Download Skeletal muscle tissue

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
Muscle tissue
Textus muscularis:
cells – myocytes
extracellular matrix
body movements
digestion
blood circulation
respiratory movements
other movement activities,
incl. cellular contraction
succession of relax and
contraction:
transformation of chemical
into mechanical energy
Prof. Dr. Nikolai Lazarov
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Muscle fibers – myofibers
Gr. sarkos, flesh
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)
myoepithelial cells
pericytes
myofibroblasts in healing wounds
myoid cells of the testis
Prof. Dr. Nikolai Lazarov
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Myofibrils and myofilaments
myofibrils: fill the muscle fibers
separated by sarcoplasmic reticulum
myofilaments:
thick and thin filaments
(contractile proteins)
Prof. Dr. Nikolai Lazarov
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Histogenesis
embryonic origin:
smooth muscle –
mesenchyme
striated – mesoblast
myoepithelial cells –
skin ectoblast
skeletal muscle – mesoderm
somites – skeletal muscles
of the trunk
general mesoderm – muscles
of the head and limbs
Prof. Dr. Nikolai Lazarov
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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
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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
Prof. Dr. Nikolai Lazarov
NB: muscles can only pull or contract, not push!
push!
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Types of muscle tissue
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Smooth muscle tissue
Textus muscularis nonstriatus (glaber)
Characteristics:
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)
Prof. Dr. Nikolai Lazarov
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Smooth muscle tissue
leiomyocyte (Gr. leios, smooth)
shape: fusiform or “spindle shaped"
length: 30-500 µm
thickness: 5-10 µm
Prof. Dr. Nikolai Lazarov
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Ultrastructure
dense bodies, corpora densa
(contain α-actinin = similar to the Z line)
caveolae (analogous to Т-tubule system)
actin filaments (4.5 µm/7 nm):
actin, tropomyosin,
calmodulin – Ca2+
myosin (2.2 µm/17 nm):
myosin II
intermediate filaments (10 nm):
desmin (skeletin), vimentin = non-contractile proteins
Prof. Dr. Nikolai Lazarov
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Smooth muscle types
two types of smooth muscle:
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
Prof. Dr. Nikolai Lazarov
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Regulation of contraction and relaxation
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Skeletal muscle tissue
Textus muscularis striatus (skeletalis)
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
Prof. Dr. Nikolai Lazarov
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Skeletal muscle development
100 myoblasts (mononucleated) – 1 mature muscle
cell (multinucleated): syncytium (symplast)
Gr. syn, together + kytos, cell
does not divide postnatally
muscle growth –
augmentation of cell
volume (hypertrophy)
satellite (myosatellite) cells: retain their potential for the
formation of new cells (stem cells)
Prof. Dr. Nikolai Lazarov
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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
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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+
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Ultrastructure
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Sarcomere
Sarcomere (Gr. sarkos + meros, part):
length: 2-3 µm (~2.5 µm) – extends from Z line to Z line
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
Prof. Dr. Nikolai Lazarov
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Sarcomere
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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
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Mechanism of contraction
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rigor mortis
Sliding Filament Hypothesis: Huxley
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Motor end plate
myoneural junction – cholinergic (ACh)
Prof. Dr. Nikolai Lazarov
Myasthenia gravis
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Neuromotor unit
motor unit = an individual
somatic 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
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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
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Cardiac muscle tissue
Textus muscularis striatus cardiacus
origin: mesenchyme
involuntary: ANS
quick continuous
automatic contraction:
conduction system
striated
in the wall of the
heart (myocardium)
some large vessels
Prof. Dr. Nikolai Lazarov
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Cardiac muscle tissue
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
Prof. Dr. Nikolai Lazarov
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Cardiomyocyte
Т-tubules: at the level of Z band
“diad” = Т-tubule +
one SR cistern
Prof. Dr. Nikolai Lazarov
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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
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Myoepithelial cells
basket cells:
sweat gland
mammary gland
lacrimal gland
salivary glands
Prof. Dr. Nikolai Lazarov
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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
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Thank you ...
Prof. Dr. Nikolai Lazarov
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