What neurotransmitter causes pupils to constrict and muscles to contract?

Neurotransmitter. Pupillary constriction is mediated by parasympathetic diners of the autonomic nervous system. Those, as well as the skeletal motor units controlling muscle contraction release acetylcholine as the neurotransmitter.
ACh. Acetylcholine. The physiology of muscle contraction is well outlined in many web sites. Happy studying!