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205textnotes33 - • calmodulin complex activates smooth...

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- actin and myosin is in a lattice/criss-cross arrangement. Fig. 12-27 - these are attached to dense bodies in the cytoplasm (not z-lines) and plaques on the cell membrane. - contracts into ball-like shape. - Sliding filaments Fig. 12-27 . B.2. Two Types of Smooth Muscle : 1. " single-unit " Fig. 12-25a = all muscle fibres in the muscle will contract if 1 or 2 of the muscle fibres are depolarized to threshold - neighbouring cells joined by gap junctions transmit action potentials - example = hollow bodied structures = stomach, uterus, bladder 2. " multi-unit " Fig. 12-25b = functionally independent units of muscle fibres that contract independently of each other. - excited by the autonomic nervous system - example = blood vessels, respiratory tract, base of the hair follicles B.3. Regulation of Smooth Muscle Contraction : Figs. 12-28, 12-29, 12-30; Ca ++ binds to calmodulin (protein in cytosol)
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Unformatted text preview: • calmodulin complex activates smooth muscle myosin ATPase through myosin light chain kinase (MLCK) (Phosphorylation of protein plays a key role in smooth muscle contraction) Fig. 12-26 • Actin regulation through caldesmon Fig. 12-27 • ATP hydrolyzed --> energized myosin • very slow ATPase activity • therefore, confraction-time is much longer, but sustain contraction for much longer duration. • energy (ATP) requirement is 1/10 to 1/30 of skeletal muscle fibres B.4. Differences in Muscle Contraction Sequence As Compared to Skeletal Muscle : Table 12-3- unitary smooth muscle can be stimulated by . .. 1) Autonomic Nervous System 2) Hormones 3) Changes in ECF composition (pH, concentration of metabolites) 4) Mechanical stretch 5) Spontaneous changes in membrane potential - cyclical changes in ion permeability....
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