Muscles and the Muscular System PDF

Muscular System  The Muscular System  Muscles are responsible for all types of body movement – they contract or shorten and are the machine of the body  Three basic muscle types are found in the body  Skeletal muscle  Cardiac muscle  Smooth muscle Skeletal Muscle (striated...

Muscular System  The Muscular System  Muscles are responsible for all types of body movement – they contract or shorten and are the machine of the body  Three basic muscle types are found in the body  Skeletal muscle  Cardiac muscle  Smooth muscle Skeletal Muscle (striated muscles)  Most are attached by tendons to bones  Cells are multinucleate  Striated – have visible banding  Voluntary – subject to conscious control  Cells are surrounded and bundled by connective tissue = great force Smooth Muscle  Has no striations  Spindle-shaped cells  Single nucleus  Involuntary – no conscious control  Found mainly in the walls of hollow organs (e.g stomach, intestine, uterus, urinary bladder, arteries an other internal organs)  Slow  Cardiac Muscle  Forms the contractile wall of the heart (Found only in the heart)  Cardiac cells are branched.  Has striations  Usually has a single nucleus  Involuntary  Types of muscle tissue in the vertebrate body involuntary, striated voluntary, auto-rhythmic striated multi-nucleated involuntary, evolved first non-striated  Function of Muscles  Produce movement  Maintain position  Stabilize joints  Generate heat  Organization of Skeletal muscle Sarcolemma – is the fiber cell membrane Sarcoplasm (cytoplasm of fiber) Fiber cell contains many of the same organelles seen in other cells. Many oxygen-binding protein called myoglobin Cells punctuated by openings called the transverse tubules (T-tubules). They are narrow tubes that extend into the sarcoplasm at right angles to the surface and filled with extracellular fluid Myofibrils - cylindrical structures within muscle fiber contain bundles of protein filaments called myofilaments Myofilaments are two types: I. Actin filaments (thin filaments) II. Myosin filaments (thick filaments) When myofibril shortens, muscle shortens (contracts) Muscle Fiber  Structure of striated skeletal muscle Sarcomere – functional unit of muscle contraction – alternating bands of thin (actin) & thick (myosin) filaments Thin filaments: Actin: – Thin filaments are Actin – Tropomyosin is protein, which lies on actin – Strands of actin & tropomyosin coiled together – Troponin molecules are protein binds to Tropomyosin fibers  Thick filaments: myosin Myosin: Thick filaments Myosin molecule are long protein with globular head (cross bridge)  Interaction of thick & thin filaments Cross bridges – connections formed between myosin heads (thick filaments) & actin (thin filaments) – cause the muscle to shorten (contract) sarcomere  Mechanism of Muscle Contraction Nerve impulse reaches myoneural junction Acetylcholine a neurotransmitter is released from motor neuron Acetylcholine binds with receptors in the muscle membrane to allow sodium to enter Sodium influx will generate an action potential in the sarcolemma Action potential travels down T tubule Sarcoplamic reticulum release stored calcium (Ca+2)  Muscle Contraction (Cont’d) At rest, tropomyosin blocks myosin-binding sites on actin Ca+2 binds to troponin complex – Shape change causes movement of tropomyosin-troponin complex – Exposes myosin-binding sites on actin Myosin globular head attach to binding sites and create a power stroke and muscle contraction occurs ATP detaches myosin heads and energizes them for another contraction When action potentials cease the muscle stop contracting Muscle Response to Strong Stimuli  Muscle force depends upon the number of fibers stimulated  More fibers contracting results in greater muscle tension  Muscles can continue to contract unless they run out of energy There are different roles that a muscle can achieve during movement, these roles are:  Agonist: is the muscle(s) that provides the major force to complete the movement. Because of this agonists are known as the prime movers  Antagonist – muscle that opposes or reverses a prime mover  Synergist – work together to produce a common effect. Muscle that aids a prime mover in a movement and helps prevent rotation  Muscles do work by contracting skeletal muscles come in antagonistic pairs flexor vs. extensor contracting = shortening move skeletal parts  Tendons: Connect bone to muscle  Ligaments : Connect bone to bone Energy for Muscle Contraction  Initially, muscles used stored ATP for energy  Bonds of ATP are broken to release energy  Only 4-6 seconds worth of ATP is stored by muscles  After this initial time, other pathways must be utilized to produce ATP Energy for Muscle Contraction  Direct phosphorylation  Muscle cells contain creatine phosphate (CP)  CP is a high-energy molecule  After ATP is depleted, ADP is left  CP transfers energy to ADP, to regenerate ATP  CP supplies are exhausted in about 20 seconds  Energy for Muscle Contraction  Anaerobic glycolysis  Reaction that breaks down glucose without oxygen  Glucose is broken down to pyruvic acid to produce some ATP  Pyruvic acid is converted to lactic acid  This reaction is not as efficient, but is fast  Lactic acid produces muscle fatigue. When a muscle is fatigued, it is unable to contract  The common reason for muscle fatigue is oxygen debt  Energy for Muscle Contraction  Aerobic Respiration  Series of metabolic pathways that occur in the mitochondria  Glucose is broken down to carbon dioxide and water, releasing energy  This is a slower reaction that requires continuous oxygen