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Muscle Tissue

Muscle Tissue. Types of Muscle Tissue. Skeletal muscle tissue Cardiac muscle tissue Autorhythmicity - pacemaker Smooth muscle tissue. Functions of Muscle Tissue. Producing body movements Stabilizing body positions Storing and moving substances within the body

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Muscle Tissue

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  1. Muscle Tissue

  2. Types of Muscle Tissue • Skeletal muscle tissue • Cardiac muscle tissue • Autorhythmicity - pacemaker • Smooth muscle tissue

  3. Functions of Muscle Tissue • Producing body movements • Stabilizing body positions • Storing and moving substances within the body • Sphincters – sustained contractions of ringlike bands prevent outflow of the contents of a hollow organ • Cardiac muscle pumps nutrients and wastes through • Smooth muscle moves food, bile, gametes, and urine • Skeletal muscle contractions promote flow of lymph and return blood to the heart • Generating heat - thermogenesis

  4. Properties of Muscle Tissue • Electrical excitability • Produces electrical signals – action potentials • Contractility • Isometric contraction – tension without muscle shortening • Isotonic contraction – constant tension with muscle shortening

  5. Properties of Muscle Tissue • Extensibility – ability of a muscle to stretch without being damaged • Elasticity • Ability of a muscle to return to its original length

  6. Connective Tissue Components • Fascia – a sheet of fibrous CT that supports or surrounds muscles and other organs • Superficial fascia (subcutaneous layer) – separates muscle from skin • Deep fascia – holds muscles with similar functions together • Epimysium – outermost layer – encircles whole muscles • Perimysium • Surrounds groups of 10 – 100 individual muscle fibers separating them into bundles called fascicles

  7. Connective Tissue Components • Endomysium • Separates individual muscle fibers within the fascicle • Tendon • All 3 CT layers may extend beyond the muscle to form a cord of dense regular CT that attaches muscle to the periosteum of bone • Aponeurosis • A broad, flat layer of CT

  8. Nerve and Blood Supply • Skeletal muscles are well supplied with nerves and blood vessels • Neuromuscular junction – the structural point of contact and the functional site of communication between a nerve and the muscle fiber • Capillaries are abundant – each muscle fiber comes into contact with 1 or more

  9. Sarcolemma, T Tubules, and Sarcoplasm • Sarcolemma – the plasma membrane of a muscle cell • T (transverse) tubules – Propogate action potentials – extend to the outside of the muscle fiber • Sarcoplasm – cytoplasm of the muscle fiber • Contains myoglobin – protein that binds with oxygen

  10. Myofibrils and Sarcoplasmic Reticulum • Myofibril – the contractile elements of skeletal muscle • Sarcoplasmic reticulum (SR) – encircles each myofibril – stores CA2+ (its release triggers muscle contractions)

  11. Atrophy and Hypertrophy • Muscular atrophy – wasting away of muscles • Disuse • Denervation • Muscular hypertrophy – an excessive increase in the diameter of muscle fibers

  12. Filaments and the Sarcomere • Filaments – structures within the myofibril • Thin • Thick • Sarcomere – basic functional unit of a myofibril • Z discs – separate one sarcomere from the next

  13. Filaments and the Sarcomere • A band – predominantly thick filaments • Zone of overlap at the ends of the A bands • H zone – contains thick, but no thin filaments • I band – thin filaments • M-line – middle of the sarcomere

  14. Muscle Proteins • Contractile proteins – generate force • Myosin • Actin • Regulatory proteins – switch contraction on and off • Structural proteins

  15. Sliding Filament Mechanism • Muscle contraction occurs because myosin heads attach to the thin filaments at both ends of the sarcomere and pull them toward the M line. • The length of the filaments does not change; However, the sarcomeres shorten, thereby shortening the entire muscle.

  16. Role of Ca2+ in Contraction • An increase in calcium ion concentration in the cytosol initiates muscle contraction and a decrease in calcium ions stops it.

  17. Rigor Mortis • After death the cellular membranes become leaky. • Calcium ions are released and cause muscular contraction. • The muscles are in a state of rigidity called rigor mortis. • It begins 3-4 hours after death and lasts about 24 hours, until proteolytic enzymes break down (digest) the cross-bridges.

  18. Neuromuscular Junction (NMJ) • Muscle action potentials arise at the NMJ. • The NMJ is the site at which the motor neuron contacts the skeletal muscle fiber. • A synapse is the region where communication occurs.

