Final answer:
Post-ganglionic sympathetic fibers generally release norepinephrine, while postganglionic parasympathetic fibers release acetylcholine. These neurotransmitters bind to their respective adrenergic and muscarinic receptors on the target cells, causing appropriate sympathetic or parasympathetic responses.
Step-by-step explanation:
The post-ganglionic neurons in the autonomic nervous system release neurotransmitters that affect target organs. Specifically:
- Postganglionic sympathetic fibers typically release norepinephrine (except for fibers that project to sweat glands and to blood vessels associated with skeletal muscles, which release acetylcholine).
- The postganglionic parasympathetic fibers release acetylcholine (ACh), which binds to muscarinic receptors on the target cells.
These neurotransmitters interact with different receptors on target cells, with norepinephrine binding to adrenergic receptors, and acetylcholine binding to muscarinic receptors, triggering the physiological responses that define the sympathetic 'fight or flight' and parasympathetic 'rest and digest' responses, respectively.