mbbs ims msu

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mbbs ims msu

  1. 1. Muscle Histology Assoc. Prof Dr. karim Al-Jashamy IMS 2009
  2. 2. Muscular Tissue  Muscle tissue is composed of cells which have the ability to contract (shorten) and relax (lengthen).  Muscle tissue is highly vascular zed and dense tissue.  Muscle tissue can not regenerate itself once it has been destroyed.  Muscle cells are called muscle fibers.  There are three types of muscle tissues: a. Striated or skeletal muscle b. Cardiac muscle or myocardial tissue c. Smooth or visceral muscle
  3. 3. Muscular Tissue Types  Striated or skeletal muscle: This muscle is composed of long, cylindrical, parallel fibers.  There are bands or striations present which run across the width of the fiber. These fibers are multinucleated (more than one nucleus present per cell).  This type of muscle tissue is under conscious or voluntary control.  This muscle has the greatest strength of contraction but tires most rapidly. It functions are locomotion and facial expressions.
  4. 4. Muscular Tissue Types  Cardiac muscle: Cardiac muscle fibers are branched at the end with striations present, usually only one nucleus is present per cell.  The branches of each fiber come into contact at specialized junctions called intercalated discs.  It is involuntarily controlled by the autonomic nervous system and hormones. Its contractions are short, but the muscle fibers are constantly contracting.  Its function is to create the pump which propels the blood throughout the body.
  5. 5. Muscular Tissue Types  Smooth or visceral muscle: These cells are spindle-shaped (tapered on the ends) and lack striations.  They have one nucleus present. They produce weaker contractions, however they contract for extended periods of time.  They are involuntarily controlled by the autonomic nervous system or hormones.  They are found in the digestive organs, arteries and veins, the trachea and bronchiole tubes, and the urogenital tract. Their contractions propels or moves substances or objects from one location to another.
  6. 6. Functions of muscle tissue  Movement  Maintenance of posture  Joint stabilization  Heat generation
  7. 7. Special functional characteristics of muscle  Contractility  Only one action: to shorten  Shortening generates pulling force  Excitability  Nerve fibers cause electrical impulse to travel  Extensibility  Stretch with contraction of an opposing muscle  Elasticity  Recoils passively after being stretched
  8. 8. Types of Muscle Tissue Skeletal •Attach to and move skeleton •40% of body weight •Fibers = multinucleate cells (embryonic cells fuse) •Cells with obvious striations •Contractions are voluntary Cardiac: only in the wall of the heart •Cells are striated •Contractions are involuntary (not voluntary) Smooth: walls of hollow organs •Lack striations •Contractions are involuntary (not voluntary)
  9. 9. Similarities…  Their cells are called fibers because they are elongated  Contraction depends on myofilaments  Actin  Myosin  Plasma membrane is called sarcolemma  Sarcos = flesh  Lemma = sheath
  10. 10. Skeletal muscle Epimysium: surrounds whole muscle Perimysium Endomysium is around each is around muscle fiber fascicle
  11. 11.  Each muscle: one nerve, one artery, one vein Skeletal Muscle  Branch repeatedly  Attachments  One bone to another  Cross at least one movable joint  Origin: the less movable attachment  Insertion: is pulled toward the origin  Usually one bone moves while the other remains fixed  In muscles of the limb, origin lies proximal to the insertion (by convention)  Note: origin and insertion may switch depending on body position and movement produced
  12. 12. Attachments continued  Many muscles span two or more joints  Called biarticular or multijoint muscles  Cause movements at two joints  Direct or “fleshy” attachments  Attachments so short that muscle appears to attach directly to bone  Indirect: connective tissue extends well beyond the muscle (more common)  Tendon: cordlike (most muscles have tendons)  Aponeurosis: flat sheet  Raised bone markings where tendons meet bones  Tubercles, trochanters, crests, etc.
  13. 13. Some sites showing animations of muscle contraction  http://entochem.tamu.edu/MuscleStrucContractswf/i ndex.html  http://www.brookscole.com/chemistry_d/templates/s tudent_resources/shared_resources/animations/musc les/muscles.html
  14. 14. Skeletal muscle  Fibers (each is one cell) have striations  Myofibrils are organelles of the cell: This big these are made up of cylinder is a -an organelle fiber: 1 cell filaments  Sarcomere  Basic unit of contraction  Myofibrils are long rows of repeating sarcomeres  Boundaries: Z discs (or lines)
  15. 15. Myofibrils  Made of three types of filaments (or myofilaments):  Thick (myosin)  Thin (actin)  Elastic (titin) ______actin _____________myosin titin_____
