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
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
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
Prof. Dr. Nikolai Lazarov 4
Myofibrils and myofilaments
� myofibrils: fill the muscle fibers
� separated by sarcoplasmic reticulum
� myofilaments:� thick and thin filaments
(contractile proteins)
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
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)
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!!!!
Prof. Dr. Nikolai Lazarov 8
Types of muscle tissue
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)
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
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
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:
Prof. Dr. Nikolai Lazarov 13
Regulation of contraction and relaxation
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)
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
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
Prof. Dr. Nikolai Lazarov 17
Organization of skeletal muscle
�Skeletal muscle
�Muscle fasciculus
�Muscle fiber
�Myofibril
�Myofilaments
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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+
Prof. Dr. Nikolai Lazarov 19
Ultrastructure
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
Prof. Dr. Nikolai Lazarov 21
Sarcomere
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
Prof. Dr. Nikolai Lazarov 23
Mechanism of contraction
rigor mortis
Sliding Filament Hypothesis: Huxley
Prof. Dr. Nikolai Lazarov 24
Motor end plate
� myoneural junction – cholinergic (ACh)
Myasthenia gravis
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
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
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
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
Prof. Dr. Nikolai Lazarov 29
Cardiomyocyte� Т-tubules: at the level of Z band
� “diad” = Т-tubule + one SR cistern
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
Prof. Dr. Nikolai Lazarov 31
Myoepithelial cells
�basket cells:
�sweat gland
�mammary gland
�lacrimal gland
�salivary glands
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
Prof. Dr. Nikolai Lazarov 33
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