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  1. 2. Skin Scales and Skeletal Muscles <ul><li>Contents: </li></ul><ul><li>Scales </li></ul><ul><li>Types of Scales:Are all scales the same size? </li></ul><ul><li>Can scale type vary with sex? </li></ul><ul><li>Slime and Spots </li></ul><ul><li>Functions of Scales </li></ul><ul><li>How old is a fish scale </li></ul><ul><li>Fish skin </li></ul><ul><li>Function </li></ul><ul><li>Skin StructureFish and Mammalian skin </li></ul><ul><li>Skin Properties </li></ul><ul><li>Hormonal control of Skin </li></ul><ul><li>Skeletal Muscles </li></ul><ul><li>Types of Muscle </li></ul><ul><li>Skeletal Muscles function </li></ul><ul><li>Properties of Muscle </li></ul><ul><li>Structure </li></ul><ul><li>Myosin (Thick) Myofilament </li></ul><ul><li>Actin (Thin) Myofilaments </li></ul><ul><li>Sliding Filament Model of Contraction </li></ul><ul><li>Neuromuscular Junction </li></ul><ul><li>Motor Unit: </li></ul><ul><li>Contractile Machinery: Sarcomeres </li></ul><ul><li>Crossbridge formation and movemen </li></ul>
  2. 3. Scales <ul><li>A rigid plate out of an animal 's skin to provide protection. </li></ul><ul><li>E volved multiple times with varying structure and function. </li></ul><ul><li>Classified as an organism's integumentary system . </li></ul><ul><li>scales usually not eaten. </li></ul>
  3. 4. Types of scales <ul><li>Ganoid </li></ul><ul><li>Leptoid </li></ul><ul><li>Placoid </li></ul><ul><li>Cosmoid </li></ul><ul><li>Scales of Rohu ( Labeo rohita ) </li></ul>
  4. 5. Ganoid Scales <ul><li>Diamond-shaped, shiny, and hard. </li></ul><ul><li>gars (family Lepisosteidae ), reed fishes (family Polypteridae ), Sturgeons and Paddlefish </li></ul><ul><li>Similar to cosmoid but ganoin lies over the cosmine layer </li></ul>
  5. 6. Leptoid scales <ul><li>Leptoid believed to derived from ganoid scales by the loss of ganoin layer </li></ul><ul><li>Single layer of bone. </li></ul><ul><li>Two forms: cycloid (circular) and ctenoid (toothed) </li></ul><ul><li>As they grow,add concentric layers. </li></ul><ul><li>Overlaping in a head-to-tail direction, like roof tiles </li></ul>
  6. 7. Leptoid scales <ul><li>Jungle Perch Kuhlia rupestris </li></ul><ul><li>Paradise Fish, Macropodus opercularis </li></ul>
  7. 8. Leptoid scales <ul><li>Cycloid scales </li></ul><ul><li>smooth outer edge, </li></ul><ul><li>primitive fish salmon , carp , trout, smelt, herrings and minnows </li></ul><ul><li>Ctenoid scales </li></ul><ul><li>a toothed outer edge, </li></ul><ul><li>derived fishes bass , crappie and perch </li></ul><ul><li>Kardong, Kenneth V. (1998) . </li></ul>
  8. 9. Placoid scales <ul><li>also called dermal denticles, tooth like structure </li></ul><ul><li>sharks and rays </li></ul><ul><li>consists of an upper layer of enamel like substance called vitrodentine, </li></ul><ul><li>a lower layer of dentine, </li></ul><ul><li>a pulp cavity, and </li></ul><ul><li>a disk like basal plate embedded in the skin. </li></ul>
  9. 10. Placoid scales <ul><li>Do not increase in size, new scales must be added as a shark grows </li></ul><ul><li>Homologous with teeth in all vertebrates. </li></ul><ul><li>Broadnose Sevengill Shark </li></ul>
  10. 11. Cosmoid scales <ul><li>primitive coelacanth ( Latimeria chalumnae ) or as fossils. </li></ul><ul><li>a four-layered bony scale. </li></ul><ul><li>upper layer is enamel like vitrodentine </li></ul><ul><li>the second layer is a hard, dentine like called cosmine </li></ul><ul><li>the third layer is spongy bone, and </li></ul><ul><li>the lowest layer is dense bone </li></ul>
  11. 12. Cosmoid scales <ul><li>In lungfishes, but highly modified, single-layered form. </li></ul><ul><li>Similar in structure to placoid probably arose from fusion of placoid scales </li></ul><ul><li>Queensland Lungfish </li></ul>
