AP Bio nervous system action potential cheat sheet

What triggers an action potential?

A stimulus that depolarizes the membrane to threshold potential, typically around -55 mV.

Define depolarization in action potentials.

A decrease in membrane potential, making it more positive. Sodium (Na+) influx is primarily responsible.

Threshold potential value?

Approximately -55 mV; the critical level for action potential initiation.

What happens during repolarization?

Potassium (K+) channels open, allowing K+ to exit, restoring resting membrane potential.

True or False: Action potentials are graded responses.

False. Action potentials are all-or-nothing responses, not graded.

Order the phases of an action potential:

1. Resting, 2. Depolarization, 3. Repolarization, 4. Hyperpolarization.

What role do voltage-gated Na+ channels play?

They open during depolarization, allowing Na+ to flow in and further depolarize the cell.

Fill in the blank: The _________ period prevents immediate re-excitation.

Refractory.

Compare action potential and graded potential.

Action potentials: all-or-nothing, long distance. Graded potentials: variable amplitude, short distance.

What restores the resting membrane potential?

Sodium-potassium pump (Na+/K+ ATPase) and K+ efflux during repolarization.

Identify the ion primarily responsible for depolarization.

Sodium (Na+).

Name the phases where Na+ and K+ currents are highest.

Na+: during depolarization. K+: during repolarization.

What is hyperpolarization?

An increase in membrane potential, making it more negative than resting potential.

What causes the rapid rise of the action potential?

Opening of voltage-gated Na+ channels.

Explain the all-or-nothing principle.

An action potential occurs fully or not at all; it cannot be partial.

Calculate the equilibrium potential for K+ if [K+] inside = 140 mM, outside = 4 mM.

Use Nernst equation: $\displaystyle E_K = 61.5 imes ext{log} \left( \\frac{[K^+]_{inside}}{[K^+]_{outside}} \right) \approx +90 mV$.

What is resting membrane potential?

The resting membrane potential is typically around -70 mV, maintained by the sodium-potassium pump and leak channels.

True or False: Action potentials are all-or-nothing events.

True. Once threshold is reached, an action potential is generated; smaller stimuli do not produce an action potential.

Fill in the blank: The primary ions involved in action potentials are __________ and __________.

Sodium (Na+) and Potassium (K+).

What happens during depolarization?

During depolarization, Na+ channels open, allowing Na+ to enter the cell, causing the membrane potential to increase towards 0 mV.

What is the role of voltage-gated ion channels?

Voltage-gated ion channels open or close in response to changes in membrane potential, crucial for action potentials.

Compare resting potential and action potential.

Resting potential: stable, negative; Action potential: transient, positive change.

Cause → Effect: Opening of K+ channels during action potential.

Effect: Repolarization of the membrane, returning to resting membrane potential.

Which channels open first during an action potential?

Voltage-gated Na+ channels open first, causing rapid depolarization.

What is threshold potential?

Threshold potential is typically around -55 mV, the level that must be reached to trigger an action potential.

During repolarization, which ion primarily moves out of the cell?

Potassium (K+) moves out of the cell, contributing to the return to resting potential.

True or False: The sodium-potassium pump requires ATP.

True. The sodium-potassium pump actively transports Na+ out and K+ into the cell using ATP.

What is hyperpolarization?

Hyperpolarization occurs when the membrane potential becomes more negative than resting potential, often due to excess K+ efflux.

List the phases of an action potential.

1. Resting Phase 2. Depolarization 3. Repolarization 4. Hyperpolarization

What is the Nernst equation used for?

The Nernst equation calculates the equilibrium potential for a specific ion based on concentration gradients.

Cause → Effect: Increased extracellular K+ concentration.

Effect: Depolarization of the cell, potentially leading to altered excitability.

What is the significance of the refractory period?

It ensures unidirectional propagation of action potentials and limits the frequency of action potentials.

What is action potential propagation?

The process by which an action potential travels along the axon, involving sequential depolarization and repolarization of the membrane.

Compare continuous and saltatory conduction.

Continuous conduction: unmyelinated axons, slower, involves every segment. Saltatory conduction: myelinated axons, faster, jumps between nodes of Ranvier.

What is the significance of refractory periods?

Refractory periods prevent the backward propagation of action potentials, ensuring unidirectional flow and limiting the frequency of firing.

True or false: Absolute refractory period allows for a new action potential.

False. During the absolute refractory period, no action potential can be initiated regardless of stimulus strength.

Fill in the blank: The ________ refractory period follows the absolute refractory period.

relative

Define the absolute refractory period.

The absolute refractory period is when a neuron cannot fire a second action potential, regardless of stimulus strength. This occurs during depolarization and the initial repolarization phase.

Fill in the blank: The ________ refractory period allows for a stronger than normal stimulus.

relative

True or false: During the absolute refractory period, a neuron can respond to a stimulus.

False - No response is possible due to inactivation of Na⁺ channels.

What prevents backward propagation of action potentials?

The refractory periods ensure that action potentials propagate in one direction, as previously activated segments of the axon are temporarily unresponsive.

Compare the duration of absolute and relative refractory periods.

Absolute refractory period lasts about 1-2 ms. Relative refractory period lasts longer, around 4-6 ms.

Cause → Effect: What causes the refractory period?

Inactivation of Na⁺ channels causes the refractory period, preventing immediate re-excitation.

Calculate: If an action potential lasts 2 ms, how long until another can occur?

At least 2 ms (absolute) + 4 ms (relative) = 6 ms before another action potential can be generated.