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How do Muscles Work? Muscles serve FOUR functions for us: -- motion; they move our skeleton -- stability and posture -- controlling organ function -- generate body heat Characteristics of Muscle Tissue Excitability – ability of the muscles to be stimulated by nerves Contractility – muscles can contract Extensibility – muscles lengthen Elasticity – after shortening or lengthening, muscle can return to its original shape Muscles PULL, they never push! Roman Ship Analogy… Muscles work much like an old roman ship that used a galley of people rowing the oars in unison. Each person had only so much strength, but together, they gave the ship’s oars incredible power. Muscles need help… Muscles need to be connected to the rest of the body -- they need motor nerves -- they need energy and O2 -- H20, CO2 waste & glucose transport Requires nerves, blood vessels, and the lymphatic system to carry them These are held in connective tissues called FASCIA Muscles need to use sugar available in blood for energy Fascia Galore! Fascia is connective tissue that surrounds muscles Provides protection and stability Superficial Fascia Closest to the skin and holds muscle to the skin Also contains adipose tissue Stores fat and water, provides insulation from heat loss, protects, and is a place for vessels and nerves to carry things in and out of muscles Separates muscle groups Allows muscles to contract without interference from other muscles Each muscle has its own outer fascia called epimysium which is then surrounded by deep fascia Deep Fascia Superficial Fascia Deep Fascia Myofibers Individual muscle fibers are called myofibers (muscle cells) Arranged in groups of 10100 myofibers and these groups are called fascicles Perimysium surrounds fascicles Endomysium surrounds individual myofibers Myofibrils (actin & myosin) Proteins are arranged in a thread-like appearance in the sarcoplasm Give skeletal and cardiac muscle tissue their striations muscle cell Skeletal Muscle Fiber Contraction “Sliding Filament Theory” When muscle fibers are stimulated to contract, myofilaments (actin and myosin) slide past one another. This causes sarcomeres (muscle units) to shorten and the whole muscle fiber shortens. Sarcomere Sarcomere Sarcomere Whole Muscle Contraction The whole length of one muscle fiber must contract; however, the whole muscle does not have to contact. The number of muscle fibers contracting determines the strength of the contraction. The Effect of Exercise A regular exercise program will bring about 1. Increased endurance 2. Increased strength of muscles. Muscle enlarge, not due to increase in number of muscle fibers, but increased amounts of actin and myosin myofibrils inside each muscle fiber making them bigger and stronger. “Use it or lose it !” Arnold….then and now! Exercise increases muscle size, strength, and endurance – Aerobic (endurance) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue Makes body metabolism more efficient Improves digestion, coordination Resistance exercise like weight lifting increases muscle size and strength Effect of Exercise on Muscles
