Muscular System - Part 1 PDF

Muscular System - Part 1 Nermin Eissa, Ph.D. College of Health Sciences Abu Dhabi University Fall-2023  Learning Outcomes: Identify the three types of muscle tissue and provide a function for each. Describe the general structu...

Muscular System - Part 1 Nermin Eissa, Ph.D. College of Health Sciences Abu Dhabi University Fall-2023  Learning Outcomes: Identify the three types of muscle tissue and provide a function for each. Describe the general structure of a skeletal muscle. Identify the structures of a muscle fiber. Summarize how activities within the neuromuscular junction control muscle fiber contraction. Explain how the sliding filament model is responsible for muscle contraction. ©2020 McGraw-Hill Education  Overview of the Muscular System 2 Muscular system Functions in: Movement of the entire organism. Movement of materials within the organism. Eg: blood, food. ©2020 McGraw-Hill Education  Types of Muscles Three types of muscle tissue: smooth, cardiac, and skeletal. The cells are called muscle fibers. ©2020 McGraw-Hill Education  Smooth Muscle 1 Fibers are: Shaped like cylinders with pointed ends. Uninucleated. Arranged in parallel lines, forming sheets. Not striated. Located in the walls of hollow internal organs and blood vessels and causes these walls to contract. Contraction is involuntary. ©2020 McGraw-Hill Education  Cardiac Muscle 1 Forms the heart wall. Fibers are: Uninucleated, striated, and tubular. Branched; interlock at intercalated disks. Relaxes completely between contractions, which prevents fatigue. Contraction: Is rhythmic. Occurs without nervous stimulation. Is involuntary. ©2020 McGraw-Hill Education  Skeletal Muscle Fibers are: Tubular, multinucleated, and striated. Make up skeletal muscles, which are attached to the skeleton. Very long; run the length of the muscle. Is voluntarily controlled. ©2020 McGraw-Hill Education  Functions of Skeletal Muscles 1 Functions of skeletal muscles: Support—muscle contraction opposes gravity and allows us to remain upright. Movements of bones and other body structures. Arms, legs, eyes, facial expressions, and breathing. Maintenance of a constant body temperature. Contraction causes ATP (adenosine triphosphate) to break down, releasing heat, which is distributed throughout the body. Protection of the internal organs Muscles pad the bones, and the muscular wall of the abdomen protects internal organs. ©2020 McGraw-Hill Education  Basic Structure of Skeletal Muscles Fascicle—bundle of skeletal muscle fibers. Within a fascicle, muscle fiber each fiber is surrounded by fascicle connective tissue; the fascia dense connective fascicle is also tissue tendon surrounded by connective tissue. ©2020 McGraw-Hill Education  Connecting muscle to bone Fascia—connective tissue muscle fiber that covers muscles and extends to become its fascicle tendon. fascia dense Small, fluid-filled sacs called connective tissue tendon bursae can often be found between tendons and bones. The bursae act as cushions, lubrication. ©2020 McGraw-Hill Education  Skeletal Muscles Work in Pairs 1 For a given movement, the origin of a muscle is the attachment site to the stationary bone, and the insertion is the attachment on the bone that moves. When a muscle contracts, it pulls on the tendons at its insertion and the bone moves. That is, when the biceps brachii contracts, it raises the forearm. 11 ©2020 McGraw-Hill Education  Skeletal Muscles Work in Pairs 2 Skeletal muscles usually function in groups. Agonist (prime mover)—the muscle that does most of the work. Antagonist—the muscle that acts opposite to a prime mover. That is, the biceps and the triceps are antagonistic muscle pair. biceps flexes the forearm, and the triceps extends the forearm. The muscle that is contracting is called the agonist and the muscle that is relaxing, or lengthening is called the antagonist. If both contract at once, there would be no movement. ©2020 McGraw-Hill Education  Check Your Progress State the three types of muscles in the human body and explain where each is found in the body. Summarize the functions of skeletal muscles. Explain how skeletal muscles work together to cause bones to move. ©2020 McGraw-Hill