The upstroke of the action potential (ie: its rising phase) is largely due to voltage activated Na channels opening, which cause depolarisation, which open more voltage activated Na channels, causing more depolarisation etc (ie: “positive feedback”). Which of the following mechanisms contributes to terminating the upstroke?  Na channels inactivate when depolarised for more than a few hundred µs   the sodium ion concentration inside the cell becomes too high to allow any more sodium ions to enter   activation of voltage-dependent chloride channels   opening of voltage dependent calcium channels   voltage-activated Na channels are only opened between threshold potential and 0mV – above this they are inhibited

The upstroke li mb of the action potential in SA node cells in the cardiac muscle is inresponse to:A. Opening of voltage gated Na+ channels.B. Opening of Transient Ca 2 + channels.C. Opening of Longer lasting Ca 2+ channels.D. Opening of voltage gated K+ channels.E. Opening of voltage gated Na+ channels

Movement of Na+ ions into a nerve cell during the upstroke of an action potential is an example of of the following transport mechanismSelect one:a. Facilitated diffusionb. Co-transportc. Primary active transportd. Simple diffusione. Counter-transport

A positive feedback loop occurs when the outcome of an event causes the event to continue occurring and amplifies its effects. Which of the following aspects of an action potential constitutes a positive feedback loop?Multiple ChoiceThe sodium-potassium pump exactly balances ion leaks by pumping three sodium and two potassium ions across the membrane.An initial flow of sodium ions into the neuron causes the opening of more voltage-gated sodium channels, rapidly causing more sodium to enter.The threshold potential is around -55mV.Opening of voltage-gated sodium channels causes voltage-gated potassium channels to open and release potassium to the extracellular environment, slowly counteracting sodium influx.

Action potentials arriving at a presynaptic terminal causeMultiple Choicebreakdown of acetylcholine.calcium ion channels to close.release of neurotransmitter.calcium ion channels to open.

Depolarization occurs becauseMultiple Choicethe extra efflux of potassium ions causes the membrane potential to become slightly more positive than the resting value.more sodium ions diffuse into the cell than potassium ions diffuse out of it.the inactivation gates of the voltage-gated sodium ion channels begin to open, and the diffusion of sodium ions decreases.potassium ions continue to diffuse out of the cell after the inactivation gates of the voltage-gated sodium ion channels begin to close.the increased potassium ion permeability lasts slightly longer than the time required to bring the membrane potential back to its resting level.