The axon hillock of a neuron reaches the threshold of excitation and the membrane potential becomes completely reversed. Then, suddenly, the membrane potential begins to return to resting membrane potential. What is the event that triggers this return to resting potential?   A. Na+ channels close in a voltage-dependent manner   B. Na+ channels close in a time-dependent manner   C. Na+ channels close in a chemically-dependent manner   D. Na+ channels open in a voltage-dependent manner

Neuron 1 fires an action potential, releasing neurotransmitters to neuron 2.  However, neuron 2 does not fire an action potential itself.  Use your understanding of neuronal signaling to identify and explain two possible reasons for this observation.

If an excitatory synapse and inhibitory synapse generate postsynaptic potentials on the same neuron what can happen? a. The generated potentials will sum up to make a larger postsynaptic potential. b. Nothing will happen, because inhibitory neurons will not form synapses on the same neurons as excitatory neurons. c. The postsynaptic potential generated by the inhibitory synapse will shunt the excitatory synapse, leading to a reduction in the postsynaptic potential. d. None of the above

Use this illustration to place these events in the order they occur during synaptic communication: Column A Column B a. Voltage gated sodium channels carry the action potential to the synapse by allowing the influx of sodium ions. 1. 1 2 b. An increase in calcium levels triggers vesicle release. 3. 3 c. Sodium enters the post-synaptic cell, causing it to depolarize. 4. 4 d. Sodium influx at the synapse activates voltage gated 5. calcium channels which allow calcium ions to enter the presynaptic neuron. 6. 6. e. Neurotransmitters are released into the synaptic cleft. f. Ligand-gated ion channels are opened by the neurotransmitters. 2.