Transcript Muscle Tissue

King Saud University
Riyadh
Saudi Arabia
Dr. Gihan Gawish
Assistant Professor
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Gihan Gawish.Dr
Muscles
 Muscle is contractile tissue of the body and
is derived from the mesodermal layer of
embryonic germ cells.
 Muscle cells contain contractile filaments
that move past each other and change the
size of the cell.
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Function of muscle tissue
 Animals use muscles to convert
the chemical energy of ATP into
mechanical work.
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Classification of Muscles
1. Heart muscle :
 also called cardiac muscle
 It makes up the wall of the heart.
 Throughout life, it contracts some 70 times
per minute pumping about 5 liters of blood
each minute .
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 Smooth muscle

It is found in the walls of all the hollow organs of
the body (except the heart).

Its contraction reduces
structures. Thus it :
the
size
of
these
1. regulates the flow of blood in the arteries
2. moves the foods
gastrointestinal tract
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along
through
your
3. expels urine from urinary bladder
4. sends babies out from the uterus
5. regulates the flow of air through the lungs
The contraction of smooth muscle is
generally not under voluntary control .
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 Skeletal muscle
 It is the muscle attached to the skeleton. It
is also called striated muscle .
 The contraction of skeletal muscle is under
voluntary control.
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Skeletal muscle cell structure
 Skeletal muscle is made
up of thousands of
cylindrical muscle fibers
often running all the way
from origin to insertion.
 The fibers are bound
together by connective
tissue through which run
blood
vessels
and
nerves .
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Structure of muscle fiber
1.Axon
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2. Neuromuscular junction
3. Muscle fiber
4. Myofibril
Each muscle fibers contains
1. an array of myofibrils that are stacked
lengthwise and run the entire length of the fiber.
2. mitochondria
3. an extensive smooth endoplasmic reticulum
(SER)
4. many nuclei.
The multiple nuclei arise from the fact that each
muscle fiber develops from the fusion of many
cells (called myoblasts).
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Myoblast
 A myoblast is a type of stem cell that exists in
muscles .
 Skeletal muscle fibers are made when myoblasts
fuse together
 Myoblasts that do not form muscle fibers
differentiate into satellite cells
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Myostatin
 known as Growth differentiation factor 8, is a
growth factor that limits muscle tissue growth
 It regulates the early fixation of the number of fibers
in the life
 It is a cytokine that is synthesized in muscle cells
(and circulates as a hormone later in life).
 It suppresses skeletal muscle development .
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Myostatin in adults,
 increased strength and muscle mass
comes about through an increase in the
thickness of the individual fibers
 and increase in the amount of connective
tissue .
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 Because a muscle fiber is not a single
cell, its parts are often given special
names such as:
 sarcolemma for plasma membrane
 sarcoplasmic
reticulum
reticulum for
 sarcosome for mitochondrion
 sarcoplasm for cytoplasm
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endoplasmic
Each myofibril is made up of arrays of
parallel filaments :
1. The thick filaments
 They have a diameter of about 15 nm.
 They are
myosin .
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composed
of
the
protein
1. The thin filaments
 They have a diameter of about 5 nm.

They are composed chiefly of the protein
actin along with smaller amounts of two
other proteins :
– troponin and
– tropomyosin.
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The Anatomy of a Sarcomere
 The thick
filaments produce
the dark A band .
 The thin filaments extend in
each direction from the Z line.
Where they do not overlap the
thick filaments, they create the
light I band .
 The H zone is that portion of the
A band where the thick and thin
filaments do not overlap.
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 Shortening
of
the
sarcomeres
in
a
myofibril produces the
shortening
of
the
myofibril and, in turn, of
the muscle fiber of
which it is a part
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The Thin Filaments - Actin
 Filamentous actin or F-Actin polymerizes
from globular G-Actin
 They are the principal components of the
thin filaments in skeletal muscle.
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 F-Actin is a helix of uniformly
oriented monomers.
 They have a polar structure and
this polarity from one end to the
other is crucial for cell motility .
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Myosins
 Myosins are a large family of motor proteins found in
eukaryotic tissues .
 They are responsible for actin-based motility.
 Domains
 Most myosin molecules are composed of both a head and
a tail domain.
