Chemical A, a chemical that binds to and blocks acetylcholine receptors of muscle cells, could be considered a good choice as a muscle relaxer. We can determine this through understanding the role of the chemical, acetylcholine, in the body. Acetylcholine is a neurotransmitter. Neurotransmitters are chemicals that are released from nerve fibers through nerve impulses and result in the transfer of the nerve impulse to another nerve fiber, muscle fiber, or other nervous system structure in the body. This transference of the nerve impulse sends information throughout the nervous system.
Acetylcholine is a neurotransmitter that is responsible for causing muscles to contract, activating pain responses, and regulating endocrine and REM sleep functions. As such, blocking the abilities for a receptor to receive the acetylcholine would result in the inability of muscles to move. In fact, in a condition called myasthenia gravis exists, a person who is deficient in acetylcholine experiences muscle weakness as a defining symptom.
Acetylcholine is one of the most abundant neurotransmitters in the body and is found in both the central nervous system and the peripheral nervous system. It is responsible for both voluntary and involuntary muscle movement. As such, the chemical would need to block acetylcholine receptors at the nicotinic acetylcholine receptor in order to not prevent functioning of involuntary muscles, such as the heart.