Nervous System and Reflex Actions

Section 1Sensitivity and coordination

Sensitivity is the ability to detect changes called stimuli. Coordination is how the body makes a suitable response. Here's the trick: the nervous system is built for fast responses, like pulling your hand away from something hot.

Section 2Main parts of the nervous system

The nervous system has the brain, spinal cord, and nerves. The brain and spinal cord make up the central nervous system. Nerves carry messages between the central nervous system and the rest of the body.

Section 3Stimulus to response

A stimulus is a change that the body detects, such as heat, light, sound, or pain. A receptor detects the stimulus. An effector, such as a muscle or gland, carries out the response.

Section 4Neurones carry impulses

Neurones are nerve cells that carry electrical messages called impulses. Sensory neurones carry impulses from receptors to the central nervous system. Motor neurones carry impulses from the central nervous system to effectors.

Section 5Reflex actions protect you

A reflex action is automatic, rapid, and does not need conscious thought first. If you step near broken glass on a Kingston sidewalk and pull your foot back quickly, that quick withdrawal helps prevent injury. Watch out: you may feel pain after the reflex has already started.