The graph shows the change in the membrane potential of an axon during an action potential.
State the approximate value of the membrane potential at X.
0 mV; (accept answers in the range of – 10 mV to +10 mV) (Units required)
Y is the threshold potential. State what happens when the threshold potential is reached.
sodium channels (start to) open
OR
depolarization/axon begins to depolarize
OR
action potential occurs;
Reject pumping of ions.
Describe the movements in ions that occur during time t.
Na+/sodium ions diffuse into the axon (in the first part/half of t);
K+ /potassium ions diffuse out of the axon (in the second half/part of t)
Do not accept the name of the element without indication that it is an ion.
Explain how a nerve impulse is passed on to other neurons.
- impulses pass to another neuron at a synapse/across synaptic gap/cleft;
- (depolarization causes) Ca2+/calcium ions to diffuse into the (presynaptic) neuron/axon;
- depolarization (of presynaptic neuron) causes release of a neurotransmitter
OR
neurotransmitters diffuse across the synapse; - (neurotransmitters) bind to receptors on postsynaptic neuron/membrane;
- (if the threshold potential is reached) an action potential occurs/sodium gates open (in the postsynaptic neuron);