  12. 13. Cosmoid scales <ul><li>scales of bony fishes evolved a long time ago </li></ul><ul><li>they had four layers, </li></ul><ul><li>one of dense bone, </li></ul><ul><li>one of spongy bone, </li></ul><ul><li>one of dentine and </li></ul><ul><li>one of enamel. </li></ul>
  13. 14. Are all scales the same size? <ul><li>No sizes vary between species. </li></ul><ul><li>freshwater eels and tunas tiny embedded scales, </li></ul><ul><li>Coral Snappers medium sized, </li></ul><ul><li>of Tarpon, Megalops cyprinoides to be used in jewelry. </li></ul><ul><li>In Indian Mahseer, reach over 10 cm in length. </li></ul>
  14. 15. Can scale type vary with sex? <ul><li>Yes. In flatfishes , males have ctenoid and females have cycloid scales </li></ul><ul><li>Sole have ctenoid scales on the 'eyed' side and cycloid scales on other side. </li></ul><ul><li>Sea Perches, have ctenoid scales above the lateral line and cycloid below </li></ul><ul><li>Not all species have scales, clingfishes are scale less. </li></ul><ul><li>Protected by a thick layer of mucous, </li></ul>
  15. 16. Function of Slime and Spots <ul><li>Hydrodynamic function to reduce water friction and resistance to forward motion </li></ul><ul><li>Enzymes and antibodies as a defensive system </li></ul><ul><li>Spots size fluctuate according to nervous stimuli. </li></ul><ul><li>The arrangement imbricate or mosaic </li></ul>
  16. 17. General Functions <ul><li>To calculate a fish’s age </li></ul><ul><li>Dried scale of a Barramundi showing annuli. </li></ul><ul><li>Times of migration, periods of food scarcity and illness </li></ul>
  17. 18. How old is a fish scale? <ul><li>As scales increase in size, growth rings called circuli visible. </li></ul><ul><li>Cooler months scale grows slowly and circuli are closer leaving a band called an annulus . </li></ul><ul><li>Source and reservoir of calcium. </li></ul>
  18. 20. Fish skin <ul><li>Barrier, strong, tough and watertight, </li></ul><ul><li>Ion- and water balance </li></ul><ul><li>The scales lie in the Dermis of skin </li></ul>
  19. 21. Skin Structure <ul><li>Two layers, the Epidermis (outer) layer and the Dermis . </li></ul><ul><li>Epidermis is made up of epithelial cells </li></ul><ul><li>Inter-spaced between epithelial cells are slime cells produce mucous secretions </li></ul><ul><li>Dermis consists of two layers: stratum spongiosum & stratum compactum. </li></ul><ul><li>Hypodermis </li></ul>
  20. 22. Comparison of Fish and Mammalian skin
  21. 23. Skin Properties <ul><li>Mucus ->fatty acid+phospholipids </li></ul><ul><li>Pigment cells (chromatophores) under hormonal or nervous system control </li></ul><ul><li>Effector organ </li></ul><ul><li>Respond to hormones & neurotransmitters via receptors </li></ul><ul><li>Xanthophores , erythrophores and melanophores </li></ul>
  22. 24. Hormonal control of Skin <ul><li>Melanin-concentrating hormone (MCH) </li></ul><ul><li>Neurotransmitter or neuromodulator </li></ul><ul><li>Sensory organs </li></ul><ul><li>Nerve endings and receives tactile, thermal, and pain stimuli e.g. teleost fish </li></ul><ul><li>Blood vessels </li></ul><ul><li>Collagen fibers </li></ul>
  23. 25. Types of Muscle <ul><li>Three types of muscle: </li></ul>Skeletal muscle Smooth muscle Cardiac muscle
  24. 27. Skeletal Muscles function <ul><li>Two groups – the axial and appendicular muscles. </li></ul><ul><li>Main function is to support the body viscera. </li></ul><ul><li>Without them animal could neither move or eat or bear young. </li></ul><ul><li>Body movement (Locomotion) </li></ul><ul><li>Maintenance of posture </li></ul><ul><li>Constriction of organs and vessel </li></ul>
  25. 28. Types of Muscle fiber <ul><li>Red muscles with capillary network mitochondria and myoglobin </li></ul><ul><li>White muscles produce tensions operative for short periods </li></ul><ul><li>pink </li></ul><ul><li>Nervous Control </li></ul><ul><li>Each myomere is controlled by a separate nerve . </li></ul>
