MUSCULAR SYSTEM   Muscles make up the bulk of the body and account for about one-third of its weight.  Their ability to contract not only enables the body to move, but also provides the force that pushes substances, such as blood and food, through the body.  Without the muscular system, none of the other organ systems would be able to function.   OBJECTIVES:  Label the major muscles of the body. Distinguish between the three types of muscle tissue. Describe the function and composition of the muscular system.  Explain how skeletal muscles contract.  Explain the relationship among muscles, bones, and joints. Explain how muscles move bones.   1. The Skeleton and its joints support, protect, and provide flexibility for the body, but the Skeleton CANNOT Move Itself.   2. That job is performed by the Muscle Tissue that makes up the MUSCULAR SYSTEM.   3. A MUSCLE TISSUE IS TISSUE THAT CAN CONTRACT IN A COORDINATED FASHION AND INCLUDES MUSCLES TISSUE, BLOOD VESSELS, NERVES, AND CONNECTIVE TISSUE.   4. Approximately 40 to 50 percent of the MASS of the Human Body is composed of Muscle Tissue.    5. THE MUSCULAR SYSTEM IS COMPOSED OF MUSCLE TISSUE (MUSCLE FIBER) THAT IS HIGHLY SPECIALIZED TO CONTRACT, OR SHORTEN, TO PRODUCE MOVEMENT WHEN STIMULATED.   6. The Word Muscle is derived from the Latin word "MUS", meaning mouse.   7. Muscle tissue is found everywhere within the body, not only beneath the skin but deep within the body, surrounding many internal organs and blood vessels.   8. The size and location of muscle tissue helps determine the shape of our bodies and the way we move.   TYPES OF MUSCLE TISSUE  (THREE TYPES)   1. There are Three Types of Muscle Tissue, or Muscles: SKELETAL, SMOOTH, AND CARDIAC.    2. EACH TYPE HAS A DIFFERENT STRUCTURE AND PLAYS A DIFFERENT ROLE IN THE BODY.     SKELETAL MUSCLE   1. Skeletal Muscle is Responsible for moving parts of the body, such as the limbs, trunk, and face.   2. SKELETAL MUSCLES ARE GENERALLY ATTACHED TO BONES AND ARE AT WORK EVERY TIME WE MAKE A MOVE.   3. SKELETAL MUSCLES ARE RESPONSIBLE FOR VOLUNTARY (CONSCIOUS) MOVEMENT. 4. A Skeletal Muscle is made of Elongated Cells called MUSCLE FIBERS.  Varying movements require Contraction of variable numbers of Muscles Fibers in a Muscle.   5. Skeletal Muscle fibers are grouped into dense bundles called FASCICLES.  A group of Fascicles are bound together by Connective Tissue to form a MUSCLE.   6. When viewed under a microscope, Skeletal Muscles appear to have STRIATIONS (BANDS OR STRIPES).  This gives Skeleton Muscle the name of VOLUNTARY OR STRIATED MUSCLE.    7. MOST SKELETAL MUSCLES ARE CONSCIOUSLY CONTROLLED BY THE CENTRAL NERVOUS SYSTEM (CNS).     8. Skeleton Muscle Cells are LARGE and have MORE than ONE NUCLEUS.  They vary in length from 1mm to 30 to 60 cm.   9. Because they are so long and slender, they are often called MUSCLE FIBERS rather than Muscle Cells.   10. Muscle Fiber together with the Connective Tissue, Blood Vessels, and Nerves form a Skeletal Muscle.   SMOOTH MUSCLES   1. SMOOTH MUSCLES ARE USUALLY NOT UNDER VOLUNTARY CONTROL.   2. SMOOTH MUSCLE CELLS ARE SPINDLE-SHAPED AND HAVE A SINGLE NUCLEUS, ARE NOT STRIATED and Interlace to form Sheets of smooth Muscle Tissue.   3. SMOOTH MUSCLES ARE FOUND IN MANY INTERNAL ORGANS, STOMACH, INTESTINES, AND IN THE WALLS OF BLOOD VESSELS.   4. Smooth muscle fibers are surrounded by connective tissue, but the connective tissue Does Not unite to form TENDONS as it does in Skeletal Muscles.   5. Most Smooth Muscle Cells can CONTRACT WITHOUT Nervous Stimulation.  Because most of its movements Cannot be consciously controlled, Smooth Muscle is referred to as Involuntary Muscle.   6. The contractions in Smooth Muscles move food through our digestive tract, control the way blood flows through the circulatory system, and increases the size of the pupils of our eyes in bright light.   CARDIAC MUSCLE   1. THE ONLY PLACE IN THE BODY WHERE CARDIAC MUSCLE IS FOUND IS IN THE HEART.   2. Cardiac Cells are Striated, but they are NOT under Voluntary Control.   3. Cardiac Muscle Contract Without Direct stimulation by the Nervous System.  A bundle of specialized muscle cells in the upper part of the heart sends electrical signals through cardiac muscle tissue, causing the heart to rhythmically contract and pump blood through the body.   4. The Cardiac Muscle Cell contains ONE Nucleus located near the center, adjacent cells form branching fibers that allow Nerve Impulses to pass from cell to cell.         