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Chapter 8:

Chapter 8:. Contraction and Excitation of Smooth Muscle by Dr. Mudassar Ali Roomi (MBBS, M. Phil.). CLASSIFICATION OF THE MUSCULAR TISSUE. Non-striated muscle (smooth muscle) Striated muscle (cardiac, skeletal muscle). SMOOTH MUSCLE. No cross striations

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Chapter 8:

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  1. Chapter 8: Contraction and Excitation of Smooth Muscleby Dr. Mudassar Ali Roomi (MBBS, M. Phil.)

  2. CLASSIFICATION OF THE MUSCULAR TISSUE • Non-striated muscle (smooth muscle) • Striated muscle (cardiac, skeletal muscle)

  3. SMOOTH MUSCLE • No cross striations • Location: in the walls of blood vessels, hollow viscera • Function: controls the size of the lumen. • Shape: each fiber is fusiform in shape. • Diameter: 3-8 um • Length: 15-200 um • No well developed sarcotubular system. Caveolae are present. • Nucleus: single, rod- shaped nucleus located in the centre of each cell.

  4. Cytoplasm of smooth muscle fiber • E/M shows that actin and myosin are present in the cytoplasm. • Actin: diamter is 5-7 nm • Myosin: diameter 12-16 nm • actin/myosin ratio: 15/1 • Desmin intermediate filaments are also present in the cytoplasm. (dia= 10 nm) • Dense bodies: intermediate filaments cross over one another to form darkly staining patches.

  5. MULTI-UNIT AND UNITARY SMOOTH MUSCLES

  6. MULTI-UNIT AND UNITARY SMOOTH MUSCLES • Location • Type of NM Junctions • Arrangement • Control • Membrane potential.

  7. MULTI-UNIT AND UNITARY SMOOTH MUSCLES MULTIUNIT: Ciliary muscle of eye, Iris of eye and pilo-erector muscle, vas deference 1: LOCATION: • UNITARY: Wall of GIT, ureter, bile duct, uterus and large blood vessels.

  8. MULTI-UNIT AND UNITARY SMOOTH MUSCLES MULTIUNIT: Individual muscle fibers. Each fiber has insulating outer membrane with glycoprotein and collagen consistency. Independently each muscle fiber is excited. 2: ARRANGEMENT: • UNITARY: Sheaths or bundles with gap junctions in between, so act as single unit. If one part is excited  whole is excited.(functinalsyncytium)

  9. MULTI-UNIT AND UNITARY SMOOTH MUSCLES 3: TYPE OF NM JUNCTION: • UNITARY: Diffuse junction. No contact with nerve fiber. Neurotransmitter is released near the fiber. • MULTIUNIT: Contact junction. One of the autonomic nerves form junction with muscle fiber and releases neurotransmitter like nor-epinephrine

  10. MULTI-UNIT AND UNITARY SMOOTH MUSCLES 4: CONTROL: • UNITARY: • Mainly non-nervous stimuli (hormonal stimuli like oxytocin and serotonin). • Nervous stimuli are less important • Show spontaneous contractions. • MULTIUNIT: • Mainly through nervous stimuli. • Does not show spontaneous contraction

  11. MULTI-UNIT AND UNITARY SMOOTH MUSCLES Types of potential in unitary smooth muscles 5: MEMBRANE POTENTIAL: • UNITARY: 3 types: • Spike potential , • Action potential with Plateau and • spikes superimposed on Slow wave. • MULTIUNIT: • action potential is not produced. • Only localized depolarization in response to excitation.

  12. EXCITATION-CONTRACTION COUPLING OF SMOOTH MUSCLE FIBERS

  13. EXCITATION-CONTRACTION COUPLING OF SMOOTH MUSCLE FIBERS

  14. MLC inactive (dephosphorylated) MLC active (phosphorylated) Contraction-Relaxation – myosin based regulation Ca2+ Ca2+ calmodulin Relaxation MLCP MLCK Contraction MLCK, myosin light chain kinase MLCP, myosin light chain phosphatase

  15. Mechanisms That Increase Intracellular Ca2+ Concentration in Smooth Muscle

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