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Cells and Systems 6-8 / Week 07 / Monday
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Week 07 · Senses and Signals

Monday

How did your hand know?
// Receptors notice, the brain decides
⏱ about 20 min

Monday: How Did Your Hand Know?

Rocket is balancing a ruler on one finger at the Windowsill when it tips. Raven's hand snaps out and catches it.

"Whoa," Rocket says. "You did not even look."

"I did look," Raven says. "My eyes saw it fall, and my hand moved. What do you notice? I never decided to."

Nova hovers over the ruler, her light steady. "Something noticed the fall before you could think about it," she says.

"My eyes noticed," Raven says. "Then a message went somewhere."

"To your brain," Rocket says. "And the brain told your hand. Fast."

Nova dims a little. "And how do you know the ruler was falling at all?" she asks. "You have seen one fall before."

Raven writes two words in the Log: notice, remember.

Raven catches a falling ruler at the Windowsill while Rocket watches with wide eyes, seed jars glowing in the sunlight behind them. Nova the drone hovers above the ruler with her light steady.

Senses gather information

Senses provide information about the body and its environment. That information can be sound, light, smells, tastes and touch.

Humans have five special senses: smell, taste, balance and body position, vision and hearing.

We also have general senses. They respond to stimuli like temperature, pain, pressure and vibration.

A stimulus is anything a sense can detect. Light is a stimulus for the eyes. Sound is a stimulus for the ears.

Receptors, signals, brain

A sensory receptor is a cell specialized to detect one specific stimulus. Touch receptors are sensitive only to touch or pressure, not to light or sound.

Sensory information is converted into nerve signals that are carried to the brain. There, the signals are turned into meaningful sensations.

The nervous system acquires information from sensory organs and processes it. Then it may start a response, such as a movement.

That is Raven's catch in three steps: receptors in the eyes noticed, signals reached the brain, and the brain moved the hand.

Stimulus: the ruler falls, light changes
Receptors in the eyes detect it
Nerve signals travel to the brain
The brain decides: act now, or remember
The hand moves
STIMULUS, RECEPTOR OR RESPONSE?
  • Read the question.
  • Tap your answer.
A ruler falls and light from it reaches your eyes. In this story, the falling ruler is the:
A cell in the eye that detects light is a:
Where are nerve signals turned into meaningful sensations?
Touch receptors in the skin are sensitive to:
Humans have ____ special senses. Type a number.
Anything a sense can detect, such as light or sound, is called a ____.
Sensory information is converted into nerve ____ carried to the brain.
StatementTrue or false?
Balance and body position count as one of the five special senses.?
Touch receptors can also detect light.?
The brain turns nerve signals into meaningful sensations.?
Temperature and pressure are detected by the general senses.?
WHY THIS EXERCISESorting what each sense detects is the first step in explaining any reaction.
Which organ turns nerve signals into meaningful sensations? Type one word.
WHY THIS EXERCISEReceptors notice, but only the brain makes sense of the signal.
Try it
Close your eyes for thirty seconds at the Windowsill. Count how many different sounds you notice.
Open your eyes. Now count how many different things you can see from your seat.
Write both numbers in your Windowsill Log, and which sense found more.
For a grown-up
This week your student studies how the senses send signals to the brain. There is a ruler-drop reaction test and a memory game.
The ruler is plastic or wooden and is held low over a table, never near a face. Nothing is tasted or sniffed up close.
The facts come from the MedlinePlus medical encyclopedia and OpenStax biology texts, which are free online.
Draw an eye, an arrow to a brain, and an arrow from the brain to a hand. Label stimulus, receptor, signal, response.

Sharp noticing. Tomorrow you will meet the receptors in each sense organ, from the retina to the taste buds.