Muscle Physciology 2.docx

Smooth muscle Found in hollow organs and tubes such as airway and blood vessels. Has single nucleus per cell. Spindle shaped cells. Has no sarcomeres like skeletal muscles. 3 types of filaments Thick filament Bundles of Myosin More heads available for binding (no gap) Arranged so it sends filaments...

Smooth muscle Found in hollow organs and tubes such as airway and blood vessels. Has single nucleus per cell. Spindle shaped cells. Has no sarcomeres like skeletal muscles. 3 types of filaments Thick filament Bundles of Myosin More heads available for binding (no gap) Arranged so it sends filaments in opposite directions rather than in the middle. Thin filaments Actin Tropomyosin No troponin Intermediate filaments For structural stability The filaments are arranged in a cris-cross pattern across the cell and held together and stabilised by ‘dense bodies’ which replaces Z lines as smooth muscles don’t have sarcomeres. When the cell contracts, the thin filaments pass in opposite directions along thick filaments. In smooth muscle, there is a myosin light chain which wraps around the neck of myosin. This plays a crucial role because myosin head will only bind to actin when the myosin light chain is phosphorylated. Release of Ca2+ causes it to bind with a signalling molecule called calmodulin. Calmodulin activates an enzyme called myosin light chain kinase. Myosin light chain kinase adds a phosphate group therefore phosphorylates the myosin light chain so the cross-bridge cycle can take place. Smooth muscle can be either multiunit or single unit. Multiunit smooth muscle Neurogenic Phasic