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Title: Muscles 1- Introduction – Bones provide the framework and leverage of the body, however, they cannot move by themselves. Locomotion results from the alternating contraction and relaxation of muscle a- Muscles make up approximately 45-50% of the body’s total weight b- Muscle strength reflects the three prime function of muscle which is to convert chemical energy into mechanical energy to generate force, perform work and produce movement c- Muscle tissue helps to stabilize the body’s position, regulate organ volume, generates heat and propels fluids and food throughout the body 2- Muscle Structure a- There are three types of muscle and while they share many properties they differ from one to another in their microscopic anatomy, location in the body and control by nervous and endocrine systems 1- Skeletal- 2- Smooth 3- Cardiac – 3- Functions of Skeletal Muscle – a- Through sustained relaxation and contraction muscle tissue has four key functions 1- Producing body movement – 2- Stabilizing body position – 3- Sharing, storage and moving substances within the body – a- Contraction of ring-like bands of smooth muscles called sphincters prevent the outflow of contents of hollow organs such as the stomach and rectum b- Temporary storage of food and urine is made possible by closing these sphincters c- Cardiac muscle contraction pumps blood out of the heart and through the vessels d- Contraction and relaxation in smooth muscles in blood vessels adjust their diameter, regulate flow, help to regulate blood pressure e- Smooth muscle contractions move food, bile and enzymes through the digestive tract and push gametes through the reproductive system f- Skeletal muscle contraction promotes the flow of lymph and returns blood to the heart 4- Heat Generation – 4- Properties of Muscle Tissue – Muscle tissue has four special properties that enable them to function and contribute to homeostasis a- Electrical excitability – A shared property of neurons and muscle cells is the ability to respond to certain stimuli by producing electrical signals known as action potentials or nerve impulses. These impulses travel along the plasma membrane in ion channels 1- b- Contractility – The ability to contract and produce force is due to its ability to respond to an action potential. When the muscle contracts it generates tension by pulling on attachment points (tendons inserted on bone) c- Extensibility – d- Elasticity - Questions: 1- Which type of muscle is controlled consciously and which is controlled unconsciously? 2- What properties do muscle tissue and neurons share in common? 3- How are extensibility and elasticity related? Title: Muscles Continued 1- The most important component of skeletal muscle are the muscle fibers 2- The diameter of mature muscle fibers range from 10 – 100 (10-6 or 1/25,000 inch) 3- A typical length of a muscle fiber is about 10 cm (4 in) 4- Embryologically, 100’s of myoblasts (muscle forming cells) fuse to form a single fiber. Therefore a mature fiber is a single cell with 100’s of nuclei 5- Skeletal muscles do not undergo mitosis – In general you are born with all the muscle fibers you are ever going to have. a- Hypertrophy – b- Hyperplasia – c- Hypertrophy results from the production of HGH and the muscles response to it and to increased levels of testosterone (primarily in men) at puberty d- Atrophy – 6- Satellite cells – a- Fibrosis – Replacement of skeletal muscle with scar tissue 7- Sarcolemma, Transverse tubules (T-tubules) and Sarcoplasm 8- Myofibrils – High magnification of the sarcoplasm shows parallel threads about 2 micron in diameter running the entire length of the fiber. These threads are called myofibrils 9- Within each myofibril are smaller structures called filaments. The filaments are directly involved with contraction. These filaments are set up as alternating thin filaments (8nm) and thick filamemts (16nm) a nanometer is 10-9 or .0001 10- Filament Structure – Thick and thin filaments overlap each other to a greater or lesser extent depending on whether the muscle is relaxed, contracted or stretched. a- A Band – b- H Zone – c- I Band – d- Z Disc – e- M line – 11- Muscle Proteins a- Myosin – b- Actin c- Myosin acts as a protein motor that pushes or pulls other structures to provide movement by converting the chemical energy of ATP into mechanical energy that can produce force d- Actin – contains a myosin binding site. When a muscle contracts the myosin attaches to the binding site of the actin and shortens its length, pulling it closer to the M-Line.