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Smooth Muscle Physiology

Smooth Muscle Physiology. Muscular System Functions. Body movement (Locomotion) Maintenance of posture Respiration Diaphragm and intercostal contractions Communication (Verbal and Facial) Constriction of organs and vessels Peristalsis of intestinal tract

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Smooth Muscle Physiology

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  1. Smooth Muscle Physiology

  2. Muscular System Functions • Body movement (Locomotion) • Maintenance of posture • Respiration • Diaphragm and intercostal contractions • Communication (Verbal and Facial) • Constriction of organs and vessels • Peristalsis of intestinal tract • Vasoconstriction of b.v. and other structures (pupils) • Heart beat • Production of body heat (Thermogenesis)

  3. Properties of Muscle • Excitability: capacity of muscle to respond to a stimulus • Contractility: ability of a muscle to shorten and generate pulling force • Extensibility: muscle can be stretched back to its original length • Elasticity: ability of muscle to recoil to original resting length after stretched

  4. Types of Muscle • Skeletal • Attached to bones • Makes up 40% of body weight • Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement • Voluntary in action; controlled by somatic motor neurons • Smooth • In the walls of hollow organs, blood vessels, eye, glands, uterus, skin • Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow, • In some locations, autorhythmic • Controlled involuntarily by endocrine and autonomic nervous systems • Cardiac • Heart: major source of movement of blood • Autorhythmic • Controlled involuntarily by endocrine and autonomic nervous systems

  5. Connective Tissue Sheaths • Connective Tissue of a Muscle • Epimysium. Dense regular c.t. surrounding entire muscle • Separates muscle from surrounding tissues and organs • Connected to the deep fascia • Perimysium. Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle • Contains b.v and nerves • Endomysium. Loose connective tissue that surrounds individual muscle fibers • Also contains b.v., nerves, and satellite cells (embryonic stem cells function in repair of muscle tissue • Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis.

  6. Nerve and Blood Vessel Supply • Motor neurons • stimulate muscle fibers to contract • Neuron axons branch so that each muscle fiber (muscle cell) is innervated • Form a neuromuscular junction (= myoneural junction) • Capillary beds surround muscle fibers • Muscles require large amts of energy • Extensive vascular network delivers necessary oxygen and nutrients and carries away metabolic waste produced by muscle fibers

  7. Muscle Tissue Types

  8. Smooth Muscle • Fusiform cells • One nucleus per cell • Nonstriated • Involuntary • Slow, wave-like contractions

  9. Smooth Muscle • Cells are not striated • Fibers smaller than those in skeletal muscle • Spindle-shaped; single, central nucleus • More actin than myosin • No sarcomeres • Not arranged as symmetrically as in skeletal muscle, thus NO striations. • Caveolae: indentations in sarcolemma; • May act like T tubules • Dense bodies instead of Z disks • Have noncontractile intermediate filaments

  10. Smooth Muscle • Grouped into sheets in walls of hollow organs • Longitudinal layer – muscle fibers run parallel to organ’s long axis • Circular layer – muscle fibers run around circumference of the organ • Both layers participate in peristalsis

  11. Smooth Muscle • Is innervated by autonomic nervous system (ANS) • Visceral or unitary smooth muscle • Only a few muscle fibers innervated in each group • Impulse spreads through gap junctions • Who sheet contracts as a unit • Often autorhythmic • Multiunit: • Cells or groups of cells act as independent units • Arrector pili of skin and iris of eye

  12. Smooth Muscle Cell

  13. Smooth Muscle Contraction: Mechanism

  14. Smooth Muscle Relaxation: Mechanism

  15. Excitation-Contraction Coupling:(below)

  16. Single-Unit Muscle

  17. Gap junctions Pacemaker cells with spontaneous depolarizations Innervation to few cells Tone = level of contraction without stimulation Increases/decreases in tension Graded Contractions No recruitment Vary intracellular calcium Stretch Reflex Relaxation in response to sudden or prolonged stretch Properties of Single-Unit Smooth Muscle

  18. Multi-Unit Muscle

  19. Multi vs. Single-Unit Muscle

  20. Comparisons Among Skeletal, Smooth, and Cardiac Muscle

  21. Disorders of Muscle Tissue • Muscle tissues experience few disorders • Heart muscle is the exception • Skeletal muscle – remarkably resistant to infection • Smooth muscle – problems stem from external irritants

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