Need help with questions 3 and 4 CL: Action Potentials Without using text or not

Question

Need help with questions 3 and 4

CL: Action Potentials Without using text or notes, diagram a graded potential and subsequent action potential (AP) passing a region of plasma membrane by graphing the membrane potential over time. Label each phase of the AP: depolarization, repolarization and hyperpolarization. Label the axes, including appropriate units, and the threshold and resting potentials. Star the point where the AP is initiated. 1. Does everyone understand the goal? What changes at the threshold potential? 2. On your drawing above, explain why the membrane potential changes as it does in each phase, by identifying which type of gated channels are open during each phase, and describing the direction of ion diffusion through those channels. Imagine that 0.3 ms after the above AP is initiated, a depolarizing stimulus that exceeds threshold is applied. Describe what would happen (i.e. would another AP be created, would the shape or amplitude of the original AP be altered?) and explain your reasoning 3. Would gated channels be open or closed? 4. Imagine that you could create AP's at opposite ends of an axon, so that the two travelled towards each other. Describe what would happen when the AP's met in the middle of the axon, and explain your reasoning. How does ion channel physiology impact this?

Explanation / Answer

Ans 3) In this situation the gated channels will be open as the depolarizing stimulus exceeds threshold that is applied. This is basically the rising phase where the voltage gated Na+ channels open when the threshold is exceeded. As the Na+ enters, the cell causes further depolarization which makes it less negative. The depolarization causes more Na+ channels to open in positive feedback. This leads to continued Na+ to diffuse into cell down the concentration gradients till no more driving force is there.

Ans 4) In this case there would be both retrograde and anterograde conduction from the stimulation point. On stimulating the movement of the AP towards the middle of axon from both sides, orthodromic impulse reach neuromuscular junction to facilitate the muscle contraction. The andridromic impulse or retrograde one will be cancelled by presence of another AP going in the same direction.

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