lecture 4: Neuronal action potential Flashcards

1
Q

What are **voltage gated **ion channels?

A
  • these channels open in response to a change in membrane potential
  • they give the membrane the ability to undergo action potentials
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2
Q

What are 2 important channels involved in the neuronal action potential?

A
  1. K+ voltage gated channel
  2. Na+ voltag gated channel
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3
Q

What are the** 3 states** of the Na+ voltage gated ion channel?

A
  • closed
  • open
  • inactivated
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4
Q

What are the** 2 states** for K+ voltage gated ion channels?

A
  • they are either
  • open or
  • closed
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5
Q

Explain the **differences **between Na+ and K+ voltage gated channels

A
  • Na+ channel **responds faster **to changes in membrane voltage (aka depolarisation)
  • Na+ channels have an extra feature in their structure called an** inactivation gate** which regulates the influx of Na+
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6
Q

Why is the resting membrane potential closer to the K+ equilibrium potential?

A
  • there are more open K+ chanels than Na+ channels
  • also due to the presence of K+ leak channels
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7
Q

What are the different steps for an action potential?

A
  1. RMP
  2. depolarising stimulus reaches threshold
  3. depolarisation
  4. peak AP
  5. repolarisation
  6. hyperpolarisation
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8
Q

Describe the mechanism of an action potential

A
  • At RMP, all voltage gated channels are closed
  • A **depolarising stimulus **(NT binding to receptor) causes membrane to reach **threshold
  • at threshold, all Na+ voltage gated channels are open and activated & there is a big depolarisation (influx of Na+)
  • At peak AP, the Na+ channel is inactivated, at the same time the K+ channel opens and K+ flows out of cell
  • Repolarisation occurs and there is a huge outflow of K+, returning it back to RMP
    *further movement of K+ out of cell causes hyperpolarisation (membrane even more neg than RMP)
  • then K+ gate closes, and membrane returns to RMP
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9
Q

in what direction does the action potential occur across the neuron?

A
  • from the cell body to the axon terminal
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10
Q

What is an absolute refractory period?

A
  • During an action potential, a second stimulus, no matter how strong will not produce a second AP
  • this region of the membrane is said to be in in its absolute refractory period
  • this occurs when the Na+ are beginning to become inactivated
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11
Q

What is a relative refractory period?

A
  • following the absolute refractory period, there is an interval, in which a** second action potential can be generated** - relative refractory period
  • but only if the stimulus is strong/depolarising enough
  • it occurs after the period of hyperpolarisation
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12
Q

Where along the axon are there a high density of Na+ voltage gated channels? What is the function of this?

A
  • the nodes of ranvier (gaps between myelin sheath)
  • this is to **rapidly propagate **the action potentials in myelinated axons
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13
Q

What is action potenial propagation?

A
  • the action potential in a region of a neuron will produce local currents that repolarize the region next to it, producing another AP at the next site
  • the** spread of AP along the neuron**
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14
Q

Explain saltatory conduction of action potentials

A

***myelin sheath **along axons acts as an insulator, but it has a **low concentration **of voltage gated Na+ channels
* therefore action potentials can only occur at the nodes of ranvier between the myelin sheath
* AP’s **jump from one node to the next **as they propagate along a myelinated fiber

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15
Q

What are examples of Na+ channels antagonist/ blocker drugs?

A
  • TTX - tetradotoxin
  • lidocaine
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16
Q

What are examples of K+ channel antagonists/blockers?

A
  • TEA
17
Q

How are nerve fibers classified into groups?

A
  • they are classified into either an** A or C group** based on** axon diamater** and **conduction velocites **
  • group A are myelinated and group C are unmyelinated
  • A group has 3 further sub groups - Aa, Ab or Ac
  • Aa has the largest axon diameter and fastest conduction velocity