Lecture8

1,064 views

Published on

Published in: Technology, Sports
0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,064
On SlideShare
0
From Embeds
0
Number of Embeds
271
Actions
Shares
0
Downloads
45
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

Lecture8

  1. 1. Lecture 8 General medicine_2nd semester <ul><li>Muscle tissue </li></ul><ul><li>General characteristics of muscle tissue and its </li></ul><ul><li>classification </li></ul><ul><li>Skeletal muscle tissue. Ultrastructure of the </li></ul><ul><li>myofibrils. Mechanism of the muscle contraction </li></ul><ul><li>Cardiac muscle tissue </li></ul><ul><li>Smooth muscle tissue </li></ul>
  2. 2. <ul><li>function of muscle tissue is to move both the body as whole and its parts </li></ul><ul><li>with respect to one another </li></ul><ul><li>m orphological and functional characteristics common to all types of muscle </li></ul><ul><li>cells are as follows: </li></ul><ul><ul><li>muscle cells retain and develop contractility to the highest extent of any cells of the body </li></ul></ul><ul><ul><li>muscle cells are elongated with well-developed nuclei </li></ul></ul><ul><ul><li>the cytoplasm (termed as sarcoplasm ) stains red with eosin and contains contractile proteins - actin and myosin- arranged in the form of thin fibers, called myofibrils that run parallel to the long axis of the cell; the plasma membrane is termed as sarcolemma </li></ul></ul><ul><li>3 types of muscle tissue are to distinguish on both a structural and a </li></ul><ul><li>functional basis: </li></ul><ul><li>smooth muscle ( involuntary or visceral ) - occurs chiefly in walls of hollow </li></ul><ul><li>organs </li></ul><ul><li>skeletal muscle ( or striated voluntary ) - is attached to bones and </li></ul><ul><li>fasciae, skin </li></ul><ul><li>cardiac muscle ( or striated involuntary ) - form s the wall of the </li></ul><ul><li> heart CONTACTING/NONCONTRACTING </li></ul>
  3. 3. Skeletal muscle giant multinucleated cylindrical cell s referred as = muscle fibers or rhabdomyocytes ( gr. rhabdos = rod) the length - mm to cm, thickness varies from 10 to 100  m
  4. 4. <ul><li>n uclei are numerous in each fiber, there being about 35 per 1 mm of length </li></ul><ul><li>the y are ovoid, loca ted peripherally at the sarcolemma whose surface is coated with the basal lamina </li></ul><ul><li>the sarcoplasm contains numerous myofibrils that are prominently cross striated with light and dark bands </li></ul><ul><li>ce ll organelles are constituted </li></ul><ul><li>with mitochondria (termed </li></ul><ul><li>as sarcosomes), </li></ul><ul><li>sarcoplasmic reticulum </li></ul><ul><li>( smooth ER), and </li></ul><ul><li>small Golgi apparatuses </li></ul><ul><li>in juxtanuclear positions </li></ul><ul><li>Cells,fibers, also contain cell </li></ul><ul><li>inclusions, mainly </li></ul><ul><li>glycogen granules and </li></ul><ul><li>Lipid droplets </li></ul>
  5. 5. sarkotubules terminal cisternae an organelle of great importance is the sarcoplasmic reticulum , a special type of sER i t consists of longitudinal sarcotubules that are confluent with transversally oriented channels called terminal cisternae p airs of parallel terminal cisternae run transversally across the myofibrils in close apposition to the T tubule T tubule is an invagination of the sarcolemma and is not part of the sarcoplasmic reticulum t wo terminal cisternae and T tubule constitute structure called as triad of skeletal muscle t riads usually occur in sites where the dark and light bands meet
  6. 8. sarcomere . . . . m yofibrils - contractile fibrils resolvable with the LM that are mostly randomly dispersed within the sarcoplasm t heir diameter is about 1 -2  m (in cross sections, the myofibrils appear as dots, in longitudinal sections, they show a conspicuous cross banding ) t he dark band is called the anisotropic , or A band , because it is doubly refractive to polarized light and appers dark in the fresh state t he light isotropic , or I band , is single refractive to polarized light and is pale in the fresh e ach I band is intersected by a thin dark line - the Z line , likewise, the dark A band is bisected by a thin, light-staining band, called H band , within it M-line is seen t he segment of myofibril extending between two Z lines is a sarcomere , its length varies from 3.5 to 4  m
  7. 10. <ul><li>Ultrastructure of myofibrils </li></ul><ul><li>b y electron microscopy, the myofibrils are composed of more slender filamentous units called </li></ul><ul><li>myofilaments </li></ul><ul><li>2 sets of filaments: </li></ul><ul><li>t he thick filaments contain myosin and are 10 nm in diameter and 1.5  m in length </li></ul><ul><li>the thin filaments contain protein actin and are 5 nm in diameter and 2  m in length </li></ul>
