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Download Muscle physiology - POLYTECH High School
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An Introduction to the Muscular System Before we can learn the names of the muscles, we need to understand what muscles are and what they do Muscle physiology includes the following: ◦ ◦ ◦ ◦ ◦ ◦ ◦ Types of muscles Functions of muscles How muscles are named Muscle strength vs. muscle endurance Types of muscle contractions Definitions for muscle movement Sliding filament theory Muscles are classified by 3 types ◦ Cardiac muscle (involuntary)– found in the heart ◦ Smooth muscle (involuntary) – found primarily in blood vessels and the GI tract ◦ Skeletal muscle (voluntary) – also known as striated muscle due to it’s lined appearance 435 skeletal muscles in the body Makes up 40-45% of our total body mass 1. Movement 2. Heat production 3. Protection 4. Shock absorption 5. Coordination/protection of entrances and exits 6. Aid in circulation 7. Maintain posture 1. 2. 3. 4. 5. 6. 7. Function Location Size # of heads Shape Attachments Direction of fibers Muscles can be named by the function they perform Pronator teres and pronator quadratus Muscles can be named by their size and where they are located Gluteus maximus ◦ Gluteus stems from the Greek word gloutos, which means buttock ◦ Maximus refers to the size Muscles are often named by the number of heads they have Biceps brachii ◦ A biceps is any muscle that has 2 origins Muscles can be named by their shape Rhomboids ◦ Shaped like a rhombus Muscles can be named by their attachment points Coracobrachialis ◦ Origin – coracoid process of the scapula ◦ Insertion – shaft of the humerus (bracchium is the Latin term for arm) Muscles can be named referring to the direction in which their fibers run Rectus abdominis The term rectus is from Latin and means straight Muscle strength – the greatest amount of force a muscle can generate at any one given time Muscle endurance – the amount of work a muscle can do over a period of time Frontalis Orbicularis Oculi Temporalis Zygomaticus Orbicularis Oris Buccinator Masseter Mentalis Triangularis Sternocleidomastoideus Trapezius Platysma Occipitalis Suprahyoid Infrahyoid Levator scapulae Pectoralis major Rectus abdominus Erector spinae Latissimus dorsi Serratus anterior Internal oblique External intercostal Splenius The construction of muscle fibers give muscles the ability to contract by shortening the distance between the ends of the fibers A muscle can perform 4 different types of contractions 1. Muscle twitch 2. Tetanic contraction 3. Isometric contraction 4. Isotonic contraction A muscle twitch is quick, jerky response to a stimulus Often called a spasm or a tic A reflex is a muscle twitch This is a more sustained and steady response to a constant stimulus Causes a maximal contraction of the muscle with no relaxation A charley horse is a tetanic contraction An increase in muscle tension without accompanying muscle shortening The muscle gets tense, but there is no movement Occurs when holding a weighted object in a stationary position An increase in muscular tension resulting in shortening of the muscle This contraction causes flexion, extension, abduction, adduction, circumduction, rotation, etc. ◦ Concentric contraction – shortening, “positive work” ◦ Eccentric contraction – lengthening, “negative work” Origin – proximal attachment; more stationary attachment; usually a broad attachment Insertion – distal attachment; more movable attachment; usually a smaller attachment Tendon – connective tissue that connects muscle to bone; fibrous, tough, elastic Prime mover – muscle mainly responsible for a movement (no one muscle ever acts alone); concentric muscle during a movement Synergist – muscle that helps the prime mover; stabilizer; concentric contractor during movement Antagonist – muscle opposite of the prime mover and synergist muscles; eccentric contractor during a movement Motor unit – a single motor neuron (motor nerve cell or fiber) plus the muscle cell it innervates Threshold stimulus – minimal level of stimulation from a motor neuron required to cause a muscle fiber to contract; you are near this threshold when you perform an isometric contraction “All or none” principle – when a muscle fiber is subjected to a threshold stimulus it contracts completely or not at all Big Bucket Muscle fiber – muscle tissue cell; striated in skeletal muscle Fascicle – bundle of muscle fibers Muscle belly – unit of skeletal muscle; multiple bundles of fascicles Actin – Thin protein myofilament in skeletal muscle Myosin – Thick protein myofilament in skeletal muscle Cross-bridges – lever that attach to the myosin and actin myofilaments, pulling them together during a muscle contraction; located on the myosin Nerve impulse is released and calcium ions and ATP are introduced, causing cross-bridges on the myosin to “reach up” and contact the actin myofilaments Cross-bridge action slides the actin myofilaments over the myosin, causing shortening of the muscle and producing a muscle contraction When the stimulus and calcium ions are removed, the myofilaments return to their resting positions A fully contracted muscle shortens to 47% of its resting length http://www.youtube.com/watch?v=Ct8AbZn_ A8A Muscle tissue ◦ Sarcomere = Section of muscle cell containing myosin and actin ◦ Muscle fiber = 1 muscle cell ◦ Fascicle = Bundle of muscle fibers (cells) ◦ Muscle belly= Bundle of fascicles ◦ ◦ ◦ ◦ Connective tissue – elastic and fibrous A muscle fiber is surrounded by endomysium A fascicle is surrounded by perimysium A muscle belly is surrounded by epimysium Endomysium + Perimysium + Epimysium = Fascia All of the connective tissue (fascia) merges together at the ends of the muscle fibers to form tendons Tendons attach the muscle to bone or to another tendon *Broad, flat tendons are called aponeuroses *The belly of the muscle is what shortens during muscle contraction
