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PNB 2XB3 (Neuroanatomy) > Lecture 4 + Assignment 4 > Flashcards

Lecture 4 + Assignment 4 Flashcards

1
Q

Spinal segment order

A

Cervical

Thoracic

Lumbar

Sacral

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2
Q

What do the spinal segments control

SLTC on the diagram

A

Trigeminal nerve
= front of head

Cervical
= behind ear/headband area to fingertips

Thoracic
= chest and underside of arms

Lumbar
= above hips down

Sacral
= butt and bits, the back of legs

look at pic of person touching the floor without bending their knees

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3
Q

Spinal cord slice components + how is thoracic different

Grey and white matter

A

White matter = myelinated axons

Gray matter = cell bodies and dendrites

Gray matter makes a butterfly with dorsal horns

Thoracic = smaller butterfly so less motor control

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4
Q

From fingertip to CNS pathway

DCML and STT

A
  1. Receptor endings

2.a) Abeta mechanosensory afferent fiber
b) Adelta or C axons pain and temperature afferent fibers

  1. Dorsal root ganglion (neuron cluster)

4.a) Abeta to dorsal column
b) Adelta/C CROSSES OVER to ventral spinothalamic tract
=anterolateral

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5
Q

Three types of somatosensory axons - facts + examples

A
  1. A Beta
    Mechanoreceptive
    touch
    merkel, meissner, pacinian, and ruffini cells
  2. A Delta
    Thermo/nociceptive
    pain, temp.
    free nerve endings
  3. C
    Thermo/nociceptive
    pain, temp., ITCH
    unmyelinated free nerve endings
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6
Q

Three types of somatosensory axons - speeds + diameters

A

A beta
- 35-75 m/s
- 6-12 nm

A delta
- 5-30 m/s
- 1-5 nm

C
- 0.5-2 m/s
- 0.2-1.5 nm

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7
Q

First and second pain

A
  1. touch sensation through Abeta axons
  2. first pain through Adelta axons
  3. second pain through c axons
  • fastest to slowest axon conductance speeds
  • due to myelination and diameter
  • we become aware of sensations when APs reach the cortex
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8
Q

Why does second pain last much longer

A
  • there is a range of velocities
  • all different “racers”
  • large diameter racers in a “team” (axon type) move faster
  • keep feeling the sensation until all team members have passed the finish line
  • difference between fastest and slowest Adelta speeds still much smaller than for the C axons
  • also gap until first of second pain racers gets there
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9
Q

Somatosensory tracts

A

DCML
- A beta
- decussates in the caudal medulla (in brain)
- after synapse 1/3 at the dorsal column nuclei

STT
- A delta and C axons
- decussates immediately

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10
Q

Somatosensory tracts - topography

A

DCML
- more caudal entry = more medial
(longest in the middle)

STT
- more caudal entry = more lateral
(longest on the side)
SWITCH TO OPPOSITE SIDE

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11
Q

Somatosensory tracts - diagrams

A

Dorsal
(A betas)
- stays on the same side
CTLS SLTC
TLS SLT
LS SL
S S

Ventral
(A deltas and Cs)
- swaps sides immediately
SLTC CTLS
SLT TLS
SL LS
S S

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12
Q

Picking lesion locations

A
  1. Touch or pain/temperature
    touch = DCML (dorsal)
    p/t = STT (ventral)
  2. Right or left
    DCML: injury right = feel on right
    ipsilateral
    STT: injury right = feel on left
    contralateral
  3. Dermatome location
    CTLSSLTC dorsal

SLTCCTLS ventral

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13
Q

Central cord syndrome / syringomyelia

A

no pain/temp in bolero region

C4-T1

single lesion in center of spinal cord

  • prevents decussating of second order neurons
  • affects both sides
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14
Q

