Final answer:
The autonomic nervous system's output is characterized by a two-neuron chain, involving preganglionic neurons releasing ACh to activate sympathetic ganglia and postganglionic neurons releasing norepinephrine or ACh to target organs. The sympathetic system induces a 'fight or flight' response, while the parasympathetic system promotes 'rest and digest'.
Step-by-step explanation:
The autonomic nervous system (ANS) output involves a two-neuron chain that connects the central nervous system (CNS) to an effector organ, comprising both preganglionic and postganglionic neurons. The sympathetic output begins at the lateral horn of the thoracolumbar spinal cord, where preganglionic neurons release acetylcholine (ACh) to activate ganglionic neurons through nicotinic receptors located within sympathetic ganglia. These ganglionic neurons, otherwise known as postganglionic fibers, then release norepinephrine onto target effectors, influencing the organ's response as part of the sympathetic 'fight or flight' activation.
There is a unique connection to the adrenal medulla, which results in the release of norepinephrine and epinephrine into the bloodstream, amplifying the sympathetic system's effects across various organ systems. Conversely, the parasympathetic system, often called the 'rest and digest' system, primarily utilizes ACh to influence target organs, and its preganglionic neurons are located in the brainstem and sacral spinal cord.