Action potentials are largely due to the movements of potassium  and sodium  across a membrane. While other ions and neurotransmitters can affect action potential firing, the movements of these two ions have the greatest effect on a neuron firing.

As an action potential is essentially an electrical current, it makes sense for it to open voltage-gated channels. Specifically, voltage-gated calcium channels are opened to allow calcium ions to flow into the cell and bind to synaptic vesicles. 

Vesicles of neurotransmitter are located at the axon terminal of the presynaptic neuron. Upon stimulation, they are released into the synapse and flow across the gap between neurons. Neurotransmitters attach to receptors located on the postsynaptic membrane after being released into the synaptic cleft. This allows the action potential to continue on to the next neuron.

In the neuron, dendrites respond to the chemical neurotransmitters released by other local neurons. These dendrites have receptors in their membranes that bind specific neurotransmitters and produce electrical signals as a result of this binding. Binding of a neurotransmitter can either excite or inhibit the neuron, influencing its ability to transmit a signal.

A hormone is a chemical that is synthesized by one group of cells, secreted, and then carried in the bloodstream to other cells whose activity is influenced by reception of the hormone. An electrolyte is a solutution that conducts electricity and generally contains ions. Enzymes are proteins that speed up chemical reactions. Proteins are organic molecules composed of amino acids that are necessary for growth and repair of tissues.

A neurotransmitter is a chemical agent that relays messages from one nerve cell to the next. An enzyme is a protein that causes other substances to change. Enzymes regulate the rate of chemical reactions. An electrolyte is a substance that, when dissolved, forms electrically charged particles. Ions have lost one or more electrons and have a positive charge, or gained one or more electrons and have a negative charge. In aqueous solutions, ions are called electrolytes because they permit the solution to conduct electricity. Interleukin is a type of protein that enables communication among cells active in inflammation or the specific immune response.

Vesicles containing neurotransmitters must bind to the membrane at the axon terminal in order to release their contents into the synapse. This binding is dependent upon an influx of calcium ions that occurs with an action potential. The other ions listed are important for other parts of the action potential, but it is calcium that is crucial for this particular step. 

Voltage-gated potassium ion channels are responsible for bringing the membrane potential back to or below resting the potential. This is achieved when these channels open, which can only happen at very positive voltages (hence voltage-gated), and as the potassium ions rapidly leave the cell, the cell repolarizes to a negative potential.

The dendrites receive the messages sent from other neurons. Neurotransmitters are released into synaptic clefts between two neurons and bind receptors on the postsynaptic neuron's dendrites. Axons are nerve fibers that carry electrical impulses away from the cell body of a neuron. The nodes of Ranvier are unmyelinated spots on myelinated axons that facilitate conduction of a nerve impulse down an axon.

The effect of acetylcholine is terminated by acetylcholinesterase breaking down acetylcholine. If acetylcholinesterase is inhibited, the degradation of acetylcholine would not occur, and the effects of acetylcholine will be prolonged. 

GABA is only found in the brain and has an inhibitory function. Although glycine is also inhibitory and found in the central nervous system, it's mainly concentrated in the spinal cord and brainstem. Glutamate and acetylcholine are also found in the central nervous system, but are excitatory. Norepinephrine is excitatory and associated with the adrenal glands, not the central nervous system.