Brown-sequard syndrome

A

Lower thoracic injury

Ipsilateral loss of touch sensation

Contralateral loss of pain and temperature sensation

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15
Q

Sensory cell pathway - touch

4 things

A

All A beta

  1. Meissner corpuscle
  2. Merkel-cell neurite complex
  3. Ruffini ending
  4. Pacinian corpuscle
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16
Q

Different sensory cells - mechanoreceptors

receptive field size + respond best to

A

Meissner
- small
- low frequency vibrations (2-50)

Merkel
- small
- static indentation

Ruffini
- large
- skin stretch (dynamic)

Pacinian
- large
- high frequency vibrations (50+ Hz)

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17
Q

Benefit of vibration sensation

A
  • lets us feel textures, slippage, and light vibration of tools
  • low frequency = feeling texture
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18
Q

Stimulus-response graphs

  • adaption types
A

Slowly adapting
- merkel and ruffini
- first fast dynamic phase, then static phase
|||| | | | | | |

Rapidly adapting
- meissner and pacinian
||||
- only respond initially

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19
Q

Ellen Lumpkin - merkel mechanotransduction

what do piezo let in

A

Merkel cells
- mechanically-gated piezo cation channels sensitive to pressure
- cation nonspecific, allow any in once they feel pressure

  • merkel cells release neurotransmitters to Abeta axon
  • similar to neurons bc have channels (piezo and Ca) + release neurotransmitters
20
Q

Ardem Patapoutain

A
  • Nobel prize in physiology or medicine in 2011
  • piezo mechanically gated ion channels
21
Q

Merkel cell mechanotransduction overview

A
  1. Piezos in Abeta open and let in ions
  2. Causes dynamic phase action potentials
  3. Piezos in Merkel open and let in ions
  4. Depolarizes Merkel = opens voltage-gated Ca channels
  5. Neurotransmitter (norepinephrine) released onto Abeta terminal
  6. Causes static phase action potentials
22
Q

Two-point discrimination

A

If points have a faster spike rate in the single middle circle (b) than in the two side circles (a/c):

AP will be felt as one point

23
Q

Two-point discrimination - best and worst spots

A

Best (most accurate)
- shoulder + arm
- torso + leg

Worst (least accurate)
- toes + fingers
- cheek + nose + lip + forehead

24
Q

Goldreich two-point discrimination experiment

A

2POD: two-point orientation discrimination

  • instead of 2v1 points = tactile spatial acuity..

determine orientation

25
Q

Why receptive fields smaller on finger than forearm

A

1 A-beta axon:3-5 merkel cells

Merkel cells more densely packed on fingers

Smaller receptive field contains the same # of cells

26
Q

Thalamus

contains what

A

VPL
- ventral posterior lateral nucleus receives signals from the body axons
- from the dorsal column nuclei

LGN
- lateral geniculate nucleus info from the retina

  • different parts of the nucleus receive info from different parts
27
Q

Primary somatosensory cortex (S1)
+ subdivisions

A

More caudal than central sulcus

In order:
3a - proprioceptive (movement, action, location)

3b - light touch, small receptive fields

1 - light touch, large multi-digit rfs

2 - proprioceptive and light touch

shape: ^
3a/3b by central sulcus
1 at top
2 by posterior parietal complex

28
Q

Homunculus

A
  • coronal slice

most lateral
- tongue
- face
- arm
- trunk
- leg
- foot
- toes
- genitalia

29
Q

Ratunculus

A
  • vibrissae / whiskers
  • barrels in cortex level IV respond to specific whiskers
30
Q

Owl monkey amputation

A
  • somatic sensory cortex
  • third finger amputated
  • second and fourth finger representations take up the brain space after 2 months

= somatosensory plasticity from deafferentiation

31
Q

Phantom limb

A
  • nerve endings still send pain signals although limb is gone
  • feel like the limb is still there
  • especially first few years after amputation
  • phantom limb shrinks over time
32
Q

