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PhysioEx Ex3Actvy1+3
Action Potential
| Question | Answer |
|---|---|
| What are axons? | They are long, thin structures than conduct a signal called an action potential |
| What is a nerve? | A bundle of axons |
| What occurs at the trigger zone? | An action potential is usually initiated at the junction of the axon hillock at the initial segment |
| What is the initial segment? | A myelinated axon's first region |
| What happens once an action potential is generated? | It is regenerated down the membrane of the axon. In other words the action potential is propagated or conducted down the axon. |
| An action potential is usually initiated in an axon or near... (3) | axon hillock, initial segment and the trigger zone |
| The initiation of an action potential in a sensory neurone in the body normally... | follows a sufficiently large depolarising receptor potential |
| What is the threshold voltage? | The voltage at which you first observe action potential |
| What change in membrane potential triggers a change for action potential? (2) | A depolarization in the membrane potential results in an action potential. The membrane potential must become less negative in order to trigger an action potential. |
| How did the action potential at R1 (or at R2) change as you increased the stimulus voltage above the threshold voltage? | The action potential didn't change as the stimulus voltage increased. This is because once the threshold is met, the even is all or none, not graded. |
| An action potential is an "all-or-nothing" event. Explain what is meant by this phrase. | This means that once the threshold is met, an action potential occurs. If the stimulus is too small an action potential does not occur. |
| What is the approximate concentration of K+ inside a typical cell (intracellular concentration)? | 150 mM |
| What is the approximate concentration of K+ outside a cell (extracellular concentration)? | 5mM |
| What is the approximate concentration of Na+ inside a cell (intracellular concentration)? | 5 mM |
| What is the approximate concentration of Na+ outside a cell (extracellular concentration)? | 150 mM |
| What does it mean that the voltage just inside the membrane is negative? | There are more negative charges than positive charges just inside the membrane. |
| The membrane of most cells, including neurons, contains passive, open, K+ leak channels. Given the normal K+ concentrations and the resultant concentration gradient, which direction would K+ be expected to move (diffuse) through these leak channels? | Out of the cell |
| What effect does increasing extracellular K+ have on the net diffusion of K+ out of the cell? | It decreases the net diffusion of K+ . |
| Which way would Na+ move across the membrane if there were open Na+ channels? | Na+ would diffuse into the cell. |
| Changing the extracellular Na+ concentration does not significantly change the membrane potential. What do your results suggest about the number or state (open or closed) of Na+ channels in the resting membrane of a neuron? | Na+ channels are mostly closed. |
| Which of the following caused a change in membrane potential from -70 to -40 in the cell body? | an increase in extracellular K+ |
| A negative membrane potential was recorded when the tip of the microelectrode was | both inside the cell body and inside the axon. |
Created by:
meunid