A person touches a hot pan. In the reflex, the afferent and efferent fibres are each 0.9 m long and…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A person touches a hot pan. In the reflex, the afferent and efferent fibres are each m long and conduct at m/s, and there are synapses of ms each. The pain impulses climb a path of m at m/s with synapses of ms each. The brain then needs ms to register pain. These are model values.
- How long does the reflex take?
- When is the pain felt, counted from the touch?
- How much earlier does the hand move than the pain is felt?
Need a reminder? The key ideaShow
A reflex is an involuntary response that needs a part of the CNS. The reflex arc has at least one afferent neuron, which enters the CNS by a dorsal root, and one efferent neuron, which goes to the effector. Time equals distance divided by speed, and each chemical synapse adds about . A body falling from rest covers .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Reflex: m at m/s, synapses. Pain: m at m/s, synapses, ms in the brain.
Plan. Add the times of each path, then subtract.
Step 1. Reflex. ms in the fibres, and ms at the synapses. Total: ms.
Step 2. Pain. ms, plus ms at the synapses, plus ms in the brain. Total: ms.
Step 3. The difference. ms.
Answer: ms; ms; ms.
Check. The hand moves first, and the pain follows. The brain's decision time is the largest part of the pain time.
Watch out. The reflex does not wait for the brain. It runs in the spinal cord, and the brain learns about it at the same time as the muscle does.
Discussion (0)
Log in to join the discussion.
Loading…