Question

The smallest diameter motor neuron is found with which fiber type:

a) SO

b) FG

c) FOG

d) all have the same size neuron

Answer 1

The smallest diameter motor neuron is found with which fiber type?

Answer: a) SO (slow oxidative)

Explanation: Small diameter, slow conducting motor neurons innervate slow oxidative fibers. Slow twitch fibers (type l fibers) are also known as slow oxidative fibers as mainly rely on aerobic oxidation for energy production. Therefore they contain large number of mitochondria and myoglobin. Slow oxidative fibers are smallest in diameter as well as in length. Since slow oxidative derive energy through aerobic oxidation, they contract slowly but for longer duration without getting fatigued. Since they do not rely much on glycolytic pathway for energy production, there is very less lactic acid production hence the chances of fatigue are less. Examples:- antigravity posture maintaining muscles, leg muscles. Slow oxidative fibers are mainly used during long distance marathon running.

Large diameter, fast conducting motor neurons innervate fast glycolytic fibers. Fast glycolytic fibers (type II fibers) rely mostly on glycolytic pathway for energy production hence they can get fatigued easily due to lactic acid production during glycolysis. They have large diameter and long length than slow oxidative fibers. They have more glycolytic enzymes and very less amount of mitochondria and myoglobin. They generate fast contraction for less duration of time. Hence, these muscle fibers are used during sprinting.