 The head domain binds the filamentous actin ,and uses
ATP hydrolysis to generate force and to "walk"
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Myosin II
 Myosin II, responsible for skeletal muscle contraction
 Myosin II contains two heavy chains ,each about 2000
amino acids in length, which constitute the head and tail
domains.
 Each of these heavy chains contains the N-terminal head
domain, while the C-terminal tails take on a coiled-coil
morphology, holding the two heavy chains together
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Myosin Dissection. Treatment of muscle myosin with
proteases forms stable fragments, including heavy
meromysin (subfragments S1 and S2) and light
meromyosin.
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Myosin - the Thick Filaments
 Myosin comes in a greater variety than Actin.
 The filaments of Myosin in skeletal muscle are
much larger than in nonmuscle cells.
 The myosin molecule consists of two identical
heavy chains and two pairs of light chains.
 The alpha-coil tail is responsible for the
spontaneous assembly of myosin molecules into
thick filaments.
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 The heads are responsible for moving the
thick filaments against adjacent F-actin
filaments in the thin filaments in skeletal
muscle.
 The structure of thick filaments that myosin
molecules form in muscles depends on ionic
interactions between the tails.
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Sliding Filament
 When Myofibrils contract the thin and thick filaments
move past each other.
 Each sarcomer unit of the myofibrils
proportionally to the muscle contraction.
shortens
 Upon contraction, it is the light bands which shorten
whereas the dark bands do not change in length.
 This is explained by the Actin filaments sliding into the
dark region of Myosin filaments .
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 In the overlapping regions cross-bridges
extend about 13 nm from the thick Myosin
filaments to the thin Actin filaments.
 These cross-bridges are mainly composed of
the Myosin heads which are attached to the
end of two coiled alpha-helices typically 150nm
in length.
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1. The
thin
and
thick
filaments don’t change
during muscle contraction
2. The length of sarcomere
decrease
during
contraction.
3. The force of contraction is
generated by a process
that actively moves by
sliding of filaments.
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Sliding-Filament
Model.
Muscle contraction depends
on the motion of thin
filaments (blue) relative to
thick filaments (red).
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Muscle contraction
and cell motility
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 The energy for muscle contraction comes
from ATP hydrolysis .
 The contraction of striated muscle is
2+
controlled by the concentration of Ca.
 Which is
reticulum
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regulated
by
sarcoplasmic
Myosin Motion Along Actin
(hydrolyzed ATP)
ATP + H2O
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+
ADP + Pi + H
(hydrolyzed ATP)
 A myosin head in the ADP form is bound to an
actin filament
1. The exchange of ADP for ATP
2. The release of myosin from actin and substantial
reorientation of the lever arm of myosin.
3. Hydrolysis of ATP
4. allows the myosin head to rebind at a site
displaced along the actin filament
5. The release of Pi accompanying this binding
increases the strength of interaction between
myosin and actin and resets the orientation of the
lever arm.
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Troponin and tropmyosin
mediate calcium ion
regulation of muscle
contraction
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 The physiologic regulator
contraction is Ca2+.
of
muscle
 The effect of calcium ion on the interaction
of actin and myosin is mediated by
tropomyosin and the troponin complex.
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Tropomyosin
 It is a two stranded alpha –helical
rod (70kdal).
 This highly elongated protein is
aligned nearly parallel to the long
axes of the thin filament.
Troponin
is a complex of three
polypeptide chains :
 TnC (18kdal): binds Ca ions
 TnI (24kdal): binds to actin
 TnT
(37kdal):
binds
to
tropomyosin.
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 The troponin
located in the
at intervals
period set by
tropomyosin.
complex is
thin filaments
of 385A a
the length of
 A troponin complex bound
to
a
molecule
of
tropomyosin regulates the
activity of about 7 actin
monomers.
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 The interaction of actin and myosin is
inhibited by troponin and tropomyosin in the
2+
absence of Ca.
 Tropomyosin blocks the binding sites on
actin unit in an inhibited thin filament.
2+
 Nerve excitation triggers the release of Ca
by the sarcoplamic reticulum.
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2+
 The released Ca binds to the TnC component of
troponin and causes conformational changes that
are transmitted to tropomyosin and then to actin.
 Specifically, tropomyosin moves toward the
center of the long helical groove of the thin
filament .
 Consequently, the S1 heads of myosin molecules
can then interact with actin units of the thin
filament.
