Muscle Tissue -...
Transcript of Muscle Tissue -...
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Muscle Tissue
1.Muscle tissue – organization,
histogenesis and functions
2.Classification of muscle tissue
3.Smooth muscle tissue
4.Striated (skeletal) muscle tissue
5.Cardiac (heart) muscle tissue
6.Regeneration of muscle tissue
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Prof. Dr. Nikolai Lazarov 2
Muscle tissue
� body movements
� digestion
� blood circulation
� respiratory movements
� other movement activities,
incl. cellular contraction
� succession of relax and contraction:
� transformation of chemical into mechanical energy
� Textus muscularis:� cells – myocytes� extracellular matrix
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Prof. Dr. Nikolai Lazarov 3
Muscle fibers – myofibers
� muscle cells = myocytes (leiomyocytes, rhabdomyocytes, cardiomyocytes):� elongated, cylindrical or fusiform = myofibers� sarcolemma = plasmalemma� sarcoplasm = cytoplasm� sarcoplasmic reticulum =
smooth endoplasmic reticulum� sarcosomes = mitochondria� myoglobin: oxygen-binding protein� connective tissue components:
� endomysium (Gr. endon, within + mys, muscle)� perimysium (Gr. peri, around, near + mys)� epimysium (Gr. epi, upon + mys)
Gr. sarkos, flesh
�myoepithelial cells�pericytes�myofibroblasts in healing wounds�myoid cells of the testis
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Prof. Dr. Nikolai Lazarov 4
Myofibrils and myofilaments
� myofibrils: fill the muscle fibers
� separated by sarcoplasmic reticulum
� myofilaments:� thick and thin filaments
(contractile proteins)
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Prof. Dr. Nikolai Lazarov 5
Histogenesis
� skeletal muscle – mesoderm� somites – skeletal muscles
of the trunk
� general mesoderm – muscles of the head and limbs
� embryonic origin:� smooth muscle –
mesenchyme
� striated – mesoblast
� myoepithelial cells –skin ectoblast
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Prof. Dr. Nikolai Lazarov 6
Functions
� movements of the body
as a whole
� body posture stabilization
� volume regulation of the
internal organs: sphincters
� movement of substances
within living organisms:
blood, lymph, air, food and
fluids, urine, sperm
� heat production: involuntary
contractions of the skeletal
muscles (trembling)
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Prof. Dr. Nikolai Lazarov 7
Properties of muscle tissue
� irritability� the ability of a muscle to respond
to a stimulus
� conductivity� the ability of a muscle to conduct
electrical impulses across the membrane
� contractility� the ability of a muscle to shorten
and to produce energy
� extensibility� the ability of a muscle to lengthen
beyond its resting length
� elasticity� the ability of a muscle to return to
its original length without damage
NB:NB:NB:NB:muscles can only pull or contract, not pushmuscles can only pull or contract, not pushmuscles can only pull or contract, not pushmuscles can only pull or contract, not push!!!!
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Prof. Dr. Nikolai Lazarov 8
Types of muscle tissue
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Prof. Dr. Nikolai Lazarov 9
Smooth muscle tissue
� origin: mesenchyme
� involuntary: ANS innervation
� tonus
� peristalsis
� nonstriated
� in the walls of hollow and tubular organs:� blood vessels
(with exception of capillaries)
� alimentary canal
� respiratory tract
� urogenital system
� associated with hair follicles in the skin (arrector pili muscles)
� Characteristics:Textus muscularis nonstriatus (glaber)
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Prof. Dr. Nikolai Lazarov 10
Smooth muscle tissue
� leiomyocyte (Gr. leios, smooth)
�shape: fusiform or “spindle shaped"
�length: 30-500 µm
�thickness: 5-10 µm
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Prof. Dr. Nikolai Lazarov 11
Ultrastructure
� actin filaments (4.5 µm/7 nm):
� actin, tropomyosin, calmodulin – Ca2+
� myosin (2.2 µm/17 nm):
� myosin II
� dense bodies, corpora densa
(contain α-actinin = similar to the Z line)
� caveolae (analogous to Т-tubule system)
� intermediate filaments (10 nm):
� desmin (skeletin), vimentin = non-contractile proteins
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Prof. Dr. Nikolai Lazarov 12
Smooth muscle types
� visceral (single-unit) smooth muscles� in the walls of hollow organs� small blood vessels
• relatively poor nerve supply• abundant gap junctions �
function in syncytial fashion
� multi-unit smooth muscles� large arteries� upper respiratory tract� muscles of hair follicles� iris and ciliary body of the eye
• rich nerve supply
• innervate individual cells
• allow for fine control
• provide very precise and graded contractions
� two types of smooth muscle:
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Prof. Dr. Nikolai Lazarov 13
Regulation of contraction and relaxation
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Prof. Dr. Nikolai Lazarov 14
Skeletal muscle tissue
� the most abundant tissue in the vertebrate body– 40% of the body mass
� origin: mesoblast (myotomes)
� voluntary: CNS innervation� strong, quick voluntary control
of contraction/relaxation
� cross-striated
� skeletal muscles
� initial and end parts of the digestive tract
� muscles of the head(incl. eye, ear)
� muscles of respiration
Textus muscularis striatus (skeletalis)
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Prof. Dr. Nikolai Lazarov 15
Skeletal muscle development
� 100 myoblasts (mononucleated) – 1 mature musclecell (multinucleated): syncytium (symplast)
� satellite (myosatellite) cells: retain their potential for theformation of new cells (stem cells)
