nerve impulse overview

Nerve Impulse Overview

  • A nerve impulse is an electrical current that travels along dendrites or axons of neurons.

  • This current is caused by the movement of ions through voltage-gated channels in the neuron's plasma membrane.

Voltage-Gated Channels

  • Voltage-gated channels open and close in response to changes in electrical voltage, influenced by the surrounding electrical charge.

  • These channels are critical for the generation and propagation of nerve impulses.

Resting Membrane Potential

  • At rest, neurons maintain a charge difference between the inside and outside of the cell, known as the resting membrane potential.

  • This charge difference is largely maintained by sodium-potassium pumps, which:

    • Actively transport sodium ions (Na+) out of the cell.

    • Bring potassium ions (K+) into the cell.

  • Other channels allow some K+ to flow back out, but Na+ cannot easily re-enter the cell, resulting in:

  • A net positive charge outside the neuron.

  • A net negative charge inside the neuron.

Initiation of a Nerve Impulse

  • A nerve impulse begins when a stimulus disturbs the plasma membrane on a dendrite, leading to:

    • Opening of sodium channels, allowing Na+ ions to flow INTO the cell.

    • This influx reduces the charge difference temporarily at that location.

  • If this charge change is significant, it triggers nearby voltage-gated sodium channels to open.

Depolarization Phase

  • As Na+ continues to flood into the cell, the local region becomes depolarized:

    • Inside the cell becomes net positive.

    • Outside the cell becomes net negative.

  • This depolarization spreads along the membrane, affecting and opening additional sodium channels leading to a cascading effect.

  • This propagating depolarization is referred to as an action potential.

Repolarization and Restoration

  • Following the peak of depolarization, there is a rapid restoration phase:

    • Voltage-gated sodium channels close.

    • Voltage-gated potassium channels open, facilitating K+ ions to rapidly exit the cell.

  • This outflow helps to repolarize the membrane, reversing the internal charge to negative and the external charge to positive again.

Restoration of Resting Membrane Potential

  • To fully restore the resting membrane potential and the correct distribution of sodium and potassium ions:

    • Sodium-potassium pumps are activated again to re-establish ion concentrations inside and outside the cell.