Please help with this animal physiology (neural physiology) question in a profes
ID: 3518365 • Letter: P
Question
Please help with this animal physiology (neural physiology) question in a professional manner. The last time i posted this question someone copied a documnet off the internet which did not expain the question. Please help answer only if you know the answer. And please no copy and paste from internet. and make sure to thouroughly answer what the question is asking. I need to understand. Thank you
Question: 4. 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
Action potential in terms of neuroscience is nothing but nerve impulse.its a momentary change in the electrical potential on the neuron membrane.its through this action potential the impulses/ messages are transmitted from one neuron to another,it conveys information and it's the path which orders an action.
Resting membrane potential is -70 mV.stimulus depolarises the membrane towards 0.as the potential reaches -55 mV ( this is the threshold) the action potential is triggered through sodium ion channels of neuron membrane which( remains closed during rest) opens.as the outside of neuron has more of Na+ ,it rushes into the neurones until the neuron inside is more positive than the outside.so what has happened is the resting potential of the neuron is negative which has now become positive due to influx of Na+ ions,there is rapid opening of Na channels when the .this phase is called depolarization.
Following this, Na+ channels become inactive( not closed)and potassium ion channels get activated and open as a result of depolarised state.as the inside is more positively charged than the outside,potassium ions move out,thereby again bringing negative ( resting potential- original) potential with neuron .this is called repolarization. actually following this the neuron becomes more negative than its resting potential which is termed as hyperpolarization( overshooting).
Neuronal voltage gated Na channel existence in any one of the three states- open,close ,inactive .
Now coming to refractory period,it's the time taken by a neuron to respond to a new stimuli after it has reached its resting phase following an excitation.
When the sodium channels are in inactive form then they don't open in response to depolarization.the period during which most of the sodium channels are in inactive state is the absolute refractory period.
absolute refractory period prevents the initiation of action potential in the region that has just produced an action potential hence it prevents back flow of conduction and facilitates unidirectional flow.
Following absolute refractory period, sodium channels get back to active form,hence there will be enough closed ( active) sodium channels,however the potassium channels that opened during repolarization has not closed as quickly as sodium channels,to return to the active closed state.so there is still potassium conductance,more the conductance,higher the threshold,so with greater stimuli,action potential can be triggered as the sodium channels are active now,which is called relative refractory period.
Maximum frequency is usually limited by absolute refractory period because it limits the maximum number of action potential generated in an axon in a unit of time.