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Smooth Muscle Physiology

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Presentation on theme: "Smooth Muscle Physiology"— Presentation transcript:

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 Smooth Cardiac 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

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 Smooth muscle is found in the walls of hollow organs. *Their muscle cells are fusiform in shape. *Smooth muscle cells have just on nucleus per cell. *Smooth muscle is nonstriated. *Smooth muscle is involuntary. *The contractions of smooth muscle are slow and wave-like.

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 Smooth Muscle

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 Properties of Single-Unit Smooth Muscle
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

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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