MediumBiologyHigh School (9–10)GeneralHuman Body › Nervous System and Sense OrgansNumericalConceptual
A message from the hand goes through the spinal cord along 1.0 m of nerve in a reflex.
Contributed by StemPy LabTry 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 m of nerve in a reflex. Through the brain, the path is m. Impulses travel at 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: , with in metres and .
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.
Step 1. Spinal cord. s ms.
Step 2. Brain. s ms.
Step 3. Other reasons. The path through the brain crosses more synapses, and each synapse adds a delay. The brain also takes time to decide what to do.
Answer: (a) ms and ms. (b) more synapses, and time for the brain to decide.
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