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CBNS106 > Lecture 4 > Flashcards

Lecture 4 Flashcards

1
Q

What are other names for action potential?

A

spike
nerve impulse
discharge

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2
Q

What is action potential?

A

A rapid reversal of membrane potential where the inside becomes positively charged for 2-3 msec

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3
Q

What is synaptic transmission?

A

transfer of information from neuron to neuron
- frequency and pattern of action potentials constitute the code used by neurons to transfer information from one to another

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4
Q

How does action potential travel?

A

Starts at axon hillock (zone of integration) and travels down the axon to the presynaptic terminal (zone of output) = neurotransmitter release

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5
Q

Define depolarization

A

membrane voltage is more positive

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6
Q

Define hyperpolarization

A

membrane voltage is more negative

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7
Q

What results in depolarization?

A

Positive ion influx and negative ion efflux

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8
Q

What results in hyperpolarization?

A

positive ion efflux and negative ion influx

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9
Q

How is action potential generated?

A

Requires depolarization current
- occurs naturally via excitatory synaptic transmission
- artificially via current injection current into a neuron with microelectrode

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10
Q

What does the depolarizing current tell you about firing frequency from the generation of multiple action potentials?

A

Firing frequency reflects the magnitude of the depolarizing current.
Action potential firing rate increases as the depolarizing current increases
- if the current doesn’t depolarize the membrane to threshold, no action potential is generated
- if injected current depolarizes beyond threshold, action potentials will be generated

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11
Q

What’s the difference between electrical properties of neurons vs glia?

A

Neurons: electrically active - fire action potentials
Glia: electrically silent cells

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12
Q

What are the properties of the action potential?

A
  • caused by depolarization of membrane beyond threshold
  • All or None
  • Chain reaction
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13
Q

What is the graph readings of an action potential?

A

1) Resting potential
2) Rising phase
3) Overshoot
4) Falling phase
5) Undershoot (after-hyperpolarization)

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14
Q

What are the necessary characteristics for action potentials?

A

1) ~10 mV depolarization above rest for initiation
2) below threshold = none, above threshold = all
3) Always depolarizing
4) Constant amplitude ~100 mV
5) Constant duration ~2-3 msec
6) Propagate without decrement
7) 2 part refractory period: absolute during falling phase and relative during undershoot

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15
Q

What is depolarization and repolarization in terms of Na+ and K+?

A

Depolarization: influx of Na+
Repolarization: efflux of K+

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16
Q

What is membrane current?

A

net movement of K+ across membrane
potassium current = flow and driving force

17
Q

What’s the equation that links current, conductance, and driving force?

A

current = conductance* (membrane voltage - driving force)

18
Q

What’s the ins and outs of action potential?

A

Rising phase: inward sodium current
Falling phase: outward potassium current

19
Q

Define law of permeability.

A

Membrane potential is always driven toward the equilibrium potential of the ion to which the membrane is most permeable.

20
Q

What’s the purpose of Hodgkin and Huxley model?

A

Demonstrates properties of action potentials using patch-clamp electrophysiology
- rising phase = transient increase of influx of Na+ ions
- falling phase = increase in efflux of K+ ions

21
Q

What’s the structure of the voltage-gated sodium channels?

A

transmembrane domains and ion-selective pore

22
Q

What’s the difference between voltage when the voltage-gating sodium channel when it’s open vs. closed?

A

Closed: -65 mV
Open: -40 mV

23
Q

How does the voltage-gated sodium channel selective permeability?

A

Size exclusion filter
- partially hydrated Na+ ion fits
- partially hydrated K+ doesn’t fit

24
Q

What is the cycle of the voltage gated sodium channel?

A

Closed (-65 mV) -(~10 mV Depolarization)->
Open (-55 mV) -(~1 ms delay)->
Inactivated -(channel requires -Vm reset)->
Closed

25
Q

Define absolute refractory period.

A

Channels are inactivated

26
Q

What are some diseases associated with voltage-gated sodium channels?

A
  • Generalized epilepsy
  • Febrile seizures
27
Q

What are some toxins that target voltage-gated sodium channels?

A

1) tetrodotoxin (puffer fish) - clogs Na+ permeable pore
2) Red tide saxitoxin - Na+ channel-blocking toxin
3) Batrachotoxin (frogs) - blocks inactivation so channels stay open
4) Veratridine (lilies)
5) Aconitine (buttercups)

28
Q

Compare and contrast VGSC and VGKC

A

Both open in response to depolarization
- Potassium opens ~1 ms after sodium
- Potassium conductance serves to rectify or rest membrane potential

29
Q

When are the Na+ channels open when looking at the action potential graph?

A

At AP Threshold for initiation (~10 mV above baseline)

30
Q

When are Na+ channels inactive when looking at the action potential graph?

A

At the peak of the graph

31
Q

When are K+ channels open when looking at the action potential graph?

A

At the peak of the graph, when Na+ channels are inactive

32
Q

When are K+ channels closing when looking at the action potential graph?

A

At the lowest point of the graph, stopping K+ efflux

33
Q

When is the absolute refractory period? What happens here?

A

From the peak to threshold
VGSC inactivated

34
Q

When is the relative refractory period? What happens here?

A

VGSC are reactivated but membrane potential is below resting and would require greater depolarization current to fire another action potential than at rest

35
Q

What are factors influencing conduction velocity?

A
  • Spread of action potential along membrane (dependent on axon structure)
  • Path of positive charge (faster inside axon and slower across the axonal membrane)
  • Axonal excitability (bigger axonal diameter = faster) also depends on number of voltage-gated channels
  • Myelination
  • Saltatory conduction at nodes of Ranvier
  • VGSC concentrated at nodes
36
Q

What does orthodromic mean?

A

Action potential travels in one direction (down axon to the axon terminal)

37
Q

What does antidromic mean?

A

Backward propagation (only experimental)

38
Q

What is myelin?

A

layers of this facilitate current flow

39
Q

What is optogenetics? Where was it tested?

A

Introduction of foreign genes to express membrane ion channels (opens in response to light)
- tested in mouse brain

CBNS106 (9 decks)

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