Illinois State University Muscular Control of Movement Chapters 17 and 18 Review of Gross Anatomy: l 430 voluntary muscles in the body. l The muscle is »75% water, »20% protein, »and 5% inorganic salts and other substances.

Illinois State University Types of Muscles: l 1. Smooth - blood vessels and organs. l 2. Cardiac - heart. l 3. Skeletal - movement muscles.

Illinois State University Origins and Insertions l The origin of the muscle is the relatively stable skeletal part to which the muscle attaches. »This is usually more proximal.

Illinois State University Origins and Insertions l The insertion of the muscle is the more mobile skeletal part to which the muscle attaches and is more distal.

Illinois State University Connective Tissue Components

Illinois State University The Structure and Function of Skeletal Muscle l An individual muscle cell is called a muscle fiber. l A muscle fiber is enclosed by a plasma membrane called the sarcolemma.

Illinois State University Sarcolemma

Illinois State University The Structure and Function of Skeletal Muscle: l The cytoplasm of a muscle fiber is called the sarcoplasm. l The extensive tubule network found in the sarcoplasm includes: » t-tubules - allow communication and transport of substances throughout the muscle fiber »sarcoplasmic reticulum - which stores calcium.

Illinois State University Sarcoplasm

Illinois State University The Structure and Function of Skeletal Muscle: l Myofibrils are composed of sarcomeres, the smallest functional units of muscle. l A sarcomere is composed of filaments of two proteins, which are responsible for muscle contraction.

Illinois State University The Structure and Function of Skeletal Muscle: l Myosin is a thick filament, folded into a globular head at one end. l An actin filament is composed of actin, tropomyosin, and troponin.

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The Structure and Function of Skeletal Muscle: l One end of each actin filament is attached to a z disk.

Illinois State University Sarcomere: l The bands are named according to their optical properties. l The I band (isotropic) - velocity of light is same in all directions. »Contains actin only.

Illinois State University Sarcomere: l A band (anisotropic) - light does not scatter equally. »Contains both actin and myosin. l Z disk (zwischen) - German word for between.

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Sarcomere: l H zone - center of A band. »Contains myosin only.

Illinois State University The Sliding Filament Theory: l Muscle action is initiated by a motor nerve impulse.

Illinois State University The Sliding Filament Theory: l The action potential travels along the sarcolemma, then through the tubule system, and eventually causes stored calcium to be released from the sarcoplasmic reticulum.

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The Sliding Filament Theory: l Calcium binds with troponin, and then troponin lifts the tropomyosin molecules off of the active sites on the actin filament, opening these sites for binding with the myosin head.

Illinois State University The Sliding Filament Theory: l Once it binds with the actin active site, the myosin head tilts, pulling the actin filament so that the two slide across each other. »The tilting of the myosin head is the power stroke.

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The Sliding Filament Theory: l Energy is required before muscle action can occur. »The myosin head binds to ATP, and ATPase found on the head splits ATP into ADP and P i, releasing energy to fuel the contraction.

Illinois State University The Sliding Filament Theory: l Muscle action ends when the calcium is actively pumped out of the sarcoplasm back into the sarcoplasmic reticulum for storage. »This process, leading to relaxation, also requires energy supplied by ATP.

Illinois State University Skeletal Muscle and Exercise l Most skeletal muscles contain both ST and FT fibers.

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Skeletal Muscle and Exercise: l The different fiber types have different ATPases. l The ATPase in the FT fibers acts faster, providing energy for muscle action more quickly than the ATPase in ST fibers.

Illinois State University Skeletal Muscle and Exercise: l FT fibers have a more highly developed sarcoplasmic reticulum, enhancing the delivery of calcium needed for muscle action.

Illinois State University Skeletal Muscle and Exercise: l Motor neurons supplying FT motor units are larger and supply more fibers than do neurons for ST motor units. l Thus FT motor units have more fibers to contract and can produce more force than ST motor units.

Illinois State University Skeletal Muscle and Exercise: l The proportions of ST and FT fibers in an individual’s arm and leg muscles are usually quite similar.

Illinois State University Skeletal Muscle and Exercise: l ST fibers have high aerobic endurance and are well suited to low-intensity endurance activities.

