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1. Muscle fiber All muscles contain mixture of fiber types. Among individual the same muscle can vary in its proportion of fiber types Sprinter: more white muscle fibers, fast twitch, fatigue prone Long distance runner: more red muscle fiber, slow twitch, fatigue resistant
2. Muscle Atrophy Weakening and shrinking of a muscle May be caused Immobilization Loss of neural stimulation
3. Muscle Hypertrophy Increase total mass of the muscle Increase fiber diameter due to increase actin and myosin filaments More capillaries More mitochondria
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5. Rigor Mortis Stiffening of the body beginning 3 to 4 hours after death Deteriorating sarcoplasmic reticulum releases calcium Calcium activates myosin-actin cross-bridging and muscle contracts, but can not relax. Muscle relaxation requires ATP and ATP production is no longer produced after death Fibers remain contracted until myofilaments decay
6. Smooth Muscle Composed of spindle-shaped fibers with a diameter of 1-5 m and lengths of several hundred m Found in walls of hollow organs, such as stomach, urinary bladder Not striated and involuntary Same mechanism of muscle contraction between myosin and actin filament in smooth muscle as in skeletal muscle
7. Microscopic Anatomy of Smooth Muscle SR is less developed than in skeletal muscle Plasma membranes have pouch like folding called caveoli T tubules are absent There is no troponin complex There are no visible striations No sarcomere Thin and thick filaments are present
8. Types of smooth muscle Multiunit smooth muscle Single unit (unitary) smooth muscle
9. Types of Smooth Muscle: Multi-unit Compose of discrete, separate smooth muscle fiber. Each fiber operates independently of the other fibers. Each fiber can contract independently of each other Multiunit smooth muscles are found: Attached to hair follicles, In the internal eye muscles
10. Types of Smooth Muscle: Single Unit The cells of single-unit smooth muscle, commonly called visceral muscle: Hundreds of smooth muscle contract together as a single unit The cell membranes are adherent to one another at multiple points, so force generated in one muscle fiber can transmitted to the next Cell membranes are joined by gap junction to one another via gap junctions so action potentials can travel from one fiber to the next and caused the muscle fiber to contract together
12. Organization and Contraction of Myofilaments in Smooth Muscle Dense body which are similar to Z line Actin and myosin absence of banding pattern Thick and thin filaments are arranged diagonally Myosin cross bridge arranged in opposite direction. This allows myosin to pull actin in one direction in one side while pulling another actin on the opposite direction on the other side
14. Contraction Mechanism Ca2+ is released from the SR and from the extracellular space Ca2+ binds to calmodulin and activates it The calmodulin-calcium combination joins with and activates myosin light chain kinase (phosphorylation enzyme) Activated kinase transfers phosphate from ATP to myosin cross bridges Phosphorylated cross bridges interact with actin to produce shortening
16. Cessation of Contraction Smooth muscle relaxes when intracellular Ca2+ levels drop Require myosin phosphatase which splits the phosphate from myosin Cycle stops and contraction ceases The time required for relaxation of muscle contraction is determined by the amount of active myosin phosphate in the cell
18. Source of Ca ions Sarcoplasmic reticulum is slightly developed in most smooth muscle. Almost all Ca ions that caused contraction enter the muscle cell from extracellular fluid. When extracellular fluid Ca ion concentration falls, smooth muscle contraction ceases. To cause relaxation of smooth muscle, Ca pumps used to pump calcium ions out back in to extracellular fluid. This pump is slow acting. Smooth muscle contraction last for few seconds rather than hundredths to tenths of a second as for skeletal muscle
