The Reflex Arc
Build the path, then fire it.
You touch something hot and your hand pulls back before you have thought about it. Build the path the impulse actually takes.
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The whole point of a reflex arc is that it bypasses the brain. The impulse turns around in the spinal cord, which is why the action happens before you consciously feel anything.
Free play — put the stages in order yourself, then play the whole thing through as one continuous process. Switch to when you're ready to test yourself.
What this lesson covers
Challenges to clear
- Build the whole reflex arc in order.
- Lay the relay neuron in its correct place — the step that keeps the brain out of it.
The task
You touch something hot and your hand pulls back before you have thought about it. Build the path the impulse actually takes.
What this lesson covers
- Stimulus — The hot object — the change that starts everything.
- Receptor — Heat and pain receptors in the skin of the finger detect the stimulus.
- Sensory neuron — Carries the impulse from the receptor along the dorsal root into the spinal cord.
- Relay neuron in the spinal cord — Inside the grey matter of the spinal cord the impulse is passed straight across to a motor neuron. The spinal cord — not the brain — issues the command, which is what makes the response so fast.
- Motor neuron — Carries the impulse out through the ventral root to the muscle.
- Effector muscle — The biceps of the arm — the muscle that will act.
- Response — The muscle contracts and the hand is withdrawn. The brain is informed a moment later, which is why you feel the pain AFTER you have already moved.
Hint
The whole point of a reflex arc is that it bypasses the brain. The impulse turns around in the spinal cord, which is why the action happens before you consciously feel anything.