  26. 29. Properties of Muscle <ul><li>Excitability : capacity of muscle to respond to a stimulus </li></ul><ul><li>Contractility : ability of a muscle to shorten with force </li></ul><ul><li>Extensibility : muscle can be stretched to its normal resting length and beyond to a limited degree </li></ul><ul><li>Elasticity : ability of muscle to recoil to original resting length after stretched </li></ul>
  27. 30. Structure <ul><li>Muscles are layered rather than bundled as in other vertebrates </li></ul><ul><li>Myomere or myotome, Septa,epaxial & hypaxial </li></ul>
  28. 31. Structure <ul><li>Muscle cells long and cylindrical and have many nuclei. </li></ul><ul><li>Actin and myosin with controlling proteins </li></ul><ul><li>In other vertebrates muscles connected to bone through a tendon. </li></ul><ul><li>In fish, arranged vertically throughout whole length of fish. </li></ul>
  29. 32. Muscle Fiber Anatomy <ul><li>Sarcolemma - cell membrane </li></ul><ul><ul><li>Surrounds the sarcoplasm (cytoplasm of fiber) </li></ul></ul><ul><ul><ul><li>Contains oxygen-binding protein myoglobin </li></ul></ul></ul><ul><ul><li>Punctuated by openings called the transverse tubules (T-tubules) </li></ul></ul><ul><ul><ul><li>Narrow tubes that extend into the sarcoplasm </li></ul></ul></ul><ul><ul><ul><li>Filled with extracellular fluid </li></ul></ul></ul><ul><li>Myofibrils -cylindrical structures within muscle fiber </li></ul><ul><ul><li>Are bundles of protein filaments (= myofilaments ) </li></ul></ul><ul><ul><li>When myofibril shortens, muscle shortens (contracts) </li></ul></ul>
  30. 33. Sarcomere <ul><li>repeating functional units of a myofibril </li></ul><ul><ul><li>About 10,000 sarcomeres per myofibril, end to end </li></ul></ul><ul><ul><li>Each is about 2 µm long </li></ul></ul><ul><li>Differences in size, density, and distribution of thick and thin filaments gives the muscle fiber a striated appearance. </li></ul><ul><ul><li>A bands : a dark band; length of thick filaments </li></ul></ul><ul><ul><ul><li>M line - protein to which myosins attach </li></ul></ul></ul><ul><ul><ul><li>H zone - thick but NO thin filaments </li></ul></ul></ul><ul><ul><li>I bands : a light band; from Z disks to ends of thick filaments </li></ul></ul><ul><ul><ul><li>Thin but NO thick filaments </li></ul></ul></ul><ul><ul><ul><li>Extends from A band of one sarcomere to A band of the next sarcomere </li></ul></ul></ul><ul><ul><li>Z disk : filamentous network of protein. Serves as attachment for actin myofilaments </li></ul></ul><ul><ul><li>Titin filaments : elastic chains of amino acids; keep thick and thin filaments in proper alignment </li></ul></ul>
  31. 34. d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly Components of skeletal muscle
  32. 35. Nerve and Blood Vessel Supply <ul><li>Motor neurons: stimulate muscle fibers to contract. Nerve cells with cell bodies in brain or spinal cord; axons extend to skeletal muscle fibers through nerves </li></ul><ul><li>Axons branch so that each muscle fiber is innervated </li></ul><ul><li>Capillary beds surround muscle fibers </li></ul><ul><ul><li>Muscles require large amts of energy </li></ul></ul><ul><ul><li>Extensive vascular network delivers oxygen and nutrients and carries away metabolic waste produced by muscle fibers </li></ul></ul>
  33. 36. Myosin (Thick) Myofilament <ul><li>elongated molecules like golf clubs. </li></ul><ul><li>Single filament contains 300 molecules </li></ul><ul><li>Molecule consists of two heavy myosin wound together to form a rod and two heads that extend laterally. </li></ul><ul><li>Myosin heads </li></ul><ul><ul><li>Can bind to active sites on the actin molecules to form cross-bridges. (Actin binding site) </li></ul></ul><ul><ul><li>Attached to the rod portion by a hinge region that can bend and straighten. </li></ul></ul><ul><ul><li>Have ATPase activity: </li></ul></ul>
