Muscle Tissue Characteristics –Cells are referred to as fibers –Contracts or shortens with force when stimulated –Moves entire body and pumps blood Types –Skeletal:attached to bones –Cardiac: muscle of the heart. –Smooth: muscle associated with tubular structures and with the skin. Nonstriated and involuntary.

10-2 Muscular Tissue

10-3 Functions of Muscle Tissue Producing body movements Stabilizing body positions Regulating organ volumes –bands of smooth muscle called sphincters Movement of substances within the body –blood, lymph, urine, air, food and fluids, sperm Producing heat –involuntary contractions of skeletal muscle

Special functional characteristics of muscle  Contractility  Only one action: to shorten  Shortening generates pulling force  Excitability  Nerve fibers cause electrical impulse to travel  Extensibility  Stretch with contraction of an opposing muscle  Elasticity  Recoils passively after being stretched

Muscle Tissue I. Striated Muscle - regularly arranged contractile units A. Skeletal Muscle - long, cylindrical multinucleated cells with peripherally placed nuclei. Contraction is typically quick and vigorous and under voluntary control. Used for locomotion, mastication, and phonation. B. Cardiac Muscle - elongated, branched cells with a single centrally placed nucleus and intercalated discs at the ends. Contraction is involuntary, vigorous, and rhythmic. II. Smooth Muscle - possesses contractile machinery, but it is irregularly arranged (thus, non-striated). Cells are fusiform with a central nucleus. Contraction is involuntary, slow, and long lasting.

Muscle Regeneration and Growth Skeletal Muscle Increase in size (hypertrophy) Increase in number (regeneration/proliferation) Satellite cells are proposed source of regenerative cells Smooth Muscle Increase in size (hypertrophy) Increase in number (regeneration/proliferation) Smooth muscle cells are proliferative (e.g. uterine myometrium and vascular smooth muscle) Vascular pericytes can also provide source of smooth muscle Heart Muscle Increase in size (hypertrophy) Formerly thought to be non-proliferative Post-infarction tissue remodeling by fibroblasts (fibrosis/scarring) New evidence suggests mitotic cardiomyocytes and regeneration by blood or vascular-derived stem cells

Epimysium - dense irr. c.t. Perimysium - less dense irr. c.t. Endomysium - basal lamina and reticular fibers Skeletal Muscle Investments ALL MUSCLE CELLS HAVE BASAL LAMINAE!

FROM THE OUTSIDE IN

Formation of a skeletal muscle fiber (muscle cell) Skeletal muscle cells (fibers) develop from the fusion of myoblasts, resulting in large, multinuclear cells. The cells then assemble their contractile machinery in the cytoplasm. These come in the form of myofibrils, which have an alternate dark-light banding pattern when viewed from the side. The fact that the cell is chock-full of these myofibrils pushes the nuclei to the periphery of the cell.

10-11 Muscle Fiber or Myofibers Muscle cells are long, cylindrical & multinucleated Sarcolemma = muscle cell membrane Sarcoplasm filled with tiny threads called myofibrils & myoglobin (red-colored, oxygen-binding protein)

Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Microscopic anatomy of a skeletal muscle fiber Nuclei Fiber NucleusLight I band Dark A band Sarcolemma Mitochondrion H zone (b) Myofibril (a) (c) Thin (actin) filament Thick (myosin) filament Z disc

Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Composition of thick and thin filaments (b) (c) (d) (e) (a) Heads Flexible hinge region Tail Myosin head Troponin complexTropomyosin Actin Thin filamentThick filament Thin filament (actin)Thick filament (myosin)Myosin heads Myosin molecule Portion of a thick filament Portion of a thin filament Longitudinal section of filaments within one sarcomere of a myofibril Transmission electron micrograph of part of a sarcomere

10-14 Filaments and the Sarcomere Thick and thin filaments overlap each other in a pattern that creates striations (light I bands and dark A bands) They are arranged in compartments called sarcomeres, separated by Z discs. In the overlap region, six thin filaments surround each thick filament

Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Microscopic anatomy of a skeletal muscle fiber I band Z disc I bandA band H zone (c) (d) (e) Thin (actin) filament Thick (myosin) filament Thin (actin) filament Elastic (titin) filaments Z disc M line Sarcomere Thick (myosin) filament I band thin filaments only H zone thick filaments only M line thick filaments linked by accessory proteins Outer edge of A band thick and thin filaments overlap

Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle Myofibril Myofibrils Triad Tubules of sarcoplasmic reticulum Sarcolemma Mitochondrion I band A band H zoneZ disc Part of a skeletal muscle fiber (cell) T tubule Terminal cisterna of the sarcoplasmic reticulum M line

Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Connective tissue sheaths of skeletal muscle (b) (a) Bone Perimysium Endomysium Blood vessel Muscle fiber (cell) Fascicle (wrapped by perimysium) Endomysium (between fibers) Epimysium Tendon Epimysium Muscle fiber in middle of a fascicle Perimysium Blood vessel Endomysium

Cardiac Muscle Tissue Features: Striated (same contractile machinery) Self-excitatory and electrically coupled Rate of contractions modulated by autonomic nervous system –innervation is neuroendocrine in nature (i.e. no “motor end plates”) Cell Features: 1 or 2 centrally placed nuclei Branched fibers with intercalated discs Numerous mitochondria (up to 40% of cell volume) Sarcoplasmic reticulum & T-tubules appear as diads at Z lines –T tubules are about 2x larger in diameter than in skeletal muscle transport Ca 2+ into fibers

Cardiac Muscle (longitudinal section) Cardiac muscle is composed of smaller, branched muscle cells, which are connected to each other by intercalated discs. These intercalated disks, which are unique to cardiac muscle tissue, include adherent junctions for cell-cell strength, as well as gap junctions to allow electrical synchrony (so the cells contract at the same time). Similar to skeletal muscle, cardiac muscle fibers are packed with myofibrils, which are in-register, and give the tissue a striated appearance. Each cardiac muscle cell has a single nucleus that is centrally located.

Smooth Muscle Fusiform, non-striated cells Single, centrally-placed nucleus Contraction is non-voluntary Contraction is modulated in a neuroendocrine manner Smooth muscle tissue is composed of many smooth muscle cells. Although there are connective tissue elements (e.g. collagen) between the cells, smooth muscle is much more cellular than connective tissue. In addition, smooth muscle cells are smaller than cardiac and skeletal muscle cells. These features result is a tissue that has lots of nuclei. Depending on the orientation of the cells, the nuclei are slightly elongated in longitudinally-oriented cells (L), or round in transverse (cross) -sections (T). 6 major locations: 1.inside the eye 2. walls of vessels 3. respiratory tubes 4. digestive tubes 5. urinary organs 6. reproductive organs

Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings., p (b)(a) Spinal cord Motor neuron cell body Muscle Branching axon to motor unit Muscle fibers Nerve Motor unit 1 Motor unit 2 Muscle fibers Motor neuron axon Axon terminals at neuromuscular junctions

Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. The cross bridge cycle ATP ADP ATP hydrolysis ADP ATP PiPi PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Thin filament As ATP is split into ADP and P i, the myosin head is energized (cocked into the high-energy conformation). Inorganic phosphate (P i ) generated in theprevious contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released. Myosin head (low-energy configuration) Thick filament As new ATP attaches to the myosin head, the link between Myosin and actin weakens, and the cross bridge detaches

--Skeletal muscle cells have the largest diameter, cardiac muscle cells are smaller, and smooth muscle cells have the smallest diameter. --The diameter of skeletal muscle is very consistent between cells. Cardiac muscle cells are somewhat consistent in diameter (but vary in shape), while the smooth muscle cell profiles vary depending on whether the cell is sectioned through the middle (with nucleus) or near the periphery of the cell (without nucleus). --Skeletal muscle nuclei are near the plasma membrane, while cardiac and smooth muscle nuclei are centrally located. --In cuts through the nucleus of a cell, there is significant cytoplasm in skeletal and, to a lesser extent, cardiac muscle, while smooth muscle has a small rim of cytoplasm around the nucleus. --In ideal sections, stippling can be seen in skeletal and cardiac muscle, but not smooth muscle. skeletal muscle 320X smooth muscle 320X cardiac muscle 480X