Biology Forums - Study Force

Would appreciate some help with my PhysioEx 9.0 Labs. I am currently doing exercise number 3. I know I am only supposed to post two questions, so I will try to divide my questions to minimalize them. Thanks for the help!
 
Exercise 3

Activity 3
1. Explain why the threshold voltage is not always the same value (between axons and within an axon).

2. Describe how the action potential is regenerated by local ion flux at each location on the axon.

3. Why doesn't the peak value of the action potential increase with stonger stimuli?

Activity 4
1. If depolarizing membrane potentials open voltage-gated sodium channels, what closes them?

2. Why must a sushi chef go through years of training to prepare puffer fish for human consumption?

3. For action potential generation and propagation, are there any other cation channels that could substitute for the voltage-gated sodium channels if the sodium channels were blocked?

This has to do with the absolute refractory period. All the voltage-gated channels (both for sodium and for potassium) open if a threshold change in the electrical potential of the axon occurs.  If there's enough of an electrical stimulus from that electrical event, whatever it is, the voltage-gated channels will open and the entire action potential will occur.  If there's not enough of an electrical stimulus, nothing will happen.  If there's a really, overly-large electrical stimulus, an action potential will occur just like when an electrical stimulus occurs that is just at threshold.  There's no such thing as a big and a little action potential.  An action potential is an action potential, and it either occurs or it doesn't.  It is the all or none principle

Post Merge: 11 years ago

That was #3,
# 4 is that first the Voltage gated channels begin to inactivate on their own.   Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state.