3. Skeletal muscle
Consists of muscle
fibres (cylindrical,
multinucleated cells)
Muscle fiber=syncytium
Attention! A muscle
fiber should not be
confused with a
connective tissue fiber.
Muscle fibers are
cellular elements ,
connective tissue fibers
are extracellular
products of connective
tissue.
4.
Nuclei: oval, located
peripherally under the
cell membrane.
Multinucleation results
from the fusion of
embryonic
mononucleated
myoblasts( muscle cell
precursors) during
development.
5.
6. Sarco…
Sarco… - a prefix that means „muscular”.
For example:
Sarcolemma- the plasma membrane of the
muscle fiber
Sarcoplasm = cytoplasm of muscle fiber
Sarcoplasmic reticulum = smooth
endoplasmic reticulum in muscle fibers
7. SKELETAL MUSCLE
The connective tissue associated with muscle is
given a specific set of names describing its
relationship with the muscle fibers.
Endomysium- is the delicate layer of reticular
fibers that immadietely surrounds individual
muscle fibers. Blood and lymphatic vessels run
between muscle fibres and parallel to them.
8. SKELETAL MUSCLE
Perimysium- a thicker connective tissue layer that
surround a group of fibers to form a bundle or a
fascicle.Larger blood vessels and nerves travel in
the perimysium.
Epimysium- is a dense connective tissue that
surrounds the collection of fascicles that
constitute the muscle.The major vascular and
nerve supply of the muscle penetrates through
the epimysium.
9. Myofibrils
The strucural and functional subunit of
the muscle fiber is the
myofibril.Muscle fibers are filled with
these longitudinally arrayed
subunits.
Myofibrils are composed of bundles of
myofilaments.
11. Myofilaments
Myofilaments are the individual
filamentous polymers of different
proteins.They form a myofibril and
are the acurate contractile elements
of striated muscle.
Two kinds of filaments:
1.
Thick filaments
2.
Thin filaments
12.
13. The arrangement of thick and thin
filaments gives rise to the
density differences that produce
the cross-striations.
14. Cross- striations
Cross-striations are the principal histologic
feature of striated muscle.
Longitudinally sectioned muscle fibres show
cross-striations of alternating light and dark bands.
15. Cross-striations
Cross-striations are evident in
HE( hematoxylin-eosin) stained
preparations of longitudinal sections
of muscle fibers.
The dark and light bands are termed:
the A band, the I band and the Z line
16. Cross-striations
1.Dark stained bands = A bands=
anisotropic
(are birefringent in polarized light)
2.Light stained bands= I bands=
isotropic
(do not alter polarized light)
17.
18. The Z line, H zone, M line
The Z line= Z disc, is a dense zone
that bisects the I band
The H zone/band- is a light zone that
bisects the A band
M line- is located in the middle of H
band
19. Sarcomere
- The functional unit of the myofibril.
- it`s a segment of the myofibril
between 2 Z lines.
- It measures 2-3 um in relaxed
muscle, may be stretched to more
than 4 um, and in extreme
contraction, may measure as little as
1 um.
21. The structure of the sarcomere
1.
2.
3.
4.
5.
6.
Z line- a borderline of sarcomere.Thin filaments are
attached to it. Main protein- alfa actinin.
Thin filaments- extend from the Z line to the H band.
The thin and thick filaments run between and parallel
to each other.
Thick filaments- occupy the A band, the central
portion of the sarcomere.
I – band- contains thin filaments fixed to Z line.
A -band- consist of two parts: 1. thin filaments
overlapping thick filaments 2. thick filaments (H
band)
M line- a region of a H band, at which lateral
connections are made between adjacent thick
filaments.
22. M line
The major protein of the M line is
creatine kinase.Creatine kinase
catalyzes the transfer of a phosphate
group from phosphocreatine to
adenosine diphosphate(ADP)
resulting adenosine triphosphate
( ATP). The energy from ATP is
needed for the muscle contraction.
ATP
ADP + Pi
23.
24. The structure of thin and thick
myofilaments
A)
B)
C)
Thin filaments are composed of 3
different proteins:
Actin
Tropomyosin
Troponin
Thick filaments are composed of myosin.
25. Actin
-
-
-
-
Is present as long filamentous (F-actin) polymers
consisting of 2 strands of globular( G- actin )
monomers.
The polymers are twisted around each other in a
double helical formation.
