Final answer:
An agonist is a chemical that activates a receptor site, mimicking the effects of a neurotransmitter.
Step-by-step explanation:
An agonist is a chemical that activates a receptor site, mimicking the effects of a neurotransmitter. In the case of morphine sulfate, it is an opioid agonist that activates opioid receptors in the brain, spinal cord, and gastrointestinal tract. By activating these receptors, morphine sulfate relieves the patient's postoperative pain.
Neurotransmitters are chemical messengers that transmit signals between neurons (nerve cells) in the nervous system. They play a crucial role in the communication and functioning of the brain and other parts of the nervous system. These chemical substances facilitate the transmission of signals across synapses, which are the junctions between neurons.