How Animals Respond

How do animals respond to events around them?

Animals must often respond to events or environmental conditions within seconds, or even tiny fractions of a second. Sometimes they need to catch food. Other times, they need to escape predators. Most animals have evolved specialized nervous systems that enable them to respond to events around them. Nervous systems are composed of specialized nerve cells, or neurons. The structure of neurons enables them to receive and pass on information. Working together, neurons acquire information from their surroundings, interpret that information, and then “decide” what to do about it.

Detecting Stimuli Information in the environment that causes an organism to react is called a stimulus (plural: stimuli). Chemicals in air or water can stimulate the nervous system. Light or heat can also serve as a stimulus. The sound of your phone ringing on a Friday night is a stimulus to which you might respond by running to answer it!

Animals' ability to detect stimuli depends on specialized cells called sensory neurons. Each type of sensory neuron responds to a particular stimulus such as light, heat, or chemicals. Humans share many types of sensory cells with other animals. For that reason, many animals react to stimuli that humans notice, including light, taste, odor, temperature, sound, water, gravity, and pressure. But many animals have types of sensory cells that humans lack. That's one reason why some animals respond to stimuli that humans cannot detect, such as very weak electric currents or Earth's magnetic field.