Final answer:
Serotonin is the neurotransmitter associated with sleep disturbances like those experienced by Jim. Acetylcholine is the neurotransmitter that leads to pupil constriction, and caffeine inhibits adenosine receptors to promote wakefulness.
Step-by-step explanation:
If Jim suffers from sleep disturbances, the neurotransmitter most likely associated with this effect is serotonin. Serotonin is a monoamine neurotransmitter that plays an important role in regulating sleep and mood, among other functions. Disturbances in serotonin levels can lead to various sleep issues. However, it should be noted that the other neurotransmitters listed, such as dopamine and norepinephrine, can also influence sleep and arousal in complex ways.
Regarding pupil constriction, the neurotransmitter responsible for this is acetylcholine. In contrast, neurotransmitters like norepinephrine and epinephrine typically cause pupil dilation.
In terms of promoting wakefulness, substances like caffeine act as adenosine antagonists, which inhibit the adenosine receptors leading to a decrease in sleepiness. And whilst not directly related to the original question, at the neuromuscular junction, the neurotransmitter released is acetylcholine, which is crucial for muscle contraction.