Musculoskeletal System PDF

The Musculoskeletal System Muscle Contraction Muscle Metabolism Concept Map Download Muscle Contraction App Expected Learning Outcomes Explain how muscles produce movement at joints. Describe how antagonistic muscles work at a joint. Explain the sliding filament mechani...

The Musculoskeletal System Muscle Contraction Muscle Metabolism Concept Map Download Muscle Contraction App Expected Learning Outcomes Explain how muscles produce movement at joints. Describe how antagonistic muscles work at a joint. Explain the sliding filament mechanism of muscle contraction Describe the role of calcium in muscle contraction. Differentiate between slow-twitch and fast-twitch muscle fibers Smooth and cardiac muscles In mammals, bones retain internal blood vessels A. True B. False 3 4  Skeletal Muscle Movement Two ways skeletal muscle fibers are attached to bones: Directly to the periosteum (external layer of the bone) Through a tendon attached to the periosteum One attachment of the muscle, the origin, remains stationary during contraction Muscles can be antagonistic § One counters the action of The other end, the insertion, the other is attached to a bone that *Try this: Stand and put one hand on moves when muscle contracts your back thigh muscles and one hand on your front thigh muscle. Bend your leg at the knee  Muscle contraction Each skeletal muscle contains numerous muscle fascicle 6 Muscle structure Myocyte = Muscle cell Sarcolemma = plasma membrane of the myocyte Each muscle fascicle contains bundle of Sarcoplasmic reticulum = muscle fibers endoplasmic reticulum of the =muscle cell myocyte Striate Muscle cells are fused together therefore multinucleate Muscle fiber = muscle cell = myocyte 7 Muscle structure Each muscle fiber (muscle cell) encloses a bundle of 4 to 20 elongated structures called myofibrils 8 Muscle structure Each myofibril in turn is composed of thick and thin myofilaments 9 Muscle structure ¡ Myofibrils have alternating dark and light bands because the thick and thin myofilaments overlap (dark) or do not overlap (light) 10 Myofibril structure Myofibrils are made of thin and thick myofilaments Thin myofilaments are composed of Actin Thick myofilaments are composed of myosin Sarcomere Smallest subunit of muscle contraction sarcomere  OPTIONAL Myofibril structure A bands - dark bands consist of stacked thick and thin myofilaments (made of myosin and actin respectively) H zone - no overlap of actin and myosin-consist only of thick myofilaments (myosin) I bands – consist only of thin myofilaments (actin) – Light bands – Divided into two halves by a disc of protein called the Z line Sarcomere – distance between two Z lines 12  OPTIONAL Myofibril structure Smallest subunit of muscle contraction Titin —the largest protein in the body, runs the full length of the sarcomere. Bundles of myosin filaments are held in the center of the sarcomeres by titin.  How does Skeletal Muscle Contract? 14 Muscle contracts and shortens because Myofilaments themselves do not the myofibrils (all the adjacent shorten sarcomeres) contract and shorten Instead, the thick and thin filaments slide relative to each other  Watch the video Muscle contraction process https://vimeo.com/101470181 Main information to retain is to understand how the contraction happens: sequence of events in the muscle cells Slide #17 to #32 is only supporting material to understand the mechanisms! Muscle contraction process Motor neuron terminus Muscle cell membrane Sarcolemma = endoplasmic reticulum Muscle cell cytoplasm where the myofibrils are (organised in sarcomeres)  How does Skeletal Muscle Contract? Note: The width of 17 the A band does not change. The width of Sliding Filament Thin filaments slide deeper into the sacromere Mechanism the A bands, making the H and I changes bands narrower  How does Skeletal Muscle Contract? 