Muscular System PDF

MUSCULAR SYSTEM  There are more than 600 skeletal muscles in the body. From 40% to 50% of our body weight is skeletal muscle. Muscles, along with the skeleton, determine the form and contour of our body. SKELETAL MUSCLE STRUCTURES CONNECTIVE TISSUE COMPONENT Endomysium Delicate co...

MUSCULAR SYSTEM  There are more than 600 skeletal muscles in the body. From 40% to 50% of our body weight is skeletal muscle. Muscles, along with the skeleton, determine the form and contour of our body. SKELETAL MUSCLE STRUCTURES CONNECTIVE TISSUE COMPONENT Endomysium Delicate connective tissue membrane that covers specialized skeletal muscle fibers. Perimysium Tough connective tissue binding together fascicles. Epimysium Coarse sheath covering the muscle as a whole. These three fibrous components may become a tendon or aponeurosis. Size, Shape, and Fiber Arrangement. Size- range from extremely small to large masses. Shape- variety of shapes, such as broad, narrow, long, tapering, short, blunt, triangular, quadrilateral, irregular, flat sheets, or bulky masses. Arrangement- parallel to long axis, converge to narrow attachment, oblique, pennate, bipennate, or curved. ATTACHMENT OF MUSCLES ORIGIN- point of attachment that does NOT move when muscle contracts. INSERTION- point of attachment that moves when the muscle contracts. MUSCLE ACTION Most movements are produced by the coordinated action of several muscles, some muscles in the group contract while others relax.  PRIME MOVER A muscle or group of muscles that directly performs a specific movement. ANTAGONIST Muscles that, when contracting, directly oppose prime movers. Provide precision and control during contraction of prime movers. SYNERGISTS Muscles that contract at the same time as the prime movers and they facilitate movers action to produce a more efficient movement. Fixator muscles- joint stabilizes. LEVER SYSTEM Rigid bar Fulcrum Load Pull FIRST CLASS LEVER Fulcrum lies between the pull and the load. Not abundant in the human body. SECOND CLASS LEVER Load lies between the fulcrum and the joint at which the pull is exerted. THIRD CLASS LEVER Pull is exerted between the fulcrum and load. Permit rapid and extensive movement. Most common. HOW MUSCLES ARE NAMED? Location, function, and shape. Direction of fibers Number of heads and divisions. Point of attachment. Relative size. IMPORTANT SKELETAL MUSCLES  Muscle of facial expression Unique in that at least one point of attachment is to deep layers of the skin over the face or neck. Muscles of mastication Responsible for chewing movement. Muscles that move the head Paired muscles on either side of the neck are responsible for head movements. TRUNK MUSCLES  Muscles of the thorax Critical importance in respiration. Muscles of the abdominal wall Arranged in three layers with fibers in each layer running in different directions to increase strength. Muscles of the back Bend to stabilized the back. Muscles of the pelvic floor Support the structures in the pelvic cavity. UPPER LIMB MUSCLES  Muscles acting on the shoulder girdle Muscles that attach the upper extremity to the torso are located anteriorly or posteriorly. Muscles that move the upper arm The shoulder is a synovial joint allowing extensive movement in every plane motion. Muscles that move the forearm Found proximally to the elbow and attach to the ulna and radius. Muscles that move the wrist, hand, and fingers. These muscles are located on the anterior or posterior surfaces of the forearm. LOWER LIMB MUSCLES  The pelvic girdle and lower extremity function in locomotion and maintenance of stability. Muscles that move the thigh and lower leg. Muscles that move the ankle or foot.  Extrinsic foot muscles Located in the leg and exert their actions by pulling on tendons that insert on bones in the ankle and foot. Responsible for dorsiflexion, plantar flexion, inversion, and eversion. Intrinsic foot muscles Located within the foot and responsible for flexion, extension, abduction, and adduction of toes. POSTURE  Maintaining posture of the body is one of the major roles muscles play. “GOOD POSTURE”- body alignment that most favors functions and requires the least muscular work to maintain and keeping the body’s center of gravity over its base. How Posture is Maintained? Muscle exert a continual pull on bones in the opposite direction from gravity. Structures other than muscle and bones have role in maintaining posture. Nervous System. Respiratory, digestive, excretory, and endocrine. MUSCULAR PHYSIOLOGY GENERAL FUNCTIONS Movement of the body as a whole or of its part. Heat production. Posture.  