Sensory cell pathway - temp and pain

A
  1. Free nerve endings
  2. Axons
33
Q

STT pathway

A
  1. Nociceptors and thermoreceptors
  2. Adelta and C axons
  3. Spinothalamic tract
  4. Thalamus / VPL nucleus
  5. Thalamocortical axons
  6. Parietal cortex (S1)
34
Q

Hot vs. cold receptors

A
  • some Abeta heat receptors, some cold
  • both slowly adapt
  • fire more when first made hot (heat receptors)
  • fire more when first made cold (cold receptors)
  • both fire less over time

= adaptation in thermoreceptors

35
Q

How heat receptors work

A
  • ion channels open in response to heat

“transient receptor potential channels”

  • open in response to heat = heat-gated
  • TRPV1 permeable to Na and Ca cations in
  • causes depolarizations and APs
  • allows us to know were getting warm
36
Q

Capsaicin - david julius

A

TRPV1 also responds to capsaicin in spicy peppers

  • lipophilic
  • goes straight through bilayer
  • binds to INTRAcellular TRPV1 channel
  • opens channel and makes us feel heat
37
Q

Menthol - Julius and Payapoutain

A
  • menthol/mint opens cold channels

TRPM8
- also permeable to Na and Ca

38
Q

Referred pain

A
  • you feel pain from an internal organ somewhere else in your skin
  • skin and organ afferent nerves converge onto a single dorsal horn neuron
  • brain infers pain from the place pain is more often felt = skin
39
Q

Gate hypothesis - rub stubbed toe to get rid of pain

A
  • Abeta mechanoreceptor and C fiber nociceptor neurons converge onto dorsal horn projection neuron (second order)
  • between Abeta and dorsal horn is an inhibitory interneuron/local circuit neuron
  • releases GABA or glycine = open Cl channels
  • when mechano activated, inhibits neuron that nociceptor also touches
  • makes slightly less pain bc reduces # of APs
40
Q

Extracellular recording

A

oscilloscope measures voltage changes

audio amplifiers hear APs

  • electrode oustide neuron bc brain inflates and deflates with heartbeats
    = hard to get inside brain that’s bouncing

extracellular graph kinda like upside down graph of AP
- smaller amplitude bc more ions not in a confined space
- Na enters cell so leaves extracellular space and makes it more negative

41
Q

Microelectrode mapping - vernon mountcastle

A
  • mapped different hand segments to parts of the brain

cortical columns
- same receptive field
- vertical

different receptive fields horizontally

42
Q

Cortical columns - order

A

2 mm thick in all mammals

  1. pyramidal cell
  2. local axon collateral
  3. stellate cell
  4. dendrites
  5. descending axon -> output
43
Q

Pyramidal vs. stellate cells

prevalence, function

A

Pyramidal cells
- projection neuron axons travel far
- excitatory (glutamate)
- 70% of cortical neurons

Stellate cells
- non-pyramidal
- interneuron
- aka local circuit neuron
- excitatory (glutamate) or inhibitory (GABA)
- 30% of cortical neurons

44
Q

Cortical column inputs and outputs

A

1 no cell bodies, yes axons and dendrites
2/3 sends axons to and receives axons from other cortical areas (including the opposite hemisphere)
4 receives axons from thalamus
5 sends axons to brainstem and spinal cord
6 sends axons to thalamus

45
Q

Enkephalinergic inhibitory local circuit interneuron

A

Enkephalin = peptide neurotransmitter

  • synapses axon terminal to axon terminal (instead of to dendrites) of C-fiber

= axo-axonic synapse

  • blocks voltage-gated Ca channels and opens K channels
  • reduces the release of neurotransmitters from the C-fiber onto the dorsal horn projection neuron
46
Q

Pain is personal

A

two ppl might feel the same amounts of pain differently
ex. placebo effect

pain -> amygdala -> raphe nuclei -> brain stem enkephalinergic interneuron APs

  • bc linked to amygdala activity activating enkephalin
  • goes to raphe nucleus

no enkephalin = no placebo

PNB 2XB3 (Neuroanatomy) (10 decks)

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