IB Biology SL C Interaction and Interdependence Topic Practice

a. carry (rapid) electrical impulses/messages/signals from CNS/brain/spinal cord to effectors/muscles/glands;
b. (neuron) activates effectors/causes muscles to contract/causes movement;

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;