Question

The Chippendale Mupp is a mythical creature who bites his tail before going to sleep. As the poets have sung, his tail is so long that he doesn’t feel the pain until it’s time to wake up, eight hours after going to sleep. Suppose that a single unmyelinated axon connects the Mupp’s tail to its spinal cord and use axon parameters appropriate to squid. Given that the range of axon diameters in real organisms is 0.2–1000 µm, estimate how long the Mupp’s tail must be.

Answer 1

The speed of conduction of an action potential in an unmyelinated axon is proportional to the square root of the axon diameter.

That's why invertebrates have large-diameter axons due to which , signals can be propagated quickly.

For 1 mm in diameter an unmyelinated axon, conducts at 25 m s−1 (at 25  °C), and is formed by the fusion of axons of many neurons.

So for unmyelinated axon ( 0.2 - 1000µm ) average speed of transmission is 2 ms-1.

Length of tail = average speed of transmission * time of transmission

Time of transmission = 8 hour = 28800 seconds

Average speed = 2ms-1

Length = 2 * 28800 = 57600m = 57.6 km