Education  Muscle Fibers and How They Slide 1 Cellular components of a muscle fiber: Sarcolemma—plasma membrane. Sarcoplasm—cytoplasm. Sarcoplasmic reticulum—endoplasmic reticulum. Calcium storage site. T (transverse) tubules—penetrate the cells; come close to portions of the sarcoplasmic reticulum. ©2020 McGraw-Hill Education  Muscle Fibers and How They Slide 2 Cellular components of a muscle fiber, continued: The sarcolemma contains many myofibrils, the contractile parts of muscle fibers. The sarcoplasm also contains glycogen, which provides energy for muscle contraction. The sarcoplasm includes the red pigment myoglobin, which binds oxygen. CHECK POINT ©2020 McGraw-Hill Education  The Structure of a Skeletal Muscle Fiber Cylindrical in shape. Grouped inside this larger cylinder are smaller cylinders called myofibrils. Myofibrils run the entire length of the muscle fiber. Made of smaller cylinders called myofilaments. Two types of myofilaments: Thick myofilaments are made up of myosin. Thin myofilaments are composed of actin. 16 ©2020 McGraw-Hill Education  Anatomy of a Muscle Fiber Table Name Function Sarcolemma The plasma membrane of a muscle fiber. Sarcoplasm The cytoplasm of a muscle fiber that contains the organelles, including myofibrils Myoglobin A red pigment that stores oxygen for muscle contraction T tubule An extension of the sarcolemma that extends into the muscle fiber and conveys impulses that cause Ca2+ to be released from the sarcoplasmic reticulum Sarcoplasmic The smooth endoplasmic reticulum (ER) of a muscle fiber that reticulum stores Ca2+ Myofibril A bundle of myofilaments that contracts Myofilament An actin or a myosin filament, whose structure and functions account for muscle striations and contractions ©2020 McGraw-Hill Education  Myofibrils and Sarcomeres 3 Myofibrils are further divided into sarcomeres. Sarcomeres extend between two dark vertical lines called Z lines. I band—light colored; made of only thin myofilaments. A band—made of overlapping thin and thick myofilaments. Centered within the A band is a vertical H band, which contains only thick myofilaments. ©2020 McGraw-Hill Education  Thick and Thin Myofilaments 1 Thick filaments. Thin filaments. Composed of the Made of two protein myosin. intertwining strands Each myosin molecule is of the protein shaped like a golf club, actin, with with the straight portion of the molecule tropomyosin, and ending in a globular troponin. head, or cross-bridge. ©2020 McGraw-Hill Education  Sliding Filament Model 1 Sliding filament model: the muscle fiber contracts as the sarcomeres shorten. ATP supplies the energy for muscle contraction. Note that when the sarcomere contracts, the filaments themselves remain the same length. The thin filaments slide past the thick filaments. The I band shortens, the Z lines move inward, and the H band almost disappears. ©2020 McGraw-Hill Education  Muscle Fiber Contraction 1 Motor neuron—a type of nervous system cell that stimulates muscle fibers to contract. Nerve—group of neurons. Axon—the part of a neuron that stimulates a muscle fiber. Branches, so can stimulate several muscle fibers. ©2020 McGraw-Hill Education Motor Neurons and Skeletal Muscle Fibers Join Neuromuscular Junctions ©2020 McGraw-Hill Education  Muscle Fiber Contraction 2 Neuromuscular junction. Where an axon terminal (end of an axon) comes near the sarcolemma. Synaptic cleft—the space that separates the two. Axon terminals contain synaptic vesicles filled with the neurotransmitter acetylcholine (ACh). When nerve signals traveling down the axon arrive at an axon terminal, synaptic vesicles release ACh into the synaptic cleft. ©2020 McGraw-Hill Education Motor Neurons and Skeletal Muscle Fibers Join Neuromuscular Junctions ACh diffuses across the cleft and binds to receptors in the sarcolemma. This generates electrical signals that spread across the sarcolemma and down the T tubules. This causes calcium to be released from the sarcoplasmic reticulum. 24 ©2020 McGraw-Hill Education  More Muscle Fiber Contraction When Ca2+ is released from the sarcoplasmic reticulum, it binds to troponin. The tropomyosin threads move, exposing myosin-binding sites. The Role of Calcium Ions and ATP During Muscular Contraction Threads of tropomyosin wind around the strands of actin, covering binding sites for myosin. Troponin occurs at intervals along the threads. 