Sensory processing and the brain | Cells and organisms | Middle school biology | Khan Academy

As humans, we have a lot of senses that we put to use on a regular basis. They include sight, smell, taste, touch, and hearing. But have you ever wondered how it all works? How do you look at a beautiful painting in an art museum, or smell the rain outside on a stormy day, or feel that your favorite pair of socks are still a little damp and need another cycle in the dryer? How does that information make its way from our sensory organs to our brains?

Well, the answer lies in the nervous system. If you remember, our bodies are made up of multiple complex organ systems that work together to perform all different kinds of functions. Today, let's talk specifically about the nervous system, which is an organ system that allows us to sense and respond to our environment.

To begin, the nervous system contains specialized cells and cell parts called sensory receptors, which are able to pick up signals from the environment. These signals are called stimuli, or stimulus if you're talking about just one. Stimuli can come in many different forms. For instance, mechanical stimuli are physical in nature and are involved with our senses of touch and hearing. You can strum a guitar, feeling the strings against your fingertips and listening to the unique tones it produces as the strings vibrate. Those are all mechanical stimuli.

Chemical stimuli are made up of molecules and are involved with our senses of smell and taste. To illustrate an example, imagine eating a tasty bowl of chicken noodle soup. As you spoon mouthfuls of soup into your mouth, your taste and olfactory receptors are flooded with molecules that signal the qualities of the food you're eating. These molecular signals are chemical stimuli, and in this case, the molecules from the chicken noodle soup convey that the food you're eating is savory and extremely delicious.

Lastly, electromagnetic stimuli are involved with our sense of sight and include the light that comes into our eyes every day. The sunlight that makes you squint, the traffic lights you see on the street, and the vibrant and diverse colors all around you. These are just a few examples of electromagnetic stimuli in the form of light.

So then, what happens after sensory receptors detect stimuli? Well, once a sensory receptor receives the information, it passes this information along nerve cells. Here's a picture of a nerve cell, which is specialized to transmit information in the form of electrical signals. These signals are transmitted along nerves to the brain, which is then responsible for processing or organizing sensory information from different sensory receptors. After processing the information, the brain can elicit a response and also store the information in the form of a memory for future use.

For example, imagine you're playing catch with friends in a park. Your sensory receptors pick up information as you watch the ball come towards you and feel the wind on your skin. Signals from these receptors travel along nerve cells to your brain, where all these different signals are organized. Then, your brain elicits a response, such as moving to just the right spot and putting your hands out to catch the ball. And the brain also stores a memory, perhaps remembering playing catch as a fun activity that you'd want to do again.

You can almost think of this flow of information from a stimulus to sensing, to processing, and finally to eliciting a response or storing information, like a complex relay race. Sensory receptors pick up the message in the form of stimuli and pass this information along to nerves and to the brain. Only in this relay, the end result at the finish line is a response to the stimulus and information storage.

So, to summarize, today we talked about how our bodies sense and respond to the environment. Information is transferred from a stimulus to a sensory receptor to nerve cells and finally to the brain, where processing occurs. Whether we're aware of it or not, our nervous system is working at rapid-fire speed every day to provide us with the information our bodies need to sense what's in our environment and thrive in it.