Download Muscular Tissue

Dr. Sami Zaqout
IUG
Types of muscles
• There are three types
of muscles:
• 1. Skeletal
• 2. Smooth
• 3. Cardiac
Dr. Sami Zaqout
IUG
General characteristics of muscles
• The structural and functional units of muscles are formed
of special elongated cells known as muscle fibers.
• The cell membrane of these muscle fibers is known as
sarcolemma.
• The cytoplasm of these muscle fibers is known as
sarcoplasm.
• Smooth endoplasmic reticulum is called sarcoplasmic
reticulum.
• The muscle fibers may have transverse striations as the
skeletal and cardiac muscle fibers, or they may show no
striations as the plain or smooth muscles.
Dr. Sami Zaqout
IUG
Dr. Sami Zaqout
IUG
1. SKELETAL MUSCLES
Dr. Sami Zaqout
IUG
Sites
• The skeletal muscles are attached to the skeleton.
• They are present also in the diaphragm, tongue,
muscles of the face, eye, pharynx and upper third of
esophagus.
• Skeletal muscles are voluntary muscles except in:
– The upper third of esophagus
– Some muscles of the pharynx
– Cremasteric muscles of the spermatic cord.
Dr. Sami Zaqout
IUG
Connective tissue around muscle fibers and bundles
 The epimysium is the C. T.
around the whole muscle.
 The perimysium is the C. T. septa
between the muscle bundles.
 Each muscle fiber is surrounded
by C. T. endomysium.
• In the connective tissue of the
muscles, B. V., nerves and lymph
vessels are present.
• C.T. Mechanically transmit the
forces generated by contracting
muscle cells
Dr. Sami Zaqout
IUG
Characteristics of skeletal muscles
• They are formed of striated
muscle fibers.
• Each muscle fiber is a single cell
which varies in length from 1
mm up to 30 cm.
• The muscle fibers do not
branch except in the tongue
and face muscles.
Dr. Sami Zaqout
IUG
Characteristics of skeletal muscles
• Each muscle fiber is a
multinucleated cell, it has
many oval nuclei.
• The nuclei are peripheral in
position, present under the
sarcolemma.
• The sarcoplasm is acidophilic
rich in glycogen and myoglobin.
• The myoglobin is formed of
pigmented protein.
Dr. Sami Zaqout
IUG
Characteristics of skeletal muscles
• The sarcoplasm contains many mitochondria and many smooth
endoplasmic reticulum which is called sarcoplasmic reticulum.
• The sarcoplasm contains also longitudinal fibrils known as myofibrils.
• Mature muscle cells have negligible amounts of rough endoplasmic
reticulum and ribosomes
Dr. Sami Zaqout
IUG
The myofibrils of skeletal muscles
• The myofibrils are the
contractile threads which
are arranged longitudinally
in the sarcoplasm of each
muscle fiber.
• The arrangement of
myofibrils near each other
shows transverse striations.
• The transverse striations in
the muscle fibers are due to
presence of alternating dark
and light bands on each
myofibril.
Dr. Sami Zaqout
IUG
The myofibrils of skeletal muscles
• Each dark band of one
myofibril is present
beside the dark band of
the adjacent myofibril.
• These arrangements of
dark and light bands
give the muscle fiber
the appearance of
transverse striations.
Dr. Sami Zaqout
IUG
The myofibrils of skeletal muscles
• The dark bands have double refraction to
polarized light. They are called Anisotropic bands
or A-Bands.
• Each dark band is further subdivided by a pale
area in its centre called Hensen's zone or H-Band.
• Bisecting the H band is the M-line, a region at
which lateral connections are made between
adjacent thick filaments.
• The major protein of the M-line is creatine kinase.
• The light bands are not refractile to polarized
light.
• They are called Isotropic bands or I-Bands.
• Each light band is also further subdivided by a
darkly-stained zone present at its center and is
called Z-line.
Dr. Sami Zaqout
IUG
The sarcomere
•
•
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•
The area of the muscle fiber
enclosed between two Z-Discs is
called Sarcomere.
The sarcomeres are the functional
contractile units of the muscle
fiber.
Each Sarcomere includes the whole
dark band and the two halves of the
two light bands on both sides.
The sarcomeres of each muscle
fiber contract and relax as one unit.
Their contractions are due to the
presence of longitudinally arranged
very fine electron microscopic
threads known as myofilaments.