Each G-actin monomer contains a binding site for
myosin
Actin filaments are fixed to the Z line by a protein
called alfa-actinin.
26. Tropomyosin
-
-
-
-
long, thin molecule, built up of 2 polypeptide
chains
Molecules are bound head to tail, forming
filaments
Tropomyosin filaments lie along the two twisted
actin strands
Each tropomyosin molecule covers 7 G-actin
molecules and has one troponin- binding place.
27. Troponin
1.
2.
3.
A complex of 3 subunits:
Troponin T ( TnT)- attached to
tropomyosin
Troponin C ( TnC)- binds calcium
ions
Troponin I ( TnI)- inhibits the actinmyosin interaction
28.
29. Myosin
Composed of 2 heavy
chains and 4 light chains.
Heavy chains are twisted
together
At one end of each heavy
chain- „heads”
The heads have ATPbinding sites and the
enzymatic capacity to
hydrolyze ATP.They have
also ability to bind to actin.
30.
31.
32. The primary proteins ( actin , myosin,
trpomyosin, troponin) constitute
more than 75% of the total protein
of the muscle fiber and are visible as
the thick and thin filaments.The
remaining structural proteins
include:
- Titin
- Nebulin
- Alfa-actinin
- Myomesin
- C protein
33. Contractile mechanism-sliding
filament model
When a muscle contracts, each
sarcomere shortens and becomes
thicker , but the myofilaments
remain the same length. It means
that the shortening of the sarcomere
must be due to an increase in the
overlap of thick and thin filaments.
34. Sarcoplasmic reticulum
-
-
-
Is arranged in networks around or
between a group of myofilaments
One network of sarcoplasmic reticulum
surrounds the A band, and another
network surrounds the I band
Where the two networks meet, at the
junction between A and I bands, the
sarcoplasmic reticulum forms a ringlike
channel- terminal sac (cisterna) around
the filaments of the myofibril.
Main function: magazine and regulator of
calcium ions!
35. TRIADS
Invaginations of the plasma
membrane of the muscle cell form
the T system. The T tubules are
located between the adjacent ER`s
terminal cisternae.
- The complex of T tubule and two
terminal cisternae is called TRIAD.
TRIAD= 1 T TUBULE+ 2 TERMINAL
CISTERNAE
-
36.
37. Mechanism of contraction
1.
2.
3.
4.
5.
Depolarization of the sarcoplasm
The depolarization signal is transmitted through
the T tubule to the sarcoplasmic reticulum
membrane.
Calcium ions are released into the vicinity of the
overlapping thick and thin filaments.
Calcium ions are bined to the TnC subunit of
troponin.
The comlex of troponins changes its structure
and drives the tropomyosin deeper into the
groove of the actin helix. Consequence:
exposition the myosin –binding sites on the
actin
38. Mechanism of contraction
6. Interaction=bridgening between the myosin head
and actin. Result:
ATP
ADP + Pi
7.Deformation=bending of the myosin head
8. Movement of the myosin heads pulls the actin
past the myosin filament.
39.
40. SEQUENCE OF EVENTS IN
CONTRACTION
1. Nerve impulse travels down axon
2. Acetylcholine released into synaptic cleft, depolarizing the
sarcolemma
3. Voltage gated Na+ channels open, Na+ enters muscle cell
4. Depolarization spreads including traveling down t-tubule
5. Voltage sensor proteins in t-tubules change conformation
6. Ca2+ rapidly released from sarcoplasmic reticulum (via Ca2+
release channels)
7. Ca2+ binds to the TnC subunit of troponin
a) Troponin shifts tropomyosin deeper into groove, b) ADPPi-myosin complex binds to active site on actin c) Pi is released
d) myosin has conformational change pulling actin is pulled
toward m-line releasing ADP e) ATP binds to Myosin
releasing it from actin f) ATP hydrolyzed into ADP and Pi
8. Ca2+ is sequestered into the sarcoplasmic reticulum
44. THE MOTOR UNIT
Each muscle is served by at least
one motor nerve containing
hundreds of motor axons.
A motor neuron and all the fibers
it supplies is called a MOTOR UNIT.
These fibers may be spread
throughout the muscle.
When a motor neuron transmits an
electrical impulse all the fibers it
innervates contract.
Muscles that exert fine control have
small motor units (e.g. eyes, fingers).
Large muscles have large motor units
and have less precise control (e.g. muscles
of weight bearing, locomotion).