� does not divide postnatally
� muscle growth –
augmentation of cell
volume (hypertrophy)
Gr. syn, together + kytos, cell
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Prof. Dr. Nikolai Lazarov 16
Skeletal muscle tissue
� rhabdomyocyte (Gr. rhabdo, striped)
�shape: elongated, cylindrical
�length: 1-40 cm
�diameter: 10-100 µm
�numerous nuclei: 10-100/cell, located right up under the plasma membrane
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Prof. Dr. Nikolai Lazarov 17
Organization of skeletal muscle
�Skeletal muscle
�Muscle fasciculus
�Muscle fiber
�Myofibril
�Myofilaments
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Prof. Dr. Nikolai Lazarov 18
Myofibril
� 85-90% of the myofiber volume
� 2500-3500/rhabdomyofiber
� long cylindrical filamentous structure
with a diameter of 0.5-2 µm
� system of transverse (T-) tubules –
encircle the boundaries of the А-I bands
� “triad” = Т-tubule + 2 terminal cisternae:
depot of Ca2+
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Prof. Dr. Nikolai Lazarov 19
Ultrastructure
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Prof. Dr. Nikolai Lazarov 20
Sarcomere
� А band (anisotropic, i.e., birefringent in polarized light)
� H zone (from the German “Hell”, bright)
� М line (mesophragm, "Mittel", middle of the sarcomere): creatine kinase
� I band (isotropic, does not alter polarized light, monorefrigent)
� Z disk (“Zwischenscheibe”, the band in between the I bands)= telophragm: α-actinin
� Sarcomere (Gr. sarkos + meros, part):
�length: 2-3 µm (~2.5 µm) – extends from Z line to Z line
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Prof. Dr. Nikolai Lazarov 21
Sarcomere
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Prof. Dr. Nikolai Lazarov 22
Myofilaments� thin (actin) filaments – 1 µm long/8 nm wide:
� actin – long filamentous polymers of F-actin;• 2 twisted strands of G-actin – globular monomer, 5.6 nm in diameter
� tropomyosin – 40 nm in length extending over 7 G-actin molecules• 2 polypeptide chains
� troponin – ТnT, TnI, TnC at intervals of 40 nm, attached to tropomyosin
� thick (myosin) filaments – 1.6 µm long/15 nm wide:� head (ATPase activity) + proximal 60 nm of tail = heavy meromyosin� distal 90 nm of the tail = light meromyosin� 2 identical heavy chains and 2 pairs of light chains
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Prof. Dr. Nikolai Lazarov 23
Mechanism of contraction
rigor mortis
Sliding Filament Hypothesis: Huxley
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Prof. Dr. Nikolai Lazarov 24
Motor end plate
� myoneural junction – cholinergic (ACh)
Myasthenia gravis
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Prof. Dr. Nikolai Lazarov 25
Neuromotor unit
� motor unit = an individualsomatic motoneuron and all the skeletal muscle fibers(cells) it innervates
� a single nerve fiber (axon) can innervate up to 160 muscle fibers (cells), that all contract at the same time
� the number of motor units and the variable size of each unit can control the intensity (force) of a muscle contraction
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Prof. Dr. Nikolai Lazarov 26
Types of muscle fibers
� Red fibers (slow oxydative) – type I
� White fibers (fast glycolytic) – type IIb
� Intermediate (slow oxydative) – type IIa
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Prof. Dr. Nikolai Lazarov 27
Cardiac muscle tissue
� origin: mesenchyme� involuntary: ANS
� quick continuous automatic contraction:
conduction system
� striated� in the wall of the
� heart (myocardium)� some large vessels
Textus muscularis striatus cardiacus
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Prof. Dr. Nikolai Lazarov 28
� cardiomyocyte (Gr. cardia, heart)
�three types of cardiac myocytes: contractile, conductive, secretory
�shape: cylindrical, bifurcated
�length: 85-100 µm
�diameter: 15-20 µm
�only 1 (or 2) centrally located pale-staining nuclei
�delicate sheath of endomysial connective tissue containing a rich capillary network
Cardiac muscle tissue
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Prof. Dr. Nikolai Lazarov 29
Cardiomyocyte� Т-tubules: at the level of Z band
� “diad” = Т-tubule + one SR cistern
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Prof. Dr. Nikolai Lazarov 30
Ultrastructure� mitochondria: 40% of the cytoplasmic volume� atrial granules (ANF and BNF): 300-400 nm
� lipid droplets and lipofuscin� glycogen granules� intercalated discs:
� fascia adhaerens – in the transverse portion� macula adhaerens (desmosomes) – in the vicinity,
bind the cardiac cells together � gap junction (nexus) – in the lateral portion,
provides ionic continuity between cells
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Prof. Dr. Nikolai Lazarov 31
Myoepithelial cells
�basket cells:
�sweat gland
�mammary gland
�lacrimal gland
�salivary glands
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Prof. Dr. Nikolai Lazarov 32
Regeneration of muscle tissue
� Cardiac muscle has almost no regenerative capacity beyond early childhood:
� mature cardiac muscle cells do not divide
� proliferation of connective tissue �
myocardial scars
� Skeletal muscle can undergo limited
regeneration
� source of regenerating cells is believed
to be the satellite cell (stem cell)
� Smooth muscle is still capable of an active
regenerative response (division)
� viable mononucleated smooth muscle cells
and pericytes from blood vessels provide
for the replacement of the damaged tissue
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Prof. Dr. Nikolai Lazarov 33
Thank youThank youThank youThank you ............