Dr. Sami Zaqout
IUG
Myofilaments
• The myofilaments are 2 types:
– Thin myofilaments
– Thick myofilaments
• 1. Thin filaments or actin
filaments which are formed
mainly by actin protein.
• They extend from the Z line till
the middle of the dark band
• They terminate just before the
middle of the dark band,
therefore, the middle of the
dark band appears light and is
called H-band.
Dr. Sami Zaqout
IUG
Thin myofilaments
Dr. Sami Zaqout
IUG
Thick myofilaments
• Thick filaments or myosin
filaments which are
formed of protein known
as Myosin.
• They extend in the dark
bands only.
• Both ends of the thick
filament are free, while
the thin filament has only
one free end and the
other end is attached to
the Z-line.
Dr. Sami Zaqout
IUG
Thick myofilaments
• Myosin, a much larger complex,
can be dissociated into two
identical heavy chains and two
pairs of light chains.
• Myosin heavy chains are thin,
rodlike molecules made up of two
heavy chains twisted together.
• Small globular projections at one
end of each heavy chain form the
heads, which have ATP-binding
sites as well as the enzymatic
capacity to hydrolyze ATP (ATPase
activity) and the ability to bind to
actin.
• The four light chains are
associated with the head
Dr. Sami Zaqout
IUG
Cross-bridges between thin and thick filaments
• These bridges, which are
known to be formed by
the head of the myosin
molecule plus a short part
of its rodlike portion, are
involved in the conversion
of chemical energy into
mechanical energy.
Dr. Sami Zaqout
IUG
Sarcoplasmic reticulum & transverse tubule system
• To provide for a uniform
contraction, skeletal muscle
possesses a system of
transverse T tubules.
• These fingerlike invaginations
of the sarcolemma form a
complex anastomosing
network of tubules that
encircles the boundaries of
the A-I bands of each
sarcomere in every myofibril.
• Adjacent to opposite sides of
each T tubule are expanded
terminal cisternae of the
sarcoplasmic reticulum.
Dr. Sami Zaqout
IUG
The triad of tubular system
• The triad of tubular
system includes:
– One Transverse Tubule
Surrounded By
– Two Sarcoplasmic Tubules
Dr. Sami Zaqout
IUG
The role of tubular system in
muscular contractions
During muscular contraction the nerve
impulse reaches the sarcolemma, then it
passes through the transverse T-tubules.
The impulse then goes into the two tubules of
the endoplasmic reticulum.
These tubules pump calcium ions between
the myosin and actin molecules.
This will result in muscular contraction.
Dr. Sami Zaqout
IUG
Contraction of muscles
• The energy needed for
muscle contraction
comes from the
transformation of ATP
into ADP.
• This energy causes the
gliding of the thin
filaments over the
thick filaments.
Dr. Sami Zaqout
IUG
Contraction of muscles
• The thin filaments thus slide
towards the middle of the
sarcomere.
• This will result in pulling the
two Z-lines behind them.
• The H-Zones disappear during
muscular contractions,
because they will contain both
thick and thin filaments.
Dr. Sami Zaqout
IUG
Contraction of muscles
Dr. Sami Zaqout
IUG
Innervation of muscles
• Myelinated motor nerves
branch out within the
perimysial connective tissue,
where each nerve gives rise
to several terminal twigs.
• At the site of innervation,
the nerve loses its myelin
sheath and forms a dilated
termination that sits within a
trough on the muscle cell
surface.
• This structure is called the
motor end plate ,or
myoneural junction
Dr. Sami Zaqout
IUG
Myasthenia gravis
• An autoimmune disorder characterized by
progressive muscular weakness caused by a
reduction in the number of functionally active
acetylcholine receptors in the sarcolemma of the
myoneural junction.
• This reduction is caused by circulating antibodies
that bind to the acetylcholine receptors in the
junctional folds and inhibit normal nerve muscle
communication.
Dr. Sami Zaqout
IUG
Dr. Sami Zaqout
IUG
Types of skeletal muscle fibers
• According to the amount of myoglobin, the type
of innervation and the mode of contraction, the
muscle fibers are classified into:
• 1. Type I: Red Muscle Fibers
– They have large amounts of myoglobin, mitochondria
and cytochrome.
– They have small diameters.
– They can sustain contraction for a long time without
fatigue.
– Their energy is derived from oxidation of fatty acids.
