A nerve fibre from the spinal cord to the foot is 1.2 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.
A nerve fibre from the spinal cord to the foot is long. A myelinated fibre conducts at , and an unmyelinated fibre conducts at .
- How long does the impulse take in the myelinated fibre, in milliseconds?
- How long does it take in the unmyelinated fibre, in milliseconds?
- How many times longer is the second time than the first?
Need a reminder? The key ideaShow
Neural tissue controls the responses of the body. The neuron is the unit of the nervous system. A neuron has a cell body (cyton) with the nucleus and Nissl granules, dendrites that bring impulses to the cell body, and an axon that carries impulses away. The axon ends in axon terminals. A myelinated axon has a myelin sheath with gaps called nodes of Ranvier. The impulse jumps from node to node, so a myelinated fibre conducts faster than an unmyelinated one. Neuroglia support and protect neurons and make up more than half the volume of neural tissue. The time taken by an impulse is the distance divided by the speed.
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. Length . Speeds and .
Plan. Use for each fibre, and change to milliseconds.
Step 1. Myelinated. .
Step 2. Unmyelinated. .
Step 3. The ratio. .
Answer: ; ; times.
Check. The speeds are in the ratio , and the times are in the opposite ratio.
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