L18-acrtion potential

what is an action potentials

a brief change in the voltage across the membrane due to flow of certain ions into and out of the neuron

explain the all or nothing law

• the action potential is always a full response there is no such thing as a strong or weak action potential

• once the threshold is reached the action potential reaches its full size

• but stronger stimuli causes a higher frequency of them

explain all the phases of an action potential

• action potential is relative to the resting potential which is -70mv

• hyperpolarisation- depolarisation begins when the membrane potential becomes less negative and reaches the threshold for activation

• depolarisation- this is the potential moving to less negative values

• overshoot-this is the peak of the action potential at about 40mv

• repolarisation- this is when potential is moving back to -70mv

• undershoot- when the potential is moving away from the resting potential to less negative values

describe the sequence of events in an action potential

• at resting the sodium voltage gated ion channels and the potassium ones are closed

• the sodium/potassium pump pumps 3Na out for every 2k that’s inside

• the stimulus causes depolarisation which causes the sodium voltage gated ion channels to open ( once threshold is met ) allowing the influx of Na⁺ ions into the membrane - depolarisation

• at this point the potassium channel is still closed

• once the peak has been reached the sodium voltage gated ion channels close and the entry of the ions slows and the potassium channels open allowing the k⁺ ions to leave the membrane- repolarisation

• it gets to a point where too many k⁺ ions leave the membrane causing hyperpolarisation

• then the pump restores the resting potential

what is an absolute refectory period

it is when the action potential cannot be generated as the sodium voltage gated ion channels are inactivated and cannot be activated until the membrane is repolarised and resting state is restored

what is relative refectory period

it is when the action potential can be generated if the stimulus strength is strong enough to overcome the hyperpolarisation

which two factors effect the velocity of an action potential