Chapter 6 THE MUSCULAR SYSTEM Three Types

Chapter 6 THE MUSCULAR SYSTEM

Three Types of Muscle Tissue 1. Skeletal 2. Cardiac 3. Smooth

Similarities of Muscle 1. All muscle cells are elongated and are therefore called muscle fibers. 2. Muscle has the ability to shorten, or contract. 3. All muscle cells contain one of the following prefixes: myo-, mys-, or sarco-

Skeletal Muscle Fibers – Are packaged into organs called skeletal muscles that attach to the body’s skeleton. Cover our bony “underpinnings” and help form the smoother contours of the body.

Skeletal Muscle Fibers: Characteristics Cigar-shaped Multinucleate cells Largest of the muscle fiber types Known as striated muscle because its fibers appear to be striped. Only muscle type subject to conscious control (voluntary control). Can also be activated by reflexes (without our “willed command”) Can contract rapidly and with great force, but tires easily and must rest after short periods of activity.

Skeletal Muscle Fibers: Anatomy Skeletal muscle fibers are soft and surprisingly fragile. Yet skeletal muscles can exert tremendous power - how so? The reason they are not ripped apart as they exert force is that thousands of their fibers are bundled together by CT, which provides strength and support to the muscle as a whole.

Skeletal Muscle Fibers: Anatomy Endomysium – A delicate CT sheath that encloses each muscle fiber. Perimysium – A coarse fibrous membrane that are wrapped around several sheathed muscle fibers. Fascicle – A bundle of muscle fibers.

Skeletal Muscle Fibers: Anatomy Epimysium – An even tougher “overcoat” of CT that bounds together many fascicles; Covers the entire muscle. The epimysia blend into the strong, cordlike tendons , which attach muscles indirectly to bones, cartilages, or CT coverings of each other.

Functions of Tendons 1. Anchor Muscles Tendons attach muscles to bones. 2. Provide Durability Tendons are mostly tough collagenic fibers, so they can cross rough bony projections. 3. Conserve Space Because of their relatively small size, more tendons than fleshy muscles can pass over a joint. http: //www. davidlnelson. md/T endon_Surgery. htm

Shape of Skeletal Muscles Many people think of muscles as having an enlarged “belly” that tapers down to a tendon at each end. However, muscles vary considerably in the way their fibers are arranged. Many are spindle-shaped as just described above. Other fibers are arranged in a fan shape or a circle.

Smooth Muscle Characteristics No striations. Involuntary (cannot consciously control it). Found mainly in the walls of hollow visceral organs such as the stomach, urinary bladder, and respiratory passages. Propels substances along a definite tract, or pathway, within the body.

Smooth Muscle Cells Spindle-shaped. Have a single nucleus. Arranged in sheets or layers. Most often, there are two such layers, one running circularly and the other longitudinally. As the two layers alternately contract and relax, they change the size and shape of the organ. Contraction is slow and sustained. Examples: Movement of food through the digestive tract and emptying the bowels and bladder.

Cardiac Muscle Found only in the heart. The heart serves as a pump, propelling blood into the blood vessels and to all the tissues of the body. Is striated. Involuntary. Cardiac muscle fibers are branching cells joined by special junctions called intercalated discs.

Cardiac Muscle Fiber Anatomy The cardiac fibers are cushioned by small amounts of soft CT and arranged in spiral or figure 8 -shaped bundles. When the heart contracts, its internal chambers become smaller, forcing the blood into the large arteries leaving the heart.

Cardiac Muscle Contraction The structural features and arrangement allows the heart activity to be closely coordinated. Cardiac muscle contracts at a fairly steady rate set by the heart’s “in-house” pacemaker. Can also be stimulated by the nervous system to shift it into “high gear” for short periods, as when you race to catch the bus.

Muscle Functions 1. 2. 3. 4. Produces Movement Maintains Posture Stabilizes Joints Generates Heat

Muscle Functions: Produce Movement Just about all movements of the human body are a result of muscle contraction. Mobility of the body, which includes all locomotion and manipulation. Enable us to respond quickly to changes in the external environment. Allow us to express our emotions silently (smiles and frowns). Smooth and cardiac muscles work together to circulate blood and maintain blood pressure. Smooth muscle forces fluids such as bile and urine through internal body channels.

Muscle Functions: Maintaining Posture The skeletal muscles function continuously to maintain body posture. Making one tiny adjustment after another. So that we can maintain an erect or seated posture despite the never-ending downward pull of gravity.

Muscle Functions: Stabilizing Joints As the skeletal muscles pull on bones to cause movements, they also stabilize the joints of the skeleton. Muscle tendons are extremely important in reinforcing and stabilizing joints that have poorly fitting articulating surfaces. For example: The shoulder joint

Muscle Functions: Generating Heat Generation of body heat is a by-product of muscle activity. As ATP is used to power muscle contraction, nearly ¾ of its energy escapes as heat. Skeletal muscle is most responsible for generating heat. This heat is vital in maintaining normal body temperature.

Muscular System The term muscular system applies specifically to skeletal muscle. Therefore, we will be concentrating on this muscle type only in this unit.