Muscular Tissues
Part 2
O. Hara
Cardiac Muscle
• Myofibers – branching; syncytial cardiomyocytes
• Cardiomyocyte: 1-2 central nucleus;
• Striated
• Myofib...
Cardiac Muscle
• T-tubules and SR (dyads at Z-disks)
• Diad – formed by T-tubule and SR cistern
• Intercalated disks – gap...
The transversely oriented parts of the intercalated disk consist of a fascia adherens and numerous desmosomes. The
longitu...
• Contact between cells is accomplished by interdigitation in the transverse region; contact is broad and flat in the
long...
Intercalated Disks
• Transverse portion:
1. Cardiac myofiber are connected by z. adherens in
Z-lines (actin filament)
2. D...
• Sarcomere units and SR (sarcoplasmic reticulum) cisterns and T-tubules (diad) near Z-disks.
Purkinje fibers
• Excitation in cardiac muscles
• Modified cardiac cells in the Bundle of His
• Rich in glycogen and mitoc...
• Bundles of Purkinje fibers are
present in areas of connective
tissue between areas of
"normal" cardiac muscle
tissue and...
Cardiac contraction
• Relax: calcium leaks into the sarcoplasm at a slow
rate -> automatic rhythm
• Calcium reaches calciu...
SMOOTH MUSCLES
• found in the walls of hollow organs
– gastrointestinal tract, the bladder, and the uterus
– in the vascul...
SMOOTH MUSCLES
• specialised for continuous contractions of
relatively low force, producing diffuse
movements resulting in...
Smooth muscle
Characteristics:
• elongated, spindle-shaped cells
(which may be branched occasionally).
• no cross striatio...
Smooth muscle fibers
• bound together in irregular, branching fasciculi -- the
functional contractile units.
• individual ...
Smooth muscle: 2 orientations when cut
Longitudinal section Transverse section
Generalised gut cross-section
Peristalsis
• In many tubular
visceral structures
(ex. intestine)
• smooth muscles are
disposed in layers
• the cells of o...
With minimal amount of
supporting tissue
between
– contains clumps of
large cells with pale
nuclei which
represents
parasy...
Contractile proteins
of smooth muscle
• Thin filament: actin
• anchored either to the plasma membrane or to cytoplasmic
st...
Contractile proteins
of smooth muscle
- arranged in a criss-cross
lattice inserted around the
cell membrane
No regular ali...
Smooth muscle contraction
• Controlled by the autonomic nervous system,
hormones, autocrine/paracrine agents, and
other lo...
Smooth muscle contraction
• Influx of Ca2+
• Because smooth muscle does not contain
troponin, Ca2+
binds to calmodulin
• C...
References
• Junquiera LC, Carneiro J. 2005. BASIC
HISTOLOGY : TEXT AND ATLAS 11th
Edition.
McGraw-Hill’s ACCESS MEDICINE....
Lect. 8   muscular tissues - part 2
Lect. 8   muscular tissues - part 2
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Lect. 8 muscular tissues - part 2

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Lect. 8 muscular tissues - part 2

