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somatosensory system overview (cutaneous nerves (inactivation and…
somatosensory system overview
cutaneous nerves
A-delta fibers: pain and temp
C fibers: pain and temp
A-beta and A-alpha fibers: touch
increase in diameter of nerve fiber corresponds to increase in conduction velocity
inactivation and activation depends on neuron fiber diameter
local anesthetics inactivate C fibers first
compression/ischemia will inactivate A-alpha and A-beta nerve fibers first
electrical stimulation activates A-alpha and A-beta nerve fibers before it activates C fibers
skin receptors
epidermis
(superficial): smaller receptive field and more sensitive
meissner corpuscle:
rapidly adapting, senses light touch, numerous in the pads of the fingers
merkel cell:
slowly adapting, pressure, deep static touch, position sense,
fingertips
and superficial skin
dermis
(deep): larger receptive field and less sensitive
pacinian corpuscle:
rapidly adapting, sense vibration and pressure
ruffini endings:
slowly adapting, respond to pressure
free nerve endings are present in
joints: detect extreme range of motion
hair: they detect bending of the hair
skin: they detect crude touch, pain and temp
two point discrimination improves as innervation density increases (fingertips are more sensitive, your arm isn't as sensitive)