Organisms need to respond to stimuli (changes in the environment) in order to survive
A single-celled organism can just respond to its environment, but the cells of multicellular organisms need to communicate with each other first
As multicellular organisms evolved, they developed nervous and hormonal communication systems
The nervous system detects and reacts to stimuli
The nervous system means that humans can react and coordinate their behaviour
(CNS) Central nervous system: In vertebrates (animals with backbones) this consists of the brain and the spinal chord only. In mammals, the CNS is connected to the body by sensory neurones and motor neurones
Sensory neurones: The neurones that carry impulses from the receptors to the CNS
Motor neurones: The neurones that carry electrical impulses from the CNS to effectors
Effectors: All your muscles and glands, which respond to nervous impulses
