A motor unit controls a muscle fiber and consists of a motor neuron. A muscle comprises numerous motor units managed by distinct motor neurons which react to different levels of stimulation. Electric shock changes membrane permeability to permit passage of sodium and potassium ions which act as an action potential. As the motor neurons stimulate a motor unit at varying levels of stimulation, more motor units become active with increased stimulation.
Starting at a shock of 0.3 volts, there was a minimal reaction with shock due to a contraction of a limited number of muscle fibers. When the shock was increased to 1 volt, the amount of contracting muscle fibers increased, resulting in an elevated tension in the muscle. However, at approximately 1 volt, the muscle tension remained similar as all possible motor units had been activated in the muscle. High-voltage shocks resulted i
...n contractions that produced constant maximum tension, creating a single twitch-type contraction in each fiber within the muscle.
During the Length-Tension Lab, it was observed that at a maximum tension of 28mm, the sarcomeres reach an ideal level for generating maximum cross-bridge coupling. As the muscle contracts, the thin filaments slide past each other and the sarcomere shortens, causing the cross-bridges to form and then break down. No other length is capable of facilitating the same amount of travel and coupling. However, at 30mm, the sarcomere becomes too taut to permit cross-bridges to form and contract.
When the sarcomeres reach 26mm, their ability to contract further is greatly restricted. In terms of muscle contractions, summation occurs when the muscle doesn't fully relax between contractions and was initially noticed after 200 milliseconds. Incomplete tetanus
refers to increased tension during repeated contractions and was first observed after 170 milliseconds.
The observation of complete tetanus revealed a prolonged contraction that obscured individual contractions, with onset at 70 milliseconds. Frog Muscle Labs (by kmwalls) define a motor unit as a motor neuron and the corresponding muscle fiber it controls, whereas a whole muscle exhibits varying levels of responsiveness to stimulation. An electric shock serves as an action potential trigger, with no reaction occurring at 0 or low voltage levels unable to reach the threshold required for action potential production.
The least response of the muscle occurs when the shock is at a low voltage. However, a 1 volt shock increases the tension of each muscle fiber as a result of high-voltage shocks. These shocks cause contractions that make the sarcomere so tense that cross-bridges cannot form and contract. The contractions were not observable at 26mm, but complete tetanus was observed after 70 milliseconds.
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