The Peripheral Network
The Peripheral Nervous System (PNS) links the central nervous system to the rest of the body. It splits into two major functional divisions.
The somatic nervous system handles voluntary control. Afferent (sensory) nerves carry information inward from skin, muscles, and joints, while efferent (motor) nerves carry commands outward to skeletal muscles.
The autonomic nervous system (ANS) governs involuntary functions like heart rate, digestion, and glandular secretion.
Sympathetic vs Parasympathetic
The ANS splits into two opposing branches:
| Branch | Nickname | Typical Effects |
|---|---|---|
| Sympathetic | Fight-or-flight | Heart rate up, pupils dilate, digestion inhibited |
| Parasympathetic | Rest-and-digest | Heart rate down, pupils constrict, digestion stimulated |
The adrenal medulla amplifies sympathetic stress signals via adrenaline. The vagus nerve dominates parasympathetic restoration.
Common pitfall: Treating these as good/bad switches. Both are constantly active, and organ state reflects the balance between them. Chronic stress damages health.