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Biology171 > Electrophysiology > Flashcards

Electrophysiology Flashcards

1
Q

Describe the mechanisms that generate resting potentials in cells

A
  • Leak channels in membrane (usually open)
  • Gated channels in membrane (usually closed; open in response to stimulus)
  • Na+-K+-ATPase Pump (pumps 3 Na+ out per 2 K+ in)
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2
Q

Define Membrane Potential

A

Diff. in voltage (electrical gradient) btwn inside and outside of a cell
Exists in all living cells

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3
Q

Define Resting Potential

A

Membrane potential of non-excitable or excitable cells in their baseline (unstimulated) state

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4
Q

Define Graded Potential

A

A change in membrane potential w/ varying amplitude that is proportional to the stimulus

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5
Q

Define Action Potential

A

A rapid, stereotyped series of changes in membrane potential that is conducted along the axon of a neuron or t he membrane of a muscle fiber

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6
Q

Define Chemical (concentration) Gradient?

A

Unequal distribution of ions across cell membrane

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7
Q

Define Electrical Gradient (membrane potential)

A

Unequal distribution of positive and negative charges acros cell membrane

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8
Q

What is the Membrane Potential determined by?

A
  1. Concentration gradients of ions (& proteins) across the membrane (Na+, Ca2+, Cl- outside cell > inside)
  2. Membrane permeability to these ions (at rest, permeability to K+ > Na+ or Ca++)
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9
Q

What is the Equilibrium Potential of an Ion? (Eion)

A

Membrane potential (Vm) produced if membrane were permeable to only a single ion

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10
Q

Write the Nernst Equation

A

Eion = 61/z log ([ion]out/[ion]in)

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11
Q

What is the Goldman-Hodgin-Katz (GHK) equation?

A
  • Calculates resting membrane pot. (Vm) produced by all ions to which the membrane is permeable
  • Says Vm is determined by (conc. gradient) x (membrane permeability) for each ion
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12
Q

Describe the mechanism of a Graded Potential

A

Stimulus -> changes in ion permeability of neuron cell membrane (ion channels open or close) -> changes in membrane pot. -> electrical signals

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13
Q

Describe the 3 types of Stimuli involved in a Graded Potential

A
  1. Chemical stimuli -> open/close chemically gated ion channels (most neurons)
  2. Electrical stimuli -> open/close voltage-gated ion channels (all neurons)
  3. Mechanical stimuli (pressure, stretch, etc.) -> open or close mechanically gated ion channels (some sensory neurons)
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14
Q

What are the features of a Graded Potential?

A
  • Can be hyperpolarization or depolarization
  • Usually in dendrites and cell bodies
  • Variable in amplitude
  • Amplitude is proportional to strength of stimulus
  • Decay over time/space
  • Travel short distances
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15
Q

What are the features of an Action Potential?

A
  • Large depolarizations (~100mV)
  • Constant amplitude
  • Do not decay over time/space
  • “All or none”
  • Used for rapid, long-distance communication within individual neurons
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16
Q

Describe the mechanism of an Action Potential

A
  • Depolarization to threshold -> voltage-gated Na+ channels open rapidly, voltage-gated K+ channels begin to open slowly
  • Na+ rushes into cell, down electrical/chemical gradients
  • Cell depolarizes, overshoots
  • Voltage-gated Na+ channels close, voltage-gated K+ channels open
  • K+ rushes out of cell, down its electrical/chemical gradients
  • Cell repolarizes, hyperpolarizes
  • Voltage-gated K+ channels close
  • Cell returns to resting potential
17
Q

During and Action Potential, why do voltage-gated Na+ channels close while the neuron is depolarized? (describe the mechanism)

A
  • At resting membrane potential, the activation gate closes the channel
  • Depolarizing stimulus arrives at the channel. Activation gate opens
  • With activation gate open, Na+ enters the cell
  • Inactivation gate closes and Na+ entry stops
  • During repolarization caused by K+ leaving the cell, the 2 gates reset to their original position
18
Q

How do neurons return to resting potential after Action Potentials?

A
  • Membrane permeability to Na+ and K+ returns to normal
  • Na+/K+ ATPase pumps Na+ out of and K+ into the cell
    (but each AP involves movement of a small fraction of Na+ and K+ ions around neuron so it doesn’t significantly change the ion conc. gradients across the membrane –> a neuron can conduct many APs before it must use the Na+/K+ ATPase to reset ion conc. gradients)
19
Q

Describe Absolute Refractory Period and its significance

A

Na+ channels cannot be activated; no AP’s possible

  • prevents overlap of APs
  • prevents backwards propagation of APs
  • lasts ~2msec
20
Q

Describe Relative Refractory Period and its significance

A

some Na+ channels cannot be activated; K+ channels still open

  • APs can be triggered by large graded potentials
  • APs are smaller than normal (because K+ channels still open)
  • lasts ~2msec
21
Q

Describe how an Action Potential is propagated down an axon (involving local current flow)

A
  • Depolarization of one segment of membrane -> local current flow -> depolarization of adjacent segments
  • Voltage-gated Na+ channels open in adjacent segments of membrane
  • AP is re-generated at each segment of axon
  • Refractory period prevents backwards propagation of AP
22
Q

In a small axon, APs conducted continuously travel at only ~5m/sec. How can we speed this up?

A
  1. Increase diameter of axon
    - increased axon diameter -> decreased membrane resistance to ion flow -> increased speed of AP conduction
    - [but neurons would be too big to fit_
  2. Insulate the axon
    - Myelin -> decreased leakage of ions into ECF -> exit cell only at nodes of Ranvier (only nodes contain voltage-gated Na+ channels)
    - AP is generated only at nodes (saltatory conduction)
    - Increased rate of conduction (~150m/sec)
23
Q

Describe Saltatory Conduction

A
  • APs jump from one node of Ranvier to the next

- Only nodes have voltage-gated Na+ channels

24
Q

In demyelinating diseases, why does conduction slow?

A

current leaks out of the previously insulated regions between the nodes

25
Q

Where is the Neurotoxin, Tetrodotoxin (TTX) from? What does it do?

A
  • from pufferfish, some newts, toads, octopus, starfish, etc.)
  • Blocks some types of voltage-gated Na+ channels
26
Q

Where is the Neurotoxin, Maurotoxin (MTX) from? What does it do?

A
  • from scorpions

- Blocks some types of voltage-gated K+ channels

27
Q

Where is the Neurotoxin, Batrachotoxins (BTX) from? What does it do?

A
  • from poison dart frogs

- Activates voltage-gated Na+ channels in the peripheral NS

28
Q

What do local anesthetics such as novocaine, lidocaine, procaine do?

A

Block voltage-gated Na+ channels

29
Q

What is Hyperkalemia? How does it affect the generation of APs?

A
  • increased [K+] in blood
  • resting potential is less negative (less polarized)
  • APs are initiated more readily
  • Decrease K+ concentration gradient -> decrease leakage form neuron
30
Q

What is Hypokalemia? How does it affect the generation of APs?

A
  • decreased [K+] in blood
  • resting potential is more negative (more polarized)
  • APs are initiated less readily
  • Increase K+ concentration gradient -> increase leakage from neuron
31
Q

Describe Multiple sclerosis

A
  • Demyelinating disease (destruction of myelin in the CNS)
  • Though to be an autoimmune disease
  • Leads to slowing or cessation of AP conduction, and nerve damage
  • Symptoms may include fatigue, muscle weakness, loss of vision and hearing, inability to walk or speak, partial or complete paralysis, abnormal sensations)
  • Irreversible

Biology171 (3 decks)

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