Question

Use diagrams and sentences to explain action potentials, being sure to include the following terms: Stimulus, depolarization, repolarization, after hyperpolarization, subthreshold stimulus, threshold stimulus, resting membrane potential, activation gates, inactivation gates, mechanical stimulation, hyperpolarization, axon hillock or trigger zone, Na+ channels, K+ channels, refractory period

Answer 1

Action potentials are caused when different ions cross the neuron membrane. A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Remember, sodium has a positive charge, so the neuron becomes more positive and becomes depolarized. It takes longer for potassium channels to open. When they do open, potassium rushes out of the cell, reversing the depolarization. Also at about this time, sodium channels start to close. This causes the action potential to go back toward -70 mV (a repolarization). The action potential actually goes past -70 mV (a hyperpolarization) because the potassium channels stay open a bit too long. Gradually, the ion concentrations go back to resting levels and the cell returns to -70 mV.

Stimulus:- a stimulus (plural stimuli or stimuluses) is a detectable change in the physical or chemical structure of an organism's internal or external environment.

Subthreshold stimulus:- Sub-threshold (or subthreshold) refers to a stimulus that is too small in magnitude to produce an action potential in excitable cells. In general, a sub-threshold stimulus leads to the depolarization of the membrane, but the magnitude of the depolarization is not large enough to reach the threshold voltage.

Threshold stimulus:- The threshold stimulus is the weakest stimulusthat could generate an action potential in a neuron.

Resting membrane potential:- Movement of the membrane potential closer to zero is depolarization. Theresting membrane potential is mainly due to efflux of potassium (K⁺) ions via leak channels. This depends on the steep concentration gradient for potassium.

inactivation gate:-

At the peak of the action potential, when enough Na⁺ has entered the neuron and the membrane's potential has become high enough, the Na⁺ channels inactivate themselves by closing theirinactivation gates.

Activation gate :-

Before an action potential occurs, the axonal membrane is at its normalresting potential, and Na⁺ channels are in their deactivated state, blocked on the extracellular side by their activation gates.

Axon hillok :-The axon hillock decides. It resides in the area of the neuron that connects the cell body with the axon. Neurons only have one axon, which is the extension that allows nerve impulses to move away from the cell body and toward other nerve cells.

Refractory period:- Refractory period is a period immediately following a stimulus during which further stimulation has no effect.