I. Visceral Muscles.

    A. Location.
        1. Lining of organs: walls of arteries, veins, gut, bladder, uterus.
        2. Opens and closes iris.
        3. Most sphincters are visceral.
            a. Circular muscles that regulate tubular openings.
            b. E.g. both ends of stomach.

    B. Involuntary.

    C. Structure.
        1. Smooth (not striated).
        2. Individual cells in sheets, each packed with contractile proteins.

    D. Function.
        1. Squeeze the space they surround.
        2. Gradual contraction of variable force.
        3. Can sustain prolonged contraction without fatigue.

II. Cardiac Muscles.

    A. Location: heart only.

    B. Involuntary.

    C. Structure.
        1. Striated, but irregularly.
        2. Individual cells in long columns of fibers.

    D. Function: beat.
        1. Each beat is initiated by spontaneous electrical activity of the heart’s pacemaker, the sinoatrial node in the wall of the right atrium.
        2. The impulse spreads to all the cells of the atria, triggering simultaneous contraction.
        3. The impulse reaches the atrioventricular node between the partition of the two ventricles.
        4. The atrioventricular node spreads the impulse to all the cells of the ventricles, triggering simultaneous contraction.
        5. These impulses travel from cardiac cell to cell, not involving any nerve cells.
        6. Some cardiac cells can transmit the electrical impulse particularly fast by means of a gap junction, pores in the membrane through which ions can pass.
        7. Gap junctions are arranged such that the impulse leaving the node arrives at all cells at the same time, causing simultaneous contraction.
        8. The heart will beat without change even if the nerve to the central nervous system is severed.
            a. It will even adapt to changing demands of exercise.
            b. Cardiac muscle contracts without nervous stimulation.
            c. Rate and force of heart beats are governed partly by hormones and partly by reflex nerves within the heart itself.
        9. Highly resistant to fatigue.

IV. Skeletal Muscles.

    A. Location.
        1. Skeletal bones.
        2. Tongue, jaw, pharynx.
        3. Abdomen, diaphragm.
        4. Anal sphincter.

    B. Voluntary.

    C. Gross Structure.
        1. Striated (striped).
        2. Each fiber arises from a fusion of several embryonic cells called myoblasts.
        3. Each fiber is a syncytium, a structure with many nuclei not separated into separate cells.
        4. The nuclei are arranged along the outside edge of the fiber.
        5. The fiber is enclosed by a sarcolemma – corresponds to a cell membrane.
        6. The fiber is innervated by a motor neuron.
        7. 10 to 100 fibers are bound together in a bundle.
        8. The bundles are enclosed in a connective tissue layer to form the muscle.
        9. The fiber is packed with myofibrils.

    D. Myofibril Structure.
        1. Z line, sarcomere.
        2. Thin filaments.
            a. Twisted double strand of actin (globular protein).
            b. Tropomyosin.
            c. Troponin.
        3. Thick filaments.
            a. Myosin.
            b. Shaft with double head.

    E. Function.
        1. Sliding Filament mechanism.
        2. Myosin bonds to actin.
        3. Bond swivels, pulling filaments together.
        4. Myosin detaches, returns to original shape.
        5. Repeat.
        6. ATP and Ca⁺⁺ needed, for contraction and relaxation.

    F. Energy Source.
        1. ATP is provided by cellular respiration of glucose.
        2. When muscles are taxed, the O₂ supply becomes depleted.
        3. Glucose then breaks down to pyruvic acid and a small amount of ATP.
        4. Pyruvic acid is metabolized to lactic acid.
        5. Lactic acid is transferred to the liver where it is converted to glucose.
        6. Muscle soreness is a symptom of an accumulation of lactic acid.
 

I. Introduction

    A. Oxygen
        1. Needed for cellular respiration; i.e. burning food to produce energy.
        2. Can't be stored in body: organic molecules easily oxidized.
        3. Found dissolved in air and water.
        4. Oxygen content of respiratory media: ml/l.
            a. 5° C sea water              6.4
            b. 5° C fresh water            9.0
            c. 25° C fresh water          5.8
            d. Air                            209.5
        5. Diffuses .5 million times faster in air than in water.

    B. Ventilation
        1. Moving respiratory medium past respiratory surface.
        2. Surface-to-volume ratio.
        3. Types of surfaces.
            a. Body - worm.
            b. Tracheae - insect.
            c. Gills - fish.
            d. Lungs - mammal.
        4. Surface must be kept moist.

II. Parts of Respiratory System.

    A. Nose and mouth.
    B. Pharynx -- throat.
    C. Larynx -- voice box.
    D. Trachea - lined with cilia to expel foreign particles.
    E. Bronchi (2).
    F. Bronchioles.
    G. Alveoli.
        1. Tiny sacs.
        2. Walls surrounded by capillaries.
        3. Coated with fluid.

III. Ventilation Process.

    A. Negative Pressure.
        1. Chest cavity enlarges.
            a. Diaphragm lowers.
            b. Rib cage rises.
        2. Air rushes in.

    B. Positive Pressure: Air forced into lung (frog).

IV. Oxygen Transport.

    A. Water with salts cannot dissolve much oxygen.