Muscles and Muscle Contractions PDF

Outcome D4 Explain the role of the motor system in the function of other body systems. Muscles and Muscle Contractions Outcome D4, Lesson 1 Muscle Facts! The human body has more than 650 muscles Waste energy keeps you warm! No two muscles in the body have exactly the same...

Outcome D4 Explain the role of the motor system in the function of other body systems. Muscles and Muscle Contractions Outcome D4, Lesson 1 Muscle Facts! The human body has more than 650 muscles Waste energy keeps you warm! No two muscles in the body have exactly the same function Muscles are efficient, using about 35 – 50% of their potential energy Muscle fibers are thinner than a human hair and can support up to 1,000 times its own weight Muscle is Latin for “little mouse” Human Muscles Muscle cells - highly specialized to convert chemical energy (ATP) into kinetic energy 3 Types: Smooth Cardiac Skeletal Smooth Muscles Cells Long, tapered cells arrange in parallel lines forming sheets Non-striated (no lines) Each cell has a single nucleus Contract involuntarily Found in walls arteries and internal organs Ex. Esophagus does peristalsis Contracts slowly but can sustain prolonged contraction without fatigue Ex iris constriction Cardiac Muscle Cells Striated, tubular, and branched Striated = have bands of light and dark Each cell has a single nucleus Contract involuntarily Found in walls of heart Skeletal Muscle Cells Striated and tubular Very long, each have many nuclei The needs for energy and materials are too great to be coordinated by one nucleus Contract voluntarily Usually attached to bones of skeleton The “meat” of animal bodies is skeletal muscle Because of their length and the way they are organized, skeletal muscles cells are often called muscle fibres Skeletal Muscle Function Support – contraction of muscles opposes force of gravity Movement – allows for movement of bones (ex. arms and legs) as well as eyes and face Maintain body temperature – ATP breakdown releases heat which spreads throughout the body! Protection – pads bones and cushions organs Stabilize joints – tendons help hold bones to joints Cooperation of Skeletal Muscles When muscles contract, they shorten Muscles can only pull they CANNOT push! Muscle contraction = work Muscle relaxation = passive Muscles are found in pairs One action always has an opposing action Ex. Bicep contraction = bent arm; triceps contraction = straight arm  Skeletal Muscle Structure Muscles – An organ surrounded by connective tissue and composed of several tissues, largest unit, attached to bone by tendons  Skeletal Muscle Structure Muscle-fibre bundles – a large number of muscle fibres bundled together and wrapped in connective tissue, blood vessels and nerves run between the bundles  Skeletal Muscle Structure Muscle fibres – muscle cells, up to 20 cm long, each fibres has approximately 300 mitochondria, connective tissue also wraps each fibre  Skeletal Muscle Structure Myofibrils – hundreds of thousands of cylindrical subunits that make up muscle fibres  Skeletal Muscle Structure Myofilaments – protein structures responsible for muscle contraction, two different types: Actin – thin filament Myosin – thick filament  Skeletal Muscle Structure Sarcomere – functional unit of a muscle, composed of many myofilaments Muscle Fibre Components Myoglobin – oxygen-binding pigment; stores oxygen for muscle contractions Sarcolemma – membrane of muscle fibre; regulates entry and exit of materials Sarcoplasm – cytoplasm of muscle fibre; site of metabolic processes; contains myoglobin and glycogen Sarcoplasmic reticulum – smooth ER in muscle fibre; stores calcium ions Myofilaments Actin (thin) myofilaments – consists of two strands of protein (actin) molecules that are wrapped around each other Myosin (thick) myofilaments – also consist of two strands of protein molecules wound around each other, but is about 10 times longer than an actin filament One end consists of a long rod The other end has a double-headed globular region The Sliding Filament Model Sliding of actin past myosin during a muscle contraction Major Steps: Myosin heads chemically bind to actin Myosin head flexes backward, pulling the actin filament Actin myofilament slides past myosin myofilament Myosin head releases and unflexes  requires ATP Myosin head reattaches to actin further down and repeats The Role of Calcium When a muscle is relaxed, the myosin attachment sites on actin are physically blocked another protein called tropomyosin Myosin cannot bind, filaments cannot slide For contraction to take place, they must be moved which requires a protein called troponin to bind to the tropomyosin This binding is regulated by calcium ion concentration Calcium + Sliding Filament Model Signal to muscle from a nerve to contract Sarcoplasmic reticulum releases Ca2+ Ca2+ binds to troponin which binds to tropomyosin Troponin-tropomyosin complex is shifted away from actin and myosin head binding sites are exposed Myosin heads attach and slide actin filaments closer together – muscle fibre shortens Myosin heads release, powered by ATP, and they reset to attach again at new spot on actin (if Ca 2+ is still present) Ca2+ is returned to the SR through active transport when the contraction stops Tropomyosin covers binding sites again Sarcomere One sarcomere is composed of both actin and myosin filaments Sarcomere Z lines divide one sarcomere from another They are pulled closer together when muscle contracts Sarcomere H zone shows just myosin Shortens during contraction Sarcomere A band shows overlap of actin and myosin Dark band Stays the same length during contraction Sarcomere I band shows just actin Light band Shortens during contraction Sarcomere Contracted muscles have shorter sarcomeres When all sarcomeres shorten, so does the length of the muscle  Sarcomere The repeating patterns of light (I) and dark (A) bands is what give skeletal muscles their striations relaxed sarcom ere elaxed m uscle tracted m uscle contracted sarcom ere Energy for Muscle Contractions ATP is required for: Breaking the actin-myosin cross-bridges Active transport of calcium ions back into the sarcoplasmic reticulum Without the addition of new ATP molecules, the bridges remain attached to the actin filaments This is why corpses become stiff with rigor mortis Usually lasts 36 hours Energy for Muscle Contractions ATP produced before exercise gets used up very quickly Muscle cells must acquire new ATP Three mechanisms to make ATP: 1. Breakdown of creatine phosphate* 2. Aerobic cellular respiration 3. Fermentation* * No oxygen required Breakdown of Creatine Phosphate Creatine phosphate is a high energy molecule that is built up during rest Cannot directly participate in muscle contraction but can generate ATP for it creatine phosphate + ADP  creatine + ATP Reaction takes place in the midst of the sliding filaments Very fast way of making ATP for muscles! Provides enough ATP for ~8 seconds of intense activity Can regenerate when at rest Aerobic Cellular Respiration Provides the majority of ATP to muscles When oxygen is present, glucose (from glycogen) or fatty acids (from fat) can be converted to ATP Myoglobin (oxygen carrying pigment) is made in muscle cells Its presence gives our muscles their reddish-brown colour Has higher affinity for oxygen than hemoglobin Can store oxygen for mitochondria doing cellular respiration Fermentation Can create ATP without oxygen Lactic acid is a by-product Makes sarcoplasm more acidic Enzymes stop working If fermentation continues longer than two or three minutes, cramping and fatigue set in Oxygen Deficit If muscles use fermentation, it incurs an oxygen deficit Muscles can function well in an oxygen deficit Brain tissue cannot Muscles can use glucose or fatty acids to make ATP whereas the brain can only use glucose Athletic training increases muscle mitochondria, allowing fatty acids to be used by muscles and saving blood glucose for brain Increase in mitochondria number also means more ATP is made through aerobic respiration, and fermentation does not happen as frequently Blood pH remains more steady as less lactic acid is produced and there is less of an oxygen deficit