Programme 15: Responding to Stimuli

Activity Sheet 2

Speedy Reflexes

Ben was helping in the kitchen. He picked up a metal spoon and without thinking dropped it. The spoon was hot but Ben had dropped it without thinking.

1. Find out from your teacher what to do with the following words and definitions.

Words	Definitions
Receptor	A nerve cell that transmits a nerve impulse from a relay nerve cell to an effector, eg a muscle.
Stimulus	Information from the environment, eg light, sound, heat, chemicals, texture, pressure.
Sensory Nerve	The action that an organism makes after receiving a stimulus, eg a movement, secreting saliva.
Effector	An organ that responds to a stimulus. Usually a muscle, eg salivary gland.
Motor Nerve	A nerve cell that transmits a nerve impulse from a receptor to the central nervous system.
Relay Nerve	A nerve cell in the central nervous system that transmits a nerve impulse from a sensory nerve cell to a motor nerve cell.
Response	Cells or organs that can detect a stimulus and pass information to a sensory nerve, eg light receptors in the retina of the eye, chemoreceptors in the nose and on the tongue.

2. What are reflexes for?

3. Which reflex actions can you control consciously, and which cannot be controlled?

4. If we can control a reflex, what should we add to the diagram of the reflex arc?

5. Are we born with reflexes, or are they learned.

6. Which parts of the reflex arc are in the central nervous system and which are part of the peripheral nervous system?