Action potential

Your body sends fast signals.

These signals move like tiny sparks. They help your muscles move. They also help you think. This is how you feel things.

Inside your cells, tiny gates open and close. These gates let small bits move in and out. When bits move in, the cell gets a spark. This spark travels down a long path. It only moves in one direction.

This spark tells your body what to do. It can make a muscle pull. It can tell a gland to work. Even plants use these sparks! These fast signals help all living things work well.

Your body uses fast signals to work. Scientists call these signals action potentials.

They are quick changes in electric power. These changes happen across a cell membrane. A membrane is the thin skin around a cell.

Most cells have a steady electric charge. This is called a membrane potential. In many cells, the inside is more negative than the outside.

Action potentials happen in steps. First, the cell must reach a threshold. This is a specific level of electric charge. When it hits this level, tiny gates open. These gates are called voltage-gated ion channels.

These channels let small bits called ions move. Sodium ions rush into the cell. This makes the inside more positive. This step is called depolarization.

Next, the cell must reset. Potassium channels open up. Potassium ions move out of the cell. This change is called repolarization. This brings the cell back to its resting state. In neurons, these signals travel down a long path called an axon. They can move very fast. In some neurons, it takes only a tiny fraction of a second! These signals help muscles move and help cells talk to each other.

An action potential is a very fast electrical signal. It is also called a nerve impulse or a spike.

These signals are vital for many living things. They help animal cells like neurons and muscle cells talk to each other. Even some plant cells and endocrine cells can use them. In the pancreas, these signals help release insulin. In muscle cells, they are the first step to making the muscle contract.

To understand how it works, look at the cell membrane. The membrane is like a thin skin around the cell. It acts as an insulator to keep charges separate. Inside the cell, there is a resting potential of about -70 mV. This means the inside is more negative than the outside.

For a signal to start, the cell must reach a threshold potential. In a typical neuron, this happens at -55 mV. When the cell hits this level, special gates called voltage-gated ion channels open up.

The signal happens in a quick series of steps. First, sodium channels open and sodium ions rush into the axon. This makes the inside more positive, which is called depolarization. This causes even more channels to open in a fast cycle. Next, the sodium channels close and the cell must reset. Potassium channels open and potassium ions move out of the axon. This step is called repolarization. It brings the charge back toward its resting state.

Scientists have learned a lot about these tiny electrical jumps. Alan Hodgkin and Andrew Huxley studied these channels deeply. Their work on the biophysics of action potentials won them a Nobel Prize.

They studied what are now called Hodgkin-Huxley sodium channels. There are different types of these electrical spikes. Sodium-based spikes usually last less than one millisecond. However, calcium-based spikes can last 100 milliseconds or much longer.

You can think of an action potential like a wave in the ocean. One part of the wave moves, which then triggers the next part. In a neuron, the impulse travels down a long path called an axon. It moves in only one direction toward the axon terminal.

This allows the signal to reach other neurons or glands. This process is how your brain tells your body what to do. It is a wonderful way that nature uses electricity to share information.

An action potential is a rapid series of voltage changes across a cell membrane.

It is also known as a nerve impulse or a "spike." These electrical signals are essential for communication in many living systems. They allow neurons to send messages to other cells. They also trigger important functions in muscle cells and endocrine cells. In the pancreas, for example, these impulses provoke the release of insulin.

To understand this process, we must look at the cell membrane. The membrane is a lipid bilayer, which is a thin layer of molecules. This bilayer acts as an insulator to prevent charges from moving freely. Embedded within this membrane are large proteins called voltage-gated ion channels. These channels act like gates that open or close based on the electrical charge. Most cells maintain a resting potential, which is a steady voltage difference. In animal cells, the interior is typically around -70 mV relative to the exterior.

An action potential begins when the membrane potential reaches a specific threshold. In a typical neuron, the resting potential is -70 mV, but the threshold is about -55 mV. When a stimulus causes the voltage to rise to this threshold, a massive change occurs. This process is driven by a positive feedback loop involving sodium ions. First, voltage-gated sodium channels open up. This allows sodium ions (Na+) to rush into the axon. This influx makes the inside of the cell more positive, a process called depolarization.

As the interior becomes more positive, it causes even more sodium channels to open. This creates an explosive cycle where the membrane potential shoots upward. The potential can reach a peak of approximately +40 mV. Once the channels are fully open, they rapidly inactivate and close. To reset the cell, potassium channels then open. This allows potassium ions (K+) to move out of the axon. This outward flow is called repolarization, which returns the charge toward the resting state.

Sometimes, the voltage drops even lower than the resting potential. This transient negative shift is known as afterhyperpolarization. Because only a small number of ions move, the total concentrations of ions do not change much. The cell eventually reestablishes its resting potential of -70 mV. The entire up-and-down cycle in a mammalian neuron takes only a few thousandths of a second. In contrast, action potentials in plant cells may last for several seconds.

There are different types of action potentials depending on the cell. In animal cells, the two primary types use different ions. Sodium-based action potentials are very fast, usually lasting under one millisecond. Calcium-based action potentials are much slower and may last 100 milliseconds or longer.

In some neurons, slow calcium spikes help drive bursts of fast sodium spikes. In cardiac muscle cells, a fast sodium spike acts as a primer for a calcium spike. This calcium spike is what ultimately produces muscle contraction.

Our understanding of these mechanisms comes from groundbreaking scientific work. Alan Hodgkin and Andrew Huxley characterized the biophysics of these channels. Their research on sodium channels earned them a Nobel Prize. These are often called Hodgkin-Huxley sodium channels or NaV channels.

They discovered that these channels switch between deactivated, activated, and inactivated states. This discovery helped explain how electrical signals propagate through the nervous system. The impulse travels down the axon in one direction toward the axon terminal.

Once it reaches the end, the signal can connect with other neurons at synapses or trigger glands. This precise movement of ions is how life processes information and movement.