MUSCLES AND HOW THEY MOVE skenovat0002 Contents Learning Objectives w learn the bacis components of skeletal muscle, muscle fiber w discover how muscle functions during exercise w consider the differences in fibre types w diagnostika svalových vláken Illustration SKELETAL MUSCLE STRUCTURE 20640Bv Illustration MUSCLE FIBER Key Points Key Points w An individual muscle cell is called a muscle fiber. w A muscle fiber is enclosed by a plasma membrane called the sarcolemma. Muscle Fiber w The cytoplasm of muscle fiber is called the sarcoplasm. w Within the sarcoplasm, the T tubules allow transport of substances throught the muscle fiber. w The sarcoplasmic reticulum stores calcium. Illustration ARRANGEMENT OF FILAMENTS Illustration ARRANGEMENT OF FILAMENTS IN A SARCOMERE Illustration ACTIN FILAMENT Illustration MOTOR UNIT Key Points Key Points w Myofibrils are the contractile elemets of skeletal muscle, with several hundred to several thousand composing a single muscle. w A sarkomere is composed of filaments of two proteins, myosin and actin, which are responsible for muscle contraction. Myofibrils w Myosin is a thick filament with a globular head at one end. w An actin filament – composed of actin, tropomyosin, and troponin – is attached to a Z disk. w Myofibrils are made up of sarcomeres, the smallest functional units of a muscle. Contents 1. A motor neuron, with signals from the brain or spinal cord, releases the neurotransmitter acetylcholine (Ach) at the neuromuscular junction. 2. ACh crosses the junction and binds to receptors on the sarcolemma. 3. This initiates an action potential, providing sufficient ACh. Excitation/Contraction Coupling 4. The action potential travels along the sarcolemma and through the T tubules to the SR releasing Ca2+. 5. The Ca2+ binds to troponin on the actin filament, and the troponin pulls tropomyosin off the active sites, allowing myosin heads to attach to the actin filament. (continued) Contents 6. Once a strong binding state is extablished with actin, the myosin head tilts, pulling the actin filament (power stroke). 7. The myosin head binds to ATP, and ATPase found on the head splits ATP into ADP and Pi, releasing energy. 8. Muscle action ends when calcium is actively pumped out of the sarcoplasm back into the sarcoplasmic reticulum for storage. Excitation/Contraction Coupling Illustration EVENTS LEADING TO MUSCLE ACTION Illustration CONTRACTING MUSCLE FIBER skenovat0010 Key Points skenovat0010 Key Points Key Points w Muscle action is initiated by a nerve impulse. Muscle Fiber Action w Ca2+ ions bind with troponin, which lifts the tropomyosin molecules off the active sites on the actin filament. These open sites allow the myosin heads to bind to them. w The nerve release Ach, which allows sodium to enter and depolarized, an action potential occurs which releases stored Ca2+ ions. Key Points Key Points w Once myosin binds with actin, the myosin head tills and pulls the actin filament so they slide across each other. w Muscle action ends when calcium is pumped out of the sarcoplasm to the sarcoplasmic reticulum for storage. Muscle Fiber Action w Energy for muscle action is provided when thy myosin head binds to the ATP. ATPase on the myosin head splits the ATP into a usable energy source. Contents w High aerobic (oxidative) capacity and fatigue resistance w Low anaerobic (glycolytic) capacity and motor unit strength w Slow contractile speed (110ms to reach peak tension) and myosin ATPase Slow-Twitch (ST) Muscle Fibers w 10–180 fibers per motor neuron Skier Contents w Moderate aerobic (oxidative) capacity and fatigue resistance w High anaerobic (glycolytic) capacity and motor unit strength w Fast contractile speed (50 ms to reach peak tension) Fast-Twitch (FTa) Muscle Fibers w 300–800 fibers per motor neuron Hurdler Contents w Low aerobic (oxidative) capacity and fatigue resistance w High anaerobic (glycolytic) capacity and motor unit strength w Fast contractile speed (50 ms to reach peak tension) Fast-Twitch (FTb/FTx) Muscle Fibers w 300–800 fibers per motor neuron Hitter Contents Characteristic of muscle fibers Slow-Twitch (ST) SO Fast-twitch (FTa) FOG Fast-Twitch (FTx) FG Contractile speed slow fast fast Contractile force low moderate high Fatigue resistance high moderate low Glycogen capacity low high high Diameter small moderate big Mitochondrials density high high low Capilars density high high low Activity of ATPase low high high Glycolytic capacity low high high Illustration SLOW- AND FAST-TWITCH FIBERS SPRINTERS MARATHON RUNERS DISTANCE RUNNERS CYCLISTS AVERAGE FG/FOG SO Contents ► muscle biopsy ► magnetic resonance imaging ► 1MR (one-repetition maximum) and subsequent exrecise with 80%. (1RM) is a functional test of the maximum weight that can be lifted just one time=100% < 8 rep. predominance FG/FOG 8-12 rep. 50%:50% > 12 rep. predominance SO ► Bocso test (jump test) DIAGNOSTIC OF MUSCLE FIBERS Contents w Hollow needle is inserted into muscle to take a sample. w Sample is mounted, frozen, thinly sliced, and examined under a microscope. w Allows study of muscle fibers and the effects of acute exercise and exercise training on fiber composition. Muscle Biopsy Key Points Key Points w Skeletal muscles contain both ST and FT fibers. w ATPase in FT fibers acts faster providing energy for muscle action more quickly than ATPase in ST fibers. Slow- and Fast-Twitch Muscle Fibers (continued) w FT fibers have a more highly developed sarcoplasmic reticulum enhancing calcium delivery. Key Points Key Points w Motor units supplying FT fibers are larger (e.g., more fibers per motor neuron) than those supplying ST fibers; thus, FT motor units can recruit more fibers. w ST fibers have high aerobic endurance and are suited to low-intensity endurance activities. Slow- and Fast-Twitch Muscle Fibers w FT fibers are better for anaerobic or explosive activities. Contents Agonists – prime movers, responsible for the movement Functional Classification of Muscles Antagonists – oppose the agonists to prevent overstretching of them Synergists – assist the agonists and sometimes fine-tune the direction of the movement Dancer Illustration TYPES OF MUSCLE ACTION Contents w Number of motor units activated w Type of muscle fibers (FT or ST) w Muscle size Factors Influencing Force Generation w Initial muscle length w Joint angle w Speed of muscle action (shortening or lengthening) Handstandman Contents w Dynamometry menas testing of muscles strenght. w Strenght is defined as a peak force of torque development during a maximum voluntary contraction under a given set of conditions. DYNAMOMETRY – muscle strenght testing w For the International System of Units (SI) units for force and torque are the Newton (N) and the Newton meter (N.m) Handstandman Contents w Isometric strenght is usually measured as the peak force produced by a maximum voluntary isometric contraction. w The dynamometric measurements shoul be made at standardised positions. ISOMETRIC DYNAMOMETRY w Dynamometers convert the deformation produced by tension or pressure into srenght (N) Handstandman