Your heart rate can change due to a number of things including even breathing a certian speed, people who exercise has a slower heart beat then someone who doesnt exercise.
Or even if something is wrong with your heart, your heart rate can change too.
That is this sign right here
Answer: The correct answer is (D) Both A and B
Explanation:
When an axon is depolarized at halfway to the threshold level,the action potential will be generated that would travel 'downstream' i.e towards the synapse and 'upstream' i.e back towards the cell body. This is because both channels on either sides are not under refractory period,i.e they are open.