BIOFOUND 5.7 Nerve Signaling pt 2

Depolarization

a type of membrane potential change with a decrease in membrane negativity (e.g., from -70 mV to -55 mV); usually caused by opening sodium or calcium channels.

Hyperpolarization

a type of membrane potential change with an increase in membrane negativity (e.g., from -70 mV to -80 mV); often caused by opening potassium or chloride channels.

Repolarization

a type of membrane potential change with the return of the membrane to resting potential after depolarization; usually involves potassium channels opening.

Neuron structure

Neurons have dendrites (receive signals), a cell body (integrates signals), an axon (transmits signals), and a synapse (communicates with other cells).

Dendrites

Branch-like structures that receive incoming signals from other neurons or sensory receptors.

Axon

A long projection that carries electrical signals (action potentials) away from the cell body to other neurons or effectors.

Cell body (soma)

Contains the nucleus and integrates incoming signals to determine whether to generate an action potential.

Synapse

The junction between neurons or between a neuron and another cell; site of chemical communication.

Neurotransmitter

A chemical released at the synapse that binds to receptors on the next cell to transmit a signals

Threshold potential

The membrane voltage (usually around -55 mV) that must be reached for an action potential to begin.

Action potential

A rapid, large change in membrane potential that travels along the axon; it is all-or-none and does not weaken with distance.

Key behaviors of action potentials

All-or-none (either happens or not), unidirectional (moves one way), non-decremental (same strength along axon), has a refractory period.

Channels used in action potentials

Voltage-gated sodium channels (Na⁺) and voltage-gated potassium channels (K⁺); both can be open, closed, or inactivated.

States of sodium channels

Closed (before threshold), open (during depolarization), inactivated (during repolarization and early recovery).

States of potassium channels

Closed (at rest and during depolarization), open (during repolarization), then close again after returning to rest.

Resting

First stage of action potential where channels are closed, -70 mV.

Depolarization

Second stage of action potential where sodium channels open, Na⁺ floods in.

Repolarization

Third stage of action potential where sodium channels inactivate, potassium channels open, K⁺ exits.

Hyperpolarization

Fourth stage of action potential where potassium channels remain open briefly, membrane becomes more negative than resting.

Absolute refractory period

A period during and immediately after an action potential when another action potential cannot occur because sodium channels are inactivated.