What is the difference between a motor unit and a motor neuron pool in spinal cord physiology?

What is the difference between a motor unit and a motor neuron pool in spinal cord physiology?

• A. Both terms refer to single motor neurons.
• B. A motor unit is one neuron and all muscle fibers it innervates; a motor neuron pool comprises all motor neurons supplying a single muscle.
• C. Motor unit refers to muscle groups; motor neuron pool refers to a single neuron.
• D. A motor unit is all motor neurons in a limb; a motor neuron pool is the spinal cord segment.

Answer: (B)

A motor unit is the functional contractile entity: it consists of a single alpha motor neuron and all the skeletal muscle fibers it innervates. When that neuron fires, all those fibers contract together, making up the smallest unit of force production. The number of fibers per motor neuron varies by muscle, from very few in fine motor muscles to hundreds in larger ones. A motor neuron pool, on the other hand, is the group of all motor neurons that supply a single muscle. These neurons reside in the spinal cord (and brainstem for some muscles) and together form multiple motor units that can be recruited to produce graded force. So, the difference is one neuron plus its innervated fibers versus all neurons that innervate the same muscle. The other descriptions misstate the scale: a motor unit isn’t just a single neuron, and a pool isn’t about a limb or muscle groups as a whole.

A motor unit is the functional contractile entity: it consists of a single alpha motor neuron and all the skeletal muscle fibers it innervates. When that neuron fires, all those fibers contract together, making up the smallest unit of force production. The number of fibers per motor neuron varies by muscle, from very few in fine motor muscles to hundreds in larger ones.

A motor neuron pool, on the other hand, is the group of all motor neurons that supply a single muscle. These neurons reside in the spinal cord (and brainstem for some muscles) and together form multiple motor units that can be recruited to produce graded force.

So, the difference is one neuron plus its innervated fibers versus all neurons that innervate the same muscle. The other descriptions misstate the scale: a motor unit isn’t just a single neuron, and a pool isn’t about a limb or muscle groups as a whole.