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Flashcard 1

Front:
What determines the resting potential of a cell?

Back:
The resting potential is determined largely by the difference in K⁺ concentration between the inside and outside of the cell, along with a small Na⁺ permeability. The Goldman-Hodgkin-Katz (GHK) equation accurately predicts the resting potential.

Flashcard 2

Front:
What is the typical resting membrane potential of a neuron?

Back:
The resting membrane potential is about -70 mV , with the inside of the cell being more negative than the outside.

Flashcard 3

Front:
Why can't neurons transmit signals over long distances with only K⁺ channels?

Back:
Signals would die out quickly because:

  1. Positive charges injected into the axon are attracted to negative charges lining the membrane but dissipate quickly.

  2. Depolarization reduces the negativity inside the cell, decreasing the electrical force holding K⁺ in, causing K⁺ efflux and restoring the resting potential.

Flashcard 4

Front:
What are voltage-gated ion channels?

Back:
Voltage-gated ion channels are proteins in the cell membrane that open or close in response to changes in membrane potential. They include voltage-gated sodium (Na⁺) channels and voltage-gated potassium (K⁺) channels , which generate action potentials.

Flashcard 5

Front:
What are the two gates in voltage-gated sodium (Na⁺) channels?

Back:

  1. Activation gate : Closed at rest, opens with depolarization.

  2. Inactivation gate : Open at rest, closes shortly after the activation gate opens.

Flashcard 6

Front:
What happens when the activation gate of a voltage-gated Na⁺ channel opens?

Back:
Na⁺ ions flow into the cell, driven by both their concentration gradient and the electrical attraction of the negatively charged interior. This causes rapid depolarization of the membrane potential.

Flashcard 7

Front:
What is the role of the inactivation gate in voltage-gated Na⁺ channels?

Back:
The inactivation gate closes shortly after the activation gate opens, stopping the influx of Na⁺ ions. This self-limiting mechanism ensures the channel remains open for only about 1 ms .

Flashcard 8

Front:
What is the sequence of events during an action potential?

Back:

  1. Depolarization : Na⁺ channels open, allowing Na⁺ influx and driving the membrane potential to +55 mV .

  2. Repolarization initiation : Inactivation gates begin to close, shutting off Na⁺ influx.

  3. Rapid repolarization : Voltage-gated K⁺ channels open, causing K⁺ efflux and returning the membrane potential to a very negative value.

  4. Undershoot : Membrane potential becomes more negative than the resting potential.

  5. Resetting : Both Na⁺ and K⁺ channels reset, ready to generate another action potential.

Flashcard 9

Front:
What is the refractory period, and why does it occur?

Back:
The refractory period is the time after an action potential during which another action potential cannot be generated. It occurs because:

  1. The Na⁺ channel activation gate is closed, and the inactivation gate is still plugged.

  2. Voltage-gated K⁺ channels remain open, causing K⁺ efflux and hyperpolarizing the membrane.
    This limits the maximum firing rate of neurons to about 1000 spikes/sec .

Flashcard 10

Front:
What is meant by the "all-or-none" nature of action potentials?

Back:
An action potential is an all-or-none event:

  • If the membrane potential reaches the threshold (about -55 mV ), an action potential is triggered, driving the membrane potential to +55 mV .

  • Subthreshold depolarizations do not produce action potentials because K⁺ efflux balances Na⁺ influx.

Flashcard 11

Front:
What is Ohm's Law, and how is it applied to ion channels?

Back:
Ohm's Law relates current (I), conductance (g), and driving force (Eion - Vm):

I=g×(Eion​−Vm​)

  • Membrane Potential (Vm) : The electrical potential difference across the cell membrane.

  • Current (I) : Flow of ions through channels.

  • Conductance (g) : Ease with which ions pass through channels.

  • Driving Force : The net force driving ions into or out of a cell, calculated as Eion​−Vm​.

Flashcard 12

Front:
What is the voltage clamp technique, and why is it important?

Back:
The voltage clamp technique holds the membrane potential constant while recording ion currents. It allows researchers to:

  1. Measure Na⁺ and K⁺ currents separately.

  2. Calculate conductances using Ohm’s Law.

  3. Understand the dynamics of ion channels during an action potential.

Flashcard 13

Front:
How did Hodgkin and Huxley use the voltage clamp to study ion channels?

Back:
Hodgkin and Huxley used the voltage clamp to:

  1. Hold the membrane potential constant.

  2. Measure inward (Na⁺) and outward (K⁺) currents.

  3. Separate Na⁺ and K⁺ currents using substitution experiments (e.g., removing Na⁺ or adding toxins like TTX or TEA).

  4. Calculate conductances and plot their time courses.

Flashcard 14

Front:
What is the role of tetrodotoxin (TTX) in studying ion channels?

Back:
TTX is a neurotoxin that selectively blocks voltage-gated Na⁺ channels. When applied, it eliminates the inward Na⁺ current, proving that the early inward current during an action potential is carried by Na⁺.

Flashcard 15

Front:
What is the role of tetraethylammonium (TEA) in studying ion channels?

Back:
TEA selectively blocks voltage-gated K⁺ channels. When applied, it eliminates the delayed outward K⁺ current, proving that the outward current during an action potential is carried by K⁺.