These questions are general concept questions I am having a hard time understand

Question

These questions are general concept questions I am having a hard time understanding the full concepts, regarding muscle contraction & the membrane potentials of such activity...

•Why does contraction last longer than calcium elevation?

•Is there a theoretical analogy between tetanic contraction and an electric light bulb heated by AC?

•If only a few fibers in a muscle are activated, what do you think would happen to the rest of the fibers?

If you all could give your insight upon these questions I would greatly appreciate it!

Explanation / Answer

A tetanic contraction is a normal type of muscle contraction in which a skeletal muscle stays full contracted, under voluntary control, until the mind decides to relax it. During this state a motor unit has been maximally stimulated by its motor neuron and remains that way for some time. This occurs when a muscle’s motor unit stimulated by multiple impulses at a sufficiently high frequency. Each stimulus causes a twitch. If stimuli are delivered slowly enough, the tension in the muscle will relax between successive twitches. If stimuli are delivered at high frequency, the twitches will overlap, resulting in titanic contraction.

MUSCLE FIBRES: There are three primary muscle fiber types in humans Type I, Type IIA, and Type IIB . Type I are referred to as “slow twitch oxidative”, Type IIA are “fast twitch oxidative” and Type IIB are “fast twitch glycolytic”. As their names suggest each type has very different functional characteristics. Type one fibers are characterized by low speed production and high endurance, Type IIB by high speed production and low endurance while Type IIA fall in between. These characteristics are as a result, primarily of the fiber’s Myosin heavy chain composition with Myosin heavy chain isoforms I, IIA and IIX corresponding with muscle fiber types I,IIA and IIB.

Individual muscles are made up of individual muscle fibers and these fibers are further organized into motor units grouped within each muscle. A motor unit is simply a bundle or grouping of muscle fibers. When you want to move the brain nearly instantaneously sends a signal or impulse through the spinal cord that reached the motor unit. The impulse then tells that particular motor unit to contract its fibers. When a motor unit fires all the muscle cells in that particular motor unit then contract with 100% intensity. So, a muscle cell either contracts 100% or not at all. A motor unit is either recruited 100% or not at all. Therefore, there is no such thing as a partially firing motor unit or a partially contracted muscle fiber.

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