generation of action potential

In what part of the neuron does the action potential typically initiate?

initial segment of the axon (The initial segment has the lowest threshold and, therefore, is the place where most action potentials are initiated.)

During an action potential of a neuron, what directly causes the different channels to open and close?

the transmembrane potential (voltage) Changes in transmembrane potential directly cause voltage-gated channel proteins to change shape and allow the flow of ions across the cell membrane. The tiny electrical current associated with a single channel opening can actually be measured with sensitive recording techniques.

What is the typical duration of a nerve action potential?

2 ms From initiation to completion, the action potential is rarely over a few milliseconds. This is an extremely brief period of time-about as long as it takes for a handgun bullet to travel one meter.

Around what transmembrane potential does threshold commonly occur?

-60 mV At approximately -60 mV, an action potential is initiated. A transmembrane potential -60 mV corresponds to a depolarization of 10-15 mV away from the resting membrane potential.

What ion is responsible for the depolarization of the neuron during an action potential?

Na+ (sodium) The influx of sodium ions causes the rapid depolarization during the action potential. The influx of sodium ions through open channels is favored by two factors. (1) The sodium concentration inside the neuron is only about 10% of the sodium concentration outside the neuron. (2) Most of the time, the interior of the cell is electrically negative, which is attractive for the positively charged sodium ions.

What type of membrane transport causes the depolarization phase of the action potential in neurons?

facilitated diffusion Ions move through channels according to their electrochemical gradient from one side of the membrane to the other. This movement is known as channel-mediated diffusion. The transport rate for channels, unlike that for the carrier proteins involved in facilitated diffusion, does not saturate when the electrochemical gradient for the diffusing ion is increased.

During an action potential, after the membrane potential reaches +30 mV, which event(s) primarily affect(s) the membrane potential?

Voltage-gated sodium channels begin to inactivate (close) and voltage-gated potassium channels begin to open. The repolarization phase of the action potential involves decreasing sodium influx via inactivation of sodium channels and increasing potassium efflux (exit) via opening potassium channels. Both of these processes begin near the peak of the action potential.

What ion causes repolarization of the neuron during an action potential?

K+ (potassium) The exit of potassium from the cell causes the cell to become more negative, repolarizing the membrane. The exit of potassium ions through open channels is caused by the large concentration of potassium ions inside the neuron compared to the concentration of potassium ions outside the neuron (the chemical gradient for potassium). Even though the transmembrane potential during most of the repolarization phase is negative, this small electrical gradient (tending to pull potassium ions inward) is not enough to change the overall outward direction of the potassium electrochemical gradient.

What causes repolarization of the membrane potential during the action potential of a neuron?

potassium efflux (leaving the cell) Positively charged potassium ions flowing out of the cell makes the transmembrane potential more negative, repolarizing the membrane towards the resting potential.

What is primarily responsible for the brief hyperpolarization near the end of the action potential?

voltage-gated potassium channels taking some time to close in response to the negative membrane potential Although both types of voltage-gated channels open and close in response to changes in membrane voltage, the voltage-gated potassium channels open and close much more slowly than the voltage-gated sodium channels. This slowness means that voltage-gated potassium channels do not immediately close after the resting potential (-70 mV) is reached. Instead, they drag the membrane potential briefly towards the potassium equilibrium potential (-90 mV).

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels Yes! The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm.

What characterizes depolarization, the first phase of the action potential?

The membrane potential changes from a negative value to a positive value. yes! The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to a positive value.

What characterizes repolarization, the second phase of the action potential?

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV. The plasma membrane was depolarized to a positive value at the peak of the first phase of the action potential. Thus, it must repolarize back to a negative value.

What event triggers the generation of an action potential?

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

What is the first change to occur in response to a threshold stimulus?

Voltage-gated Na+ channels change shape, and their activation gates open Yes! The activation gates of voltage-gated Na+ channels open very rapidly in response to threshold stimuli. The activation gates of voltage-gated K+ channels are comparatively slow to open.