  8. 11. <ul><li>Myosin filaments are confined to the A band and show slight thickening at their centers </li></ul><ul><li>th ese thickenings give rise to the transverse density at the midpoint of A band recognized as M line </li></ul><ul><li>in cross sections, they are seen to be arranged in a regular hexagonal pattern </li></ul><ul><li>Actin filaments extend in either direction from the Z line and thus constitute the I band </li></ul><ul><li>t hey are not limited to this band, but extend some distance into the adjacent A bands </li></ul><ul><li>where ends of filaments overlap each other, the cross bridges are developed between them </li></ul><ul><li>t he part of the A band that is free of actin filaments is called the H zone </li></ul>
  9. 13. <ul><li>Molecular components of filaments </li></ul>Thick myofilament - 300 to 400 molecules of myosin ( asymetric protein consisting of two identical heavy chains and two pairs of light chains
  10. 14. Thin myofilament - from F-actin + protein complex composed of troponin and tropomyosin t ropomyosin runs around F-actin in 40 nm distances troponin: of 3 proteins Troponin I, C and T
  11. 16. <ul><li>Mechanism of contraction </li></ul><ul><ul><li>by the sliding filament theory of Huxley </li></ul></ul><ul><ul><li>this concept says : </li></ul></ul><ul><ul><li>as a muscle fiber is stimulated to contract, the actin and myosin filaments react by sliding past each other but with no change s in length of either myofilaments </li></ul></ul><ul><ul><li>the thick myosin filaments in the A band are relatively stationary , whereas the thin actin filaments, attached to the Z disks, extend further into the A band and may eventually obliterate the H zone </li></ul></ul><ul><ul><li>b ecause the thin filaments are attached to Z disks, the disk are drawn toward each other, the sarcomeres are compressed, the myofibril is shortened, and contraction of the muscle occurs </li></ul></ul><ul><ul><li>Note : contraction is not due to a shortening of the actin and myosin filaments but to an increase in the overlap between the filaments </li></ul></ul><ul><ul><li>e nergy for the contraction process is produced by the breakdown of ATP by ATPase localized in the cross bridges that interconnect the actin and myosin filaments </li></ul></ul>
  12. 18. Muscles - structure
  13. 20. Cardiac muscle <ul><li>cardiac muscle cells, termed a cardiomyocytes </li></ul><ul><li>c ardiac muscle occurs in the myocardium (muscle layer </li></ul><ul><li>of the heart) and in the walls of large vessels joining the </li></ul><ul><li>heart </li></ul><ul><li>ň </li></ul>
  14. 21. cardiomyocytes: contracting and non contracting Contracting (working) cardiomyocytes cells are of cylindrical form, 20  m in diameter and 50 to 200  m in length at specialized junctional zones called intercalated discs , cardiac muscle cells are joined end to end and form a linear unit - cardiac muscle fiber intercalated discs - sites of intercellular contacts
  15. 23. the cardiomyocyte is enveloped by a thin sarcolemma and contains one elongated nucleus situated centrally between diverging myofibrils , in its vicinity a small Golgi apparatus, lipid droplets and deposits of lipofuscin pigment are found myofibrils are oriented parallel and run from one end to another and show the cross banding, the sarcomeres are composed of the same parts as in skeletal muscle (A, I bands, Z, M lines, H zone) n umerous mitochondria arranged in rows and sarcoplasmic reticulum are seen among the myofibrils
  16. 24. T he intercalated discs are areas of extensive cell contact a t the sites of intercalated discs, special adhering and communicating junctions are fascia adherens (corresponds to the zonula adherens,belt desmozone.), macula adherens (spot desmosome) and nexus (gap junction) Non-contracting cardiomyocytes (subendocardial layer, develops from cardiac jelly) i n addition to the cardiomyocytes whose primary function is contraction, there are specialized cells whose function is to generate the stimuli for the heart beat cells are located just beneath the endocardium,subendocardial layer.) and in a whole represent impuls conducting system of the heart (sinoatrial node - node of Keith-Flack, atrio- ventricular node - node of Tawara, atrioventricular bundle - bundle of Hiss) b y light microscopy, cells of the conducting system are larger, thicker and more palely stained, with abundant central sarcoplasm and relatively few myofibrils, located usually in a peripheral position t he cells contain also large quantities of glycogen noncontracting cells form similar to contractile cardiac muscle cells fibers called Purkinje fibers
