Muscle tissue
1) Striated skeletal muscle tissue.
2) Striated cardiac muscle tissue.
3) Smooth muscle tissue.
General characteristic
of muscle tissue
Origin: mesoderm and mesenchyme
Excitability
Contraction + relaxation  movement
Composition: muscle cells + connective
tissue, blood vessels
Long axe of cells is oriented paralelly with
direction of contraction
mys/myos (muscle) sarx/sarcós (meat):
cell membrane = sarcolemma
cytoplasm = sarcoplasm
sER = sarcoplasmic reticulum
rhabdomyocyte
kardiomyocyte
leiomyocyte
Ø 25-100 µm
Ø 15 µm
Ø 3-10 µm
MUSCLE CELLS (-myocytes)
Muscle tissue in LM
Connective tissue of muscle
Endomysium – around each muscle
cell (fiber)
Perimysium – around and among the
primary bundles of muscle cells
Epimysium – connective tissue
„capsule“ covering the surface of
muscle
Connective tissue in skeletal muscle
contains vessels and nerves
1)Cross-striated skeletal muscle tissue
morphological and functional unit: muscle fiber
(rhabdomyocyte) – elongated, cylindrical shape,
multinucleated cell (=syncytium) – nuclei are located
at the periphery (beneath sarcolemma), myofibrils
show cross striation
diameter of muscle fiber: 25-100 m
length: milimeters - centimeters (up 15)
Skeletal muscle cell (fiber)
< rhabdomyocyte >
Remember used terms:
Muscle fiber = myofiber = syncitium = rhabdomyocyte
Muscle fiber – morphologic and functional unit
of skeletal muscle [Ø 25 – 100 ]
Myofibrils – compartment of fiber sarcoplasm
[Ø 0.5 – 1.5 ]
Myofilaments – actin and myosin, are
organized into sarcomeres (several in the
length of myofibril) [Ø 8 and 15 nm]
Sarcomere – the smallest contractile unit
[2.5 m in length]
Structure or rhabdomyocyte
Sarcolemme + t-tubules,
In sarcoplasm:
Nuclei,
Mitochondria,
Golgi apparatus,
Glycogen (beta granules)
(sarcoplasm with organelles
forms columns among
myofibrils)
Sarcoplasmic reticulum
(smooth ER) – reservoir
of Ca2+
Myofibrils (parallel to the
length of the muscle fiber)
Myofibrils
elongated structures [Ø 0.5 – 1.5 ] in
sarcoplasm of muscle fiber,
are oriented parallely to the length of the
fiber,
contain 2 types of myofilaments: actin and
myosin, arranged into the smallest
contractile units – sarcomeres,
organization of myofilaments causes cross
striation of myofibrils.
myofibrils columns of sarcoplasm
sarcoplasm
Sarcomere
A–band
I–band½
I-band
H-zone
Rhabdomyocyte
Sarcoplasmic reticulum, t-tubule
Terminal cisterna
T-tubule
Terminal cisterna
TRIAD
Forms transversal terminal
cisternae and longitudinal
tubules.
Function: reservoir of Ca ions
T-tubule is invagination of sarcoplasm and leads action
potential to terminal cisternae (they change permeability
of membrane for Ca ions)
Contraction
propagation of action potential (depolarization) via T-tubule
(= invagination of sarcolemma),
change of terminal cisternae permeability – releasing of Ca+
ions increases their concentration in sarcoplasm,
activation of binding sites of actin for myosin,
myosin contacts actin and sarcomera shortens by sliding
movement – contraction,
relaxation: repolarization, decreasing of Ca2+ ions
concentration, inactivation of binding sites of actin for
myosin.
2) Cardiac muscle - myocardium
is made up of long branched fibers,
composed of cells – cardiomyocytes,
cardiomyocytes are cylindrical cells, which
can be branched on one or both ends (Y, X
shaped cells),
Sarkoplasm: 1 nucleus in the center of cell,
striated myofibrils, numerous mitochondria,
cells are attached to one another by end-toend
junctions – intercalated discs.
chains of cardiomyocytes blood capillary with erythrocytes
Intercalated disc
DIFFERENCES BETWEEN CARDIAC AND
SKELETAL MUSCLE TISSUES
there are no triads, but diads: 1 t-tubule + 1 cisterna
t-tubules encircle the sarcomeres at the Z lines
rather than at the zone of overlap between A/I-bands
sarcoplasmic reticulum via its tubules contact
sarcolemma as well as the t-tubules
cardiac muscle cells are totally dependent on
aerobic metabolism to obtain the energy needed to
continue contracting. The sarcoplasm thus contains
large numbers of mitochondria and abundant
reserves of myoglobin (to store oxygen). Energy
reserves are maintained in the form of glycogen and
lipid inclusions.
Intercalated disc
„scalariform“ shape of
cell ends
fasciae adherentes
(adhesion of cells)
Nexus
(quick intercellular
communication –
transports ions and
electric impulses)
nexus fascia adherens
Cell 1
Cell 2
Intercalated disc:
Actin myofilaments
Myofibril of cardiomyocyte
Actin + myosin myofilaments
Sarcomere
Z-line
M-line and H-zone
I-band, A-band
T-tubule + 1 cisterna = diad (around Z-line)
Purkinje fibers
are located in the inner
layer of heart ventricle
wall
are specialized cells
fibers that conduct an
electrical stimuli or
impulses that enables
the heart to contract in
a coordinated fashion
numerous sodium ion
channels and
mitochondria, fewer
myofibrils
3) Smooth muscle tissue
spindle shaped cells (leiomyocytes) with
myofilaments not arranged into myofibrils (no
striation), 1 nucleus in the centre of the cell
myofilaments form bands throughout the cell
actin filaments attach to the sarcolemma by
focal adhesions or to the dense bodies
substituing Z-lines in sarcoplasm
calmodulin (as troponin)
sarcoplasmic reticulum forms only tubules with
Ca ions, which are also transported to the cell
through pumps and ions channels in caveolae
zonulae occludentes and nexuses connect cells
Caveolae are equivalent to t-tubule
and in their membrane ions channel
are present to bring Ca needed fo
contraction.
Caveolae are in contact with
sarcoplasmic reticulum.
Leiomyocyte
Leiomyocyte:
contractile filaments
+
nexuses
Myosin flaments
Actin filaments
(as Z line)
Leiomyocytes are arranged into laeyers of wall of hollow (usually tubular) organs
Cross section
Longitudinal section
Motor end plate