  19. Neuromuscular Juntcion (NMJ) • The neuron cell communicates with the second by releasing a chemical called a neurotransmitter. • Synaptic vesicles containing the neurotransmitter acetylcholine (ach) are released at the NMJ. • The motor end plate is the muscular part of the NMJ. It contains acetylcholine receptors. • The enzyme acetlycholineesterase (AChE) breaks down ACh.

  20. Production of ATP • 1. From creatine phosphate. • When muscle fibers are relaxed they produce more ATP than they need. This excess is used to synthesize creatine phosphate (an energy rich compound).

  21. Production of ATP • 2. Anaerobic cellular respiration. • Glucose undergoes glycolysis, yielding ATP and 2 molecules of pyruvic acid. • Does not require oxygen.

  22. Production of ATP • 3. Aerobic cellular respiration. • The pyruvic acid enters the mitochondria where it is broken down to form more ATP. • Slower than anaerobic respiration, but yields more ATP. • Utilizes oxygen. • 2 sources of oxygen. • Diffuses from bloodstream. • Oxygen released from myoglobin.

  23. Muscle Fatigue • Muscle fatigue is the inability of a muscle to contract forcefully after prolonged activity. • Central fatigue – a person may develop feelings of tiredness before actual muscle fatigue.

  24. Oxygen Debt or Recovery Oxygen Uptake • Added oxygen, over and above resting oxygen consumption, taken in after exercise. • Used to restore metabolic conditions. • 1. To convert lactic acid back into glycogen stores in the liver. • 2. To resynthesize creatine phosphate and ATP in muscle fibers. • 3. To replace the oxygen removed from hemoglobin.

  25. Motor Units • A motor unit consists of the somatic motor neuron and all the skeletal muscle fibers it stimulates. • A single motor neuron makes contact with an average of 150 muscle fibers. • All muscle fibers in one motor unit contract in unison.

  26. Twitch Contraction • A twitch contraction is the brief contraction of all the muscle fibers in a motor unit in response to a single action potential. • A myogram is a record of a muscle contraction and illustrates the phases of contraction.

  27. Refractory Period • A period of lost excitability during which a muscle fiber cannot respond to stimulation.

  28. Motor Unit Recruitment • The process in which the number of active motor units increases. • The weakest motor units are recruited first, with progressively stronger units being added if the task requires more force.

  29. Muscle Tone • Even at rest a muscle exhibits a small amount of muscle tone – tension or tautness. • Flaccid – when motor units serving a muscle are damaged or cut. • Spastic – when motor units are over-stimulated.

  30. Isotonic and Isometric Contractions • Concentric isotonic contraction – a muscle shortens and pulls on another structure. • Eccentric isotonic contraction – the length of a muscle increases during contraction. • Isometric contraction – muscle tension is created; However, the muscle doesn’t shorten or lengthen.

  31. Types of Skeletal Muscle Fibers • Slow oxidative (SO) fibers. • Smallest of the fibers. • Least powerful. • Appear dark red – much myoglobin and many capillaries. • Resistant to fatigue.

  32. Types of Skeletal Muscle Fibers • Fast oxidative-Glycolytic (FOG) fibers. • Intermediate in diameter. • Appear dark red – much myoglobin and many capillaries. • High level of intracellular glycogen. • Resistant to fatigue.

  33. Types of Skeletal Muscle Fibers • Fast Glycolitic (FG) fibers. • Largest in diameter. • Contain the most myofibrils, therefore more powerful contractions. • Appear white – low myoglobin and few capillaries. • Large amounts of glycogen – anaerobic respiration. • Fatigue quickly.

  34. Distribution and Recruitment of Different Types of Fibers • Most skeletal muscles are a mixture of all three types. • The continually active postural muscles have a high concentration of SO fibers.

  35. Distribution and Recruitment of Different Types of Fibers • Muscles of the shoulders and arms are used briefly and for quick actions, therefore they have many FG fibers. • Muscle of the legs support the body and participate in quick activities, therefore they have many SO and FOG fibers.

  36. Cardiac Muscle Tissue • The principle tissue in the heart is cardiac muscle tissue. • Cardiac muscle fibers have intercalated discs, which connect the ends of the cardiac muscle fibers together. • Cardiac muscle tissue remains contracted 10 to 15 times longer than skeletal muscle. • Requires a constant supply of oxygen and contains larger and more numerous mitochondria.

  37. Smooth Muscle Tissue • Activated involuntarily. • Two types. • Visceral (single-unit) smooth muscle. • Walls of small blood vessels and walls of hollow organs (I.E. Stomach, intestines, uterus, and urinary bladder). • Multi-unti smooth muscle. • Walls of large ateries, in the airways of lungs, in arrector pili muscles.

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