Question

An axonal process 2 meter long is originating in spinal cord and terminating in the muscles of toes. If the average velocity of a vesicle is \(1\ \mu\text{m/s}\) how long does it take a vesicle to move from a cell body in the spinal cord to the axonal tip in the toes?

• A. $2 \times 10^{5}$ sec \
• B. $2 \times 10^{3}$ sec \
• C. $2 \times 10^{4}$ sec \
• D. $2 \times 10^{6}$ sec

Hint:

Always convert your units first! Since 1 meter equals $10^{6}$ micrometers, a 2-meter axon spans $2 \times 10^{6}\ \mu\text{m}$. At a speed of $1\ \mu\text{m/s}$, it takes exactly $2 \times 10^{6}$ seconds.

Answer 1

The Correct Option is D

Step 1: Concept Axonal transport moves organelles, vesicles, and proteins along the axon of a neuron using motor proteins that travel along microtubule tracks.

Step 2: Meaning The total time required for transport can be calculated by dividing the total physical distance of the axon by the average velocity of the moving vesicles: $$\text{Time} = \frac{\text{Distance}}{\text{Velocity}}$$

Step 3: Analysis * First, convert the total distance from meters into micrometers ($\mu\text{m}$) to match the velocity units: $$\text{Distance} = 2\text{ meters} = 2 \times 10^{6}\ \mu\text{m}$$ * Next, use the given average vesicle transport velocity: $$\text{Velocity} = 1\ \mu\text{m/s}$$ * Now, calculate the transport time: $$\text{Time} = \frac{2 \times 10^{6}\ \mu\text{m}}{1\ \mu\text{m/s}} = 2 \times 10^{6}\text{ seconds}$$

Step 4: Conclusion Thus, it takes exactly $2 \times 10^{6}$ seconds for the vesicle to travel the entire length of the axon. This matches option D. Final Answer: (D)