18 Muscle contracts and shortens Myofilaments themselves do not shorten because the myofibrils contract Instead, the thick and thin filaments slide and shorten relative to each other  How do the myofilaments slide? Thick filament – Composed of several myosin subunits packed together – Myosin consists of two polypeptide chains wrapped around each other – Each chain ends with a globular head Thin filament – Composed of two chains of actin proteins twisted together in a helix 19  How do the myofilaments slide? Cross-bridge cycle Hydrolysis of ATP by myosin activates the head for the later power stroke https://vimeo.com/101470181 20  How do the myofilaments slide? Cross-bridge cycle Hydrolysis of ATP by ADP and Pi remain bound to myosin activates the the head, which binds to head for the later actin forming a cross-bridge power stroke 21  How do the myofilaments slide? Cross-bridge cycle Hydrolysis of ATP by ADP and Pi remain bound to myosin activates the the head, which binds to head for the later actin forming a cross-bridge power stroke During the power stroke, myosin returns to its original shape, releasing ADP and Pi 22  How do the myofilaments slide? Cross-bridge cycle Hydrolysis of ATP by ADP and Pi remain bound to myosin activates the the head, which binds to head for the later actin forming a cross-bridge power stroke During the power stroke, ATP binds to the myosin returns to its head which original shape, releasing releases actin ADP and Pi 23  How do the myofilaments slide? Cross-bridge cycle Hydrolysis of ATP by ADP and Pi remain bound to myosin activates the the head, which binds to head for the later actin forming a cross-bridge power stroke The living body always contain ATP. How is this cycle regulated to Stop or Go During the power stroke, ATP binds to the myosin returns to its head which original shape, releasing releases actin ADP and Pi 24  How is the cross bridge cycle regulated? When a muscle is relaxed, its myosin heads cannot bind to actin because the attachment sites are blocked by tropomyosin In order for muscle to contract, tropomyosin must be moved aside by troponin This process is regulated by Ca2+ levels in the muscle fiber cytoplasm 25  How is the cross bridge cycle regulated? In low Ca2+ levels, tropomyosin inhibits cross-bridge formation In high Ca2+ levels, Ca2+ binds to troponin – Tropomyosin is displaced, allowing the formation of actin-myosin cross-bridges RELAXATION CONTRACTION 26  How is the cross bridge cycle regulated? In low Ca2+ levels, tropomyosin inhibits cross-bridge formation In high Ca2+ levels, Ca2+ binds to troponin –Tropomyosin is displaced, allowing the formation of actin- myosin cross-bridges Where does Ca+ come from and How its availability regulated 27 RELAXATION CONTRACTION  How are Ca+ levels regulated in the muscle fiber Cell? ¡ Ca+ in the muscle cell is stored in the sacroplasmic reticulum ü In a relaxed state, Ca+ is sequestered in the SR RELAXATION 28 How are Ca+ levels regulated in the muscle fiber Cell? ¡ Muscle fiber is stimulated to contract by motor neurons, which secrete acetylcholine at the neuromuscular junction Membrane becomes depolarized 29  How are Ca+ levels regulated in the muscle fiber Cell? ü Released neurotransmitter depolarizes the muscle cell ü Depolarization is conducted down the transverse tubules (T tubules) 30  How are Ca+ levels regulated in the muscle fiber Cell? Ø Release of Ca2+ links excitation by motor neuron to contraction of the muscle ü Muscle cell depolarization stimulate the release of Ca++ from the sarcoplasmic reticulum (SR) ü Ca++ released from the SR allows contraction to occur 31  Muscle contraction process Fill In the Blanks ¡ Use the following terms to fill in the blanks: A. Troponin Tropomyosin B. Acetylcholine ATP C. D. 32  optional In the sliding filament mechanism of muscle contraction, thin filaments are being pulled towards the — A. Z disc B. Sarcolemma C. M line D. Zone of overlap E. I band 33  Skeletal Muscle contraction physiology Motor unit – 1 Motor neuron and all the muscle fibers (muscle cells) that it innervates – All muscle fibers contract together when the motor neuron produces impulses Division of the muscle into units allows the strength of the More motor contraction to be finely units = stronger graded contraction Muscles that Muscles in charge of require finer degree exerting more force = of control = precise Large muscle movements require larger require motor units smaller motor units 34  Skeletal muscle contraction ¡ Muscles contain motor units in a variety of sizes ¡ They can be selectively activated by the nervous system Weak contraction = few motor units Strong contraction = more motor units & larger motor units Increase in numbers and sizes of motor units to produce stronger contraction is called recruitment 35 Functionally: 2 Types of Muscle Fibers A muscle stimulated with Summation = Tetanus = sustained a single electric shock sum of closely contraction with no quickly contracts and spaced