45. Motor innervation
Skeletal muscle fibers are richly innervated
by motor neurons that originate in the
spinal cord or brain stem.
The axons of the neurons branch as they
near the muscle, giving rise to twigs that
end on individual muscle fibers.
The Motor End Plate is the contact made by
the terminal branches of the axon with the
muscle.
46. Types of muscle fibres
Type I (slow)
Type II ( quick)
Rich in sarcoplasmmyoglobin- dark red
colour
Related to continous
contraction
Contain less
myoglobin-light red
colour
Related to rapid
contraction
Types: IIA,
IIB(fastest), IIC
47. THE MOTOR UNIT
Each muscle is served by at least
one motor nerve containing
hundreds of motor axons.
A motor neuron and all the fibers
it supplies is called a MOTOR UNIT.
These fibers may be spread
throughout the muscle.
When a motor neuron transmits an
electrical impulse all the fibers it
innervates contract.
Muscles that exert fine control have
small motor units (e.g. eyes, fingers).
Large muscles have large motor units
and have less precise control (e.g. muscles
of weight bearing, locomotion).
48. THE MOTOR END PLATE
ACh, released from the axon terminal, binds to receptors on the junctional folds
of the sarcolemma which then depolarizes. This depolarization is passed via the
t-tubules and triad to the sarcoplasmic reticulum and results in the release of
calcium which initiates the contraction cycle.
53. TYPE OF
MUSCLE
SKELETAL
CARDIAC
T tubules
-more
numerous and
larger
- found at the
level of A-I
junction
-less number
and smaller
-found at the
level of the Z
line
Sarcoplasmic
reticulum
- well developed
- Well developed
but not as well
as in skeletal
muscle
54. CARDIAC
MUSCLE
1 T tubule+1 sarcoplasmic
reticulum cisterna=DIAD
SKELETAL
MUSCLE
1 T tubule+2 sarcoplasmic
reticulum cisternae=TRIAD
58. Smooth muscle
Where??
- Alimentary canal
- Genitourinary tract
- Blood vessels
- Respiratory tract
- Other localisations: iris, ciliary body
of the eye, arrector pili muscles
(skin)
59. Smooth muscle
-composed of elongated, nonstriated cells
-each cell is enclosed by basal lamina and a
network of reticular fibres.
-the cells are larger at their midpoints and taper
toward the ends.
-single nucleus located in the central part of cell
-cytoplasmic organelles are concentrated at each
end of the nucleus.
-ER well developed
- Absence of T tubules
60. Smooth muscles
-the narrow part of one cell lies
adjacent to the broad parts of
neighboring cells.
- Not striated! No sarcomers.
62. DIAGRAM OF A SMOOTH MUSCLE CELL
Dense body
Actin
filament
Myosin
filament
63. Mechanism of contraction
In smooth muscles bundles of
myofilaments crisscross obliquely
through the cell, forming a
latticelike network.
Three kinds of filaments:
1.
Thin filaments ( actin, tropomyosin)
2.
Thick filaments( myosin)
3.
Intermediate filaments(desmin,
wimentin)
64. The dense bodies
Two kinds:
1.
Membrane associated
2.
Cytoplasmic
Content: alfa-actinin
Function: transmition of contractile force to
adjacent smooth muscle cells
66. Mechanism of contraction
Calcium ions in the cytosol
Calcium ions+calmodulin(protein)
(Ca++ - calmodulin) complex
Activation of myosin light-chain kinase(the enzyme responsible for
the phosphorylation of myosin)
67. Mechanism of contraction
Activation of myosin light-chain kinase(the enzyme responsible for
the phosphorylation of myosin)
Phosphorylation of myosin
Reaction between the myosin`s head and actin
contraction
70. Innervation of smooth muscle
Autonomic system( sympathetic and
parasympathetic)
Spontaneus activity of the muscle
even without the nervous stimuli
71. Regeneration of muscle tissue
CARDIAC- no
regeneration
capacity.
Damage( infarct) is
replaced by the
proliferation of
connective tissue.
72. Regeneration of muscle tissue
SKELETAL-limited regeneration.
Satellite cells= regenerating cells
-population of mononucleated cells, that lies
within the basal lamina surrounding each
mature muscle fiber.After injury become
activated, proliferate and fuse to form a
new skeletal muscle fibers.
73. Regeneration of muscle cells
Similar activity of
satellite cells may
cause a muscle
hypertrophy- for
example after
extensive exercise.
