ESS 205 Anatomy and Physiology Lecture 14Outline of Last Lecture I. Parts of Skeletal MusclesII. Skeletal Muscle ShapesIII. Muscle ActionsIV. Muscle InnervationV. Athletic InjuriesOutline of Current LectureVI. Universal Characteristics of MusclesVII. Skeletal MuscleVIII. CT Elements of MuscleIX. Skeletal Muscle FiberX. Regulatory vs. Contractile ProteinsXI. Organization of FilamentsCurrent Lecture1. There are five main characteristics of muscle. a. Responsiveness means the capability of response to chemical signals. It responds to electric changes across plasma membrane. b. Conductivity is the electrical change that triggers excitation.c. Contractility is the ability to shorten when stimulated.d. Extensibility is the capability of being stretched.e. Elasticity is how quickly it returns to its original resting length after being stretched. 2. Skeletal muscle is a voluntary striated muscle attached to bone. It can be as long as 30 cm (12in). It exhibits an alternating pattern between light and dark which is due to overlapping These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.arrangement of proteins. These proteins are actin and myosin. Skeletal muscles are under our conscious control. A big thing to note is that skeletal muscle is not only made up of muscle fibers. It is also made up connective tissue. There are two components:a. Parallel elastic components surround contractile parts. Endomysium perimysiumepimysium. b. Series elastic components are joined at the end- tendon, periosteum, and bone matrix. It returns muscles to their resting lengths. 3. Connective Tissue of Muscle is found between muscle fiber and bone. They are not excitable or contractible but they can stretch and have elasticity. 4. Muscle fiber, muscle cell, and myofiber are all SYNONOMOUS. A skeletal muscle fiber has multiple nuclei against inside of plasma membrane. There are four primary parts of a muscle fiber. a. Sarcolemma is the muscle cells plasma membrane. It has tunnel-like infoldings that penetrate the cell. Called transvers (T) tubules. They carry an electrical current to cell interior. b. Sarcoplasm is equivalent to cytoplasm. It is filled with long protein bundles called myofibrils. These bundles of parallel protein myofilaments are composed of actin and myosin. There is also glycogen for storing energy and myoglobin for binding oxygen within the sarcoplasm. c. The sarcoplasmic reticulum (SR) is the same as endoplasmic reticulum. It is an interconnected network as well as a calcium reservoir. d. Last is sarcomere. **UNDERSTAND THIS 100%** A sarcomere is 1 contractile unit. It is composed of myofilaments, contractile proteins, myosin, actin, and elastic filaments. i. Myofilaments= actin (thin) and myosin (thick).ii. Myosin is made of 200-500 myosin molecules. There are two entwined polypeptides that look similar to a golf club. They are arranged in bundles with heads directed outward. The central (middle) area is a bare zone with no heads. iii. Actin has two intertwined fibrous (F) strands. Each subunit has globular (G) actin with an active site. There is also a groove that holds tropomyosin whichblocks the active sites of actin from myosin. On top of these grooves are small calcium-binding troponins. They are stuck to each tropomyosin molecule. iv. Elastic filaments are huge springy proteins called TITIN. They connect the thick filament (myosin) to Z disc. The function of the elastic filaments is to keep thin and thick filaments aligned with each other, to resist overstretching, and helps cells recoil. 5. Myosin and Actin are CONTRACTILE proteins meaning that they do all the work. Tropomyosin and Troponin are regulatory proteins. They act as a switch to start and stopcontractions and release calcium to activate contractions. Troponin removes tropomyosin off active sites. 6. Organization of filaments. The A band is a thick filament region (dark). An H band contains no thin filaments (bare zone). An I band is a thin filament region (light) that is bisected by Z disc protein called connectinconnectin connects actin to Z disc. The I band has half a band on one sarcomere and the other half on a second sarcomere. The boundaries of a sarcomere are 1 Z disc to the next Z disc. The M line is the middle of