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Muscular System Muscles: Designed for Motion How Muscles are Classified • Muscles – The three main types of muscles are skeletal, smooth, and cardiac – Voluntary Muscles – Muscles that are generally under conscious control (usually skeletal) – Involuntary Muscles – Muscles that not under conscious control (smooth and cardiac) • Skeletal Muscles – Primary function is to move the skeleton, made of muscle fibers – Muscle Fibers (Cells) – Bound together in parallel bunches, the contracting mechanism causes the muscle to be striated or striped. – Striated Muscle – Another name for skeletal muscle • Smooth Muscle – Shorter, wider cells in a looser arrangement, specialized for long, slow, powerful contractions, used in circulatory and digestive systems, in the iris, and in women during birth • Cardiac Muscles – Similar to skeletal muscle but designed to contract continually, only found in the heart and is self stimulating Important Muscles • Sternocleidomastoid – Connect the temporal bones to the sternum and clavicle, Allows for movement of the head • Temporalis – Moves the lower jaw when it is chewing or talking • Masseter – Located near your lower jaw and works with the Temporalis • Trapezius – Connected to the spine, head, and scapula, moves shoulders back and up, raises the head • Intercostal Muscles – Muscles between the ribs, used to raise the rib cage and expand the thoracic cavity when they contract • Pectoralis Major – Connected to the sternum, extends across the chest and connects to the humerus, used when you push your hands in front of your body • Deltoid – Connected to your clavicle and humerus (shoulder), used in raising your arm away from your body • Latissimus Dorsi – Connects each humerus to the lumbar region, used for drawing your arms toward your body • Biceps Brachii – Located on the front of each upper arm, used to bend your forearm toward your body • Triceps Brachii – Located on the back of each upper arm, used to straighten the arm • Fingers Flexed/Extended – Muscles in the forearm connected to tendons that run to the hands allow the fingers to be flexed and extended • Rectus Abdominus – (6-pack Abs) Extend from the bottom of the sternum to the top of the pelvic girdle, used when you sit up from reclining • External Oblique – Connect the ribs to the pelvis, used for bending sideways (Laterally) • Erector Spinae – Extend vertically along the spine from the upper back to the pelvis, used to hold your body upright • Gluteus Maximus – (butt) Largest and strongest muscle in the whole body, connected to pelvis and femur, used to move the leg downward and to the rear • Quadriceps Femoris – A group of four muscles on the front of the upper leg, used to straighten the leg • Sartorius – Connects the outside of the pelvic bone to the inside of the tibia, used to lift the lower leg and turn it inward • Hamstrings – A group of three muscles on the back of the upper leg, used to bend the leg at the knee • Gastrocnemius – Largest muscle on the back of the lower leg, used to extend the foot downward 1 4 2 5 3 6 7 9 8 10 Engineered for Power The Design of Skeletal Muscle • Fascia (8) (Epimysium) – The tough translucent sheath that covers the entire muscle • The fascia tapers at each end into tendons (7) that connect the muscle to the bone • Fascicle (9) – Inside the muscle there are bundles of muscle cells called fascicles • Perimysium (1) – The outer covering of a fascicle made of connective tissue • Nerves and vessels (2) run between the fascicles to supply food and oxygen and signal the muscle to contract • Muscle Fiber (Cell) (4) – Inside the fascicle there are many muscle fibers that are made of many microfibrils – Each muscle is made of millions of muscle fibers (cells) – Each muscle cell has many nuclei and an unusually large amount of mitochondria • Microfibril (6) – Long tubes bunched together to make each muscle fiber; they are made of many sarcomeres • Endomysium (3) – Tough connective tissue between the muscle fibers • Sarcolemma (Cell Membrane) (5) - The outer covering of the muscle fiber (cell) • Sarcomere (12) – Overlapping protein fibers made of thick (myosin) and thin (actin) filaments that work together to contract the muscle (this is why skeletal muscles have a striated appearance) 7 8 4 9 1 2 3 5 6 12 Muscle contraction • Neuromuscular Junction – Where the nerve connects to the muscle, triggers the muscle to contract • On average one nerve can stimulate 100 muscle cells • The group of muscle cells stimulated by a nerve cell is called a motor unit • A motor unit allows there to be less nerve cells for every muscle cell • If there are less muscle cells per nerve cell, those muscles are more precise • If there are more muscle cells per nerve cell, those muscles are less precise • Each muscle has thousands of motor units, when you use a muscle some of the units contract while others are relaxed • All-or-none Principle – When motor units are stimulated, they completely contract and completely relax until stimulated again Muscles in Strength and Weakness Exercise is Healthy for Muscles • Hypertrophy – The enlargement of muscles through use • Atrophy – The degeneration of muscles through the lack of use • Red Fibers – Muscle fibers that contain a large amount of mitochondria and myoglobin; have a pronounced red color – Contract more slowly, but have more endurance, are called slow-twitch fibers – Myoglobin – A protein that stores oxygen • White Fibers – Muscle fibers that contain smaller amounts of mitochondria and myoglobin; do not have a pronounced red color – Have more myofibrils and contract faster and more strongly, are called fast-twitch fibers • You can train your muscles to perform a certain task • A weightlifter and marathon runner have about the same amount of muscle cells, they are just trained for a different task. • Weight Lifter Has more White Fibers • Marathon Runner Has more Red Fibers Exercise • We need to continue to exercise so the muscle will at least remain in the same condition • If we do not exercise our muscles will deteriorate • Warming up – Allows muscle contraction and cellular respiration to occur more efficiently • Cooling down – Allows excess lactic acid to be removed from the muscle to reduce soreness • If a muscle is strained, there is usually no noticeable strength loss after healing • Muscle Fatigue – When a muscle becomes stiff, sore, and difficult to contract – Caused by a build-up of waste products in the muscle • Cramp – A sudden , painful, involuntary contraction, caused by a lack of ATP • Muscle Tone – A state of slight tension in a relaxed muscle, which a small number of cells are contracted – Allows your muscles to be ready for action – Needed for good posture • A Functioning Unit • Both skeletal and muscular systems need all the other systems to be working together with them. • Skeletal system gives the muscular system a support • Nervous system sends electrochemical signals to the muscular system to contract • Muscle Sense – Sensors in the muscle tissue relay messages to the brain, informing it of location and tension