muscle tissue department of histology and embryology medical college in three gorges university
TRANSCRIPT
Muscle tissue
Department of Histology and Embryology Medical college in Three Gorges University
• Muscle tissue can be divided into three
types:
Skeletal muscle
Cardiac muscle
Smooth muscle
Skeletal muscles
• Skeletal muscle is composed of
extremely elongated, multinucleate
contractile cells, often described as
muscle fibres, bound together by
collagenous supporting tissue.
• The connective tissue associated with muscle is named according to its relationship with muscle fiber:
endomysium
perimysium
epimysium
• Endomysium the delicate layer of
reticular fibers that immediately
surrounds individual muscle fibers.
picture
• Perimysium is a thicker connective tissue
layer that surrounds a group of fibers to form a
bundle or fascicle.Fascicles are functional
units of muscle fibers that tend to work
together to perform a specific function.
• Epimysium is a thicker layer connective
tissue which invested the whole muscle
mass, large blood vessels and nerves enter
the epimysium and divide to ramify
throughout the muscle in the perimysium
and endomysium.
17 18
perimycium
endomycium
The histological features of skeletal
muscle fibres in longitudinal section:
1) extremely elongated, unbranched
cylindrical cells
2) with regular cross-striations
3) numerous flattened nuclei located at
fairly regular intervals just beneath the
sarcolemma (plasma membrane)..
the cross-striations result from the
arrangement of the contractile proteins.
Cross striation means alternating light and
dark bands in the longitudinal sectioned
skeletal muscle.
Tran
sverse section
perimycium
endomycium
This micrograph of skeletal muscle cut
in transverse section shows the extreme
peripheral location of the nuclei of
skeletal muscle fibres. In cross-section
muscle fibres appear polyhedral with
flattening of adjacent cells.The cell is
spherical, polyhedral or irregular shape.
Tran
sverse section
Myofibrils
Connective tissue
• Sarcomere : the part of a myofibril situated
between two consecutive Z-band is called
a sarcomere. Each of them is composed of
I ½+ A band + I ½. It is the stuacture and
function unit of myofibrils
• The sarcomere consists of two types of myofilaments, thick filaments and thin filaments.
Why do the myofibril display cross striation?
Myofilaments
Thick filaments
Thin filaments
• Each type remains constant in length
irrespective of the state of contraction of the
muscle. The thick filaments, which are
composed mainly of the protein myosin, are
maintained in register by their attachment to
a disc-like zone represented by the M line.
• Similarly the thin filaments, which are
composed mainly of the protein actin, are
attached to a disc-like zone represented by
the Z line. The I and H bands, both areas of
low electron density, represent areas where
the thick and thin filaments do not overlap
one another.
light band dark band
Z 线
H
M
肌节: 1/2I 带 + A 带 + 1/2I 带
Thick filaments Thin filaments
sacomere
Thick filaments: Myocin
Thin filaments: actin, tropomyosin and troponin
Thick filaments
Thin filaments
Myocin
actin , tropomyocin , troponin
• Transverse tubules :
These fingerlike invaginations of the sarcolemma form a complex anastomosing network of tubules that encircle the boundaries of the A-I bands of each sarcomere in every myofibrils.
Function: rapidly conduct impulse for contraction to every myofibrils in the muscle fiber.
Sarcoplasmic R
Transverse tubules
Triad Terminal cisterna
Sarcoplasmic reticulum:
• Sarcoplasmic reticulum is a specialized smooth endoplasmic reticulum. It forms extensive anastomosing network which runs between and around the myofibrils in a longitudinal direction. Adjacent to opposite sides of each T tubule are expanded terminal cisternae of the sarcoplasmic reticulum
• Triad:
• This specialized complex consist of a T
tubule with 2 lateral terminal cisternae of
sarcoplasmic reticulum is known as the
triad.
Cardiac muscle
• Cardiac muscle fibers are essentially short
cylindrical cells with one or at most two
nuclei, centrally located within the cell. The
ends of the fibers are split longitudinally
into a small number of branches.
Intercalated disc
disc
• Micrograph illustrates an extremely thin resin-embedded section at very high magnification. The branching cytoplasmic network is readily seen with prominent intercalated discs marking the intercellular boundaries. Note the typical cross-striations.
• Summing: Feature of cardiac muscle in LM
• 1. short cylindrical ,one or two nuclei, located
in the center of the cardiac muscle.
• 2. cross-striations of cardiac muscle , are not
very clear than that of the skeletal.
• 3.Intercalated disc闰盘 ,
• it is dark-staining transverse line that
cross the chains of cardiac muscle.
located between the ends of adjacent
cardiac muscle cells,which can cause the
adjacent cells to contract almost
simultaneously.
Feature of cardiac muscle in EM
• 1. myofibrils is less than that of SM
• 2. Tranverse tubules is thick
• 3. Sarcoplasmic reticulum is less
• 4. terminal cisternae is small,
• 5. mitochondria is aboundant
Mitochondria
Sarcoplasmic reticulum
Intercalated disc
desmosome
SR Terminal cisternaeT tubulesdyad
Triad
Sarcoplasmic R
T C
T tubules
dyad
Smooth muscle
• Smooth muscle is involuntary and
unstriated. They are often seen as
individual fibers or slender bundles or
fascicles, however they are predominantly
found lining the visceral organ and blood
vessels.
• Smooth muscle fibers are elongated, spindle-
shaped cells with tapered ends which may
occasionally be bifurcated. Smooth muscle fibers
are generally much shorter than skeletal muscle
fibers and contain only one nucleus which is
elongated and centrally located in the cytoplasm
at the widest part of the cell.
• Smooth muscle fibres are bound together in
irregular, branching fasciculi.Within the
fasciculi, individual muscle fibres are
arranged roughly parallel to one another
with the thickest part of one cell lying
against the thin parts of adjacent cells.
• The contractile proteins of smooth muscle
are not arranged in myofibrils as in skeletal
and cardiac muscle, and thus visceral
muscle cells are not striated.
•This micrograph illustrates smooth muscle cut in longitudinal section. At this magnification, the micrograph demonstrates the spindle-shaped and elongated central nuclei of smooth muscle cells.
• In this case, the fibres are arranged in a highly regular manner and packed so closely that it is difficult to identify individual cell outlines although cell shape can be deduced from that of the nuclei.