Nerve Impulses Flashcards
Explain how is resting potential maintained.
- the sodium-potassium pump means that 3 sodium ions exit the neurone when 2 potassium ions enter
- the membrane is less permiable to sodium ions (less diffuse in) where as it is more permiabl to potassium ions (more diffuse out)
- this means that there is more positvely charged ions outiside the neurone than in, keeping the membrane polarised and at -70mV
Explain the stages of an action potential.
- stimulus detected by receptor and nervous impulse sent down axon
- threshold is met so the voltage-gated sodium channels open
- sodiums diffuse (through facilitated diffusion) into the axon
- inside of membrane becomes more positive (depolarised)
- membrane reaches potentil of +40mV
What is the all or nothing principle
action potential is only stimulated if the stimulus is above a certain threshold
How is resting potential restored
- after the action potential the sodium gates are stimulated to close and the potassium gates to open
- sodium ions don’t diffuse in and potassium ions diffuse out
- charge of inside the membrane changes back to negative (repolarisation)
- hyperpolarisation occurs (becomes slightly more negative than the action potential)
- potassium gates close and resting potential is restored
Why does hyperpolarisation occur?
the potassium gates are slow to close
Describe how the action potential is transfered?
in a unmyelinated sheath
- after the membrane is stretched and sodium ions flood in the membrane is depolaried
- these sodium ions move to the adjacent axon as they are attracted to the negatively charged axon (localised electrical circuit)
- this causes the adjacent axon more positvely charged so their voltage-gated sodium channels to open
- thus causing sodium ions to flood in and the membrane to depolarise
- when this appens the previous axon’s sodium channels close and the potassium open
- this causes the potassium ions to flood in, repolarising the membrane
- this occurs again along the axon
What is the refractory period?
a period of time where the action potential can’t be passed on
Why does the refractory period occur?
- the electrochemical gradient needs time to be reestablished
- after the voltage-gated sodium ion channels open they can’t open again for a while
Why is the refractory period important?
- it makes sure the action potential is unidirectional
- makes sure they don’t overlap
- it limits the amount of action potentials that can happen in a time period therefore there is a maximum strength that can be detected (in a unmyelinated neurone)
Describe how the action potential is transfered?
in an myelinated neurone
this is called saltatory conduction
- voltage-gated sodium ions open in a node of ranvier
- this depolarises it because the sodium ions flood in down the electrochemical gradient
- the sodium ions are attracted to negative charge in adjacent nodes (creates a localised electric circuit) between the two nodes
- while this happens the previous node repolarises and this continues down the axon
What is the difference between myelinated transmission and saltatory conduction?
- saltatory conduction is faster as it occurs only in the nodes of ranvier this means that the action potential jumps down the axon rather than transmission occuring over the whole axont
- it also means that repolarisation occurs quicker which requires ATP, thus less ATP is needed for saltatory conduction
How does the diameter of the axon effect transmission of the action potential?
the greater the diameter the faster the rate of conduction
How does temperature effect the rate of transmission of the action potential?
it increases the rate of diffusion and therefore the rate of depolarisation down the axon
it also effects the rate of respiration and therefore the rate of ATP made that can be used needed for the sodium-potassium pump
