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Ana-physi 6.ppt

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Histology of muscle
Histology of muscle
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Ana-physi 6.ppt

  1. 1. 5. The Muscular System
  2. 2.  Muscle tissue specialized for contraction and is responsible for body movements and changes in size and shape of internal organs.  The prefixes myo and sacro refers to muscle, the terms such as myofibril and myofilaments reference structure with in the muscle.  The plasma membrane of muscle cell is called the sarcolemma.  The cytoplasm is termed as sarcoplasm.  Endoplasmic reticulum is termed as sarcoplasmic reticulum(SR).  A single skeletal muscle is called a muscle fiber.
  3. 3. Properties of muscle Excitability: Sometimes called irritability. Muscle cell maintain a membrane potential and are able to respond to a stimulus such as a neurotransmitter by developing an electrical impulse. Contractility: When stimulated, the electrical impulse spreading across a muscle cell can cause the cell to contract. Extensibility: In addition to contraction, muscle cell can lengthen in response to stretch. Elasticity: Once stretched, muscle fibers can recoil to their original resting length due to the elastic elements with in the muscle.
  4. 4. Functions of muscle Production of movement: The action of skeletal muscle is responsible for moving joints and thus allowing locomotion. Maintaining posture: through the action of signals generated from sensors located in joint, tendons, and muscles, minute adjustments are anatomically made to maintain the position. Generation of body heat: skeletal muscles are an important organ in heat production, such as through the process of shivering. Stabilizing joints: In addition to moving joints, muscle also stabilizes the joints, thus minimizing dislocations.
  5. 5. Classifications Smooth  Individual cells are spindle shaped with centrally located nuclei  Regulated by the autonomic nervous system  Located in visceral structures  Aggregates of myofilaments are composed of actin and myosin  Filaments are not arranged in order
  6. 6. Smooth Muscle
  7. 7. Classifications Cardiac  Found only in the heart  Regulated by the autonomic nervous system  Characterized by alternating white and dark bands  Composed of elongated, branching cells with irregular contours at junctions with other cells
  8. 8. Classifications  Boundary area where cells meet is called intercalated disk  This specialized structure facilitates transmission of nerve impulses  Each cell has a nucleus (sometimes 2) that is centrally located
  9. 9. Cardiac Muscle
  10. 10. Classifications Skeletal muscle Long bundles of cells – striated Multinucleated with nuclei at periphery of cells Innervated by spinal or cranial nerves Three types red or dark (highest myoglobin and mitochondria content) white or pale (lowest myoglobin and mitochondria content) intermediate (characteristics between white and red fibers)
  11. 11. Classifications Skeletal muscle comprises majority of body muscle mass. Skeletal muscle fiber can run the length of the muscle with which it is a part. Skeletal muscle fibers do not branch or anastomose.
  12. 12. Classifications Often described according to type of movement performed Flexors – if they are located on the side of the limb towards which the joint decreases the joint angle Extensors – if they are located on the side of the limb towards which the joint increases the joint angle Adductors – if they pull a limb toward the median plane Abductors – if they pull a limb away from the median plane Sphincters – are arranged circularly to constrict body openings
  13. 13. Skeletal Muscle
  14. 14. Arrangement  Function of muscles is to contract or shorten and thereby move an object.  Primary consideration for accomplishing this goal is arrangement.  Examples include:  Sheets  Sheets rolled into tubes  Bundle  Rings  Cones  Discrete cells or clusters of cells
  15. 15. Arrangement  The effects of skeletal muscles (apart from sphincters) are noted some distance from their location.  This means the contraction must be transmitted.  One end must be anchored and the other attached directly to a tendon or moveable part.  Accordingly, anatomic description of a skeletal muscle sometimes refers to its origin and insertion.
  16. 16. Skeletal Muscle Harnessing  Skeletal muscle accounts for approximately 40% of body weight.  Each skeletal muscle is considered as an organ and is made up of:- connective tissue muscle fiber blood vessels  nerve fibers
  17. 17. Connective tissue  Muscle cell has three connective tissue layers. Epimysium: The entire cell muscle is surrounded by a dense, irregular connective tissue layer called the epimysium containing a dense concentration of collagen fibers.  This layer separates the muscle from surrounding tissue. Perimysium: In cross section, a muscle consists of multiple grouping of muscle fibers called fascicles (bundles). Each fascicles surrounded by the perimysium (peri – around) containing collagen and elastic fibers.  This layer contains blood vessels and nerves supplying the fascicles.