  17. 25. Smooth muscle <ul><li>s mooth muscle tissue is structurally the simplest of the muscle types , i t is called smooth </li></ul><ul><li>because it has no visible cross striation, involuntary because it is not under conscious control, </li></ul><ul><li>and visceral because it is predominantly found in organs </li></ul><ul><li>is composed of spindle shaped cells with one nucleus 3–10 µm thick and 20 - 50 0  µm long - </li></ul><ul><li>leiomyocytes (gr. leios = smooth) </li></ul>
  18. 26. c ell nuclei have a cigar shaped form in dilated cells, but are of corkscrew appearance in cells which are contracted cells vary greatly in length, from 20  m (in the walls of small ducts and blood vessels) to 500  m (in the pregnant human uterus) t he cytoplasm - called sarcoplasm - appears rather homogeneous and is filled with fine contractile filaments (myofilaments) that are hardly seen R emember : the spindle-shaped form is imperceptible only in the longitudinal sections of smooth muscle i n the transverse section the smooth muscle cells appear as homogenous discs of various diameters - t he largest of the discs are cut through the middle of the cells and usually contain the nucleus
  19. 27. <ul><li>The fine structural parameters of smooth muscle </li></ul><ul><li>cells are as follows: </li></ul><ul><li>- nucleus is elongated or cigar- shaped and </li></ul><ul><li>smoothly contoured </li></ul><ul><li>- juxtanuclear sarcoplasm contains long slender mitochondria, a few tubules of smooth endoplasmic reticulum, free ribosomes and small Golgi apparatus </li></ul><ul><li>- the plasma membrane is characteristically studded with small vesicular inpocketings or caveoli (micropinocytosis) </li></ul><ul><li>- the surface of each smooth muscle cell is invested by a thick extracellular coating that corresponds to the basal lamina of epithelial cells </li></ul><ul><li>- in certain limited areas of the surface of smooth muscle cells, the basal lamina is lacking and the membranes of neighboring cells come into very close association; such sites are termed as nexuses or gap junctions </li></ul><ul><li>they constitute low resistance pathways, permitting a spread of excitation from one cellular unit to another </li></ul>
  20. 28. the bulk of the cytoplasm is occupied by two sets of myofilaments : actin filaments are dominant myosin filaments occur only in a small amount myofilaments do not exhibit the paracrystalline organization that is seen in the skeletal or cardiac muscle Physiology: smooth mucle cells contract slowly and have low force of contraction t hey are innervated with adrenergic and cholinergic nerve fibers that act antagonistically nucleus thick filament thin filaments dense body intermediate filament
  21. 30. <ul><li>Regeneration of muscle tissue </li></ul><ul><li>c ardiac muscle cells ha ve no regenerative capacity </li></ul><ul><li>(d efects or damage of heart muscle are generally replaced by proliferation of </li></ul><ul><li>connective tissue forming myocardial scars ) </li></ul><ul><li>rhabdomyocytes undergoes regeneration in a limited extent </li></ul><ul><li>as a source of regenerating cells serve the satellite cells , mononucleated spindle cells located beneth the lasal lamina surrounding mature muscle fiber </li></ul><ul><li>(s atellite cells are inactive myoblasts that persist after muscle differentiation , cells are activated following injury, they proliferate and fuse to form new skeletal muscle fibers ) </li></ul><ul><li>s mooth muscle cells are capable of a modest regenerative response </li></ul><ul><li>(f ollowing injury, viable mononucleated smooth muscle cells undergo mitosis and provide for the replacement of the damaged tissue ) </li></ul>
  22. 31. <ul><li>Histogenesis of muscle tissue </li></ul><ul><li>in vertebrates, muscles develop from mesoderm , except some intrinsic muscles of the eye and skin that are ectodermal in origin </li></ul><ul><li>s mooth muscle , the most primitive of the three forms of muscle, derives from the (spnachic?) embryonic connective tissue - mesenchyme </li></ul><ul><li>m ost skeletal muscle s develop from the paired mesodermal somites </li></ul><ul><li>t he middle portion of the somite, the myotome (muscle plate) thickens and differentiates into myoblasts that give rise to multinucleated cylindrical cells, called muscle fibers </li></ul><ul><li>c ardiac muscle cells develop from splanchnic mesoderm that surrounds the primitive heart tubes (MYOEPICARDIAL MANTLE-MYOBLASTS.) </li></ul>

×