Question

what is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?
a skeletal muscle fiber is innervated by multiple motor neurons.
typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
a motor neuron typically innervates only one skeletal muscle fiber.
motor neurons always innervate thousands of skeletal muscle fibers.

Explanation:

In the neuromuscular system, a motor neuron forms a motor unit. A motor unit consists of a single motor neuron and the skeletal muscle fibers it innervates. Typically, one motor neuron innervates multiple skeletal muscle fibers. The number can range from a few (in muscles requiring fine control like the extra - ocular muscles) to hundreds (in large, powerful muscles like the quadriceps).

• Option A: A skeletal muscle fiber is innervated by only one motor neuron (not multiple), so this is incorrect.
• Option B: This is correct as a single motor neuron typically innervates hundreds of skeletal muscle fibers (depending on the muscle's function).
• Option C: A motor neuron innervates more than one skeletal muscle fiber. If it innervated only one, it would be very inefficient for muscle contraction and movement, so this is incorrect.
• Option D: The term "always" is too absolute. While some motor neurons (in large muscles) may innervate thousands, it's not a universal rule. For example, in muscles with fine control, the number is much less.

Answer:

B. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.