Muscular System Human A & P
There are 3 types of muscle tissue: A. Skeletal B. Smooth C. Cardiac The essential function of a muscle is contraction, or shortening, and are responsible for essentially all of the body s ability to move.
They attach to bones. They are huge, cigar-shaped, multinucleated cells. The largest type (up to 30 cm). Striated (stripes in the fibers) Voluntary (conscious control except reflexes) Contract rapidly and with great force, but also tire easily and require reset after short periods of activity. Skeletal Muscle Description
Thousands of skeletal muscle fibers are bundled together by connective tissue, which provides strength and structure to the muscle as a whole. Each individual fiber is enclosed in an endomysium. Several fibers are bundled together into a fascicle and covered with a coarse perimysium. Several fasciles are bound together and covered by an epimysium, which covers the entire muscle. Skeletal Muscle Structure
Skeletal muscle fibers blend or taper into tendons or aponeuroses. Aponeuroses attach indirectly to bones, cartilage, or connective tissue coverings. Tendons anchor muscle to bone, but also provide durability and conserve space. They are tough collagenic fibers, so they can cross rough bony projections without tearing like muscles would. Tendons and Aponeuroses
Tendon pictures and diagrams
Apopneuroses
Smooth muscle has no striations. It is involuntary (cannot consciously control it). They are found mainly in the walls of hollow visceral (internal) organs, such as the stomach, urinary bladder, and repertory passages. They propel substances along a definite tract or pathway within the body, such as moving food through the digestive tract and emptying bowels and bladder. Smooth Muscle Description
Smooth muscle is spindle shaped with a single nucleus and are surrounded by a small endomysium. They are arranged in layers, usually 2, one is circular, the other longitudinal. The 2 layers alternately contract and relax as they change the size and shape of the organ. The movement is slow and sustained. Smooth Muscle Structure
Smooth Muscle
Cardiac muscle is found only in the heart. It forms the bulk of the heart walls. It is striated and involuntary. The cardiac fibers are cushioned by small amounts of soft connective tissue (endomysium) and arranged in spiral bundles (figure 8 shaped). Cardiac fibers are branching cells joined by special junctions called intercalated discs. Cardiac Muscle
Cardiac Muscle Fibers
When the heart contracts, its internal chambers become smaller, forcing the blood into the large arteries leaving the heart. Cardiac muscle usually contracts at a fairly steady rate set by the heart s inhouse pacemaker. How the heart muscle works
1. Produce Movement they enable us to respond quickly to changes in the external environment, as well as force fluid and other substances through internal channels. 2. Maintaining Posture- 3. Stabilizing Joints (muscle tendons) 4. Generating Heat As ATP is used to power muscle contraction, nearly three fourths of its energy escapes as heat. Muscle Functions
Cells = Fibers Endomysium Fascile Perimysium Epimysium Connective tissue converges into either a tendon or aponeuroses. Fascia Organization of Skeletal Muscle
Muscles are organs connective tissue (CT), blood vessels, nerves. Muscles are arranged in different ways:
Most are attached to two bones. Origin Fixed Insertion Moves Attachment
Skeletal Muscle cells have multiple nuclei. Many nuclei can be seen just below the plasma membrane (called a sarcolemma in muscle cells). They have lots of mitochondria. The nuclei are pushed aside by long ribbonlike organelles, the myofibrils, which nearly fill the cytoplasm. Myofibrils are bundles of fibers that fill the cell (1000+). They are composed of thick and thin microfilaments (thousands). Skeletal Muscle Micro-anatomy
Myofibril
Muscle Fibers
Alternating bands, light (I) and dark (A) bands give the muscle cell its striped appearance. The light I band has a midline interruption, a darker area called the Z line or disc. The dark A band has a lighter central area called the H zone. The M line in the center of the H zone contains protein rods that hold adjacent thick filaments together. Striations
Alternating dark and light bands are due to the arrangement of thick and thin myofilaments. A band, I band Striations
Thin filament 3 proteins Actin, troponin, tropomyosin Actin is anchored to Z disc. Do not extend, leaving the bare H zone. Thick filament 1 protein Myosin Contain ATPase enzymes, which split ATP to generate power for muscle contraction. Extend entire length of A band. Myofilaments
Z line to Z line is a sarcomere the functional unit of muscle contraction.
Label the Sarcomere
1. With a few exceptions, all skeletal muscles cross at least one joint. 2. Typically, the bulk of a skeletal muscle lies proximal to the joint crossed. 3. All skeletal muscles have at least two attachments: the origin and the insertion. 4. Skeletal muscles can only pull; they never push. 5. During contraction, a skeletal muscle insertion moves toward the origin. The 5 golden rules of skeletal muscle activity
In the sliding filament theory of muscle contraction, the actin fibers move inside myosin and cause the sarcomere to shorten and contract. A motor unit is the motor neutron and the muscle fibers it controls Sliding Filament Theory of Muscle Contraction
When a muscle cell contracts, the thin filaments slide past the thick filaments, and the sarcomere shortens. This process comprised of several steps is called the Sliding Filament Theory. It is also called the Walk Along Theory or the Ratchet Theory. Sliding Filament Theory