Please help only if you are an expert in physiology. Please clearly explain answ

Question

Please help only if you are an expert in physiology. Please clearly explain answer in ledgable handwriting (typed is perffered) . Thank you .

Animal physiology question on neuro physiology: The absolute and relative refractory periods of an action potential determine other parameters of action potentials such as causing unidirectional conduction and limiting the frequency (i.e. how often) they can be fired. Describe what is happening during each of the refractory periods. Then use this information to describe how the different periods affect conduction and frequency.

Explanation / Answer

At the peak of action potential all sodium ions are inactivated.When Na+ channels are inactivated, they cannot be immediately opened again.Recovery from inactivation is a time- and voltage-dependent process, and full recovery usually takes about 3-4 ms. Therefore, it takes about 3-4 ms for all Na+ channels to come out of inactivation and to be ready for activation (opening) again. The period from the initiation of the action potential to immediately after the peak is referred to as the absolute refractory period (ARP) This is the time during which another stimulus given to the neuron (no matter how strong) will not lead to a second action potential. Thus, because Na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials. The absolute refractory period takes about 1-2 ms.

After the absolute refractory period, Na+channels begin to recover from inactivation and if strong enough stimuli are given to the neuron, it may respond again by generating action potentials. However, during this time, the stimuli given must be stronger than was originally needed when the neuron was at rest. This situation will continue until all Na+ channels have come out of inactivation. The period during which a stronger than normal stimulus is needed in order to elicit an action potential is referred to as the relative refractory period (RRP). During the relative refractory period, since pKremains above its resting value , continued K+ flow out of the cell would tend to oppose any depolarization caused by opening of Na+channels that have recovered from inactivation.

No stimulus, no matter how strong, will bring the neuron to threshold during the absolute refractory period. During the relative refractory period, the neuron can be excited with stimuli stronger than that needed to bring a resting neuron to threshold. The strength of of the stimulus required is very high early in the relative refractory period and gradually becomes smaller throughout the relative refractory period as Na+ channels recover from inactivation and as K+permeability returns to its resting level. At the end of the relative refractory period, when the neuron is back to its resting state, the stimulus strength is at the minimum level required to bring a resting neuron to threshold.

Inactivation of Na+channels is solely responsible for the absolute refractory period. Both Na+channel inactivation and greater than resting pK value are responsible for the relative refractory period.

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.