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The Muscular System Muscles are responsible for all types of body movement Three basic muscle types are found in the body 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle Characteristics of Muscles Skeletal and smooth muscle cells are elongated (muscle cell muscle fiber) Contraction and shortening of muscles is due to the movement of microfilaments All muscles share some terminology o Prefixes myo and mys refer to “muscle” o Prefix sarco refers to “flesh” Skeletal Muscle Characteristics Most are attached by tendons to bones Cells are multinucleate Striated—have visible banding Voluntary—subject to conscious control Connective Tissue Wrappings of Skeletal Muscle Cells are surrounded and bundled by connective tissue o Endomysium—encloses a single muscle fiber o Perimysium—wraps around a fascicle (bundle) of muscle fibers o Epimysium—covers the entire skeletal muscle o Fascia—on the outside of the epimysium Skeletal Muscle Attachments Sites of muscle attachment o Bones o Cartilages o Connective tissue coverings Smooth Muscle Characteristics Lacks striations Spindle-shaped cells Single nucleus Involuntary—no conscious control Found mainly in the walls of hollow visceral organs (such as stomach, urinary bladder, respiratory passages) © 2015 Pearson Education, Inc. Cardiac Muscle Characteristics Striations Usually has a single nucleus Involuntary Found only in the walls of the heart Skeletal Muscle Functions Produce movement Maintain posture Stabilize joints Generate heat Microscopic Anatomy of Skeletal Muscle Sarcolemma—specialized plasma membrane Myofibrils—long organelles inside muscle cell o Light (I) bands and dark (A) bands give the muscle its striped appearance Microscopic Anatomy of Skeletal Muscle Banding pattern o I band light band Contains only thin filaments Z disc is a midline interruption o A band dark band Contains the entire length of the thick filaments H zone is a lighter central area M line is in center of H zone Microscopic Anatomy of Skeletal Muscle Sarcomere—contractile unit of a muscle fiber Organization of the sarcomere o Myofilaments produce banding (striped) pattern Thick filaments myosin filaments Thin filaments actin filament Stimulation and Contraction of Single Skeletal Muscle Cells Irritability (also called responsiveness)—ability to receive and respond to a stimulus Contractility—ability to shorten when an adequate stimulus is received Extensibility—ability of muscle cells to be stretched Elasticity—ability to recoil and resume resting length after stretching © 2015 Pearson Education, Inc. Mechanism of Muscle Contraction: The Sliding Filament Theory Activation by nerve causes myosin heads (cross bridges) to attach to binding sites on the thin filament Myosin heads then bind to the next site of the thin filament This continued action causes a sliding of the myosin along the actin The result is that the muscle is shortened (contracted) Energy for Muscle Contraction ATP o Immediate source of energy for muscle contraction o Stored in muscle fibers in small amounts that are quickly used up o After this initial time, other pathways must be utilized to produce ATP Energy for Muscle Contraction Three ways to generate ATP 1. Direct phosphorylation of ADP by creatine phosphate 2. Aerobic respiration 3. Anaerobic glycolysis and lactic acid formation Energy for Muscle Contraction Direct phosphorylation of ADP by creatine phosphate (CP)—fastest o Muscle cells store CP, a high-energy molecule o After ATP is depleted, ADP remains o CP transfers a phosphate group to ADP to regenerate ATP o CP supplies are exhausted in less than 15 seconds o About 1 ATP is created per CP molecule Energy for Muscle Contraction Aerobic respiration o Glucose is broken down to carbon dioxide and water, releasing energy (about 32 ATP) o A series of metabolic pathways occurs in the mitochondria o This is a slower reaction that requires continuous oxygen o Carbon dioxide and water are produced Energy for Muscle Contraction Anaerobic glycolysis and lactic acid formation o Reaction that breaks down glucose without oxygen o Glucose is broken down to pyruvic acid to produce about 2 ATP o Pyruvic acid is converted to lactic acid This reaction is not as efficient, but is fast o Huge amounts of glucose are needed o Lactic acid produces muscle fatigue © 2015 Pearson Education, Inc. Muscle Fatigue and Oxygen Deficit If muscle activity is strenuous and prolonged, muscle fatigue occurs because: o Ionic imbalances occur o Lactic acid accumulates in the muscle o Energy (ATP) supply decreases After exercise, the oxygen deficit is repaid by rapid, deep breathing Types of Muscle Contractions Isotonic contractions o Myofilaments are able to slide past each other during contractions o The muscle shortens, and movement occurs o Example: bending the knee; rotating the arm Isometric contractions o Tension in the muscles increases o The muscle is unable to shorten or produce movement o Example: pushing against a wall with bent elbows Muscle Tone Muscle tone keeps muscles healthy and ready to react o Result of a staggered series of nerve impulses delivered to different cells within the muscle o If the nerve supply is destroyed, the muscle loses tone, becomes paralyzed, and atrophies Effect of Exercise on Muscles Exercise increases muscle size, strength, and endurance o Aerobic (endurance) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue Makes body metabolism more efficient Improves digestion, coordination o Resistance (isometric) exercise (weight lifting) increases muscle size and strength Muscles and Body Movements Movement is attained as a result of a muscle moving an attached bone Muscles are attached to at least two points 1. Origin: attachment to a moveable bone 2. Insertion: attachment to an immovable bone Types of Body Movements Flexion o Decreases the angle of the joint o Brings two bones closer together o Typical of bending hinge joints (e.g., knee and elbow) or ball-and-socket joints (e.g., the hip) Extension © 2015 Pearson Education, Inc. o o o o Opposite of flexion Increases angle between two bones Typical of straightening the elbow or knee Extension beyond 180° is hyperextension Types of Body Movements Rotation o Movement of a bone around its longitudinal axis o Common in ball-and-socket joints o Example: moving the atlas around the dens of axis (i.e., shaking your head “no”) Types of Body Movements Abduction o Movement of a limb away from the midline Adduction o Opposite of abduction o Movement of a limb toward the midline Types of Body Movements Circumduction o Combination of flexion, extension, abduction, and adduction o Common in ball-and-socket joints o Proximal end of bone is stationary, and distal end moves in a circle Special Movements Dorsiflexion o Lifting the foot so that the superior surface approaches the shin (toward the dorsum) Plantar flexion o Depressing the foot (pointing the toes) o “Planting” the foot toward the sole Special Movements Inversion o Turning sole of foot medially Eversion o Turning sole of foot laterally Special Movements Supination o Forearm rotates laterally so palm faces anteriorly o Radius and ulna are parallel Pronation © 2015 Pearson Education, Inc. o Forearm rotates medially so palm faces posteriorly o Radius and ulna cross each other like an X Special Movements Opposition o Moving the thumb to touch the tips of other fingers on the same hand Interactions of Skeletal Muscles in the Body In general, groups of muscles that produce opposite actions lie on opposite sides of a joint We will explore examples in Figure 6.14 next Types of Muscles Prime mover—muscle with the major responsibility for a certain movement Antagonist—muscle that opposes or reverses a prime mover Synergist—muscle that aids a prime mover in a movement and helps prevent rotation Fixator—stabilizes the origin of a prime mover Naming Skeletal Muscles By direction of muscle fibers o Example: rectus (straight) By relative size of the muscle o Example: maximus (largest) Naming Skeletal Muscles By location of the muscle o Example: temporalis (temporal bone) By number of origins o Example: triceps (three heads) Naming Skeletal Muscles By location of the muscle’s origin and insertion o Example: sterno (on the sternum) By shape of the muscle o Example: deltoid (triangular) By action of the muscle o Example: flexor and extensor (flexes or extends a bone) © 2015 Pearson Education, Inc.