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Chapter 8:

Chapter 8:. Contraction and Excitation of Smooth Muscle. Slides by Thomas H. Adair, PhD. Bio 411 Relevant Info:. Today – smooth muscle (Guyton Ch. 8). Quiz at end of class over last week’s material.

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Chapter 8:

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  1. Chapter 8: Contraction and Excitation of Smooth Muscle Slides by Thomas H. Adair, PhD

  2. Bio 411 Relevant Info: • Today – smooth muscle (Guyton Ch. 8). • Quiz at end of class over last week’s material. • Wednesday – finish smooth muscle, begin overview of nervous system/spinal nerves/cranial nerves (Moore, Introduction pp. 47-58) • Next quiz – Friday Oct. 24 • Lab tomorrow – continue working on pectoral region. May start abdominal region (dissector pp. 78-86).

  3. Types of Smooth Muscle • Mononucleate cells with no striations (smooth in polarized light). • Form muscular walls of hollow organs - gut, airways, blood vessels & urogenital system • 2 sorts of organization • Unitary: sheets of electrically coupled cells which act in unison (a ‘syncytium’ e.g. gut and bladder) • Multiunit: tissue made of discrete bundles of cells (no coupling) which are densely innervated and contract only in response to its innervation (e.g. iris, piloerectors) Figure 8-1; Guyton & Hall

  4. intermediate filament (form structural backbone) thick filament thin filament dense body (membrane dense area analogous to Z discs) mechanical junction (coupling cells) gap junction (electrical coupling) Special features of smooth muscle Smooth muscle: • Can operate over large range of lengths • Is very energy efficient • Can maintain force for long periods (hours, days, weeks) via latch state • Can be myogenic (spontaneously active) • Has Ca2+ action potentials. Ca entering through channels is a very important source of calcium • Poorly developed SR

  5. Smooth Muscle Neuromuscular Junction • Important points • Autonomic nerve fibers branch and form “diffuse junctions” with underlying smooth muscle fibers. • Varicosities in the terminal axons contain neurotransmitter. • Excitation is transmitted by Ca action potential or simple diffusion of Ca into fiber. Figure 8-3; Guyton & Hall

  6. MLC inactive (dephosphorylated) MLC active (phosphorylated) Contraction-Relaxation – myosin based regulation Ca2+ • Important points: • Initiated by calcium • Calcium binds to calmodulin • (instead of troponin as in skm) • Ca-calmodulin-MLCK complex • leads to phosphorylation of MLC • (requires 1 ATP) • MLC is part of myosin head • Phosphorylated myosin head • binds to actin and power stroke • occurs automatically • A second ATP is required to release myosin head from actin • Cross-bridge cycling requires both • MLCK and MLCP Ca2+ calmodulin Relaxation MLCP MLCK Contraction MLCK, myosin light chain kinase MLCP, myosin light chain phosphatase

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