Can someone explain to me what happens in graph A an explanation can help me und
ID: 3477023 • Letter: C
Question
Can someone explain to me what happens in graph A an explanation can help me understand this
Recruitment/Derecruitment of Motor Unit . What happen to the derecruitement threshold compare to MU2: contraction time 31.6 ms the recruitment? Always lower. No clear explanation of this hysteresis effect 30 Muscle fiber thixotropv (change in viscosity)? Residual actomyosin bonds? Recruitment threshold 2.4 N l Derecruitment i threshold 1.6 N 5 S What other (than more fiber recruitment) mechanisms could explain increase in force production? n-100 0 1 23 Recruitment Threshold (N) 4 5 67Explanation / Answer
MU2 are the medium size muscle fibers of the extensor carpii radialis(ECR). Time required by MU2 from resting membrane potential to go to action potential and return back to resting membrane potential - is 31.6ms
At resting membrane potential - the conductance for K+ ions is 50 to 100 times as great as the conductance for sodium ions. At the onset of the action potential, the Na+ channels instantaneously become activated
and allow up to a 5000-fold increase in Na+ conductance. Through the voltage gated Na+ channel - Na+ enters the muscle membrane leading to depolarisation of the membrane potential. This leads to recuritment of a muscle fiber. During, repolarisation - the Na+ channels begin to close and the K+ channels open more than normal. Then, rapid diffusion of K+ ions to the outside of muscle cell membrane, re-establishes the normal negative resting membrane potential leading to de-recruitment of the muscle fiber.
Hennemenn's Sixe principle, states that under load, motor units are recruited from smallest to largest. This means that slow-twitch, low-force, fatigue-resistant muscle fibers are activated before fast-twitch, high-force, less fatigue-resistant muscle fibers. It was proposed by De:Elwood Henneman.
Now we put together the physiology behind, when a MU2 of ECR contract isometrically, a recuritment threshold of 2.4N is required to generate an action potential across the muscle cell membrane, and a potential of 1.6N is required as derecuritment threshold, to restore the resting membrane potential.