Download Structure of muscles tissues

NAME: ALADE ADETUTU SEFINAT
MATRIC NO: 14/MHS02/008
DEPT: NURSING SCIENCE
LEVEL: 200L
COURSE: HISTOLOGY
MUSCLES TISSUES
Structure of muscles tissues
all muscles tissues have a superficial covering of vary thickness called fascia,
made of connective tissue and laced with adipose tissue inside the facia, the
muscles tissue is surrounded by epimysium and individual muscles bundles or
faciculus are surrounded by perimysium.
There are three types of muscles tissue which can be described from the level of
details of the muscles fibre (muscles cells) through all the other muscles
structures and parts of structures that bind muscles cells together enabling them
to perform their functions. They are:
SKELETAL MUSCLE TISSUE
Structure: A skeletal muscles is called “striated” because of its appearance
consisting of light and dark bands visible using a light microscope. A single cell
skeletal muscle cell is long and approximately cylindrical in shape, with many
nuclei located at the edges (periphery) of the cells.
Functions:
Movement of the skeleton: under conscious control including movement of
limbs, fingers, toes, neck, etc.
Movement of tissue: of facial expression under conscious control, e.g ability to
smile and to frown.
CARDIAC MUSCLE TISSUE
Structure: found in the heart and responsible for contraction of cardiac tissue
and distribution of blood cardiac muscles fibers are striated, branched
(sometimes described as y-shaped), and have single central nucleus. these
fibers are attached at their ends to adjoining fibers by thick plasma membranes
called intercalated discs.
Function
Pumping of blood through the heart: Alternate contraction and relaxation of
cardiac muscle pumps (de-oxygenated blood through the right atrium and right
ventricle to the lungs and oxygenated blood through the left atrium and left
ventricle to the aorta, then the rest of the body)
SMOOTH MUSCLES TISSUE
Structure: unlike skeletal and cardiac muscle tissue, smooth muscles “Is nonstriated, anucleated”, but similar to cardiac tissue relative to functional
spontaneity and long sustained contraction. Smooth muscle fibers are small and
tapered with the ends reducing in size, in contrast to the cylindrical shape of
skeletal muscle. Each smooth muscle fiber has a single centrally located nucleus.
It is found in the lining of blood vessels, urinary bladder, kidneys, esophagus
and small intestines.
FUNCTION
Contraction of smooth muscle constrict (i.e narrow= reduce the diameter of) the
vessels they surround. This is particularly important in the digestive in which the
action of smooth muscles helps to move food along the gastrointestinal tract as
well as breaking the food down further. Smooth muscles also contributes to the
moving fluids through the body and to the elimination of indigestible matter
from the gastrointestinal system.
COMPARISM OF THE 3 TYPES OF MUSCLES TISSUE
LOCATIONS OF
MUSCLE TYPE
Voluntary or
involuntary
Striations
Cell nuclei
SKELETAL
MUSCLE
TISSSUE
Attached to
bones, in the
case of facial
muscles
CARDIAC
MUSCLE
TISSUE
Wall of the
heart
voluntary
involuntary
striated
Many nuclei
(located at the
periphery of long
cylindrical
muscle fiber
striated
one
SMOOTH
MUSCLE TISSUE
Wall of hollow
internal
structure(blood
vessels, stomach,
urinary bladder,
airways to the
lungs, intestines)
involuntary
nonstriated
One( centrally
located) nucleus
BANDS AND LINES
Muscle contraction based on sliding filament hypothesis
The sarcomeres are what give skeletal and cardiac muscles their striated
appearance. [1]
· A sarcomere is defined as the segment between two neighbouring Z-lines
(or Z-discs, or Z bodies). In electron micrographs of cross-striated
muscle, the Z-line (from the German "Zwischenscheibe", the disc in
between the I bands) appears as a series of dark lines.
·
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·
Surrounding the Z-line is the region of the I-band (for isotropic). I-band
is the zone of thin filaments that is not superimposed by thick filaments.
Following the I-band is the A-band (for anisotropic). Named for their
properties under a polarizing microscope. An A-band contains the entire
length of a single thick filament.
Within the A-band is a paler region called the H-zone (from the German
"heller", brighter). Named for their lighter appearance under a polarization
microscope. H-band is the zone of the thick filaments that is not
superimposed by the thin filaments.
Inside the H-zone is a thin M-line (from the German "Mittelscheibe", the
disc in the middle of the sarcomere) formed of cross-connecting elements
of the cytoskeleton.
The relationship between the proteins and the regions of the sarcomere are as
follows:
·
Actin filaments, the thin filaments, are the major component of the I-band
and extend into the A-band.
·
Myosin filaments, the thick filaments, are bipolar and extend throughout
the A-band. They are cross-linked at the centre by the M-band.
·
The giant protein titin (connectin) extends from the Z-line of the
sarcomere, where it binds to the thick filament (myosin) system, to the
M-band, where it is thought to interact with the thick filaments. Titin (and
its splice isoforms) is the biggest single highly elasticated protein found in
nature. It provides binding sites for numerous proteins and is thought to
play an important role as sarcomeric ruler and as blueprint for the
assembly of the sarcomere.
Another giant protein, nebulin, is hypothesised to extend along the thin
filaments and the entire I-Band. Similar to titin, it is thought to act as a
molecular ruler along for thin filament assembly.
Several proteins important for the stability of the sarcomeric structure are
found in the Z-line as well as in the M-band of the sarcomere.
Actin filaments and titin molecules are cross-linked in the Z-disc via the Zline protein alpha-actinin.
The M-band proteins myomesin as well as C-protein crosslink the thick
filament system (myosins) and the M-band part of titin (the elastic
filaments).
The interaction between actin and myosin filaments in the A-band of the
sarcomere is responsible for the muscle contraction (sliding filament
model).[1]
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REFERENCES
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