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A message from the hand goes through the spinal cord along 1.0 m of nerve in a reflex…

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A message from the hand goes through the spinal cord along $1.0$ m of nerve in a reflex. Through the brain, the path is $1.8$ m. Impulses travel at $50$ m/s. (a) How long does each path take, leaving out the synapses? (b) Give two other reasons why the path through the brain is even slower.

Need a reminder? The key ideaShow

A reflex is a quick, automatic response. Its path, the reflex arc, is receptor, sensory neuron, relay neuron in the spinal cord, motor neuron, effector. The ruler-drop test gives a reaction time: $t = \sqrt{\dfrac{2d}{g}}$ , with $d$ in metres and $g = 9.8\ \text{m/s}^2$ .

The worked solution

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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.

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