Lecture 3: Somatosensory pt II

Question 1

where are free nerve endings found and what is their innervation

Answer 1

peripheral processes in the epidermis

c fibers (no myelin) or a delta fibers (poor/thin myelin)

Question 2

types of free nerve endings

Answer 2

chemoreceptors
thermoreceptors
mechanoreceptors
nociceptors (independent or poly modal)

Question 3

where is the density of cutaneous receptors high/low

Answer 3

high in fingertips and around mouth

low in trunk

not as diffuse as other fine touch receptors in the body

Question 4

functions of cutaneous free nerve endings

Answer 4

crude/nondiscriminatory touch

itch

temp

noxious stimuli

taste/smell

Question 5

describe how free nerve endings act like the post synaptic membrane

Answer 5

naked axon terminal; no special encapsulation

i.e. thermoreceptor detecting menthol is like a gated ionotropic receptor

Question 6

how are signals transformed with free nerve endings

Answer 6

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)

Question 7

how is duration and intensity of a stimuli encoded

Answer 7

duration = AP stops when stimulus stops

intensity = encoded through the AP frequency

Question 8

what are the 3 sensory results of a thermoreceptor

Answer 8

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

Question 9

describe peripheral sensitization

Answer 9

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

Question 10

where are silent nociceptors common

Answer 10

joint capsule and visceral organs

Question 11

describe the axonal reflex

Answer 11

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)

Question 12

free nerve endings involved in muscle pain/what type of info they transmit

Answer 12

A delta fibers = stretch or contraction after exertion

C fibers = ischemia after injury (i.e. with chronic LBP)

Question 13

describe what you might see in regard to ischemic S&S for chronic LBP

Answer 13

can no longer localize pain

more diffuse

Question 14

free nerve endings involved in joint pain/what type of info is transmitted

Answer 14

A delta and C fibers = both send info about inflammation and peripheral sensitization

Question 15

free nerve endings involved in visceral pain and what type of info is transmitted

Answer 15

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

Question 16

what is radiculopathy

Answer 16

spinal nn axon bundles are compromised along a specific dermatome distribution

Question 17

what are you testing when you test a patients dermatomes and how

Answer 17

looking for nn function/injury; peripheral and central processes overlap along dermatomes

testing A delta fibers

test via pin prick, temp, or crude touch

Question 18

describe alpha motor and Ia/Ib sensory fibers

Answer 18

largest axon

highly myelinated

very fast

Question 19

describe gamma motor neurons and type II/A beta sensory fibers

Answer 19

medium sized axons

highly myelinated

fast

Question 20

describe B visceral motor (preganglionic) and A delta sensory fibers

Answer 20

small axons

poorly myelinated

slow

Question 21

describe C fibers [visceral motor or sensory]

Answer 21

smallest axon

unmyelinated

very slow

Question 22

clinical importance of understanding the different types of nerve fibers

Answer 22

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

Question 23

where do A delta fibers generally project and what do they release

Answer 23

mainly project to laminae I but some V as well

release glutamate (ionotropic)

Question 24

where do C fibers generally project and what do they release

Answer 24

mainly project to laminae II but some to I and V

release substance P (metabotropic)

Question 25

both A delta and C fibers project to which laminae

Answer 25

III and IV

Question 26

where do second order neurons relay information if they are transmitting innocuous input and noxious input respectively

Answer 26

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

Question 27

information carried via A delta fibers in the anterolateral system

Answer 27

sharp pain, crude touch, and temperature

A delta fibers have contralateral projections in anterolateral systems

Question 28

describe the path of A delta fibers in the anterolateral system

Answer 28

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

Question 29

describe the transition from the SC to the medulla

Answer 29

Lissauer’s tract transforms to spinal trigeminal tract

laminae II-IV transform to spinal trigeminal nuclei

posterior SC region = tegmental region of medulla

Question 30

where are the somata of the 1st order neurons of the spinal trigeminal path

Answer 30

CN V = trigeminal ganglion

CN VII = geniculate ganglion

CN IX = superior ganglion

CN X = superior ganglion

Question 31

where are the 2nd order neurons for the spinal trigeminal tract

Answer 31

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

Question 32

where is the 3rd order neuron for the spinal trigeminal path

Answer 32

VPM of thalamus

then further projections to lateral postcentral gyrus; somatotopy is maintained

Question 33

what falls under the umbrella of conscious sensation

Answer 33

esteroception (stimuli outside of body) and proprioception

proprioception is made up of position sense and kinaesthetic sense

Question 34

what falls under the umbrella of unconsious proprioception

Answer 34

enteroception (i.e. internal organ sensory) and proprioception (to cerebellum)

Question 35

where are conscious and unconscious stimuli sent to in the brain respectively

Answer 35

conscious stimuli sent to cerebrum

unconscious sent to cerebrum and cerebellum

conscious and unconscious sensations are interchangeable in the cerebrum

Question 36

blood supply to the SC portion of the anterolateral system

Answer 36

posterior to anterior spinal arteries

Question 37

blood supply to the medulla portion of the anterolateral system

Answer 37

posterior spinal aa

branches from PICA

Question 38

blood supply to the anterolateral system from midbrain higher follows the same blood supply as what

Answer 38

DCML

Question 39

what is PICA syndrome

Answer 39

aka lateral medullary/wallenberg syndrome

alternating hemiplegia

impairments in pain, temp, crude touch

S&S = contralateral body and ipsilateral face

Question 40

with PICA syndrome, why are the symptoms contralateral on the body but ipsilateral on the face

Answer 40

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

Question 41

describe the return of somatic sensation following stroke

Answer 41

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

Question 42

A delta fibers give what information about pain

Answer 42

perception of pain

localized/conscious/cortical

can pinpoint exact location

Question 43

C fibers give what info about pain; signals sent where?

Answer 43

diffuse pain/subcortical/unconsious awareness

chronic pain/suffering

signals sent to medulla RF, other parts of RF, hypothalamus, and limbic system

Question 44

function of valium with pain

Answer 44

aka benzodiazepines

decrease the unpleasant pain but it still exists

Question 45

describe how central sensitization occurs with chronic pain/how nociplastic pain occurs

Answer 45

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

Question 46

what is allodynia

Answer 46

pain sensation to non-noxious stimuli