Illinois State University Skeletal Muscle and Exercise: l FT fibers are better for anaerobic activity. l FT a fibers are well utilized in explosive bouts of exercise.

Illinois State University Skeletal Muscle and Exercise: l Fiber type is predominantly determined by genetics. l Composition will change over the course of your life as FT fibers atrophy and die.

Illinois State University Classification of Muscle Fibers l Characteristic Type IType II a TypeII b l Oxidative capacity HighMod. HighLow l Glycolytic capacity LowHighHighest l Contractile speed SlowFastFast l Fatigue resistant HighModerateLow l Motor unit strength LowHighHigh

Illinois State University Characteristics of Muscle Fiber Types CharacteristicST FT a FT b l Fibers per motor neuron l Motor neuron sizeSmall LargeLarge l Nerve conduction velocitySlow FastFast l Contraction speed (ms) l Type of myosin ATPaseSlow FastFast l Sarcoplasmic Ret. Dev.Low HighHigh

Illinois State University Motor Units A motor unit consists of a single motor neuron and all the muscle fibers it supplies

Illinois State University Neuro-muscular Interaction l Motor units give all-or-none responses. l For a unit to be recruited into activity, the motor nerve impulse must meet or exceed the threshold. l Threshold of excitation.

Illinois State University Neuro-muscular Interaction l When this occurs, all muscle fibers in the motor unit act maximally. l If the threshold is not met, no fibers in that unit act.

Illinois State University Neuro-muscular Interaction l More force is produced by activating more motor units, and thus more muscle fibers.

Illinois State University Neuro-muscular Interaction l In low-intensity activity, most muscle force is generated by ST fibers. l As the resistance increases, FT a fibers are recruited, and at even higher intensities, the FT b fibers are activated.

Illinois State University Ramping of Muscle Fibers

Illinois State University Neuro-muscular Interaction l The same pattern of recruitment is followed during events of long duration.

Illinois State University Muscle Action: l Muscles involved in a movement can be classified as: »agonists (prime movers) »antagonists (opponents or resistors) »synergists (assistants) »fixator, neutralizer, stabilizer

Illinois State University Muscle Action: l The three main types of muscle action are: »concentric, in which the muscle shortens; »static, in which the muscle acts but the joint angle is unchanged; »eccentric, in which the muscle lengthens.

Illinois State University Generation of Force l The number of motor units activated. » Force production can be increased by recruiting more motor units. l The type of motor units activated. l The size of the muscle.

Illinois State University Generation of Force: l The muscle’s initial length when activated. »Force production can be maximized if the muscle is stretched 20% prior to action. »At this point, the amount of energy stored and the number of linked actin-myosin cross-bridges are optimum.

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Generation of Force: l The angle of the joint. »All joints have an optimal angle at which the muscles crossing the joint function to produce maximum force. »This angle varies with the relative position of the muscle’s insertion on the bone and the load placed on the muscle.

Illinois State University Generation of Force: l The muscle’s speed of action. »Speed of action also affects the amount of force produced. »For concentric action, maximum force can be achieved with slower contractions. »The closer you get to zero velocity (static), the more force can be generated.

Illinois State University Muscle Action: l With eccentric actions, however, faster movement allows more force production. Concentric Eccentric

Illinois State University Requirements for Large Muscle Development l Proper nutrition »65% CHO, 20% Fat, 15% Protein l Resistance Training l Genetics l Hormonal Secretion Levels »Testosterone and Androgens

Illinois State University ACSM Strength Guidelines l F = 2-3 days per week. l I = intensity »>85% of max for strength, »50-65% for muscular endurance. l T = duration »30-90 secs per set, »8-12 reps, »1:4 work:rest ratio l S = resistance of any type.

Illinois State University Types of Training l Isometric muscular tension, no movement.

Illinois State University Types of Training l Isotonic - muscular tension, movement. »Set resistance »Variable resistance

Illinois State University Types of Training l Isokinetic - muscular tension, speed of movement is controlled.

Illinois State University Strength Training Myths l Strength training will cause “muscle boundness”. l Women who strength train will become masculinized. l Strength training reduces speed. l “No pain - No gain”.

Illinois State University Strength Training Myths l It takes hours of training daily to gain muscle mass. l Food supplements will speed up or cause muscle and strength development. l Anabolic steroids are a safe and effective aid.