Muscular System Chapter 9

3 types of muscular tissue:

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

Muscle structure 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 Antagonist – relax during the action Synergists – muscles that steady the movement (helpers)

The Neuromuscular Junction: Neurons 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 Action potential – steps in the nerve impulse 3 stages of : polarization, depolarization, repolarization

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

Polarization continued Inside of the cell is – charged Outside of cell is + charged Due to sodium-potassium pump –2 K + ions go in as 3 Na ++ go out b.html

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

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

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

Disorders at the neuromuscular junction Myasthenia gravis Botulism Curare tetanus

Step 2: Sarcoplasmic reticulum stimulated to release calcium ions.

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

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

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

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

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

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

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

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

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

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

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

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

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