Skeletal Muscle Lab Report

In this lab report I will be talking about exercise 3, the skeletal muscle lab. I will be going over the contraction of a frog’s gastrocnemius muscle. An overview of muscle contraction is based on the organization of the cytoskeletal proteins. The contraction is the shortening of a sarcomere, which is caused by the thick myosin filaments sliding past the thin actin filaments. The actual filaments aren’t getting shorter just sliding past each other. The contraction is caused by physical interaction of the myosin heads and the adjacent actin filaments, which is governed by regulatory proteins, tropomyosin and troponin. Tropomyosin is part of the thin filament and troponin is a Ca++ binding protein that controls the shape of the tropomyosin. The process of contraction begins when the action potential travels down the T-tubules of the sarcolemma, which then activates the release of Ca++ . The Ca++then binds to troponin triggering the movement of tropomyosin away from its blocking position at the myosin and actin binding sites. The binding and hydrolysis of ATP to the myosin head produces changes, causing the filament to slide against the myosin filament and the sarcomere to shorten (Johnson 37-38).
As talked about in lecture excitable tissues will not respond or depolarize to a stimulus unless the stimulus is strong enough and last long enough. Once threshold has been reached the muscle will then react or in the case of this lab the muscle will twitch. This is called the all-or-none law, which means, the nature of the response does not depend on the strength or duration meaning if that were to increase the amplitude would not also increase. Therefore the strength of the muscle response could be altered by the initial length of the muscle, degree of relaxation, the temperature of the muscle, and the types of ions surrounding the muscle