MUSCLE STRUCTURE   1. A Muscle Fiber is a single, Multinucleated Muscle Cell.   2. A Muscle made be made up of hundreds or even thousands of Muscle Fibers, depending on the Muscles Size.   3. Although Muscle Fiber makes up most of the Muscle Tissue, a large amount of Connective Tissue, Blood Vessels, and Nerves are also present.   4. Connective Tissue Covers and Supports each Muscle Fiber and reinforces the Muscle as a whole.   5. The health of Muscle depends on a sufficient Nerve and Blood Supply.  Each Skeletal Muscle has a Nerve Ending that controls its activity.   6. Active Muscles use a lot of Energy and require a continuous supply of Oxygen and Nutrients, which are supplied by Arteries.  Muscles produce large amounts of Metabolic Waste that must be removed by Veins.   7. Muscle Fibers consist of Bundles of threadlike structures called MYOFIBRILS.    8. Each Myofibril is made up of TWO Types of Protein Filaments- Thick ones and Thin ones.   9. The THICK FILAMENTS are made up of a PROTEIN called MYOSIN.   10.  The THIN FILAMENTS are made of a PROTEIN called ACTIN.   11.  Myosin and Actin Filaments are arranged to form overlapping patterns, which are responsible for the Light and Dark Bands that can be seen in Skeletal (Striated Appearance) Muscle.   12.  Thin Actin Filaments are Anchored at their Midpoints to a structure called the Z-LINE.   13.  The Region From one Z-line to the next is called a SARCOMERE the Functional Unit of Muscle Contractions.       MECHANISM OF MUSCLE CONTRACTIONS   1.  The Sarcomere is the functional unit of Muscle contractions.   2. When Muscle Cells Contract, the light and dark bands contained in Muscle Cells get closer together.   3. This happens because when a Muscle Contracts, Myosin Filaments and Actin filaments interact to shorten the length of a Sarcomere.   4. When Myosin Filaments and Actin Filaments come near each other, many knob (heads) like projections in each Myosin Filament form CROSS-BRIDGES with an Actin Filament.   5. When the Muscle is Stimulated to Contract, the Cross-bridges MOVE, PULLING the Two Filaments past each other.   6. After each Cross-bridge has moved as far as it can, it releases the Actin Filament and returns to its original position.  The Cross-bridge then attaches to the Actin Filament at another place and the cycle is repeated. This action Shortens the Length of the Sarcomere.   7. The synchronized shortening of Sarcomeres along the full length of a Muscle Fiber causes the Whole Fiber, and hence the Muscle, to Contract.   8. WHEN THOUSANDS OF ACTIN AND MYOSIN FILAMENTS INTERACT IN THIS WAY, THE ENTIRE MUSCLE CELL SHORTENS.   9. THIS CONCEPT IS THE SLIDING FILAMENT THEORY.   10. Muscle Contractions require Energy, which is supplied by ATP.  This Energy is used to Detach the Myosin Heads from the Actin Filaments.   11. Because Myosin Heads must Attach and Detach a number of times during a Single Muscle Contraction, Muscle Cells must have a Continuous Supply of ATP.   12. Without ATP the Myosin Heads would stay Attached to the Actin Filaments, keeping Muscles Permanently Contracted.   13. A Muscle Contraction, like a Nerve Impulse, is an All-or-None Response- either Fibers Contract or they Remain Relaxed.   14. The force of a Muscle Contraction is determined by the number of Muscle fibers that are Stimulated.  As more fibers are activated, the force of the contraction Increases.   15. Some Muscles, such as the muscles that hold the body in an upright position and maintain posture, are nearly always at least Partially Contracted.   CONTROL OF MUSCLE CONTRACTION   1. Muscles are useful only if they Contract in a Controlled fashion.   2. Motor Neurons connect the CNS to Skeleton Muscle Cells (EFFECTORS); Impulses (ACTION POTENTIALS) from Motor Neurons Control the Contraction of Skeleton Muscle Cells.   3. The point of contact between a Motor Neuron and a Muscle Cell is called the NEUROMUSCULAR JUNCTION.   4. Vesicles, or pockets, in the AXON TERMINALS of the Motor Neuron release molecules of the NEUROTRANSMITTER ACETYLCHOLINE.   5. These molecules Diffuse across the SYNAPSE, producing and IMPULSE in the Cell Membrane of the Muscle Cell.   6. The impulse causes the release of Calcium ions within the cell.  