IB Biology SL C2.2 Neural Signalling Questions

the neuron/membrane is not conducting an impulse/message/signal / inside of cell/neuron has a (net) negative charge/ -70 mV compared to outside / outside of cell/neuron is positive relative to inside

a. (sodium channels/voltage-gated channels open and) $\mathrm{Na}^{+}$ diffuse into neuron (down concentration gradient);
b. inside of neuron becomes positive compared to outside / potential is reversed / depolarization;
c. wave of depolarization moves (down the membrane);
d. (potassium channels open and) $\mathrm{K}^{+}$ diffuse out (down concentration gradient);
e. inside becomes negative compared with outside / potential across membrane restored / repolarization;
f. active transport of $\mathrm{K}^{+}$ (into neuron) and $\mathrm{Na}^{+}$ (out of neuron) restores resting potential;

a. action potential/nerve impulse reaches the end of the presynaptic neuron;

b. impulse/action potential/depolarization of the (presynaptic) membrane causes calcium (ions)/ $\mathrm{Ca}^{2+}$ uptake/diffusion into the neuron;

c. (calcium ions) cause vesicles to move to the (presynaptic) membrane;

d. vesicles contain neurotransmitter;

e. neurotransmitter released into the synaptic gap/cleft by exocytosis/when vesicle fuses with membrane;

a. calcium/ $\mathrm{Ca}^{2+} / \mathrm{Ca}$ moves into the presynaptic membrane
OR
neurotransmitter/acetylcholine released from presynaptic membrane;
b. (neurotransmitter) diffuses across the synapse/synaptic cleft;
c. binds to transmembrane receptors/receptors in postsynaptic membrane;
d. (protein) channels open/ Na+ /positive ions diffuse in;
e. causes depolarization (of (post synaptic) membrane) / action potential / membrane potential increases;