Skeletal Muscle Lab Report

Introduction Muscle is one of the four main types of tissue, and is primarily involved in movement. There are three types of muscle tissue: skeletal, smooth, and cardiac. Skeletal muscle was investigated in this lab. Skeletal muscle is composed of two filaments called actin and myosin, which run parallel to each other. Actin has a protein that run along it called tropomyosin, that prevents actin from binding to it, unless calcium is bound to a part of the tropomyosin called troponin. Sets of actin and myosin filaments are divided into individual units called sarcomeres. Sarcomeres are what gives skeletal muscle tissue its striations. Bundles of actin and myosin filaments are called myofibrils, and myofibrils are bundled together into
At its very base, contractions are caused from actin and myosin sliding past each other. When this happens in a large amount of motor units simultaneously, the muscle is shortened, which is a contraction. The contraction is initiated from an action potential propagating from a motor neuron. Once the action potential reaches the axon terminal, calcium flows into the cytoplasm of the terminal. This causes vesicles containing a neurotransmitter to be released. The neurotransmitter binds to receptors on the motor end plate of the muscle, causing the inflow of sodium and another action potential. This action potential propagates down the T-tubule, which causes the release of calcium from the sarcoplasm. The calcium binds to troponin, allowing Actin and Myosin to bind together, by the myosin head binding to a site on the actin. (Sadava and others
Summation was tested with two stimuli. It was hypothesized that as the interval between the 2 stimuli decreased, the strength of the second twitch would be greater. This is due to the muscle having not fully relaxed from the first twitch. It was also hypothesized, that the interval could be brief enough to when the second stimulus is applied and it would produce one large twitch rather than two small twitches. This is due to second stimulus being applied during the initial contraction before any relaxation at all. Tetanus was tested with 60 stimuli. It was hypothesizes that as the interval between the stimuli decreased, tetanus would occur due to continuous summation. It was also hypothesized that because of the constant summation, the force of the contraction from the tetanus would increase as the intervals between the stimuli decreased. Fatigue was tested with 1750 stimuli with a very small interval between each application. It was hypothesized that the muscle would fatigue, and the contraction would stop before every stimuli was applied. This would happen as the ATP needed for the contraction would run out. (Sadava and others