relaxation between relaxes in a response twitches twitches called a twitch ¡ Skeletal muscles divided based on their contraction speed § Slow-twitch or type I fibers § Fast-twitch or type II fibers A twitch can be measured in terms of the tension or FORCE it generates 36  Types of Muscle Fibers Slow-twitch or type I fibers Fast-twitch or type II fibers ü Sustain action for long ü Adapted for rapid power generation periods of time ü Adapted to respire anaerobically ü Develop tension slowly but maintain it longer 37  Types of Muscle Fibers Slow-twitch or type I fibers Fast-twitch or type II fibers ¡ Rich in: § Poor in: § Capillaries Capillaries § Mitochondria Mitochondria § Myoglobin (O2 binding Myoglobin protein) § Use stored glycogen ¡ Appear as RED fibers § Appear as WHITE fibers 38  Types of Muscle Fibers Skeletal muscles have different proportions of fast-twitch and slow-twitch fibers depending on their main function Eye muscle has a high proportion of fast twitch Deep muscle in leg has high proportion of slow twitch 39 The muscles that move the eye have a high proportion of type II fibers and reach maximum tension very fast. These are: A. slow twitch fibers B. intermediate fibers C. fast twitch fibers D. medium fibers 40  Muscle metabolism Skeletal muscles at rest During use, energy also obtain most of their comes from glycogen energy from aerobic (energy store) and respiration of fatty acids glucose delivered by blood http://2.bp.blogspot.com/- http://www.futuresobright.com/images/app- a3bpqPBB9qQ/TVqE8fCQPUI/AAAAAAA content-images/1357196443_gym-physical- AQgc/D6v_xhPbars/s1600/rest.jpg exercise.jpg Energy from cellular respiration is needed to make ATP for the cross bridge cycle to pump Ca2+ back into the SR during muscle relaxation 41  Muscle Metabolism Time Individuals differ in their maximal capacity for >2 mins if not aerobic exercise strenuous = During the first AEROBIC Aerobic capacity = max rate of O2 consumption 45-90 sec of respiration moderate-heavy exercise muscles respire ANAEROBICALLY >2 mins if vigorous = AEROBIC & ANAEROBIC respiration 42 43 OPTIONAL Controls pace maker in cardiac muscle Also controls smooth muscle 44  Cardiac muscle Cardiac muscle is also striated—cells are smaller than skeletal muscle and have one nucleus. Cardiac muscle cells also branch and interdigitate—can withstand high pressures. Intercalated discs provide mechanical adhesions between cells. Gap Junctions-protein structure that allow cytoplasmic continuity between cells  Cardiac muscle Pacemaker and conducting cells initiate and coordinate heart contractions. Pacemakers make the heartbeat myogenic—generated by the heart muscle itself (no need for nervous signal). Autonomic nervous system modifies the rate of pacemaker cells but is not necessary for their function. Animated GIF image of a single human heart muscle cell beating. Image from https://www2.estrellamountain.edu/faculty/farab ee/biobk/heartbeat.gif  Smooth Muscles Smooth muscle = Simplest muscle; long spindle shape – in most internal organs, under autonomic nervous system control. Smooth muscle cells are arranged in sheets—have electrical contact via gap junctions. Action potential in one cell can spread to all others in the sheet.  Smooth Muscles ¡ Plasma membrane of smooth muscle cells is sensitive to stretch. Important for digestion and in blood vessels Stretched cells (such as when food pass through esophagus) depolarize and fire action potentials which start contraction.  CONCEPT MAP Signal travels down neuron releases sarcolemma Located on Binds to Muscle action potential formed Causes causes A. ACh B. Na+ flows in Exposes cle C. Troponin on cy in s th e contracti Lose P D. Tropomyosin moves B eg E. Powerstroke Actin binding F. Ca++ rushes out sites G. AP travels down t-tubules Lose H. Receptors ADP I. Detachment of myosin J. Ca++ channels open\ ATP binds K. crossbridge Do not expect to listen about scientific concepts like “how the muscle work”, but a very interesting theory worth listening to! Are we made for running? Christopher McDougall explores the mysteries of the human desire to run. How did running help early humans survive -- and what urges from our ancient ancestors spur us on today? McDougall tells the story of the marathoner with a heart of gold, the unlikely ultra-runner, and the hidden tribe in Mexico that runs to live. https://www.ted.com/talks/christopher_mcdougall_are_we_born_to_run#t -932779