The nervous system lets you detect changes and respond to them. A stimulus is a change, such as a bright light or a hot surface. Receptors in sense organs detect it: the eye detects light, the ear sound, the skin touch and temperature. Electrical signals called impulses travel along nerve cells (neurones) to the brain and spinal cord, which decide what to do. Impulses then travel to effectors, such as muscles, which respond.
Some responses are reflexes. They are automatic and very fast because the signal does not wait for the brain to think. Pulling your hand from a hot pan and blinking when something comes at your eye are reflexes that protect you.
Worked example
Put in order: muscle contracts, receptor in skin, spinal cord, sensory neurone.
- The stimulus is detected first, by a receptor in the skin.
- The sensory neurone carries the impulse to the spinal cord.
- A motor neurone then carries it to the muscle, which contracts.
Answer:Order: receptor → sensory neurone → spinal cord → muscle.
Key words
- stimulus
- a change that the body can detect
- receptor
- a cell that detects a stimulus
- neurone
- a nerve cell that carries impulses
- reflex
- a fast, automatic response
- effector
- a muscle or gland that responds
New questions every time.
NGSS-referenced: MS-LS1-8