FUNCTION OF SKELETAL MUSCLE TISSUE CHARACTERISTICS OF SKELETAL MUSCLE CELL Excitability (Irritability)- ability to stimulate. Contractility- ability to contract, or shorten, and produce body movement. Extensibility- ability to extend, or stretch, allowing muscles to return to their resting length. OVERVIEW OF THE MUSCLE CELL  Muscle cells are called FIBERS because of their threadlike shape. Sarcolemma- plasma membrane of muscle fibers. Sarcoplasmic Reticulum Network of tubules and sacs found within muscle fibers. This continually pumps CALCIUM IONS from the sarcoplasm and stores the ions within its sac.  MYOFIBRILS- numerous fine fibers packed close together in sarcoplasm. SARCOMERE A segment of myofibril between 2 successive Z lines. Each myofibril consists of many sarcomeres which is the CONTRACTILE UNIT OF MUSCLE FIBERS.  STRIATED MUSCLE Dark stripes called A BANDS Light H zone runs across midsection of each dark A bands. Light Stripes called I bands. Dark Z line extends across center of each light I band.  T TUBULES Transverse tubules extend across the sarcoplasm at right angles to the long axis of the muscle fibers. Formed inward extensions of the sarcolemma. Membrane has ion pumps that continually transport Calcium Ions inward from the sarcoplasm. Allow electrical impulses travelling along the sarcolemma to move deeper into the cells. MYOFILAMENTS Each myofibril contains thousands of thick and thin myofilament. Kinds (Protein Molecule): Myosin Makes up almost all the thick filament. Myosin “Heads” are chemically attracted to actin molecules. Myosin “heads” are known as cross bridges when attached to actin.  ACTIN Globular protein that forms two fibrous strands twisted around each other to form the bulk of the thin filament. TROPOMYOSIN Protein that blocks the active sites on the actin molecules. TROPONIN Protein that holds tropomyosin molecules in place. MECHANISM OF ACTION  Excitation and Contraction A skeletal muscle fiber remains at rest until stimulated by a motor neuron. Neuromuscular Junction motor neurons connect to the sarcolemma at the motor end plate. It is a synapse where neurotransmitter molecules transmit signals. Acetylcholine The neurotransmitter released into the synaptic cleft that diffuses across the gap, stimulates receptors and initiates an impulse in the sarcolemma. SLIDING FILAMENT THEORY When active sites on the actin are exposed, myosin heads bind to them. Myosin heads bend, pulling the thin filaments past them. Each head releases, binds to the next active site, and pulls again. The entire myofibril shortens.  ENERGY SOURCE OF MUSCLE CONTRACTION MUSCLE TONE Tonic contraction- continual, partial contraction of a muscle. At any one time, a small number of muscle fibers within a muscle contract, producing a tightness or muscle tone. Muscles with less tone than normal are flaccid. Muscles with more tone than normal are spastic. LENGTH AND TENSION RELATIONSHIP  Maximal strength that a muscle can develop bears a direct relationship to the initial length of its fiber. A shortened muscle’s sarcomeres are compressed, therefore the muscle cannot develop much tension.  An overstretched muscle cannot develop much tension because the thick myofilaments are too far from the thin myofilaments. Strongest maximal contraction is possible only when the skeletal muscle has been stretched to its optimal length. ISOTONIC AND ISOMETRIC CONTRACTIONS Isotonic Contraction Contraction in which the one or tension within a muscle remains the same as the length of the muscle changes. Concentric- muscle shortens as it contracts. Eccentric- muscle lengthens while contracting.  Isometric contraction Contraction in which muscle length remains the same while the muscle tension increases. CARDIAC MUSCLE  Found only in heart, forming the bulk of the wall of each chamber. A.k.a. Striated Involuntary muscle. Contracts rhythmically and continuously to provide the pumping action needed to maintain a constant blood flow. Cardiac muscle resembles skeletal muscle but has specialized features SMOOTH MUSCLE Smooth muscle is composed of small, tapered cells with a single nuclei. No T tubules are present, and only a loosely organized sarcoplasmic reticulum is present. Calcium comes from outside the cell and binds to calmodulin instead of troponin to trigger contraction.  No striations ,because thick and thin myofilaments are arranged differently than in skeletal or cardiac muscle fibers, myofilaments are not organized into sarcomeres. TWO TYPES OF SMOOTH MUSCLE TISSUE VISCERAL MUSCLE (SINGLE UNIT) Gap junctions join smooth muscle fibers into large continuous sheet. Forms a muscular layer in the walls of hollow structures such as the digestive, urinary, and reproductive tracts. Exhibits auto-rhythmicity, producing peristalsis.  MULTIUNIT Does not act as a single unit but is composed of many independent cell units. Each fiber responds only to nervous input.