Question

1). How does the number of muscle fibers found in various motor units differ? For example, the number found in a motor unit of a muscle that moves the eye and the number found in a motor unit in the calf muscle.

2). Briefly describe the difference between fast-twitch and slow-twitch muscle fibers. Are fibers of the same type found in a single motor unit?

3). Explain the nervous system’s role in increasing the force of contraction and potential ways to avoid fatigue.

4). Explain the physiological factors associated with various types of fatigue (either central or peripheral).

Answer 1

1) Every muscle fiber is innervated by only one motor neuron. A motor unit is the group of muscle fibers in a muscle innervated by a single motor neuron.

There are two types of motor unit:

1. Small motor unit: A small number of muscle fibers in a muscle fibres are supplied by a motor neuron. Small motor units permit very fine motor control of the muscle.
2. Large motor unit: A single motor neuron supplies a large number of muscle fibers in a muscle. It helps in simple, coarse movements, such as abduction adduction, hip flexion etc.

Now as we have a neuron innervating small number of muscle fibres, it has a very exquisite degree of control like fine movements of the fingers and thumb of the hand for grasping, texting. In case of extraocular muscles, there are thousands of muscle fibers in each muscle, but every six or so fibers are supplied by a single motor neuron. This increases the rapidity and fineness of action in n eye control.

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