1. Synapses

2. C. Action potential reaches the end of a presynaptic neuron. F. Voltage gated calcium channels open D. Calcium ions flow into the presynaptic neuron. H. Vesicles with neurotransmitters inside the presynaptic neuron fuse with the plasma membrane. G. Neurotransmitters diffuse in the synaptic cleft and bind to receptors on the postsynaptic neuron. B. The receptors are channels which open and let sodium ions into the postsynaptic neuron I. The sodium ions cause the postsynaptic membrane to depolarize A. This causes an action potential which passes down the postsynaptic neuron E. Neurotransmitters in the synaptic cleft are degraded and the calcium ions are pumped back into the synaptic cleft.

4. Action potential reaches the end of a presynaptic neuron. Voltage gated calcium channels open. Calcium ions flow into the presynaptic neuron. Vesicles with neurotransmitters inside the presynaptic neuron fuse with the plasma membrane. Neurotransmitters diffuse in the synaptic cleft and bind to receptors on the postsynaptic neuron. The receptors are channels which open and let sodium ions into the postsynaptic neuron. The sodium ions cause the postsynaptic membrane to depolarize. This causes an action potential which passes down the postsynaptic neuron. Neurotransmitters in the synaptic cleft are degraded and the calcium ions are pumped back into the synaptic cleft.