LAB 4 - Michele Ahmadi Systems Physiology Lab 2 Tues...

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Michele Ahmadi: Systems Physiology Lab 2 Tues- 6:40-10:00, Jen Muscle Contraction ABSTRACT Contraction and the response amplitude of a muscle is directly controlled by the strength and frequency of the stimulus acting upon it. Recruitment of motor units can be accomplished by increasing stimulus strength. This, in turn, also increases the amplitude of response. A threshold stimulus of 0.3 volts yielded a minimal contractile response of 0.24 volts, whereas a stimulus of 1.8 volts in the same muscle yielded a significantly higher contractile response of 1.5 volts. In this manner, one muscle can give rise to a wide range of forces appropriate for various activities. Since the activation of a muscle fiber is tightly controlled by calcium levels present in the sarcoplasm, calcium accumulation also results in an increase in contractile response. Calcium accumulation can be accomplished by increasing stimulus frequency. Amplitude of a muscle contraction is also affected by fiber composition and length of muscle. Muscles composed of fast-fibers have a high capability for electrochemical transmission of action potential. These fibers are also adept in calcium release and uptake and have a high rate of cross- bridge turnover. In regards to muscle length, any deviation from the optimal length of the muscle (usually found in situ) will produce a decreased contractile response. Stretching or compressing the muscle even 1mm from resting length produced a decrease in response by 1.0 volts and 1.1 volts respectively. Electrically stimulating an isolated frog gastrocnemius attached to a force transducer, we were able to record how stimulus amplitude, stimulus frequency, muscle composition and muscle length all influenced the production of a simple muscle contraction –a twitch.
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INTRODUCTION Manipulation of an electrical stimulation to an isolated muscle can be used as a basic method to study skeletal muscle adaptation. Regulating electrical stimulation allows for a repeatable, measurable change in muscle structure. In turn, the quantifiable changes in muscle structure can also be used to track physiological changes that occur in response to different stimulations. Basic physiology of a skeletal muscle fiber is uniform throughout the vertebrates, regardless of the species. Skeletal muscle is made up of thousands of cylindrical muscle fibers. These fibers are bound together by connective tissue, which is innervated by nerves and blood vessels. Each muscle fiber is characterized by an array of myofibrils, stacked lengthwise, that run the entire length of the fiber. The myofibrils of a fiber are not composed of a single cell, and are additionally characterized by several contractile components. Every myofibril contains an inclusive sarcolemma, an inner sarcoplasmic reticulum, and myofilaments –the functional units of a muscle. The myofilaments are further differentiated into a thick filament of myosin and a thin filament of actin. The parallel structure of one actin filament and one myosin filament, a sarcomere, is the basic functional unit of a muscles’
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LAB 4 - Michele Ahmadi Systems Physiology Lab 2 Tues...

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