Every choice listed is a potential fate of neurotransmitters that have been released into the synaptic cleft. They can passively diffuse away from the synaptic cleft due to normal chemical principles. Neurotransmitters can also bind their target receptors and stimulate the post-synaptic neuron. There may also be special enzymes that inactivate or degrade neurotransmitters in the synaptic cleft, as acetylcholinesterase does with acetylcholine. It is also possible for reuptake to occur (the neurotransmitters to be taken back into the pre-synaptic neuron).

Norepinephrine (also called noradrenaline), is associated with the sympathetic nervous system. Acetylcholine is the most commonly used neurotransmitter in the autonomic nervous system, however norepinephrine is the neurotransmitter released from sympathetic postganglionic neurons to elicit sympathetic responses from target tissues.

The parasympathetic nervous system uses only acetylcholine.

Acetylcholine is the neurotransmitter that acts at neuromuscular junctions. Acetylcholinesterase degrades acetylcholine at the synaptic cleft, allowing the muscle to relax. If acetylcholinesterase is inhibited, acetylcholine will remain in the synaptic cleft and continuously stimulate the muscle. Breathing requires the ability to contract and relax respiratory muscles. Without rapid administration of an antidote, sarin gas usually results in death from asphyxiation. Acetylcholine causes pupil constriction and gastrointestinal motility. It is not associated with a rapid increase in leukocyte production.

The neurotransmitter acetylcholine is the only neurotransmitter released at the neuromuscular junctions between neurons and skeletal muscles, where it stimulates the muscles to contract.

The effects of norepinephrine prepare the body to respond to short-term threats and stressful situations. Serotonin is believed to affect mood and sleep. Serotonin imbalances have been linked to depression, and a classification of antidepressants is termed selective seratonin re-uptake inhibitors. The absence of dopamine is associated with Parkinson's disease. Endorphins produce analgesia by binding to the opiate receptor sites involved in pain perception. 

Norepinephrine is an excitatory neurotransmitter that readies the body for the "fight-or-flight" response. The sympathetic nervous system releases epinephrine and norepinephrine from postanglionic neurons to stimulate this response from targeted organs.

Acetylcholine is released from preganglionic sympathetic neurons. It is also released from both preganglionic and postganglionic neurons of the parasympathetic nervous system. It is also the primary neurotransmitter involved in neuromuscular junctions.

Serotonin affects mood and social behavior, while dopamine is involved in mood and focus. GABA, unlike acetylcholine and norepinephrine, is an inhibitory neurotransmitter.

Peptide neurotransmitters cannot be synthesized at the synaptic terminals. Since these molecules are proteins by nature, they must be constructed by ribosomes found in the soma near the nucleus. Specifically, ribosomes bound to the rough endoplasmic reticulum will synthesize peptide neurotransmitters, in order for them to be properly packaged for transmission. From the ER, the proteins iare sent to the Golgi apparatus where they are modified and packaged into vesicles, which then are transported along microtubules much like in a normal exocytosis process.

Small-molecule neurotransmitters are not stored in large dense-core vesicles, and are instead synthesized in the synaptic terminals.

GABA and glycine are the two major inhibitory neurotransmitters.

Norepinephrine, epinephrine, glutamate, and acetylcholine cause excitatory responses. Synaptobrevin is a snare protein involved in vesicle docking and fusion; it has no effect on whether or not a neurotransmitter is or is not inhibitory.

Acetylcholine is correct. We are told from the passage that the neurons which make up the Edinger-Westphal nucleus are parasympathetic neurons. Therefore, this question is really testing one's knowledge of the neurotransmitter used by parasympathetic neurons. We cannot be expected to know from the question alone which neurotransmitter these neurons use. However, we are supposed to be aware that neurons that are parasympathetic use the neurotransmitter acetylcholine. 

The presynaptic neuron require an action potential in order to open the calcium voltage channel. The opening of this calcium channel will allow the influx of calcium and trigger the release of vesicles with the neurotransmitter inside. The exocytosis of acetylcholine from the presynaptic cleft will then bind to the receptor on the postsynaptic cleft. Inhibiting acetylcholinesterase will prevent the breakdown of the neurotransmitter and allow for it to bind to the receptor longer. Decreasing the surrounding concentration of calcium will inhibit the release of the acetylcholine filled vesicles into the synaptic cleft.

Cyclic adenosine monophosphate and protein kinase A are both second messengers in the G protein-coupled receptor pathway. Since they are second messengers, they amplify and transmit the signal inside of the cell. Acetylcholine, however is a hydrophillic neurotransmitter and binds to the receptor located on the surface of the cell, thereby inducing intracellular signaling.