UNIT 7 Muscles and Muscle Tissue Chapter 9

1. UNIT 7 Muscles and Muscle Tissue (Chapter 9) Muscle Overview Skeletal Muscle Anatomy (7th edition)

2. Muscle Overview The main tissue in the heart, skeletal muscles, and the walls of hollow organs Makes up nearly half the body’s mass Types of Muscle Tissue SKELETAL muscle tissue – packaged into skeletal muscles; makes up 40% of body weight CARDIAC muscle tissue – occurs only in the walls of the heart SMOOTH muscle tissue – occupies the walls of hollow organs and other diverse places in the body (7th edition)

3. Muscle Overview Functional Features   contractility – long cells shorten and generate pulling forces excitability – electrical nerve impulse stimulates the muscle cell to contract extensibility – can be stretched back to its original length by contraction of an opposing muscle (agonist / antagonist relationship) elasticity – can recoil after being stretched   (7th edition)

4. Muscle Overview Functions of muscle tissue   movement (e.g. skeletal muscle moves body by moving the bones) squeezes fluids and other substances through hollow organs (smooth muscle) maintenance of posture – enables the body to remain sitting or standing joint stabilization heat generation – muscle contractions produce heat (“shivering”) to help maintain normal body temperature allows breathing to occur - e.g. the diaphragm contracts and relaxes to enable air to enter and exit the lungs   (7th edition)

5. SKELETAL MUSCLE ANATOMY Each skeletal muscle is an ORGAN consists mostly of muscle tissue skeletal muscle also contains connective tissue (remember that muscle tissue is not a connective tissue!), blood vessels, nerves (7th edition)

6. Macroscopic Anatomy of Skeletal Muscle FASCICLES are bundles of MUSCLE CELLS; muscle cells are also called MUSCLE FIBERS (fig. 9.2) Connective tissue sheaths bind a skeletal muscle and its fibers (cells) together EPIMYSIUM – dense connective tissue surrounding entire muscle PERIMYSIUM – surrounds each fascicle (group of muscle fibers)   ENDOMYSIUM – a fine sheath of connective tissue wrapping each muscle cell (7th edition)

7. Muscle attachments most skeletal muscles run from one bone to another ORIGIN – less movable attachment site INSERTION – more movable attachment site one bone will move (it has the insertion), while the other bone remains fixed (it has the origin) -- thus, the insertion moves toward the origin; e.g. the muscle in the picture has an origin in the humerus and insertion in the ulna; the ulna (insertion) moves toward the humerus (origin) Another example: e.g. the biceps brachii originates (at 2 points) in the scapula and inserts into the radius; the radius (insertion) moves toward the scapula (origin) muscles attach to origins and insertions by connective tissue; often the connective tissue is in the form of a TENDON or APONEUROSIS (broad tendon) bone markings are often present where tendons meet bones (e.g. tubercles, trochanters, and crests); that is why you learned the bones before studying the muscles! You will apply the bone marking terms that you learned in Units 4&5 when you learn the muscles of the body in the next unit (Unit 8) (7th edition)

8. Microscopic Anatomy of Skeletal Muscle Overview of the Muscle Fiber Structure (fig. 9.3 a,b,c) composed of MYOFIBRILS MYOFIBRILS are composed of MYOFILAMENTS MYOFILAMENTS are composed of a THIN FILAMENTS (contain ACTIN) and THICK FILAMENTS (contain MYOSIN) the plasma membrane of the muscle cell is called the SARCOLEMMA the cytoplasm of the muscle cell is called the SARCOPLASM (7th edition)

9. Table from a previous book edition: (7th edition)

10. Microscopic Anatomy of Skeletal Muscle SARCOMERE - the basic unit of contraction of skeletal muscle (fig. 9.3 c,d,e) Z discs (also called Z lines) – the boundaries of each sarcomere thin (actin) filaments – extend from Z disc toward the center of the sarcomere thick (myosin) filaments – located in the center of the sarcomere; overlap inner ends of the thin filaments A bands – full length of the thick filament; includes inner end of thin filaments (thus, there is overlap of thin and thick filaments) H zone – center part of A band where no thin filaments occur (thus, there is no overlap of thin and thick filaments) I band – region with only thin filaments (thus, there is no overlap of thin and thick filaments) (7th edition)

11. Microscopic Anatomy of Skeletal Muscle Ultrastructure and Molecular Composition of the Myofilaments (fig. 9.4) MYOSIN molecules contain the MYOSIN HEADS ACTIN chains contain TROPONIN (yellow structure), TROPOMYOSIN (brown, thread-like structure, and G-ACTIN (blue, globule structure) molecules (7th edition)

12. Microscopic Anatomy of Skeletal Muscle SARCOPLASMIC RETICULUM – a specialized smooth ER (fig. 9.5) composed of interconnecting tubules surrounding each myofibril CISTERNAE occur in pairs on either side of a T TUBULE some tubules form cross-channels called TERMINAL CISTERNAE the T TUBULE is a deep invagination of the SARCOLEMMA TRIAD is composed of a T TUBULE + 2 TERMINAL CISTERNAE the sarcoplasmic reticulum contains calcium ions; the ions are released when muscle is stimulated to contract; during stimulation calcium ions diffuse through the cytoplasm (sarcoplasm) of the muscle cell and trigger the sliding filament mechanism; when a muscle cell relaxes, calcium is actively pumped back into the sarcoplasmic reticulum (7th edition)

13. This concludes the current lecture topic Be sure to read the next lecture topic: Skeletal Muscle Physiology I (close the current window to exit the PowerPoint and return to the Unit 7 Startpage) (7th edition)