  16. 16. Sliding Filament Model __relaxed sarcomere__ _partly contracted_ fully contracted Sarcomere “A” band constant shortens because because it is actin pulled caused by towards its middle myosin, which by myosin cross doesn’t change bridges length Titin resists overstretching
  17. 17. EM (electron microscope): parts of 2 myofibrils
  18. 18.  Sarcoplasmic reticulum is smooth ER  Tubules surround myofibrils  Cross-channels called “terminal cisternae”  Store Ca++ and release when muscle stimulated to contract  To thin filaments triggering sliding filament mechanism of contraction  T tubules are continuous with sarcolemma, therefore whole muscle (deep parts as well) contracts simultaneously
  19. 19. Neuromuscular Junction Motor neurons innervate muscle fibers Motor end plate is where they meet Neurotransmitters are released by nerve signal: this initiates calcium ion release and muscle contraction Motor Unit: a motor neuron and all the muscle fibers it innervates (these all contract together) •Average is 150, but range is four to several hundred muscle fibers in a motor unit •The finer movement, the fewer muscle fibers /motor unit •The fibers are spread throughout the muscle, so stimulation of a single motor unit causes a weak contraction of the entire muscle
  20. 20. Types of skeletal muscle fibers  Fast, slow and intermediate  Whether or not they predominantly use oxygen to produce ATP (the energy molecule used in muscle contraction)  Oxidative – aerobic (use oxygen)  Glycolytic – make ATP by glycolysis (break down of sugars without oxygen=anaerobic)  Fast fibers: “white fibers” – large, predominantly anaerobic, fatigue rapidly (rely on glycogen reserves); most of the skeletal muscle fibers are fast  Slow fibers: “red fibers” – half the diameter, 3X slower, but can continue contracting; aerobic, more mitochondria, myoglobin  Intermediate: in between
  21. 21.  A skeletal muscle contracts when its motor units are stimulated  Amount of tension depends on 1. the frequency of stimulation 2. the number of motor units involved  Single, momentary contraction is called a muscle twitch  All or none principle: each muscle fiber either contracts completely or not at all  Amount of force: depends on how many motor units are activated  Muscle tone  Even at rest, some motor units are active: tense the muscle even though not causing movement: “resting tone”
  22. 22.  Muscle hypertrophy  Weight training (repeated intense workouts): increases diameter and strength of “fast” muscle fibers by increasing production of  Mitochondria  Actin and myosin protein  Myofilaments containing these contractile proteins  The myofibril organelles these myofilaments form  Fibers enlarge (hypertrophy) as number and size of myofibrils increase [Muscle fibers (=muscle cells) don’t increase in number but increase in diameter producing large muscles]  Endurance training (aerobic): doesn’t produce hypertrophy  Muscle atrophy: loss of tone and mass from lack of stimulation  Muscle becomes smaller and weaker Note on terminology: in general, increased size is hypertrophy; increased number of cells is hyperplasia
  23. 23. Tendon Anatomy  Very strong, stronger than muscle for size  As strong as bone with a failing point similar to steel!  Can transmit force through ability to glide  Passive component of the musculotendinous unit in light of their incredible influence on the foot. Tendon Histology  30% Collagen, 2% Elastin, 68% Water  Bulk is supplied by reticulin  70% Type I collagen
  24. 24. Ligament Histology  33% Composition: 90% Type I collagen, Elastin, Glycosaminoglycans. 67% Water
  25. 25. Anatomy of the Tendon  Tropocollagen – the most basic molecular unit of tendon  3 Coverings:  Endotenon- fascicles are surrounded by this areolar CT, contains BV, L, N, and FB.  Epitenon- Fascicles bound together by this 1-2 cell fibroblastic & synovial layer  Paratenon- loose areolar layer continuous with the epitenon & perimysium, straight.
  26. 26. Anatomy of the Tendon  Tendon/Synovial Sheath: acts like a pulley when tendon has an angled course.  Peritenon- term applied collectively to all CT structures associated with a tendon incl para-, meso- , epi-, and endotenon.
  27. 27. Tendon Anatomy
  28. 28. Tendon Anatomy
  29. 29. Tendon Circulation  3 Sources: a) Small amount from the central blood vessels originating in the muscle. b) Some from vessels of the bone and periosteum near the tendon’s insertion. c) Majority comes from small vessels in the paratenon or through the mesotenon. If absent then carried thru the vincula. Synovial fluid also nourishes the tendon.
  30. 30. Tendon Sheath Anatomy
  31. 31. Tendon Innervation  Afferent supply only  Source in musculotendinous junction and external local nerves.  Golgi tendon organs: monitor increases in tension rather than length.
  32. 32. Tendon Attachment to Bone  Attach at 90° angles to bone in 4 layers: 1. Tendon collagen fibers 2. Fibrocartilage 3. Bone 4. Sharpey’s fibers – originate in bone and end in perisoteum.

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