9. The autonomic nervous system. General organization of the autonomic nervous system. Au-tonomic nerve centers, ganglia, transmitters and receptors in the autonomic nervous system.

Autonomic Nervous System (ANS)

The ANS is a division of the nervous system that controls involuntary functions, including those of the visceral organs. It plays a crucial role in maintaining homeostasis, regulating processes like heart rate, blood pressure, digestion, and respiration.

The autonomic NS:

• ♦ Regulates internal organ functions.
• ♦ Not under voluntary control.
• ♦ Performs homeostatic control via reflex mechanisms.

Functional Organization

The ANS has two main divisions:

• Sympathetic Nervous System: "Fight or flight" response. Prepares the body for action and stress.
• Parasympathetic Nervous System: "Rest and digest" response. Conserves energy and promotes relaxation.

Both divisions work together in a coordinated, often reciprocal, manner to control organ function.

Efferent Pathways (Motor Output)

The efferent pathways in both divisions typically involve two neurons:

1. Preganglionic Neuron: Cell body located in the CNS (brainstem or spinal cord). Axon synapses with the postganglionic neuron in an autonomic ganglion.
2. Postganglionic Neuron: Cell body located in an autonomic ganglion. Axon extends to the effector organ.