  1. 1. Muscular Tissues Part 2 O. Hara
  2. 2. Cardiac Muscle • Myofibers – branching; syncytial cardiomyocytes • Cardiomyocyte: 1-2 central nucleus; • Striated • Myofibrils – poorly defined (possess myofilaments) • Have glycogen granules, especially at either pole of the nucleus. • Sarcomere
  3. 3. Cardiac Muscle • T-tubules and SR (dyads at Z-disks) • Diad – formed by T-tubule and SR cistern • Intercalated disks – gap junctions • Contraction – spontaneous & rhythmic (autonomic NS) • Do not regenerate – repair of cardiac tissue forms fibrous CT (scar) by fibroblasts.
  4. 4. The transversely oriented parts of the intercalated disk consist of a fascia adherens and numerous desmosomes. The longitudinal parts (arrows) contain gap junctions. Mitochondria (M) are numerous. Fibrils of reticular fibers are seen between the two cells. x18,000. (Junquiera, 2005).
  5. 5. • Contact between cells is accomplished by interdigitation in the transverse region; contact is broad and flat in the longitudinal plane (LP). A, A band; I, I band; Z, Z line. (Redrawn and reproduced, with permission, from Marshall JM: The heart. In: Medical Physiology, 13th ed, Vol 2. Mountcastle VB [editor]. Mosby, 1974. Based on the results of Fawcett DW, McNutt NS: J Cell Biol 1969;42:1, modified from Poche R, Lindner E: Zellforsch Mikrosk Anat 1955;43:104.)
  6. 6. Intercalated Disks • Transverse portion: 1. Cardiac myofiber are connected by z. adherens in Z-lines (actin filament) 2. Desmosomes (macula adherens) connects the SR cisterns 3. Gap junctions connects the underlying myofibrils • Lateral portion: Desmosomes and larger gap junctions (promotes coupling and contraction) – Functional syncytium
  7. 7. • Sarcomere units and SR (sarcoplasmic reticulum) cisterns and T-tubules (diad) near Z-disks.
  8. 8. Purkinje fibers • Excitation in cardiac muscles • Modified cardiac cells in the Bundle of His • Rich in glycogen and mitochondria • Impulse conducting system: • SA node AV node  AV Bundle of His  Purkinje fibers
  9. 9. • Bundles of Purkinje fibers are present in areas of connective tissue between areas of "normal" cardiac muscle tissue and beneath the endocardium. • Purkinje fibers appear as a chain of light blue profiles with a red rim.
  10. 10. Cardiac contraction • Relax: calcium leaks into the sarcoplasm at a slow rate -> automatic rhythm • Calcium reaches calcium channels passing through T- tubules and sarcolemma • Calcium stored in the SR is released through ryanodine receptors  • Calcium binds to Troponin C  contraction
  11. 11. SMOOTH MUSCLES • found in the walls of hollow organs – gastrointestinal tract, the bladder, and the uterus – in the vasculature, the ureters, the bronchioles – the muscles of the eye • The functions: – to produce motility (e.g., to propel chyme along the gastrointestinal tract or to propel urine along the ureter) – to maintain tension (e.g., smooth muscle in the walls of blood vessels).
  12. 12. SMOOTH MUSCLES • specialised for continuous contractions of relatively low force, producing diffuse movements resulting in contraction of the whole muscle mass.
  13. 13. Smooth muscle Characteristics: • elongated, spindle-shaped cells (which may be branched occasionally). • no cross striations • generally much shorter than skeletal muscle fibers • contain only one nucleus which is elongated and centrally located. • When contracted: – nucleus appear to be spiral-shaped.
  14. 14. Smooth muscle fibers • bound together in irregular, branching fasciculi -- the functional contractile units. • individual muscle fibres are arranged roughly parallel to one another – the thickest part of one cell lying against the thin parts of adjacent cells. – Gap junctions (nexus) are areas of close opposition (~2 nm) between plasma membranes of separate cells. • supporting collagenous tissue between individual muscle fiber and between fasciculi.
  15. 15. Smooth muscle: 2 orientations when cut Longitudinal section Transverse section
  16. 16. Generalised gut cross-section
  17. 17. Peristalsis • In many tubular visceral structures (ex. intestine) • smooth muscles are disposed in layers • the cells of one layer arranged at right angles to those of the adjacent layer. This arrangement permits a wave of contraction to pass down the tube, propelling the contents forward.
  18. 18. With minimal amount of supporting tissue between – contains clumps of large cells with pale nuclei which represents parasympathetic ganglia. longitudinal outer smooth muscle layer inner circular layer
  19. 19. Contractile proteins of smooth muscle • Thin filament: actin • anchored either to the plasma membrane or to cytoplasmic structures known as dense bodies, which are functionally similar to the Z lines in skeletal muscle fibers. • Tropomyosin; NO TROPONIN • calmodulin, a calcium-binding protein • Thick filaments: myosin
  20. 20. Contractile proteins of smooth muscle - arranged in a criss-cross lattice inserted around the cell membrane No regular alignment of filaments into sarcomeres NO STRIATIONS • No T tubule: • Caveolae - surface vesicles in individual cells which transmit action potentials similar to T tubules Contraction results in shortening of the cell, which assumes a globular shape
  21. 21. Smooth muscle contraction • Controlled by the autonomic nervous system, hormones, autocrine/paracrine agents, and other local chemical signals. • Calcium is the signal for contraction in smooth muscle. • Myosin interacts with actin only when its light chain is phosphorylated.
  22. 22. Smooth muscle contraction • Influx of Ca2+ • Because smooth muscle does not contain troponin, Ca2+ binds to calmodulin • Ca2+ - calmodulin complex activates the enzyme myosin light chain kinase – Result: Phosphorylation of myosin and thereby consumes ATP. • Phosphorylated myosin has a high affinity for actin • Crossbridges form between myosin and actin.
  23. 23. References • Junquiera LC, Carneiro J. 2005. BASIC HISTOLOGY : TEXT AND ATLAS 11th Edition. McGraw-Hill’s ACCESS MEDICINE. • Young B. 2009. WHEATER’S FUNCTIONAL HISTOLOGY. 5TH Edition. UK: Churchill Livingstone. Distributor: Phils: C & E Publishing, Inc.

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