Muscular System Chapter 9 3 types of muscular

Muscular System Chapter 9

3 types of muscular tissue:

Functions of muscular system n Stabilize joints n Muscle tone n Movement n Maintain constant body temperature

Muscle structure n n n n Fascia – connective tissue around muscle, becomes the tendon Origin – on stationary bone Insertion – on the moveable bone Fascicle – bundle of muscle fibers Muscle fiber – muscle cell Myofibril – made of sarcomeres (in-between two Z bands) Myo-filaments – actin and myosin

Group Actions Prime mover – the muscle that causes the desired movement n Antagonist – relax during the action n Synergists – muscles that steady the movement (helpers) n

The Neuromuscular Junction: Neurons n n n Parts of : Cell body Dendrites – receive impulse Axon – carries impulse away Myelin sheath- white fatty material • Schwann cells (pns) • Neurilemma (outside the sheath) • Nodes of Ranvier

The Nerve Impulse n Action potential – steps in the nerve impulse n 3 stages of : polarization, depolarization, repolarization

Step 1: Polarization n Resting state of a neuron n Sodium/potassium pump – sodium ions out of cells and potassium ions into cells

Polarization continued n Inside of the cell is – charged n Outside of cell is + charged n Due to sodium-potassium pump – 2 K+ ions go in as 3 Na++ go out http: //faculty. washington. edu/chudler/intro b. html

Step 3: repolarization n Return to resting state n Due to the pumping out of K+. n Na+ blocked n Inside of cell negative n Continues to synapse

The Sliding Filament theory: Step 1: Neuromuscular Junction Action potential – the reversal of charges across the plasma membrane. n Nerve impulse arrives at axon terminal releasing acetylcholine (Ach) n

Step 1: Neuromuscular Junction Ach diffuses across synaptic cleft, binds to receptors in the motor end plate. n Triggers action potential n Acetylcholinersteras e in cleft destroys Ach to stop action potential n

Disorders at the neuromuscular junction Myasthenia gravis Curare Botulism tetanus

Step 2: n Sarcoplasmic reticulum stimulated to release calcium ions.

Step 3 Release of Calcium causes shift in troponin (actin) n Active site on Actin is uncovered n

Step 4 n Myosin and ATP combines with active site on actin causing formation of a crossbridge

Step 5 - 7 Energy released causing filaments to slide past each other (power strokes) n ATP converted ADP n Troponin slides back n Cycle repeats if enough calcium and ATP are present n

Energy for contraction n ATP (respiration) n Creatine phosphate-can be stored longer and more abundant than ATP n Glycogen-storage of glucose in liver

Oxygen Debt-strenuous exercise Lack of oxygen availability n Accumulation of lactic acid (soreness) n Become short of breath to metabolize lactic acid n

Muscular Responses n All or nothing response single fiber contracts only maximally – Threshold stimulus n Recruitment -

Types of Whole muscle contraction Twitch contraction – not a usual method of muscle contraction

Summation Muscle not allowed to relax in-between contractions n Stronger contraction n

Tetanus sustained muscle contraction (maintaining posture or tone) n Usual means of movement n

Isotonic vs. Isometric Isotonic contraction n Movement produced as a muscle pulls on an attached bone toward a stationary structure n Isometric contraction n Muscle tension, no shortening of muscles n No movement n

Muscle Fiber types n Based on genetics n Classified by respiration and the speed of contraction n Strength Training can influence

Fast Twitch Fibers Energy for quick, forceful contractions n Contraction 2 -3 times faster than slow twitch n Anaerobic respiration n Short term activities – basketball, sprinting, volleyball n

Slow twitch muscle fibers Aerobic respiration n Slow contracting n Endurance type activities n Ex. Long distance running, soccer, football, basketball n