Module 3: Action potential Flashcards
What is depolarisation?
- Inside of membrane becomes more positive, Na+ coming into neuron
- more positive
What is repolarisation?
- return to resting membrane potential from being depolarised
- back to normal
What is hyperpolarisation?
- inside becomes more negative, K+ leaving neuron
- more negative
what triggers an Action potential in neurons?
a local or graded potential that is large enough to trigger the positive feedback cycle
what is the general threshold to trigger an action potential?
~50mV
describe the features of an action potential
- fast (1-2 ms)
- travel long distances without diminishing
- initiated in axon hillock
describe the ion flow of an action potential
- 70mV: both channels closed
- ripple of current causes a positive feeback cycle until the threshold is reached
- on reaching -50mV threshold all Na+ channels open and flood the neuron, rapidly depolarising it to +30mV
- once at +30mV the Na+ channels become inactive and the K+ channels open
- K+ channels cause repolarisation, dropping the voltage
- once voltage reaches -70mV the Na+ channels become closed
- K+channels still open, neuron becomes hyperpolar and K+ channel closes
- passive facilitated diffusion occurs due to the leak channels and the resting membrane potential is achieved again
when does NA+ channel close?
- open
- closed
- inactivated
describe how the sodium channel is positioned in the closed position
the gate is closed, the ball is at rest, no ions can pass through but it is ready to open again at the next action potential
describe how the sodium channel is positioned in the inactivated position
the gate is open, the ball is blocking the channel so sodium ions cannot pass through. It isn’t able to open again until it moves to the closed position at the end of repolarisation
describe how the sodium channel is positioned in the open position
gate is open and ball is at rest, sodium ions can pass down heir gradient as they wish
when do potassium channels become open in an action potential?
at the peak of the action potenetial
when do potassium channels become closed in an action potential?
when the action potential becomes hyper polarised (lower than -70mV)
what is the positive feedback cycle in an action potential?
when a local or graded potential is big enough to cause a ripple effect within the Na+ channels, opening enough to trigger more opening, which floods the neuron with positive ions, making it depolarise more and more until an action potential is achieved
what is action potential propagation?
the process of the action potential travelling from the axon hillock to the end of the axon