Lecture 3: Somatosensory pt II Flashcards
where are free nerve endings found and what is their innervation
peripheral processes in the epidermis
c fibers (no myelin) or a delta fibers (poor/thin myelin)
types of free nerve endings
chemoreceptors
thermoreceptors
mechanoreceptors
nociceptors (independent or poly modal)
where is the density of cutaneous receptors high/low
high in fingertips and around mouth
low in trunk
not as diffuse as other fine touch receptors in the body
functions of cutaneous free nerve endings
crude/nondiscriminatory touch
itch
temp
noxious stimuli
taste/smell
describe how free nerve endings act like the post synaptic membrane
naked axon terminal; no special encapsulation
i.e. thermoreceptor detecting menthol is like a gated ionotropic receptor
how are signals transformed with free nerve endings
if threshold is met, graded potential turns into an axon potential at the trigger zone (like a voltage gated ion channel)
act via polymodal mechanisms; different ionotropic/metabotropic receptors around the endings, and different stimulu can make the same receptor meet potential then form AP (unexplained mechanisms)
how is duration and intensity of a stimuli encoded
duration = AP stops when stimulus stops
intensity = encoded through the AP frequency
what are the 3 sensory results of a thermoreceptor
iff between 17 deg celcius and 45 deg = hot or cold detected
if above 45 of below 17 = pain detected
chemical sensation/food flavor detection; CN V
- i.e. cold thermoreceptors = coolness mint/garlic pungency
-hot thermoreceptors = spicy pepper/weak response to garlic pungency
describe peripheral sensitization
relates to polymodal activities
hyperalgesia = overreaction to pain of noxious stimuli
restining membrane potential of trigger zone is increased (less depolarization required to initiate AP)
silent nociceptors are activated
increase in receptor expression and localization to endings
where are silent nociceptors common
joint capsule and visceral organs
describe the axonal reflex
axon terminals have afferent and efferent functions
1- AP initiated at one axon terminal can reach branching points
2- central process to spinal cord conducts pain signal
3- conduction is also sent to other axon terminals (i.e. to blood vessels for leaking/causing pain and swelling or for mast cells to amplify swelling and itching)
free nerve endings involved in muscle pain/what type of info they transmit
A delta fibers = stretch or contraction after exertion
C fibers = ischemia after injury (i.e. with chronic LBP)
describe what you might see in regard to ischemic S&S for chronic LBP
can no longer localize pain
more diffuse
free nerve endings involved in joint pain/what type of info is transmitted
A delta and C fibers = both send info about inflammation and peripheral sensitization
free nerve endings involved in visceral pain and what type of info is transmitted
mainly polymodal C fibers (usually diffuse + referral pattern)
info = mechanical stimuli (i.e. overdistention or traction), ischemia, or endogenous compounds (Bradykins, H+ ions, K+ ions, prostoglandins, etc)
endogenous example = peptic ulcer
mechanical example = bowel obstruction
what is radiculopathy
spinal nn axon bundles are compromised along a specific dermatome distribution
what are you testing when you test a patients dermatomes and how
looking for nn function/injury; peripheral and central processes overlap along dermatomes
testing A delta fibers
test via pin prick, temp, or crude touch
describe alpha motor and Ia/Ib sensory fibers
largest axon
highly myelinated
very fast
describe gamma motor neurons and type II/A beta sensory fibers
medium sized axons
highly myelinated
fast
describe B visceral motor (preganglionic) and A delta sensory fibers
small axons
poorly myelinated
slow
describe C fibers [visceral motor or sensory]
smallest axon
unmyelinated
very slow
clinical importance of understanding the different types of nerve fibers
for ESTIM or NMES
different frequencies required depending on what nerve type you are trying to reach
i.e. superficial skin = A beta, needs lower frequency
where do A delta fibers generally project and what do they release
mainly project to laminae I but some V as well
release glutamate (ionotropic)
where do C fibers generally project and what do they release
mainly project to laminae II but some to I and V
release substance P (metabotropic)
both A delta and C fibers project to which laminae
III and IV
where do second order neurons relay information if they are transmitting innocuous input and noxious input respectively
innocuous input sent to the lateral dorsal horn, laminae I-V
noxious input sent to laminae I, IIo, and V
- lateral to medial = thermal, polymodal, mechanical inputs
information carried via A delta fibers in the anterolateral system
sharp pain, crude touch, and temperature
A delta fibers have contralateral projections in anterolateral systems
describe the path of A delta fibers in the anterolateral system
1st order neuron in DRG
2nd order in laminae I
decussation at anterior white commissure
fibers ascend through lateral funiculus (called the lateral spinothalamic tract)
3rd order neuron in VPL of thalamus
project to S1, Brodmanns 3b/1
describe the transition from the SC to the medulla
Lissauer’s tract transforms to spinal trigeminal tract
laminae II-IV transform to spinal trigeminal nuclei
posterior SC region = tegmental region of medulla
where are the somata of the 1st order neurons of the spinal trigeminal path
CN V = trigeminal ganglion
CN VII = geniculate ganglion
CN IX = superior ganglion
CN X = superior ganglion
where are the 2nd order neurons for the spinal trigeminal tract
spinal trigeminal nuclei
located from caudal pons to C2 level
nuclei have concentric distribution with the mouth as the center
CNs VII, IX, and X project to the adjunct nucleus inferiorly and posteriorly
where is the 3rd order neuron for the spinal trigeminal path
VPM of thalamus
then further projections to lateral postcentral gyrus; somatotopy is maintained
what falls under the umbrella of conscious sensation
esteroception (stimuli outside of body) and proprioception
proprioception is made up of position sense and kinaesthetic sense
what falls under the umbrella of unconsious proprioception
enteroception (i.e. internal organ sensory) and proprioception (to cerebellum)
where are conscious and unconscious stimuli sent to in the brain respectively
conscious stimuli sent to cerebrum
unconscious sent to cerebrum and cerebellum
conscious and unconscious sensations are interchangeable in the cerebrum
blood supply to the SC portion of the anterolateral system
posterior to anterior spinal arteries
blood supply to the medulla portion of the anterolateral system
posterior spinal aa
branches from PICA
blood supply to the anterolateral system from midbrain higher follows the same blood supply as what
DCML
what is PICA syndrome
aka lateral medullary/wallenberg syndrome
alternating hemiplegia
impairments in pain, temp, crude touch
S&S = contralateral body and ipsilateral face
with PICA syndrome, why are the symptoms contralateral on the body but ipsilateral on the face
the anterolateral system decussates along the SC; with PICA syndrome you are already above the point of decussation so the S&S are contralateral
however the spinal trigeminal tract hasnt decussated yet so the S&S related to the face are ipsilateral
describe the return of somatic sensation following stroke
ALS for crude touch, pain, temp can return back to normal levels because of the diffuse C fiber pain path
DCML path for discriminative touch, fine touch, proprioception cannot return completely
A delta fibers give what information about pain
perception of pain
localized/conscious/cortical
can pinpoint exact location
C fibers give what info about pain; signals sent where?
diffuse pain/subcortical/unconsious awareness
chronic pain/suffering
signals sent to medulla RF, other parts of RF, hypothalamus, and limbic system
function of valium with pain
aka benzodiazepines
decrease the unpleasant pain but it still exists
describe how central sensitization occurs with chronic pain/how nociplastic pain occurs
CNS ASL path gets reorganized
- with nociception = NMDA/AMPA paths
-without = deafferentation/phantom pain/allodynia
S1 reorganized; decrease of other sensory perceptions
synaptogenesis all along CNS pathways
what is allodynia
pain sensation to non-noxious stimuli
