Action Potentials

These flashcards cover key terms and concepts related to action potentials in biological systems, specifically focusing on neuron function and communication.

What is the resting membrane potential of a neuron?

-70 millivolts.

What are excitable cells?

Cells that can respond to a stimulus and have a measurable membrane potential.

What device is used to measure membrane potential?

A voltmeter.

What is an action potential?

A change in membrane potential that allows neurons to communicate with other cells.

What is depolarization?

The process of the membrane potential moving from a negative to a positive value.

What is the threshold potential for neurons?

-55 millivolts.

What ion predominantly causes depolarization during an action potential?

Sodium (Na+).

What is sodium influx?

The movement of sodium ions into the cell, contributing to depolarization.

What happens to sodium channels at +30 millivolts?

They inactivate and stop allowing sodium to enter.

What is repolarization?

The process of returning the membrane potential back to a negative value after depolarization.

What ion causes repolarization?

Potassium (K+).

What is hyperpolarization?

A state where the membrane potential becomes more negative than the resting potential.

What is the role of the sodium-potassium pump?

To maintain resting membrane potential by moving sodium out and potassium in.

What are the three states of voltage-gated sodium channels?

Closed, open, and inactivated.

What is the permeability of sodium during depolarization?

High permeability due to open voltage-gated sodium channels.

What happens during the overshoot of the action potential?

The membrane potential reaches beyond 0 mV and approaches +30 mV.

What is meant by 'all or none phenomenon'?

If the threshold is met, an action potential occurs fully; otherwise, it doesn't occur.

What is a graded potential?

A localized change in membrane potential that can vary in size and decays over distance.

How do graded potentials lead to action potentials?

If they reach threshold, they can trigger voltage-gated sodium channels to open.

What does it mean that graded potentials are decremental?

Their strength diminishes as they move away from the point of stimulus.

What is the significance of the axon hillock?

It's the site where graded potentials are summed to determine if an action potential will occur.

What two types of channels contribute to action potentials?

Voltage-gated sodium channels and voltage-gated potassium channels.

What happens during the repolarization phase?

Potassium moves out of the cell, causing the membrane potential to decrease.

What occurs during the hyperpolarization phase?

Membrane potential becomes more negative, reaching around -90 mV.

What prevents action potentials from losing strength as they travel down an axon?

The regenerative nature of voltage-gated sodium channels.

What is the role of chemically gated channels in neurons?

They respond to neurotransmitters to create graded potentials.

How does an action potential travel down an axon?

Through the sequential opening and closing of voltage-gated sodium and potassium channels.

What is the peak of an action potential?

+30 millivolts.

What happens to potassium channels during the action potential?

They open to allow potassium to leave the cell, contributing to repolarization.

What is the main purpose of an action potential in neurons?

To transmit signals along the axon to communicate with other cells.

What role does calcium play in neurotransmitter release?

Increases intracellular calcium levels trigger vesicles to release neurotransmitters.

What occurs during the inactivation of sodium channels?

Channels become non-conductive and stop allowing sodium to enter.

What is the resting membrane potential maintained by?

Leak channels and the sodium-potassium pump.

What is sodium efflux?

The movement of sodium ions out of the cell, typically not occurring during action potentials.

How are action potentials different from graded potentials?

Action potentials are all-or-nothing and propagate without diminishing, while graded potentials vary and diminish.

What happens when neurotransmitters bind to chemically gated channels?

They cause localized depolarization and may trigger an action potential if threshold is reached.

What is the role of the extracellular environment on membrane potential?

It determines the charge difference across the membrane essential for action potentials.

How is the action potential regenerated down the axon?

By local depolarization opening adjacent voltage-gated sodium channels.

What is meant by voltage-gated channels?

Channels that open/close in response to changes in membrane voltage.

Why do action potentials occur in a 'domino effect'?

Depolarization at one segment of the axon triggers depolarization in the adjacent segment.