated or unmyelinated?
unmyelinated
A delta fibers are responsible for which type of sensation?
primarily mechanical pain
C fibers are responsible for which type of sensation?
polymodal: high-intensity chemical and thermal pain (can be involved in mechanical pain as well)
what is the receptive field size of the Adelta fibers?
relatively small receptive fields
what is the receptive field size of C fibers?
receptive field size is relatively larger
with A-delta fibers, what is localization like?
precise localization of pain
with C fibers, what is localization like?
imprecise localization of pain
Phase I pain would be described as what?
sharp
Phase II pain would be described as what?
dull/throbbing
How can pain be characterized by location?
somatic/cutaneous pain, muscle pain, deep pain, or visceral pain
How is pain characterized by nociceptor modality?
mechanical pain, chemical pain, or thermal pain
what type of stimuli affect the skin?
thermal, mechanical, and chemical
what type of stimuli affect the joints?
mechanical and chemical
what type of stimuli affect the muscle?
mechanical and chemical
what type of stimuli affect the viscera?
mechanical and chemical
what are the two reasons we have referred pain?
visceral pain is not experienced often enough in early development to train the brain to localize it and afferents converge in the dorsal horn
What is one of the biggest families of receptors that respond to noxious stimuli?
TRP receptors
the TRPVI receptor is specific to what?
capsaicin
the TRPAI receptor is specific to what?
allyl isothiocyanate
the TRPM8 receptor is specific to what?
menthol
what type of receptor is the TRP family?
ligand-gated non-selective cation channel
what is the TRP receptor permeable to?
Ca2+, Na+, or K+
Many C fibers express which receptor?
TRPV1
what endogenous receptors activate the TRPVI receptor?
bradykinin (inflammatory mediator) and by heat greater than 43 degrees C
what foods have allyl isothiocyanate?
mustard oil, wasabi, and horseradish
Which receptor do anesthetics work through and what effect do they have?
they have paradoxical pro-nociceptive effects by acting through TRPAI
How can TRPM8 receptors be activated?
innocuous cooling and noxious cold temperatures as well as by cooling agents such as camphor and menthol
What do free nerve endings lack?
specialized receptor cells or encapsulations
if you have a question that is asking what nerve fiber type is this most likely to be and it is releasing EAA and SP/CGRP, what is it?
then it is going to be a C fiber
neuropeptides do peptidergic fibers express?
substance P and CGRP
which afferents are peptidergic?
most visceral afferents and half of the cutaneous afferents
what type of pain/symptoms are peptidergic fibers involved in?
chronic inflammation and visceral pain
which afferents are non-peptidergic?
very few visceral afferents and half of the cutaneous afferents
what type of pain/ symptoms are non-peptidergic fibers involved in?
somatic chronic pain states (e.g. diabetic neuropathy)
what does the activated interneuron release that inhibits the secondary sensory neuron of the nociceptive pathway?
glycine
what happens in pre-synaptic inhibition?
there is a GABAergic associated influx of Cl- into the axon, which leads to hyperpolarization and less NT release
what is the insular cortex important for?
interpretation of nociception. integrates all signals related to pain
damage to the insular cortex results in what?
asymbolia
what is the amygdala important for?
the emotional component of pain
what is responsible for the visceral input of visceral pain?
hypothalamus and medulla
What are the two nociceptive fiber types?
A-delta and C fibers
what is the location for central sensitization?
central nervous system: brain and spinal cord
what is the location for peripheral sensitization?
PNS
What is the part affected in central sensitization?
synapses between neurons (synaptic plasticity)
what is the part affected in peripheral sensitization?
free nerve endings/ nociceptor peripheral terminals (neuroplasticity)
what is the central inflammation caused by?
microglia
what is the peripheral inflammation caused by?
inflammatory soup–> most know n is bradykinin and prostaglandin E2
