Actions that are reactions to a stimulus are called

The answer is reflex actions.

A reflex action is an involuntary and rapid reaction to a stimulus. So, when a receptor detects a stimulus, the information is sent to relay neuron through a sensory neuron. Relay neuron sends information to the effector through a motor neuron and effector produces a response.

1 digestive system

2 stomach

3 bladder

4 carbon deoxide

5 tiger

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.