Dr. Sami Zaqout
IUG
Types of skeletal muscle fibers
• 2. Type II: White Muscle Fibers
– They have small amounts of myoglobin and few
mitochondria.
– They have wide diameters.
– Their contractions are quick, but they become fatigued easily.
– Their energy is derived from glycolysis.
• 3. Intermediate Muscle Fibers
– They have intermediate characters between red and white
fibers.
Dr. Sami Zaqout
IUG
Comparison of types of skeletal muscle fibers
Dr. Sami Zaqout
IUG
Hypertrophy vs. Hyperplasia
• Tissue growth by an increase of cell volume, is called
hypertrophy.
• Tissue growth by an increase in the number of cells is
called hyperplasia
• Hyperplasia does not occur in either skeletal or cardiac
muscle but does take place in smooth muscle, whose
cells have not lost the capacity to divide by mitosis.
• Hyperplasia is rather frequent in organs such as the
uterus, where both hyperplasia and hypertrophy
occur during pregnancy.
Dr. Sami Zaqout
IUG
Development of skeletal muscles
• In the embryo muscle fibers develop from
myoblast cells.
• In adults, they develop from satellite cells
present under the sarcolemma.
• Growth of muscles and repair of torn muscles
occur by the proliferation of the satellite cells
which are present under the sarcolemma and
can differentiate into new muscle fibers.
Dr. Sami Zaqout
IUG
Muscle spindles
• All human striated muscles contain
encapsulated proprioceptors
known as muscle spindles.
• These structures consist of a
connective tissue capsule
surrounding a fluid-filled space that
contains a few long thick muscle
fibers and some short thinner
fibers collectively called intrafusal
fibers.
Dr. Sami Zaqout
IUG
Golgi tendon organs
• In tendons, near the insertion sites
of muscle fibers, a connective
tissue sheath encapsulates several
large bundles of collagen fibers that
are continuous with the collagen
fibers that make up the
myotendinous junction.
• These structures, known as Golgi
tendon organs, contribute to
proprioception by detecting
tensional differences in tendons.
Dr. Sami Zaqout
IUG
2. CARDIAC MUSCLE
Dr. Sami Zaqout
IUG
Characteristics of cardiac muscle fibers
• Cardiac cells form complex
junctions between their
extended processes.
• Cells within a chain often branch
and bind to cells in adjacent
chains.
• 15µm in diameter and from 85
to 100µm in length
• They exhibit a cross-striated
banding pattern identical to that
of skeletal muscle.
Dr. Sami Zaqout
IUG
Characteristics of cardiac muscle fibers
• Unlike multinucleated skeletal
muscle each cardiac muscle cell
possesses only one or two
centrally located pale-staining
nuclei.
• Surrounding the muscle cells is
a delicate sheath of endomysial
connective tissue containing a
rich capillary network.
Dr. Sami Zaqout
IUG
Characteristics of cardiac muscle fibers
• Cardiac muscle cells contain
numerous mitochondria, which
occupy 40% or more of the
cytoplasmic volume.
• Fatty acids are stored as
triglycerides in the numerous lipid
droplets seen in cardiac muscle
cells.
• A small amount of glycogen is
present.
• Lipofuscin pigment granules often
seen in long-lived cells, are found
near the nuclear poles of cardiac
muscle cells.
Dr. Sami Zaqout
IUG
Characteristics of cardiac muscle fibers
• Membrane-limited granules are
found at both poles of cardiac
muscle nuclei and in association
with Golgi complexes in this
region.
• These granules are most
abundant in muscle cells of the
right atrium.
• These atrial granules contain
the high-molecular-weight
precursor of a polypeptide
hormone known as atrial
natriuretic factor.
Dr. Sami Zaqout
IUG
Characteristics of cardiac muscle fibers
• Intercalated disks represent
junctional complexes found at
the interface between adjacent
cardiac muscle cells.
• The junctions may appear as
straight lines or may exhibit a
steplike pattern.
• Two regions can be
distinguished in the steplike
junctions:
– Transverse portion
– Lateral portion
Dr. Sami Zaqout
IUG
Intercalated disks
•
There are three main junctional
specializations within the disk.
 Fasciae adherentes
the most prominent membrane
specialization in transverse portions
of the disk.
