Sistema Nervoso 5/6: Potencial de ação

Summary

This video explains the action potential in nerve cells, starting with the concept of resting membrane potential and how differences in ion concentrations (sodium and potassium) create electrical charge differences across the cell membrane. It then details how an electrical stimulus triggers the opening of sodium channels, leading to depolarization and a shift in membrane polarity. Following depolarization, potassium channels open, leading to repolarization, and the sodium-potassium pump restores ion balance. The process, which occurs in small sections along the neuron, enables the transmission of nerve impulses and follows the 'all-or-nothing' principle, ensuring reliable signaling throughout the body.

Takeaways

• 😀 Nerve cells and some other cells in the body have a voltage difference across their membrane, called membrane potential.
• 😀 The membrane potential results from differences in ion concentrations between the inside and outside of the cell.
• 😀 At rest, the inside of a nerve cell is negative relative to the outside, which is positive. This is called the resting membrane potential.
• 😀 Potassium (K+) is more concentrated inside the cell, while sodium (Na+) is more concentrated outside the cell during rest.
• 😀 A sodium-potassium pump helps maintain the resting membrane potential by actively transporting 3 Na+ out and 2 K+ into the cell.
• 😀 The resting membrane potential of a nerve cell is approximately -70 millivolts, with the inside being more negative than the outside.
• 😀 When a nerve cell receives a stimulus, sodium channels open, allowing Na+ to rush into the cell and depolarize it.
• 😀 Depolarization occurs when the inside of the cell becomes more positive due to the influx of Na+.
• 😀 If the depolarization reaches a certain threshold (around -50 millivolts), more sodium channels open, causing a rapid influx of Na+ and further depolarization.
• 😀 After depolarization, potassium channels open, allowing K+ to leave the cell, leading to repolarization and the restoration of the cell's negative charge.
• 😀 The sodium-potassium pump restores the original ion concentrations after the action potential, ensuring the cell returns to its resting state.

Q & A

What is the resting membrane potential of a neuron?

The resting membrane potential of a neuron is approximately -70 millivolts, where the inside of the cell is negatively charged compared to the outside.

How is the difference in voltage across the cell membrane created?

The difference in voltage is created by the unequal distribution of ions, particularly sodium (Na+) and potassium (K+), inside and outside the cell.

What ions are primarily involved in creating the resting membrane potential?

The primary ions involved in creating the resting membrane potential are sodium (Na+) and potassium (K+). Potassium is more concentrated inside the cell, while sodium is more concentrated outside.

What is the function of the sodium-potassium pump?

The sodium-potassium pump maintains the resting membrane potential by actively transporting three sodium ions out of the cell and two potassium ions into the cell, using energy from ATP.

What happens during depolarization of a neuron?

During depolarization, sodium channels open, allowing sodium ions to flow into the cell. This influx of positive ions makes the inside of the cell less negative and can eventually make it positive.

What triggers the opening of more sodium channels during the action potential?

When the neuron’s membrane potential reaches a certain threshold (around -50 millivolts), voltage-gated sodium channels open, allowing a rapid influx of sodium ions.

What occurs during repolarization?

During repolarization, potassium channels open, allowing potassium ions to exit the cell, which helps restore the negative charge inside the cell, reversing the depolarization.

Why does hyperpolarization occur after repolarization?

Hyperpolarization occurs because potassium channels close slowly, allowing more potassium to exit the cell than needed, making the inside of the cell more negative than during the resting potential.

What is the 'all-or-nothing' law in the context of action potentials?

The 'all-or-nothing' law states that once a neuron’s membrane potential reaches a threshold, an action potential will occur. If the threshold is not reached, no action potential is generated.

How does the action potential propagate along a neuron?

The action potential propagates along a neuron in small segments. As one segment depolarizes, it triggers the depolarization of the next segment, transmitting the signal down the axon.