MUSCULAR SYSTEM Pau Junyent & Aurora Nieto

What are muscles? I  contractile tissue found in animals  over 650 muscles  half the weight of the human body  produce movement & body heat  skeletal, smooth and cardiac  ability to contract and conduct electrical impulses  voluntary (biceps) or involuntary(lungs)  striated or smooth

What are muscles? II  Rigor Mortis: stiffening body after death, caused by calcium in the muscle  contract & relax; NOT stretch  made up of elastic tissue  need: Oxygen and Blood  Antagonist muscles: pair of muscles that do opposite things from one another  Elasticity: the ability to return to original shape  Flexion: ability to bend a joint

Differences  Different functions  Appearance - skeletal muscle: striated (striped) - cardiac muscle: striated but stripes less organized. contain branches, allow rapid communication - smooth muscle: composed of cells with dark nuclei; not striated

Smooth Muscle I  Involuntary muscle  Found in hollow parts of the body  Stimulated by the nervous system  Two groups: single-unit and multiunit  Single-unit: rapid and simple contractions  Multiunit: contractions depend on the nervous system  Found in: Walls, arteries, veins, urinary bladder, lymphatic vessels, uterus, respiratory tract, iris, etc…  Structure and function the same for every all organs  Said to be in charge of ‘housekeeping’ functions

Smooth Muscle II  Contracts everything at once  Cytoplasm is filled with myosin and actin molecules  Myosin: ATP-dependent motor protein  Actin: Protein found in all eukaryote cells  Contraction caused by sliding actin and myosin filaments

Skeletal Muscle I  Produce movement & supports the skeleton  Voluntary muscle  Controlled by the nervous system  Attached to bones by tendons  Made up of muscle fibers (myoblasts)  Cartilage: connective tissue found in joints

Skeletal Muscle II  Two groups: Type I and type II  Type I: red, presence of oxygen, for endurance and slow fatigue  Type II: white, absence of myoglobin, reliance on glycolytic enzymes, used shortly, use oxidative and anaerobic metabolism, fast fatigue

Skeletal Muscle III – Categorized I  Categorized not only by color but by arragement of fascicles  Parallel, convergent, pennate, sphinter  Parallel muscles:  fascicles run parallel to the direction of the muscle  most skeletal muscle (triceps, biceps)  Convergent muscles:  Fibers come out from a common point.  Cover larges surfaces.  Allow a lot of movement (pectoralis major)

Skeletal Muscle III – Categorized II  Pennate muscles:  1 or more tendons run through the muscle  the fascicles form a slanted angle to the tendons  greater amount of muscle fibers = more tension (Rectus Femoris)  Sphinter muscles (circular) :  arranged around an opening  when muscle contracts, opening gets smaller.  at the entrances and exits of passage ways

Most Important Skeletal Muscles Pectoralis Major:  Thick, fan-shaped muscle  At the front (chest) of human body  Flexes chest area Gluteus Maximus:  Largest and most superfcial of gluteal muscles  Shape and appearance of buttocks  Flexes thigh joint

Differences (Tendon & Ligament)  Ligaments:  connect bone to bone  help to stabilize joints  long, stringy collagen  Slightly elastic  Stretched to gradually increase flexibility.  Tendon:  connects muscle to bone  tough, flexible  attached to the skeletal muscles  intermediaries between the muscles

Cardiac Muscle I  Involuntary or voluntary muscle  Heart  Send blood to all the body by using contraction  Cardiomyocytes have 1-4 nuclei  Cordinated contractions  Blood is sent to clean body from waste products and keep the body active  Highly resistant to fatigue

Cardiac Muscle II  Needs a lot of calcium  Largest number of mitochondria  Cardiac muscles contract to squeeze blood out  Relaxes to fill the heart with blood

Muscle Regeneration  Occurs when a muscle is stretched or torn (muscle strain)  Muscle breaks when the stress limit is trespassed  Provides more strength and larger size  Regenerates when the body rest  Regeneration will occur no matter how old  Satellite cells fuse with the broken fibers

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