mechanism of smooth + Cardiac muscle contraction).pdf

mechanism of smooth muscle contraction. Guyton 104  Describe mechanism of smooth muscle contraction.  Describe mechanism of cardiac muscle contraction.  smooth muscle composed of smaller fibers 1 to 5 micrometers in diameter 20 to 500 micrometers in length WHILE...

mechanism of smooth muscle contraction. Guyton 104  Describe mechanism of smooth muscle contraction.  Describe mechanism of cardiac muscle contraction.  smooth muscle composed of smaller fibers 1 to 5 micrometers in diameter 20 to 500 micrometers in length WHILE skeletal muscle fibers are 30 times greater in diameter hundreds of times long same principles of contraction for smooth muscle & skeletal muscle DIFFERENCE is in physical arrangement of smooth muscle fibers TYPES OF SMOOTH MUSCLE two major types: multi-unit smooth muscle and unitary (or single-unit) smooth muscle Unitary smooth muscle also called syncytial smooth muscle or visceral smooth muscle The term “unitary” does not mean single muscle fibers Instead, it means a mass of hundreds to thousands of smooth muscle fibers that contract together as a single unit The fibers are arranged in sheets or bundles, and their cell membranes are adherent to one another at multiple points So force generated in one muscle fiber can be transmitted to the next syncytial interconnections cell membranes are joined by gap junctions so action potentials can travel from one fiber to the next and cause the muscle fibers to contract together also called visceral smooth muscle because it is found in the walls of most viscera of the body, including the gastrointestinal tract, bile ducts, ureters, uterus, and many blood vessels Multi-Unit Smooth Muscle Multi-unit smooth muscle is composed of separate smooth muscle fibers Each fiber operates independently of the others innervated by a single nerve ending outer surfaces of these fibers are covered by a thin layer of fine collagen and glycoprotein; This layer helps insulate the separate fibers from one another Characteristics of multi-unit smooth muscle fibers each fiber can contract independently of the others, and their control is exerted mainly by nerve signals examples of multi-unit smooth muscle are ciliary muscle of the eye iris muscle of the eye and the piloerector muscles (cause erection of the hairs when stimulated by the sympathetic nervous system) CONTRACTILE MECHANISM IN SMOOTH MUSCLE Chemical Basis for Smooth Muscle Contraction Smooth muscle contains both actin and myosin filaments similar to those skeletal muscle troponin complex control skeletal muscle contraction, while in smooth muscle contractile process is activated by calcium ions, influx Importance of smooth muscle organization SMOOTH MUSCLE SKELETAL MUSCLE Contract 80% of their length Contract 30% of their length Slow contraction (hours-days) Rapid contraction and due to slow calcium ion pump relaxation due to fast calcium ion pump in SR Increased force of contraction Less force due to prolonged period of attachment Require less ATP & Energy More ATP & Energy force of contraction depends force of contraction depends on extracellular fluid calcium on calcium ion concentration ion concentration in SR Membrane Potentials in Smooth Muscle depends on the momentary condition of the muscle In the normal resting state, the intracellular potential is usually about −50 to −60 millivolts Hormones effecting Sooth muscles cardiac muscle contraction Guyton 114  Acetylcholine is the chief neurotransmitter of the parasympathetic nervous system fight or flight response