Muscle functions: 1. Movement of bones or fluids (blood) 2. Maintaining postures and body position 3. Stabilizing joints 4. Support soft tissues 5. Guards entrances and exits 6. Heat generation (skeletal muscle)
Muscle Characteristics 1. Excitability (responsiveness or irritability) ability to receive and respond to stimuli 2. Contractility ability to shorten when stimulated 3. Extensibility ability to be stretched 4. Elasticity ability to recoil to resting length
THREE TYPES OF MUSCLE:
Skeletal= striated and voluntary
Smooth= not striated and involuntary
Cardiac= striated and involuntary

Muscle Tissue * Distinguished from other tissues by its ability to contract and perform work * Structural unit= muscle cell aka muscle fiber
Skeletal muscle * Each muscle is served by one artery one nerve and one or more veins * Connective tissue wrappings of skeletal muscle : * Epimysium- dense regular connective tissue surrounding entire muscle * Perimysium- fibrous connective tissue surrounding fascicles * Endomysium- fine areolar connective tissue surrounding each muscle fiber
Muscle fibers microanatomy:
Sarcolemma=muscle fiber membrane
Sarcoplasm= inner material cytoplasm of muscle cells
Myofilament= filaments that make up myofibrils (actin and myosin) surrounding fibers
Myofibrils= contractile organelles found in the

Myofibril * Contains myofilaments- Actin (thin& light – I band) & Myosin (Thick & Dark A-band) * Z line- mid line interruption in the light I band * H Zone- midline interruption in the A band

Sarcomere * Smallest unit of a muscle fiber * Composed of thick and thin myofilaments (actin & myosin) made of contractile proteins

Types of Muscle Movement 1. Prime Mover- muscle that has the major responsibility for causing a particular movement 2. Antagonistic- one muscle contracts to flex and extremity, another muscle contracts to extend 3. Synergists- help prime movers by producing the same movement or by reducing movements 4. Fixators- specialized synergists. Hold bones still or stabilize the origin of a prime mover

Types of Muscle Contractions: * Isotonic- “same tone” successful in sliding movements the muscle shortens and movement occurs * Isometric- the tension in the muscle increases but sliding does not occur.

Sliding Filament Theory: * During Muscle Contraction * Myosin heads pull the thin filaments towards the center * As the thin filaments slide over the thick filaments the I bands and H zones becomes narrower until they disappear when the muscle is contracted * During Muscle Relaxation * When myosin heads on the thick filaments