25 ©2020 McGraw-Hill Education  Steps of the Sliding Filament Theory 1 The myosin heads have ATP-binding sites. At this site, ATP is split to form ADP and P. Myosin heads attach to actin. Form temporary bonds called cross-bridges. ADP and P are then released and the myosin heads bend. This is the power stroke that pulls the actin filament toward the center of the sarcomere. 26 ©2020 McGraw-Hill Education  Steps of the Sliding Filament Theory 2 The binding of ATP to myosin heads breaks the cross-bridges. Myosin detaches from actin. The cycle begins again and myosin reattaches farther along the actin filament. The cycle recurs over and over, shortening the sarcomere (and therefore the muscle). The continuous sliding action of the myosin and actin filaments is called the ratchet mechanism. ATP 27 ©2020 McGraw-Hill Education  Steps of the Sliding Filament Theory 2 ATP and Ca2+ are important for muscle contraction  Check Your Progress Explain the role of the myofibril in a muscle fiber. Describe the role of both ATP and calcium ions in muscle contraction. CHECK POINT 29 ©2020 McGraw-Hill Education Muscular System - Part 2 Nermin Eissa, Ph.D. College of Health Sciences Abu Dhabi University Fall-2023 Learning Outcomes: Summarize how muscle cells produce ATP for muscle contraction. 2 ©2020 McGraw-Hill Education  Energy for Muscle Contraction Muscles have four different sources of energy: Two are stored in muscle (glycogen, triglycerides) and two are acquired from blood (glucose, fatty acids). Which of these are used depends on exercise intensity and duration. As time of exercise increases, use of muscle energy stores decreases and use of energy sources from the blood increases. 3 ©2020 McGraw-Hill Education  The Sources of Energy for Muscle Contraction Access the text alternative for these images 4 ©2020 McGraw-Hill Education  Sources of ATP for Muscle Contraction Muscle cells store limited amounts of ATP. Once it is used up, they have three ways to produce more ATP: The creatine phosphate (CP) pathway. Fermentation. Cellular respiration. Mitochondria uses oxygen, so is aerobic; neither the CP pathway nor fermentation requires oxygen (are anaerobic). 5 ©2020 McGraw-Hill Education  The Three Pathways by Which Muscle Cells Produce the ATP Energy Needed for Contraction Access the text alternative for these images 6 ©2020 McGraw-Hill Education  The Creatine Phosphate Pathway 1 The creatine phosphate pathway—the simplest and fastest way for muscle to make ATP 7 ©2020 McGraw-Hill Education  The Creatine Phosphate Pathway 2 Creatine phosphate is formed only when a muscle cell is resting, and only a limited amount is stored. Creatine phosphate-derived ATP powers the first few seconds of muscle contraction The CP pathway is used at the beginning of exercise. Creatine phosphate can only provide approximately 15 seconds worth of energy, at which point another energy source has to be used. 8 ©2020 McGraw-Hill Education  Fermentation 1 The anaerobic processes of glycolysis and fermentation produce two ATPs from the breakdown of glucose to lactate. Hormones signal cells to break down glycogen, making glucose available as an energy source. Fermentation, like the CP pathway, is fast-acting, but results in the buildup of lactate. Lactate produces short-term muscle aches and fatigue. 9 ©2020 McGraw-Hill Education  Fermentation 2 Oxygen debt—heavy breathing following strenuous exercise is required to complete the metabolism of lactate and restore cells to their original energy state. 10 ©2020 McGraw-Hill Education  Cellular Respiration Cellular respiration—the slowest of all three mechanisms used to produce ATP, but the most efficient. Occurs in the mitochondria. Myoglobin—a protein in muscle cells that delivers oxygen directly to the mitochondria. Can use glucose from stored glycogen, glucose in the blood, and fatty acids. 11 ©2020 McGraw-Hill Education  Check Your Progress Summarize how the CP pathway, fermentation, and cellular respiration produce ATP for muscle contraction. 12 ©2020 McGraw-Hill Education