From Senses to Responses: How Animals Process Information
Students use models and scientific texts to explain how animals, including humans, detect information with their senses, process it in the brain, and respond.
Illustrations are auto-generated and may be placeholders. They can be refreshed to match the narration.
What Is a Stimulus?
A stimulus is information from inside or outside an animal’s body that can be detected. Light, sound, odor, temperature, touch, and movement can all be stimuli. Sense organs contain special cells that detect particular kinds of information. For example, a rabbit’s ears detect the sound of rustling grass. The rustling is the stimulus, not the rabbit’s action. The rabbit may turn toward the sound, freeze, or run away. Animals can also detect internal stimuli. A thirsty dog detects changes inside its body and may search for water. The same stimulus does not always cause the same response. A dog might run toward a familiar voice but move away from a sudden, unfamiliar noise. Detecting stimuli helps animals find food, avoid danger, communicate, and meet their needs.
From Sense Organ to Brain
A sense organ receives information, but the brain processes, or makes sense of, that information. Special receptor cells in the eyes, ears, nose, tongue, and skin detect different stimuli. Messages then travel along nerves to the brain. Imagine seeing a red traffic light. Light reflected from the signal enters your eyes and is detected by cells in the retinas at the backs of your eyes. Nerves carry messages from the retinas to your brain. Your brain combines this information with what you have learned: a red traffic light means stop. The brain does not work alone. Sense organs, nerves, and the brain form a connected system. The message pathway can be modeled as a sequence: stimulus, sense organ, nerve message, and brain processing.
Choosing and Making a Response
After the brain processes sensory information, it can direct the body to respond. Nerve messages travel from the brain to muscles or other body parts that carry out the response. Some responses involve a choice based on memory and learning. When a soccer player sees a ball coming, the brain judges its direction and sends messages to the leg muscles to kick. Other responses happen very quickly and protect the body. If you touch something dangerously hot, nerve pathways help you pull your hand away rapidly. The brain also receives information about what happened. An animal may respond to one stimulus in different ways depending on its needs and surroundings. A squirrel that sees a person might freeze, climb a tree, or continue eating if it has learned that the area is safe.
Modeling a Stimulus-Response Pathway
A model can show the main parts of a stimulus-response pathway. Begin with a stimulus, then show the sense organ that detects it. Next, show a message traveling through sensory nerves to the brain. After the brain processes the information, show a message traveling through motor nerves to muscles that produce a response. For example, a bright flashlight shines near, but never directly into, a person’s eyes. The eyes detect increased light, the brain processes the information, and muscles make the person squint or turn away. Use labeled boxes and arrows to show the order. Arrows are important because they show the direction in which information travels. Models simplify real systems, so they do not show every cell or nerve. However, a good model clearly connects the stimulus, detection, processing, and response.
How Humans Extend Their Senses
People use tools to detect information that their unaided senses cannot detect well. Binoculars make faraway animals easier to see, microphones detect and strengthen quiet sounds, and thermometers measure temperature more precisely than skin can. People also adapt tools and practices to their environments, often using knowledge shared through culture. For example, Inuit communities have long used detailed observations of snow, ice, winds, and animal behavior to travel and hunt in Arctic environments. Today, people may combine such local knowledge with weather instruments, maps, radios, or satellite images. In coastal communities, fishers may use sonar to send sound through water and detect objects or schools of fish. These tools do not replace the brain. A tool gathers or changes information, sense organs receive the tool’s signals, and the brain processes them so a person can decide how to respond.
Evidence-Based Exit Check
Read this example: “At dusk, a bat sends out high-pitched sounds. The sounds bounce off a moth and return to the bat’s ears. The bat’s brain processes the returning sound patterns. It then changes direction and flies toward the moth.” Use specific evidence from the text to explain the pathway. The stimulus is the returning sound. The ears are the sense organs that detect it. Nerve messages carry information to the brain, which processes the sound patterns. The brain then directs the flight muscles, and the bat turns toward the moth. Now create or describe a model using arrows in the correct order. Include the stimulus, sense organ, brain, and response. Finally, explain why the response may help the bat survive. A strong answer states that flying toward the moth helps the bat obtain food.