  18. 18. Skeletal Muscle Harnessing  Endomysium: Within each fascicles are individual skeletal muscle cells, called muscle fibers, each surrounded by the endomysium (endo – within).  Within this connective tissue layer are capillaries supply each muscle fiber, nerve fibers controlling the muscle, and satellite cells.  These later cells serve as stem cells that can help repair damaged muscle.
  19. 19. Blood vessels and nerves  The two innermost layers of connective tissue within the muscle each contain blood vessels and nerves.  Skeletal muscle is generally under voluntary nervous control, and therefore requires stimulation for nerve fibers to initiate contraction.
  20. 20. Arrangement
  21. 21. Skeletal muscles fiber  Skeletal muscle tissue consists of large, multinucleated cells commonly referred to as muscle fiber.  Muscle fiber form the fusion of small, individual muscle cell called myoblasts during development.  Some remain unfused and become satellite cells.  Skeletal muscle fibers are incapable of dividing, new muscle fibers are produced from satellite cells located in the adult muscle.  The nuclei located immediately under the plasma membrane, which in skeletal muscle is called sarcolemma.  The cytoplasm of skeletal muscle is called sarcoplasm.
  22. 22. Formation of skeletal muscle cell
  23. 23.  Muscle fiber are composed of functional subunits called myofibrils.  Each muscle cell contains hundreds to thousands of myofibrils.  The myofibril consists of bundles of myofilaments that are protein filaments composed of primarily actin and myosin, the two contractile protein in muscle.  Actin forms – the bulk of the thin filaments  Myosin forms – the bulk of the thick filaments Myofibrils
  24. 24. Myofibrils contain three types of proteins Contractile protein: generates the force during contraction. This protein contain myosin and actin. Regulatory protein: help to initiate and terminate the contraction process and include tropomyosin and troponin found on thin filaments. Structural protein: help to maintain the alignment of the thin and thick filaments and provide elasticity and extensibility. These protein includes – titin, myomesium, and dystrophin.
  25. 25. Sarcoplasmic reticulum  Similar to the endoplasmic reticulum in nonmuscle cells, the sarcoplasmic reticulum (SR) forms a tubular network surrounding each myofibril.  The terminal cisternae have an active calcium pump that pumps calcium from the sarcoplasm in to the SR.
  26. 26. Sarcomeres  Sarcomeres is the functional unit of skeletal muscle.  Sarcomeres contain the protein myofilaments actin and myosin  In stained cross sections of skeletal muscle, alternating light and dark bands are evident, which are called the I and A bands respectively. These bands give skeletal muscle its striated appearance.  The dark bands alter the plane of the polarized light and are therefore anisotropic (not having the same properties in all direction)
  27. 27.  The light bands do not alter the plane of polarized light and are there for isotropic(appear the same in all direction), thus the name A band and I band, respectively.  Sarcomere is the region between two Z discs. It consists of one-half an I band, an A band, and one half an I band.  In muscle at rest, a lighter region can be found in the center of the A band called the H zone (from helle, meaning bright), which contains only myosin.  M – line, named for being in the middle of the sarcomere, transects the H zone and composed of protein that stabilizes the position of thick filaments.
  28. 28. Functional units of sarcomere cell
  29. 29. Skeletal muscle contraction  Each skeletal muscle fiber is innervated by a motor neuron innervating the muscle.  The release of the neurotransmitter from these motor neurons initiates excitation – coupling- contraction in which an action potential is generated within the skeletal muscle fiber.  The action potential causes the release of calcium from the SR, which the causes muscle contraction.
  30. 30. Summary of skeletal muscle contraction
  31. 31. Summary of skeletal muscle contraction Stimulation of α-motor neurons going to skeletal muscle The release of acetylcholine at the neuromuscular junction Production of an action potential in the muscle fiber Release of calcium ions from the sarcoplasmic reticulum Calcium diffuse to the thin filaments and binds to the troponin and initiate contraction