In a knee jerk, the afferent fibre is 0.55 m long and the efferent fibre is 0.55 m long…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In a knee jerk, the afferent fibre is m long and the efferent fibre is m long. Both conduct at m/s. The signal crosses one chemical synapse in the spinal cord, which adds ms.
- How long does the impulse take in the afferent fibre?
- How long does it take in the efferent fibre?
- What is the total time of the reflex?
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. Each fibre: m at m/s. One synapse: ms.
Plan. Find the time in each fibre, then add the synapse.
Step 1. Afferent fibre. s ms.
Step 2. Efferent fibre. The same: ms.
Step 3. Total. ms.
Answer: ms; ms; ms.
Check. The synapse is a small part of the time. A reflex with one synapse is among the fastest responses of the body.
Watch out. Do not forget the synapse, and do not count it twice.
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