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 Contractile force is generated and ATP is
concomitantly hydrolyzed until Ca ions is
removed and tropomyosin again blocks
access of the S1 heads.
2+
 Thus, Ca controls muscle contraction:
2+
Ca
TnC
Tropomyosin
actin
S1 heads of Myosin
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The flow of Calcium
ions is controlled
by the
sarcoplasmic
reticulum
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 The outer membrane of a muscle fiber becomes
depolarized following the arrival of a nerve
impulse at the end plate, which is the junction
between nerve and muscle.
 The depolarization of the outer membrane is
transmitted to the interior of the muscle fiber by
the transverse tubules (T tubules).
 The T tubules are in close proximity to a net work
of
extremely
fine
channels
called
the
sarcoplasmic reticulum, which is a reservoir of
calcium ion.
nd
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Schematic diagram of sarcoplasmic reticulum
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2+
 Ca is the intermediary between the nerve
impulse and muscle contraction.
+2
 In the resting state: Ca is sequestered
2+
in the sarcoplamic reticulum by a Ca
active- transport system.
2+
 The transport of Ca by the sarcoplasmic
reticulum is driven by the hydrolysis of
ATP.
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 There is an ATPase in the sarcoplasmic
2+
reticulum that is activated by the Ca .
2+
 This Ca + ATPase is an integral part of the
Ca2+pump.
 This ATP-driven
pump
lowers
the
concentrations of Ca2+ in the cytoplasm of
2+
resting muscle and increases the Ca level
inside the sarcoplasmic reticulum.
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2+
 Calsequestrin (protein): binds Ca inside
the reticulum.
 This highly 2+
acidic (44kdal) has more than 40
sites for Ca .
 Depolarization of the T tubules
membranes causes a sudden release of
2+
Ca from the sacs of the sarcoplamic
reticulum.
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 The released Ca then
stimulates muscle
contraction by binding to the
TnC components of the
troponin complex
2+
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Phosphocreatine is a
reservoir of P
 The amount of ATP in muscle suffices to
sustain contractile activity for only a fraction
of a second
 Vertebrate muscle contains a reservoir of
high potential phosphoryl groups in the form
of phosphocreatine
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 Creatine kinase catalyzes
the transfer of a
phosphoryl groups from
phosphocreatine to ADP
to form ATP
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 Some invertebrates use
phosphoarginine to store high
potential phosphoryl groups in
muscle
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2ADP
ATP + AMP
 In
active
muscle,
the
supply
of
phosphocreatine is rapidly depleted and so
the level of ATP drops.
 The concentration of ADP and Pi rises, as
does the level of AMP by the action of
adenylate kinase (myokinase)
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 the reduced energy charge of active muscle
stimulates glycolysis, the citric acid cycle, and the
oxidative phosphorylation.
 The relative contributions of these processes to
the generation of ATP depend on the type of
muscle.
 Red muscle, which derives its color from
myoglobin and the cytochromes of the respiratory
chain, has a much more aerobic metabolism than
does white muscle.
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The Link between Glycolysis and the Citric
Acid Cycle and oxidative phosphorylation
glycolysis
Citric acid cycle
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Citric acid cycle
The Cori Cycle
 In actively contracting skeletal
muscle, the rate of glycolysis far
exceeds that of the citric acid cycle,
and much of the pyruvate formed is
reduced to lactate, some of which
flows to the liver, where it is
converted into glucose
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The Cori Cycle
Lactate formed by active muscle is converted
into glucose by the liver. This cycle shifts
part of the metabolic burden of active muscle
to the liver.
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 In addition, a large amount of alanine is formed in
active muscle by the transamination of pyruvate.
Alanine, like lactate, can be converted into
glucose by the liver.
 Why does the muscle release alanine? Muscle
can absorb and transaminate branched-chain
amino acids; however, it cannot form urea.
 Consequently, the nitrogen is released into the
blood as alanine.
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 The liver absorbs the alanine, removes the
nitrogen for disposal as urea, and processes
the pyruvate to glucose or fatty acids.
 The metabolic pattern of resting muscle is
quite different. In resting muscle, fatty acids
are the major fuel, meeting 85% of the
energy needs
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Homework:
 Describe;
1. Glycolysis cycle
2. The citric acid cycle
3. The oxidative
phosphorylation
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