  34. 37. Actin (Thin) Myofilaments <ul><li>Thin Filament : 3 major proteins </li></ul><ul><ul><li>F (fibrous) actin </li></ul></ul><ul><ul><li>Tropomyosin </li></ul></ul><ul><ul><li>Troponin </li></ul></ul><ul><li>Two strands of fibrous (F) actin form a double helix extending the length of the myofilament; attached at either end at sarcomere. </li></ul><ul><ul><li>Composed of G actin monomers each of which has a myosin-binding site Actin site can bind myosin during muscle contraction. </li></ul></ul><ul><li>Tropomyosin </li></ul><ul><li>Troponin three subunits: </li></ul><ul><ul><li>Tn-A : binds to actin </li></ul></ul><ul><ul><li>Tn-T :binds to tropomyosin, </li></ul></ul><ul><ul><li>Tn-C :binds to calcium ions. </li></ul></ul>
  35. 38. Sliding Filament Model of Contraction <ul><li>Thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree </li></ul><ul><li>In the relaxed state, thin and thick filaments overlap only slightly </li></ul><ul><li>Upon stimulation, myosin heads bind to actin and sliding begins </li></ul>
  36. 39. Sliding Filament Model of Contraction <ul><li>Each myosin head binds and detaches several times during contraction, acting like a ratchet to generate tension and propel the thin filaments to the center of the sarcomere </li></ul><ul><li>As this event occurs throughout the sarcomeres, the muscle shortens </li></ul>
  37. 40. Neuromuscular Junction <ul><li>The neuromuscular junction is formed from: </li></ul><ul><ul><li>Axonal endings, which have small membranous sacs (synaptic vesicles) that contain the neurotransmitter acetylcholine (ACh) </li></ul></ul><ul><ul><li>The motor end plate of a muscle, a specific part of sarcolemma that contains ACh receptors and helps to form the neuromuscular junction </li></ul></ul><ul><li>Axonal ends and muscle fibers are always separated by a space called the synaptic cleft </li></ul>
  38. 41. Neuromuscular Junction Figure 9.7 (a-c)
  39. 42. Motor Unit: The Nerve-Muscle Functional Unit <ul><li>A motor unit is a motor neuron and all the muscle fibers it supplies </li></ul><ul><li>The number of muscle fibers per motor unit can vary from a few (4-6) to hundreds (1200-1500) </li></ul>
  40. 43. Motor Unit: The Nerve-Muscle Functional Unit Figure 9.12 (a)
  41. 44. Contractile Machinery: Sarcomeres <ul><li>Contractile units </li></ul><ul><li>Organized in series ( attached end to end) </li></ul><ul><li>Each myosin is surrounded by six actin filaments </li></ul><ul><li>Projecting from each myosin are tiny contractile myosin bridges </li></ul>Longitudinal section of myofibril (a) At rest
  42. 45. Contractile Machinery: Crossbridge formation and movement <ul><li>Cross bridge formation: - a signal comes from the motor nerve activating the fibre </li></ul><ul><li>- the heads of the myosin filaments temporarily attach themselves to the actin filaments </li></ul><ul><li>Cross bridge movement: </li></ul><ul><li>- similar to the stroking of the oars and movement of rowing shell </li></ul><ul><li>- movement of myosin filaments in relation to actin filaments </li></ul><ul><li>- shortening of the sarcomere </li></ul>b) Contraction Longitudinal section of myofibril
  43. 46. Contractile Machinery: Optimal Crossbridge formation <ul><li>Sarcomeres should be optimal distance apart </li></ul><ul><li>optimal distance is (0.0019-0.0022 mm) </li></ul><ul><li>At this an optimal number of cross bridges is formed </li></ul><ul><li>If stretched farther apart : </li></ul><ul><li>- fewer cross bridges can form  less force produced </li></ul><ul><li>If the sarcomeres are too close together: </li></ul><ul><li>- cross bridges interfere with one another  less force produced </li></ul>Longitudinal section of myofibril c) Powerful stretching d) Powerful contraction
  44. 47. Any questions …….. Don’t shy