Question

2. Write a paragraph of 3-5 sentences describing 1) whether the statement is correct or incorrect and 2) the reasoning for your answer. Your answer should demonstrate your understanding of the physiological concepts underlying the statement and be written professionally

Type I motor units are not able to generate as much force as Type IIA motor units because they are recruited less quickly.

Answer 1

A motor unit is a block of muscle fibres connected to a single motor neuron thereby connected to the central nervous system. Tension developed in response to an action potential is a common factor behind the activation of all motor units, but the recruitment of the individual motor units are not the same. The responsible force behind the orderly recruitment of motor neurons in the central nervous system. Based on the Henneman's size principle the motor units are recruited from smallest to largest based on the size of a load of force needed. The motor units are categorized based on their twitch time (how quickly the motor unit develops muscle tension when stimulated) and the resistance of the motor unit to fatigue. Based on response characteristics, two main categories of motor units are commonly used.

Type I or slow-twitch oxidative: Type I motor units can develop a low peak force in a relatively long period of time (about 60 to 120 milliseconds).They are very resistant to fatigue because of their nourishment with an extensive blood supply to maintain aerobic metabolism. Due to the less fatigability the Type I motor units are the first motor units recruited by the central nervous system (CNS) when a muscle is activated, and the recruitment continues as long as the muscle remains active.

Type II or fast-twitch motor units: Type II motor units can develop a high peak force in a relatively short period of time (10 to 50 milliseconds). Type II motor units are also known as a phasic motor unit because they are recruited after Type I motor units to provide short bursts, or phases, of higher muscle tension as required.