The rate at which a nerve impulse travels along a nerve fiber is dependent upon which factor?

The rate at which a nerve impulse travels along a nerve fiber is dependent on the diameter of the nerve fiber. The larger the diameter of the nerve fiber, the faster the nerve impulse travels. This is because the increase in diameter reduces the internal resistance, allowing the nerve impulse to travel faster. The rate at which a nerve impulse travels along a nerve fiber is known as nerve conduction velocity. 

Impulse transmission also depends on the presence or absence of the myelin sheath. The nerve impulse travels faster along a nerve fiber that is covered with a myelin sheath.