Somatosensory System Flashcards
what is somatosensation?
collection of body sensations gathered from receptors in the skin, muscle, connective, and visceral tissues
multimodal
what does somatosensation contribute to?
smooth accurate movements
prevention/minimization of injury
understanding of the external world
sensory info from skin is called
cutaneous
sensory info from touch is called
tactile
sensory info from nociception is called
pain
what does the musculoskeletal system consist of?
muscles, joints, tendons, and ligaments
detect proprioception, nociception, and stretches
chemoreceptors
respond to chemcials
ie: O2 and H+ levels that lead to pH changes
mechanoreceptors
vibration, pressure, stretch, touch
thermoreceptors
temp changes
how cold/hot something is
nociceptors
sense pain; submodality of all receptors
ex: extreme stretch activates mechanoreceptors and nociceptors
tonic receptors
slowly adapting receptor
activate at onset of stim and stays on for duration of stim
codes whole duration
pain receptor, thermoreceptor
phasic receptor
rapidly adapting
responds to onset and offset of stim
only when there’s a change
signals there’s a change
1a fibers - dynamic spindle
peripheral somatosensory afferents
cutaneous-letters
proprioceptive info-roman numerals
classification of afferents
smallest to largest:
- C/4, A delta/3, A beta/2, 1a, 1b
C, 4 fibers
small unmyelinated
slow pain/secondary pain
A delta, III fibers
small myelinated
A beta, II fibers
medium myelinated
fast pain
1a 1b fibers
large myelinated
hairy skin
a beta and a delta fibers
ruffini endings-stretch, joint sensitization
hair follicle nerve ending-hair movement
Merkel cell-texture
hairless skin
free nerve endings-nociceptive, mechanical stim
Meissner’s corpuscle-dynamic movements across skin, slippage during grip
Pacinian corpuscle-vibration
A beta fibers and their receptor end organs, stimulus, and tonic/phasic
myelinated
hair follicle-hair movement
–> phasic
Meissner’s corpuscle-dynamic movement across the skin, slippage during grip
–> tonic
Merkel cell-light pressure, curvature, edges
–> tonic
Pacinian corpuscle-vibration
–> phasic
Ruffini’s corpuscle-skin stretch
–> tonic
A delta fibers and their receptor end organs, stimulus, and tonic/phasic
lightly myelinated
hair follicle-hair movement
–> phasic
free nerve ending-nociceptive mechanical stim, cold stim
–> tonic
C fibers and their receptor end organs, stimulus, and tonic/phasic
unmyelinated
free nerve endings-nociceptive mechanical stim, pleasant mechanical stim, ticklish mechanical stim, itch, thermal stim, and chem stim
–> tonic
what is a receptive field?
area of skin innervated by a single afferent neuron
small vs large receptive fields
small receptive field=can feel 2 close points as 2 separates stimuli
large receptive field=feel only one point when 2 close points are applied to the skin
are receptive fields smaller or larger distally?
smaller
are receptive fields smaller or larger proximally?
larger
smaller receptive fields have ___ threshold and ___ density of receptors
low, higher
larger receptive fields have ___ threshold and ___ density of receptors
high, lower
what does low threshold mean?
can sense stimuli with less distance b/w 2 points
can be as close as 4mm
what does high threshold mean?
2 points have to be further apart to feel them as 2 points
first pain response
sharp, localized pain
can feel exactly where it is
fast nociception conveyed by A delta fibers (small myelinated)
fast pain
second pain response
aching, poorly localized pain conveyed by C fibers (small unmyelinated)
slow pain
what happens when A delta fibers are blocked?
no fast pain (sharp, well localized pain)
what happens when C fibers are blocked?
no slow pain (dull, aching, poorly localized pain)
spinothalamic pathway
fast pain
1st order neuron-A delta
2nd order neuron from dorsal horn SC to thalamus
3rd order neuron from thalamus to primary somatosensory cortex and secondary somatosensory cortex
3 slow pain (c fiber) divergent pathways
spinolimbic, spinomesencephalic, and spinoreticular
spinomesencephalic pathway
SC to midbrain
superior colliculus: visual reflex-look to site of pain
periaqueductal gray: suppress pain signals
spinolimbic pathway
SC to limbic system (emotion, motivation)
ventral striatum in basal ganglia: motivation, aversion, reward seeking
amygdala
trigger emotion: upset in response to pain, avoiding pain
spinoreticular pathway
SC to thalamus, hypothalamus, and reticular formation
arousal autonomic control
sharp pain
A delta
spinothalamic
dull aching pain
C fibers
divergent pathways (3)
what are the sensory organs in the muscles responsible for proprioception?
muscles spindle and GTO
large proprioceptive afferents
1a and 1b
small proprioceptive afferents
3 and 4
ligament receptors
in ligaments
1 b afferents
Ruffini’s and Paciniform endings
2 afferents
free nerve endings
3 and 4 afferents
1a axons
myelinated
nuclear bag and chain fibers
velocity of muscles stretch
phasic
intrafusal
1b axons
myelinated
GTO and ligament receptors
tension on muscle and ligament
tonic
tendons and ligaments
type 2 axons
myelinated
nuclear chain and some bag fibers - muscle length - tonic - intrafusal
Paciniform corpuscles - joint movement - phasic - joint capsule
ruffini’s endings - extreme joint stretch - phasic - joint capsule
type 3 and 4 axons
lightly/unmyelinated
free nerve endings
nociceptive stimuli
tonic
muscles, joint capsule, ligaments
how do somatosensory receptors transduce stimulus into neural code and NT released?
stimulus activates receptor, afferents neurons receive potential, AP leads to NT release
moderate stimulus (shorter duration): fire AP and some NT released
stronger stimulus: increased frequency and duration of AP = increased NT released
peripheral neuropathy
damage to one (mononeuropathy) or more (polyneuropathy) peripheral nerves
loss of sensory and/or motor function
order of sensory loss
preferentially attack large myelinated fibers first
loss proceeds in order of decreasing axon diameter
large myelinated–> medium myelinated–> small myelinated, small unmyelinated
1a/b first= proprioception lost first
A beta first=light touch lost first
order of sensory recovery
opposite of loss
small unmyelinated–> small myelinated–> medium myelinated–> large myelinated
pain is first sense back
perception
central processing of sensory stimuli into a meaningful pattern
tied with sensation
increased stim intensity=increased perception intensity
is light touch consciously or unconsciously coded?
consciously coded
are joint position and proprioception consciously or unconsciously coded?
unconsciously coded
primary somatosensory cortex (s1)
reception of info, discrimination of object size, texture, and shape
bulk of somatosensory info (touch, temp, vibration, pressure, pain)
process type and intensity of info
post central gyrus
secondary somatosensory cortex (S2)
higher level processing
analyze info from S1 and thalamus
spatial and tactile memory
not somatotopically arranged
what is stereognosis?
the ability to identify an object w/o visual info
requires lots of info from the DCML and previous experiences
what is barognosis?
perception of weight from cutaneous and proprioceptive info
what is graphesthesia?
ability to identify letters and numbers drawn on skin w/o visual input
