CSCS Chapter 1: Structure and Function of Body Systems
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CSCS Study Guide Chapter 1

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    Chapter Goals

    • Learn the macro and microstructure of both muscles and bones.
    • Be able to explain the sliding-filament theory.
    • Describe both morphological and physiological factors of muscle fiber types. Be able to determine what muscle fiber type is used in each sport.
    • Learn the physiological and anatomical characteristics of the respiratory system and the cardiovascular system.

    Musculoskeletal system

    The skeleton

    Within the axial skeleton, we have the skull, the vertebral column, the ribs, and the sternum.

    The second part of the skeleton is the appendicular skeleton and it includes the shoulder girdle, the pelvic girdle, and the bones in the body’s extremities.

    The three joints of the body: Fibrous, Cartilaginous, and Synovial.

    Joints are broken into their axes of movement too: Uniaxial, Biaxial, and Multiaxial.

    There are 7 cervical vertebrae, 12 thoracic, 5 lumbar, 5 sacral, and 3 to 5 coccygeal.

    Musculoskeletal macro and microstructure

    Every skeletal muscle has muscle tissue, connectives tissues, blood vessels, and nerves. 

    Fibrous connective tissues cover the muscles in the body. They include Epimysium, Perimysium, and Endomysium.

    A motor unit is made up of a motor neuron and the muscle fiber it is innervating. 

    The neuromuscular junction is between the muscle fiber and motor neuron. It can also be called the motor end plate.

    Myosin and Actin

    Myosin and Actin give skeletal muscles its striated appearance. 

    The action potential discharging from a motor nerve is the signal that releases calcium from the sarcoplasmic reticulum. This goes into the myofibril and causes tension to develop within the muscle.

    The Sliding Filament Theory of Muscle Contraction

    The theory states that actin that is present at the end of sarcomeres moves inward toward myosin, and this pulls the Z-lines in to the center of the sarcomere. This shortens the muscle fiber.

    The Resting Phase: There is not a lot of calcium in the myofibril, so we don’t see many myosin cross bridges bound to actin.

    The Excitation Contraction Coupling Phase: The sarcoplasmic reticulum releases calcium when it is stimulated. Calcium ions bond with troponin. All of this causes a shift in tropomyosin. Myosin cross bridges attach quicker to actin.

    The Contraction Phase: Hydrolysis of ATP occurs and causes contractions of the fibers.

    The Recharge Phase: This happens when calcium is available. 

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    The Relaxation Phase: The stimulation stops. Calcium is pumped into the Sarcoplasmic reticulum for use later, thus actin and myosin cannot link.

    The Contraction of a Myofibril

    When a muscle is in a stretched position, the H-zone and the I-bands are longer and there is a very low potential for force because of the reduced cross bridge to actin alignment.

    During contraction we see the I-band and H-zone shorten.

    Steps of Muscle Contraction

    ATP splitting begins and myosin heads become “energized”. This allows movement into position for bonding with actin to the myosin heads.

    Phosphate is released from ATP ad the myosin head changes shape and shifts.

    The power stroke occurs as the actin filament is pulled toward the center of the sarcomere.

    After the power stroke, myosin heads detach from actin as another ATP binds.

    The process is ready to happen again.

    The Neuromuscular System

    The Activation of Muscles

    The amount of control a muscle has is dependent on how many muscle fibers are within each motor unit.

    More precise muscles have as few as one fiber per motor neuron. 

    Bigger muscles requiring less precision have potentially a few hundred fibers covered by one motor neuron. 

    The All or none principle: All muscles that are within a motor unit contract at the same time, you can’t just use one fiber of a muscle unit. Also, you cannot produce a stronger contraction.

    Tetanus is the max force that can be developed by a motor unit.

    Muscle Fiber Types:

    Type I: These slow twitch fibers are efficient at using energy and resistant to fatigue, as they have a high aerobic energy capacity. They do however have a low potential for developing a rapid force, thus having low anaerobic power.

    Type IIa: These fast twitch fibers are inefficient and easily fatigued. They have a low aerobic energy supply but are able to develop rapid force more easily. Their anaerobic power is high.

    Type IIx: These are very similar to the Type IIa fibers except they show less fatigue resistance.

    The Recruitment Patterns of Motor Units

    Force output changes depending on how many motor units are recruited. For a more precise activity, one motor unit might be recruited, thus producing very little force. If a big force is needed, more muscle fibers will be recruited.

    How Can Force Production be improved in Athletes?

    We can incorporate heavier load training phases so we can optimize neural recruitment.

    Increased cross sectional areas of muscles involved in our activity will improve force production.

    Performing multi muscle and multi joint exercises done with explosive action can optimize the recruitment of the fast-twitch fibers.

    Proprioception

    This I the information we receive concerning conscious awareness of where are body parts are positioned in space.

    This is all done subconsciously.

    Proprioceptors are the sensory receptors we use for this. They provide the CNS with information.

    Muscle Spindles

    Proprioceptors consisting of modified muscle fibers that are closed within a connective tissue sheath.

    The stretching of a muscle, and subsequent deformation that occurs to the muscle spindle, activates the sensory neuron and sends an impulse to the spine. This causes a muscle contraction.

    Golgi Tendon Organ

    These GTOs are the proprioceptors that are located within tendons near the myotendinous junction.

    These are placed in a series with extrafusal muscle fibers.

    When we place an extremely heavy load on a muscle, the GTO discharges.

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