A grown-up is cooking at the stove when a pan handle gets warm. Rocket reaches past it and jerks his hand back.
"I did not even think," he says, shaking his fingers. They are fine.
Raven looks up from the Windowsill. "What do you notice? Your hand moved before you knew why."
Nova hovers between them. "That was one kind of answer from your body," she says. "Can you name the other?"
"Remembering," Rocket says slowly. "Next time I will remember the handle is warm."
"Act now, or store it for later," Raven says. "Two answers to one signal."
She writes the week's title across the top of the page and underlines it twice.
The spinal cord is a thick bundle of nerve tissue. It carries information about the body to the brain and from the brain to the body.
The spinal cord also controls motor reflexes. These are quick, unconscious movements, like automatically removing a hand from a hot object.
Reflexes are so fast because they take a very short route. The information still reaches the brain, to convey what happened.
Your ruler catch on Wednesday was a fast response too, but you aimed it. A reflex needs no aiming at all.
The hippocampus processes memory formation. It sits in the temporal lobe, near the part of the brain that interprets sounds.
When you studied the tray, signals from your eyes reached the brain. Some were stored, and you could list them later.
Memory changes behavior. Rocket will reach around the pan handle next time, before any heat touches his skin.
So a receptor's message can lead to immediate behavior, to a stored memory, or to both.
Smell and taste allow you to detect danger, such as spoiled food, gases and smoke.
Touch makes you aware of temperature and pressure, so a hand pulls back from heat. Hearing picks up a warning shout.
The threshold matters too. A certain amount of stimulation is needed before you notice. A faint smell may go unnoticed.
| Signal | Receptors | Immediate behavior | Stored as memory |
|---|---|---|---|
| Heat from a pan handle | Touch receptors in the skin | Hand pulls back | The handle gets warm |
| A falling ruler | Light receptors in the retina | Hand closes | Catch sooner next trial |
| Smoke in the air | Smell receptors in the nose | Look for the source | Smoke means check the stove |
| Ten objects on a tray | Light receptors in the retina | None needed | A list of objects |
| Week review | True or false? |
|---|---|
| A sensory receptor detects one specific kind of stimulus. | ? |
| Nerve signals are turned into sensations in the brain. | ? |
| The retina converts light into a nerve signal. | ? |
| A reflex is a slow, carefully planned movement. | ? |
| The hippocampus handles vision. | ? |
Your senses have been pointed at your own body for three weeks. Next week they turn to the seedlings on the sill.
How does a plant make its food out of air, water and light? Bring your hand lens.
Strong week, scientist. Tomorrow is Nature Day: a senses walk with your family.