Coordination & Homeostasis

Organisms respond to changes using nervous and hormonal coordination, and keep their internal conditions stable.

The nervous system

A stimulus is detected by a receptor, a signal passes along neurones to the central nervous system (CNS), which sends a signal to an effector (muscle or gland) to bring about a response: $$\text{stimulus} \to \text{receptor} \to \text{CNS} \to \text{effector} \to \text{response}$$ A reflex is fast and automatic, using a reflex arc (it does not involve conscious thought).