A neurone with a myelin sheath has a diameter of 1.0 µm. Determine the speed of an impulse in this neurone making use of the graph in Fig. 4.2. The neurone is 90 cm long. Calculate the time taken for an impulse to travel along this neurone.

Find $1.0 \text{ } \mu\text{m}$ on the horizontal axis (Diameter of neurone).

Move vertically up from $1.0 \text{ } \mu\text{m}$ until you intersect the line labeled "myelin sheath". Then, move horizontally to the left to read the value on the vertical axis (Impulse speed in m per s).

From the graph, at a diameter of $1.0 \text{ } \mu\text{m}$ for a myelinated neurone, the impulse speed is $4.0 \text{ m/s}$.

The speed of an impulse is $\boxed{\text{4.0 m/s}}$.

b) (ii) The neurone is 90 cm long. Calculate the time taken for an impulse to travel along this neurone.

The length is given as $90 \text{ cm}$.

The formula relating time, distance, and speed is:

Using the speed from part (i), which is $4.0 \text{ m/s}$:

The time taken for an impulse to travel along this neurone is $\boxed{\text{0.225 s}}$.