Physiology MD137 Lecture 3: Action Potentials

The specific membrane potential (-55mV) that needs to be reached for a neuron to fire an action potential. It's like the tipping point for a neuron to send a signal.

If the membrane potential doesn't reach the threshold, voltage-gated channels won't open, and an action potential won't be generated. It's like not pushing hard enough to open a door.

If the membrane potential surpasses the threshold, voltage-gated channels open, causing a rapid depolarization and generating a full, uniform action potential. It's like pushing the door hard enough to open it completely.

An action potential either occurs with full strength or doesn't occur at all, regardless of the stimulus strength above threshold. It's like a light switch, either on or off, there's no 'dim' setting.

While action potentials are all-or-nothing, the frequency of action potentials can change, representing stronger stimuli with faster firing rates. It's like sending more messages per second.

During an action potential, the membrane potential reverses polarity, becoming momentarily positive inside the neuron compared to the outside. It's like flipping a switch inside the neuron.

A short period after an action potential when a neuron is less responsive to new stimulation. It's like a 'cool-down' for the neuron.

Local potentials are graded, meaning their size depends on the stimulus strength. They're short-distance signals. Action potentials are all-or-nothing, uniform in size, and travel long distances.

An action potential (AP) is a rapid, short-lasting change in the membrane potential of a neuron, from negative to positive and back again. It's how neurons communicate with each other.

The main ions involved are sodium (Na+) and potassium (K+). Sodium rushes into the neuron during depolarization, making the inside more positive. Potassium then rushes out during repolarization, restoring the negative charge inside the neuron.

Ion channels are proteins embedded in the neuron's membrane that act like gates. They open and close to allow specific ions (like Na+ or K+) to pass through the membrane, controlling the flow of these ions.

Threshold is the crucial level of membrane potential that needs to be reached to trigger an action potential. If the stimulus isn't strong enough to reach threshold, no action potential will occur.

An action potential has three main phases: 1) Depolarization: The membrane potential becomes more positive due to sodium influx. 2) Repolarization: The membrane potential becomes more negative again due to potassium efflux. 3) Hyperpolarization: The membrane potential briefly becomes more negative than the resting state before returning to normal.

Depolarization is the phase of the action potential where the membrane potential becomes more positive due to the influx of sodium ions (Na+) into the neuron.

Repolarization is the phase of the action potential where the membrane potential returns to its negative resting state due to the efflux of potassium ions (K+) out of the neuron.

Graded potentials are short-distance signals that decay as they travel along a neuron's dendrites or soma. They are caused by various stimuli, and their magnitude depends on the strength of the stimulus.

The trigger zone is a specialized region of the neuron (usually the axon hillock) where action potentials are generated. It's highly sensitive to changes in membrane potential and has a high density of voltage-gated sodium channels.

Action potentials are all-or-none events. They either fire fully or not at all. They are also self-propagating, meaning they travel down the axon without losing strength.