The Calcium Ions affect regulatory proteins that allow Actin and Myosin Filaments to interact and form cross-bridges.   7. A Muscle Cell WILL remain in a state of CONTRACTION until the production of Acetylcholine STOPS.   8. An ENZYME called ACETYLCHOLINESTERASE, also produced at the Neuromuscular Junction, DESTROYS ACETYLCHOLINE, permits the reabsorption of Calcium Ions into the Muscle Cell, and Terminates the Contraction.   9. You can have a Weak or Strong Contraction depending on what you are trying to accomplish.  The BRAIN (frontal lobes of the cerebrum) decides what and how many Muscles Cells need to Contract.  Blinking your eye would be a Weak Contraction, but lifting heavy weights, the brain would signal most Muscle Cells to Contract.   10. MUSCLE SENSE IS THE BRAINS ABILITY TO KNOW WHERE OUR MUSCLES ARE AND WHAT THEY ARE DOING.  Permits us to  perform everyday activities without having to concentrate on muscle position.   HOW MUSCLES AND BONES INTERACT   1. Skeleton Muscles generate Force and produce Movement only by CONTRACTING or PULLING on Body Parts.   2. Individual Muscles can only PULL; they CANNOT PUSH.   3. Skeleton Muscles are joined to bone by TOUGH CONNECTIVE TISSUE CALLED TENDONS.   4. TENDONS ATTACH MUSCLE TO BONE; THE ORIGIN IS THE MORE STATIONARY BONE, THE INSERTION IS THE MORE MOVABLE BONE.   5. Tendons are attached in such a way that they PULL on the Bones and make them work like LEVERS.  The movements of the Muscles and Joints enable the Bones to act as LEVERS.   6. The Joint functions as a FULCRUM (The fixed point around which the lever moves) and the Muscles provide the FORCE to move the Lever.   7. Usually there several Muscles surrounding each Joint that PULL in DIFFERENT DIRECTIONS.   8. MOST SKELETAL MUSCLES WORK IN PAIRS.   9. When one Muscle or set of Muscles CONTRACTS, the other RELAXES.   10. The Muscles of the upper arm are a good example of this dual action: ANTAGONISTIC MUSCLES.  FLEXOR, A MUSCLE THAT BENDS A JOINT.  EXTENSOR, A MUSCLE THAT STRAIGHTENS A JOINT.       A. When the BICEPS Muscle (on the front of the upper arm, FLEXOR) CONTRACTS, it BENDS OR FLEXES THE ELBOW JOINT.       B. When the TRICEPS Muscle (on the back of the upper arm, EXTENSOR) CONTRACTS, it opens, or extends, the elbow joint.       C. A controlled movement requires contraction by both muscles.   11. ANTAGONISTIC MUSCLES ARE OPPONENTS, MUSCLES WHICH HAVE OPPOSING OR OPPOSITE FUNCTIONS. A muscle pulls when it contracts, but exerts no force when it relaxes and CANNOT PUSH.  When one muscle Pulls a bone in one direction, another muscle is needed to PULL the bone in the other direction.   12. SYNERGISTIC MUSCLES ARE THOSE WITH THE SAME FUNCTION, OR THOSE THAT WORK TOGETHER TO PERFORM A PARTICULAR FUNCTION.  They also stabilize a joint to make a more precise movement possible.   13. A normal characteristic of all Skeleton Muscles is that they remain in a state of PARTIAL CONTRACTION.   14. At any given time, some Muscles are being Stimulated while other are not.  This causes a TIGHTENED, or FIRMED, Muscle and is known as MUSCLE TONE.   15. Muscle Tone is responsible for keeping the back and legs straight and the head upright even when you are relaxed.   16. EXERCISE IS THE KEY TO MAINTAINING GOOD MUSCLE TONE WITHIN YOUR BODY.   17. MUSCLES THAT ARE EXERCISED REGULARLY STAY FIRM AND INCREASE IN SIZE BY ADDING MORE MATERIALS TO THE INSIDE OF MUSCLE FIBERS.   18. MUSCLE FATIGUE is a Physiological Inability of a muscle to contract.  Muscle fatigue is a result of a relative depletion of ATP.  When ATP is absent, a state of continuous contraction occurs.  This causes severe muscle cramps.   19. OXYGEN DEBT is a temporary Lack of Oxygen.  When this occurs Muscles will switch from the normal Aerobic Respiration to a form of Anaerobic Respiration called Lactic Acid Fermentation.  As the oxygen becomes Depleted, the muscle cells begin to switch.  Oxygen debt leads to the accumulation of Metabolic Waste (Lactic Acid) in the muscle fibers, resulting in muscle fatigue, pain, and even cramps.  Eventually, the lactic acid diffuses into the blood and is transported to the Liver.  So if you ever experienced Soreness after prolong exercise, it may have been caused by Oxygen Debt - Your body could not provide your Muscles the Oxygen they needed to function properly.