Autonomic Control of Visceral Organs
The autonomic nervous system (ANS) regulates the functions of visceral organs, including the heart, blood vessels, gastrointestinal tract, bronchioles, bladder, and genitalia. This control is generally involuntary and operates through a balance of activity between the sympathetic and parasympathetic divisions, often in a reciprocal or synergistic manner.
Sympathetic Nervous System (SNS):
- Originates from the thoracolumbar region of the spinal cord (T1-L3).
- Preganglionic neurons are short and synapse in paravertebral or prevertebral ganglia.
- Postganglionic neurons are long and release norepinephrine (NE) onto effector organs, except for sweat glands, which receive acetylcholine (ACh).
- General Functions: Mobilizes the body for activity, the "fight or flight" response.
Parasympathetic Nervous System (PNS):
- Originates from the craniosacral region: brainstem (cranial nerves III, VII, IX, X) and sacral spinal cord (S2-S4).
- Preganglionic neurons are long and synapse in terminal ganglia located near or within effector organs.
- Postganglionic neurons are short and release acetylcholine (ACh).
- General Functions: Conserves energy and promotes relaxation, the "rest and digest" response.