The Reflex Arc and Synapses
A reflex runs receptor to sensory neurone to relay neurone to motor neurone to effector, with no decision from the conscious brain. Covers the synapse gap and why that gap is the slow step.
What a learner can do afterwards
- Puts the parts of a reflex arc in order for a given stimulus and response.
- Explains what crosses a synapse and why that step takes time.
- Says why a reflex protects the body better than a decided response would.
1 · Read
Touch something hot and your hand jerks back before you feel the pain. That is a reflex: a fast, automatic response that skips your conscious brain. Skipping thought trades thinking for speed, which saves you from burns.
The signal runs a fixed track called the reflex arc. The receptor senses heat, the sensory neurone carries the message in, the relay neurone passes it across the spinal cord, the motor neurone carries the order out, and the muscle effector pulls your hand away.
Between neurones sit tiny gaps called synapses. A chemical messenger crosses each gap, and that crossing is the slow step of the whole journey. Inside one neurone the signal is electrical and fast, but every gap adds a chemical delay.
Your brain learns about the burn only after your hand is moving. If a question asks why reflexes beat decided responses, say they are faster because the loop runs through the spinal cord alone.
Receptor to effector through the cord, with slow chemical synapses, pulls you clear before thought.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.