Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
25 Cards in this Set
- Front
- Back
|
What is a nerve impulse? |
- information travels electrically from one end to the other |
|
|
What is a resting potential? |
- axon membrane is semi-permeable = conducting properties - positive on the outside, negative on inside - due to unequal ion distribution across membrane |
|
|
What causes the resting membrane potential? |
- Sodium-Potassium pump - relative permeability of the membrane - Potassium moves down electrochemical gradient |
|
|
How does the sodium-potassium pump maintain a resting membrane potential? |
- transmembrane protein - move 3 sodium out for 2 potassium in cell = more positive outside - requires ATP |
|
|
How does the relative permeability of the membrane maintain a resting membrane potential? |
- axon membrane 50x more permeable to potassium than sodium - Potassium ions diffuse out quicker than sodium back in - inside becomes more negative |
|
|
How does potassium moving down the electrochemical gradient maintain a resting membrane potential? |
- no net movement of potassium |
|
|
What is the average resting membrane potential? |
-70mV - difference across membrane - varies depending on cell type |
|
|
What is the membrane potential affected by? |
- membrane permeability - electrical charge on either side - concentration difference on either side |
|
|
What is an action potential? |
- rapid change in membrane potential of cell - along axon - due to change in sodium/potassium voltage dependent channel |
|
|
What are sodium and potassium voltage dependent channels? |
- channel proteins that span membrane - open/close due to change in voltage (membrane potential changes) - sodium channels activate quickly at low voltages - potassium channels activate more slowly at high membrane potentials |
|
|
What are the stages of an action potential? |
- starting nerve impulses - depolarisation - repolarisation - hyperpolarisation |
|
|
What happens in the 'starting nerve impulses' stage of an action potential? |
- neurones stimulated by receptor cells - causes sodium channels to open=sodium flows into cell |
|
|
What happens in the depolarisation stage of an action potential? |
- membrane potential moves towards 0mV - membrane more positive=opens more sodium channels - more sodium into axon=more positive membrane potential - reaches 40mV=action potential=sodium voltage gated channels close |
|
|
What happens in the repolarisation stage of an action potential? |
- potassium channels open - potassium rushes out=inside cell becomes more negative - restores membrane to original polarity |
|
|
What happens in the hyperpolarisation stage of an action potential? |
- slight overshoot in potassium movement=inside more negative than usual - gates on potassium channels close - resting potential restored by Na+/K+ ATPase pump - axon repolarised |
|
|
What does an 'all or nothing' response? |
- The action potential is the same size regardless of the size of the stimulus |
|
|
What is the absolute refractory period? |
- recovering from an action potential - totally unresponsive to stimuli |
|
|
What is the relative refractory period? |
- few milliseconds after absolute - only respond to strong stimuli - voltage-dependent K+ channels open |
|
|
What is the importance of the refractory period? |
- limits the rate at which action potentials are fired - ensures impulses only flow in one direction - until resting potential restored, part of neurone can't fire=impulse can't go backwards |
|
|
What factors affect the conduction speed of a nerve impulse? |
- myelin sheath - diameter of axon - temperature |
|
|
How does the myelin sheath affect the conduction speed of a nerve impulse? |
- electrical insulator - AP jumps from nodes of Ranvier=saltatory conduction - more myelin=faster conduction |
|
|
How does the diameter of the axon affect the conduction speed of a nerve impulse? |
- greater diameter=faster conduction - less leakage/internal resistence in thick axons=ions move faster |
|
|
How does the temperature affect the conduction speed of a nerve impulse? |
- higher temp.=faster nerve impulse - rate of diffusion faster - enzyme activity faster |
|
|
What are myelinated neurones? |
- neurones associated with Schwann cells (protect nerve) - prevents current leaving axon - myelinated area can't conduct AP - Na+ diffuse along unmyelinated area - causes region to depolarise=AP - jumps along axon between myelin |
|
|
What are non-myelinated neurones? |
- found in brain/spinal cord=grey matter - Na+ diffuse from AP area to resting area adjacent - region depolarise=AP - moves along axon |