 Maculae adherentes (desmosomes)
are also present in the transverse
portion and bind the cardiac cells
together
 Gap junctions
On the lateral portions of the disk,
provide ionic continuity between
adjacent cells
Dr. Sami Zaqout
IUG
Sarcoplasmic reticulum & transverse tubule system
• The T tubule system and
sarcoplasmic reticulum are
not as regularly arranged in
the cardiac myocytes.
• Cardiac T tubules are found
at the level of the Z band.
• The sarcoplasmic reticulum
is not as well developed
and wanders irregularly
through the myofilaments.
Dr. Sami Zaqout
IUG
The diads of tubular system
• Triads are not common in cardiac cells, because
the T tubules are generally associated with only
one lateral expansion of sarcoplasmic reticulum
cisternae.
• Thus, heart muscle characteristically possesses
diads composed of:
– One T tubule
– One sarcoplasmic reticulum cisterna.
Dr. Sami Zaqout
IUG
3. SMOOTH MUSCLES
Dr. Sami Zaqout
IUG
Characteristics of smooth muscles
• Smooth muscle is
composed of elongated,
nonstriated cells, each of
which is enclosed by a
basal lamina and a
network of reticular fibers.
Dr. Sami Zaqout
IUG
Characteristics of smooth muscles
• Smooth muscle cells are fusiform.
• They may range in size from 20
µm in small blood vessels to 500
µm in the pregnant uterus.
• Each cell has a single nucleus
located in the center of the
broadest part of the cell.
Dr. Sami Zaqout
IUG
Characteristics of smooth muscles
• The borders of the cell
become scalloped when
smooth muscle contracts,
and the nucleus becomes
folded or has the appearance
of a corkscrew.
• Two types of dense bodies
appear in smooth muscle
cells, both contain α-actinin:
– One is membrane associated
– The other is cytoplasmic.
Dr. Sami Zaqout
IUG
Characteristics of smooth muscles
• Concentrated at the poles
of the nucleus are
mitochondria,
polyribosomes, cisternae of
rough endoplasmic
reticulum, and the Golgi
complex.
• Pinocytotic vesicles are
frequent near the cell
surface.
Dr. Sami Zaqout
IUG
Characteristics of smooth muscles
• A rudimentary sarcoplasmic reticulum is present;
it consists of a closed system of membranes,
similar to the sarcoplasmic reticulum of striated
muscle.
• T tubules are not present in smooth muscle cells.
Dr. Sami Zaqout
IUG
Contraction in smooth muscle cells
• In smooth muscle cells, bundles of myofilaments
crisscross obliquely through the cell, forming a
latticelike network.
• These bundles consist of thin filaments containing
actin and tropomyosin and thick filaments consisting
of myosin.
• Ca2+ in a smooth muscle complexes with calmodulin.
• The Ca2+ - calmodulin complex activates myosin lightchain kinase, the enzyme responsible for the
phosphorylation of myosin.
Dr. Sami Zaqout
IUG
Dr. Sami Zaqout
IUG
Intermediate filaments
• Desmin has been identified as the major
protein of intermediate filaments in all smooth
muscles
• Vimentin is an additional component in
vascular smooth muscle.
Dr. Sami Zaqout
IUG
Sites Of Smooth Muscles
• 1. Digestive system: Muscles in the wall of
the lower third of esophagus, the wall of
stomach, intestine, gall bladder and wall of
salivary and pancreatic ducts.
• 2. Respiratory system: Wall of trachea,
bronchi and bronchioles.
• 3. Urinary system: Wall of ureter, urinary
bladder and urethra.
Dr. Sami Zaqout
IUG
Sites Of Smooth Muscles
• 4 Male genital system: Epididymis, vas
deferens, prostate and penis.
• 5. Female genital system: Fallopian tube,
uterus and vagina.
• 6. All the media (middle part) of blood and
lymph vessels.
• 7. Capsule of glands and spleen, ciliary muscles
and iris of the eye and also in the arrector pili
muscles of the hairy skin.
Dr. Sami Zaqout
IUG
Regeneration of Muscle Tissue
• Cardiac muscle has almost no regenerative capacity
beyond early childhood. Defects or damage in heart
muscle are generally replaced by scars.
• Skeletal muscle the tissue can undergo limited
regeneration. The source of regenerating cells is
believed to be the satellite cells.
• Smooth muscle is capable of an active regenerative
response.
Dr. Sami Zaqout
IUG
Dr. Sami Zaqout
IUG
Dr. Sami Zaqout
IUG