nj 30 nervous system function

Nervous System

  • Function of the neuron

Membrane Potential

  • All cells have an electrical charge across the membrane:

    • Different charge inside vs. outside (called membrane potential).

    • Results from ion movement in/out of the cell.

Factors Affecting Membrane Potential

  • Movement depends on:

    • Ion concentration (inside vs. outside).

    • Ability of ions to diffuse across the membrane.

    • Electrical charge of the ions.

  • Expressed in voltage, similar to a battery.

Ion Channels

  • Ions diffuse through proteins acting as ion channels:

    • Specific channels for specific ions.

    • Voltage-gated channels open/close based on membrane potential.

  • Small changes in membrane potential influence ion permeability:

    • Changes in permeability affect membrane potential.

Resting Membrane Potential

  • Neuron at rest:

    • Known as resting membrane potential.

    • Typical charge: about -70 mV (negative).

  • Cell is polarized (inside negative, outside positive).

Cause of Negative Resting Potential

  • Sodium-potassium pump functions:

    • Pumps out 3 Na⁺ for every 2 K⁺ pumped in.

    • Results in more Na⁺ outside and more K⁺ inside.

Sodium and Potassium Channels

  • During resting potential:

    • Sodium channels are closed (few Na⁺ enter).

    • Some potassium channels are open (allow K⁺ to exit).

  • K⁺ leaves cell, maintaining negative charge internally.

Action Potential

  • Represents local change in polarity (from negative to positive).

  • Moves down axon like a flame burning a fuse.

Steps of Action Potential

  • Step 1: Resting state (interior negatively charged).

  • Step 2: Stimulus causes membrane potential to become positive:

    • Sodium channels open; Na⁺ rapidly enters the axon (depolarization).

  • Peak: Membrane potential reaches about +40 mV.

  • Chain Reaction: Sodium channels open along the axon as Na⁺ enters.

  • Aftermath: Sodium channels close; potassium channels open:

    • K⁺ exit neurons, repolarizing the membrane.

    • Original ion concentrations restored by sodium-potassium pumps during refractory period.