I.Overview of Muscle Tissues (pp. 276–278; Table 9.1)
A.Types of Muscle Tissue (p. 277; Table 9.1)
1.Skeletal muscle is associated with the bony skeleton and consists of large cells that bear striations and are under voluntary control.
2.Cardiac muscle occurs only in the heart and consists of small cells that are striated and under involuntary control.
3.Smooth muscle is found in the walls of hollow organs and consists of small, elongated cells that are not striated and are under involuntary control
B.Special Characteristics of Muscle Tissue (p. 277)
1.Excitability (responsiveness) is ability to receive & respond to a stimulus
2.Contractility is the ability to contract forcibly when stimulated
3.Extensibility is the ability to be stretched.
4.Elasticity - ability to resume cells’ original length once stretched
C.Muscle Functions (pp. 277–278; Table 9.1)
1.Muscles produce movement by:
a. acting on the bones of the skeleton
b. pumping blood
c. propelling substances throughout hollow organ systems
2.Muscles aid in maintaining posture by adjusting the position of the body with respect to gravity.
3.Muscles stabilize joints by exerting tension around the joint.
4.Muscles generate heat as a function of their cellular metabolic processes.
5.Muscles enclose and protect internal organs,
6. Muscles form valves that regulate passage of substances in the body,
7. Muscles control the size of the pupil of the eye, and
8. Muscles attach to hair follicles as arrector pili muscles.
II.Skeletal Muscle (pp. 278–305; Figs. 9.1–9.24; Tables 9.1–9.3)
A.Gross Anatomy of Skeletal Muscle (pp. 278–279; Fig. 9.1; Tables 9.1, 9.3)
1.Each muscle has a nerve and blood supply that allows neural control and ensures adequate nutrient delivery and waste removal.
2.Connective tissue sheaths are found at various structural levels of each muscle:
a. endomysium surrounds each muscle fiber
b. perimysium surrounds groups of muscle fibers
c. epimysium surrounds whole muscles
3.Skeletal muscles span joints and cause movement to occur from the movable attachment (the muscle’s insertion) toward the less movable attachment (the muscle’s origin).
B.Microscopic Anatomy of a Skeletal Muscle Fiber (pp. 279–285; Figs. 9.2–9.5; Tables 9.1, 9.3)
1.Skeletal muscle fibers are large, cylindrical cells with multiple nuclei beneath the sarcolemma, or plasma membrane.
2.Sarcoplasm, the cytoplasm of a muscle cell, is similar to other types of cells, except it has large amounts of:
a. glycosomes, for glycogen storage
b. myoglobin, an oxygen binding pigment similar to hemoglobin
3.Myofibrils account for roughly 80% of cellular volume and contain the contractile elements of the muscle cell.
4.Striations are due to a repeating series of dark A bands & light I bands
5.Myofilaments make up myofibrils and consist of thick & thin filaments
6.Striations, alternating dark A bands & light I bands, extend the length of each myofibril.
a.Each A band has a lighter central region, the H zone, which is bisected vertically by an M line.
b.Each I band is bisected vertically by a Z disc, and the region extending from one Z disc to the next forms a sarcomere, the smallest contractile unit of a muscle cell.
7.There are two types of myofilaments in muscle cells: thick filaments composed of bundles of myosin & thin filaments composed of strands of actin
a.Each myosin filament consists of myosin molecules that have a rod-like tail attached to two globular heads that form cross bridges with actin during contraction.