Nervous System

The nervous system — comprising the brain, spinal cord, and peripheral nerves — coordinates the body's responses to internal and external stimuli using electrical and chemical signals. Nerve impulses (action potentials) travel at 70–120 meters per second along myelinated axons. The entire nervous system is derived from a single embryonic structure (neural tube) in the first weeks of development. The autonomic nervous system regulates unconscious functions — heartbeat, breathing, digestion — through sympathetic (fight or flight) and parasympathetic (rest and digest) divisions. Pain signals travel at two speeds: A-delta fibers (fast, sharp, 20 m/s) and C fibers (slow, burning, 1 m/s) — explaining why you feel a quick sharp pain then a dull throb. Nerve regeneration research may restore function to paralyzed patients.