Muscle lab 2

Isotonic vs isometric

In an isotonic contraction, muscle length changes during contraction, but tension will remain constant. In an isometric contraction, tension will increase or change while the length of the muscle remains the same.

Define concentric and eccentric contractions.

In an isotonic contraction, there are two types of contractions: concentric and eccentric. In a concentric contraction, the muscle will shorten and do work. In an eccentric contraction, the muscle will contract as it lengthens.

Describe how increasing the stimulus frequency affected the force developed by the isolated whole skeletal muscle in the "tetanus in isolated skeletal muscle" activity.

Increasing the stimulus frequency increased the amount of active force that was exerted by the skeletal muscle

Wave summation

Muscle semi relaxes

When you are holding an object for a short period of time does the number of motor units remain the same? Are the same motor units used throughout the duration of holding the object? Explain.

The number of motor units remains the same, and the same motor units are used throughout the duration-however they will get fatigued. The number of motor units is proportional to the amplitude of the measured EMG. Holding an object would be a weak contraction, using a few motor units. If holding the object is the only activity, a stronger contraction is not necessary, so the same number of motor units is used.

Explain why it would take you longer to perform 10 repetitions lifting a 10-kg weight than it would to perform the same number of repetitions with a 5-kg weight.

The velocity of shortening decreases with a heavier load, so the repetitions will take longer with a 10 kg weight. The influence of load is the element that affects the time period of lifting the different weights. Velocity and duration of contraction are influenced by load; The greater the load(10kg weight), the slower the contraction. Therefore, the 10kg weight or greater load will take longer to complete the repetitions than that of the 5kg weight which is lighter or less load.

Turning the stimulator off allows a small measure of muscle recovery. Thus, the muscle will produce more force for a longer time period if the stimulator is briefly turned off than if the stimuli were allowed to continue without interruption. Explain why this might occur.

When the stimulator is off, the muscle can relax and redistribute chemicals and neurotransmitters from inside the cell to outside. When the chemicals aren't built up inside the muscle, it increases the length of time that a muscle could undergo maximum tension. If muscle isn't allowed to rest, the amount of time that the muscle is fatigued becomes longer because there are chemicals and neurotransmitters built up inside the muscle.

Frequency-dependent wave summation

mpulses are delivered in succession, greater frequency equals higher magnitude until summation stops and tetanus occurs

Treppe

muscle fiber still recovers fully between twitches but each builds more tension than the one before (stairs)

Wave-summation in vivo -

nervous system increases rate of motor neurons

Skeletal muscle twitch

A single action potential produces a single muscle contraction Latent contraction and relaxation

Based on the unique arrangement of myosin and actin in skeletal muscle sarcomeres, explain why active force varies with changes in the muscle's resting length.

Active force depends on the rate of combine between actin and myosin. If the resting length of the muscle is shortened, there are more actin bound to myosin which increases the active force. When the resting length of the muscle is shortened, the active force amount increases. When the resting length of the muscle is lengthened, the active force amount decreases.

Agonist vs. Antagonist

Agonist is the primary muscle The antagonist opposed the action of another muscle or the primary muscle

What types of contractions are occurring in the right quadriceps femoris muscle as you walk up stairs (isometric, isotonic - concentric, isotonic - eccentric)? For each of the 3 steps listed below, list the specific type of contraction that occurs. Concentrate on the actions at the knee joint, not the hip joint. As you raise your right leg up to the next step: ________. As you raise your entire body up to the next step: _______. As you stand on the right leg while the left leg is being raised up to the step:____

As you raise your right leg up to the next step: ________eccentric____________ o As you raise your entire body up to the next step: _______concentric____________ o As you stand on the right leg while the left leg is being raised up to the step: ___isometric______

Latent period

(excitation) the period of time between muscle membrane depolarization, events of excitation-contraction coupling