External stimuli are communicated to the brain by means of electrical signals pr

Question

External stimuli are communicated to the brain by means of electrical signals propagating along nerve cells at a speed of approximately 28 m/s. Similarly, electrical messages are sent at the same speed from the brain along nerve cells to the muscles. Reflex actions are controlled by a relatively simple nerve circuit from a muscle to the spine and back to the muscle. Estimate the reflex time for a stimulus at the knee. (Assume that the signal resulting from the stimulus must travel a distance ?s = 1 m.)

Explanation / Answer

The signal travels up 1 meter and down 1 meter at 28 m/s. t = 2 / 28 t = 1 / 14 or about 0.0714 seconds This assumes that the "simple nerve circuit" has zero processing time.

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