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

Lecture 2 + Assignment 2 Flashcards

1
Q

Perception according to Aristotle vs. Oscar Wilde

A

A:
- brain isn’t responsible for any sensations
- like heartbreak

OW:
- in the brain everything takes place

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2
Q

Brain relation to perception

A
  • wherever we feel something, it’s due to brain activity

sensory stimuli -> electrical impulses/action potentials -> brain

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3
Q

Johannes Muller conduction belief

A
  • thought we’ll never be able to measure the velocity of a nervous action because it’s faster than the speed of light
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4
Q

Hermann von Helmholtz conduction response

+ 2 experiments

A
  • Muller’s student

Motor nerves
- measured conduction speed in frogs by shocking nerve and measuring time till muscle contraction

Sensory nerves
- did the same with humans to see how long it took participants to perceive the signal
= response time till teeth clamped

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5
Q

Experiment in class results - stimulus to perception

A

close to brain
= perception occurs with little delay

far from brain
= perception occurs with longer delay

why?
- finite travel speed
- larger travel distance

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6
Q

Sensory and motor neurons = afferent or efferent

Also formulas for calculating

A

Sensory axon = afferent

(distance from ankle to brain - distance from shoulder to brain) / (ankle time - shoulder time)

Motor neurons = efferent

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7
Q

Receptor potentials causing action potentials

A
  • receptor potentials are graded
  • if the receptor potential is big enough, an action potential will start
  • they need to make it depolarize enough

action potentials = all-or-none

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8
Q

Parts of the action potential graph

A

-65 mV
resting potential

depolarization

-50 mV
threshold

rising phase
falling phase
takes ~1 sec

< -65 mV
afterhyperpolarization / AHP
(undershoot)

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9
Q

Goldman-Hodgkin-Katz equation

A

Vm = 58log[(Pk[K]out + PNa[Na]out)/(Pk[K]in + PNa[Na]in)]

  • permeability not constant, changes during action potential
  • no units
  • shows ions relative to each other
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10
Q

Rising vs. falling phase feedback loops

A

Fast positive feedback loop
- Signal depolarizes membrane potential
- Voltage-gated Na+ channels open
- Na+ rushes in

Slow negative feedback loop
- Voltage-gated K+ channels open
- K+ rushes out
- Hyperpolarizes neuron

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11
Q

Three states of the voltage-gated sodium channel

A
  1. Closed
    ㄱ
    - at rest
  2. Open
    —- ⊦–
    - initial depolarization
  3. Inactivated
    _」
    - top of action potential
    - repels positive charges
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12
Q

End of rising phase

A
  • Na+ channels inactivate
  • Na+ stops rushing in
  • no more depolarization
  • fast positive feedback loop ends
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13
Q

Falling phase

A
  • voltage-gated K+ channels open with a delay in response to depolarization
  • K+ channel opens and K+ leaves through the creaky / slow door
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14
Q

Three states of the voltage-gated

A
  1. Closed
    - almost always — - —-
  2. Open
    - during falling phase
    __ \___
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15
Q

Action potential shape in space vs. in time (sticky note/him in Hawaii example)

A
  • Velocity goes opposite direction as time
  • Action potential has the same shape in space as it does in time
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16
Q

Pros and cons of the refractory period

A

Pros
- ensures unidirectional a.p. conduction away from point of origin

Cons
- places limit on the firing rate of a neuron (could be good or bad)

17
Q

Relative vs. absolute refractory periods

A

Relative
- relatively more difficult to elicit another action potential
- due to hyperpolarization as K+ channel takes longer to close (so K+ keeps leaving the cell)
- not all Na+ channels have gone from inactivated to closed state

18
Q

Unidirectional conduction

A
  • action potentials only move in one direction along an axon
  • due to the refractory period / refractory wake
19
Q

Voltage clamp technique

A
  1. internal electrode measures membrane potential Vm and is connected to voltage clamp amplifier
  2. voltage clamp amplifier compares membrane potential with desired (command) potential
  3. if they’re different, clamp amplifier injects current into the the axon through a second electrode
    = membrane potential the same as the command potential
  4. current measured
20
Q

Squid giant axon experiment + results

A

1963 Hodgkin + Huxley

  • used voltage clamp to discover ionic basis of action potential

Membrane potential graphs
- start at the resting -65 mV potential
- goes to the voltage they set it to

Membrane current graphs
- current needed to keep it there
- slight dip as sodium enters the cell (early inward current)
- rises as potassium leaves the cell (late outward current)

  • IF membrane potential set to the Na equilibrium potential (52 mV in squid), no early inward current
21
Q

When is current positive or negative

A

Positive charge entering the cell = negative/downward current

22
Q

Permeability change graphs during an a.p.

A

aka conductance

Na+ peaks just before 1sec

K+ peaks just after 1sec
- conductance only gets half as high as Na+ was

23
Q

Local anesthetics

A
  • block voltage-gated Na+ channels
    —– >——
    block in-between gates
    —– +>——

ex. lidocaine
- eventually dissociates / pops out of the channel

24
Q

Tetrodotoxin (TTX)

A
  • in pufferfish ovaries and liver
  • produced by bacteria that live in the fish
  • 1200 times deadlier than cyanide
  • could kill 30 adult humans
  • “fugu” delicacy in japan
  • blocks Na channels
  • dissociates much slower than lidocaine
  • death by paralysis of respiratory muscles (going to diaphragm)
  • fish themselves have TTX-resistant Na channels and so do the hearts of mammals
25
Q

Saxitoxin (STX)

A
  • in butter clam (saxidomus giganteus)
  • in other shellfish too
  • from contact with toxic algal blooms
    = toxic dinoflagellates found in red tides
  • butter clams consume the algal bloom and store in their fatty tissue for a year
  • heat stable = not destroyed by cooking
  • causes paralytic shellfish poisoning

symptoms:
- start 1hr after consumption
- paresthesia
- pins and needles
- numbness
- paresis = difficulty moving
- respiratory difficulty

26
Q

Why is the voltage at the top of the rising phase never as high as the sodium equilibrium potential

A
  • because it’s always permeable to other ions
  • could only reach if zero permeability to K+
  • but there is always some K+ permeability due to leak channels
27
Q

If voltage-gated sodium channels blocked - in the case of TTX and lidocaine

A
  • no action potentials
28
Q

If voltage-gated potassium channels blocked

A
  • slower falling phase and no hyperpolarization undershoot AHP
29
Q

The firing rate code

A
  • maximum rate 500 AP/second for typical neurons
  • even when stimulus is very intense

PNB 2XB3 (Neuroanatomy) (5 decks)

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