8.13—Coordination by nervous and hormonal control

Nervous control uses rapid electrical impulses and targeted neurotransmitter release; hormonal control uses chemicals carried in blood, usually with slower onset and longer-lasting, broader effects. Both use receptors, coordination centres and effectors.

A reflex can move a hand away quickly, while adrenaline or thyroxine changes metabolism across several tissues. The best system depends on speed, duration and distribution.

The systems can interact: neural signals can trigger hormone release, and hormones can alter the sensitivity or activity of nervous tissues.

Hormones do not always act slowly and nerves do not always produce a brief response. Compare route, target, timing and persistence rather than memorising a single slogan.