Download muscle_histology-1_1

NAME: OSEYI FAVOUR OSE
DEPT: NURSING SCIENCE
MATRIC NO: 14/MHS02/048
COURSE: HISTOLOGY
THE HISTOLOGY OF MUSCLE TISSUES AND TYPES.
THE MUSCLE
Motion as a reaction of multicellular organisms to changes in the internal and external enviroment,
is mediated by muscle cells.
The basis for motion mediated by muscle cells is the conversion of ATP into mechanical energy by
the contractile apparatus of muscle cells. The proteins action and myosin are part of the contractile
apparatus. The interaction of these two proteins mediates the contraction of muscles cells. Actin
and myosin filaments, each composed of many action and myosin molecules form myofibrils
arranged parallel to the direction of cellular contraction.
Three structurally and functionally distinct types of muscles are found in vertebrates:
1..smooth muscle
2..skeletal muscle
3..cardiac muscle
SMOOTH MUSCLE
* They consist of spindle shaped cells of variable size.
* They contain cells of one centrally placed nucleus
* Innervation of smooth muscle is provided by the autonomic nervous system.
* They make up the visceral or involuntary muscle
STRUCTURE
In cytoplasm, we find longitudinally oriented bundles of the myofilaments actin and
myosin.Action filaments insert into the attachment plaques located on the cytoplasmic surface of
the plasma membrane. From here they extend into the cytoplasm and interact with myosin
filaments. The myosin filaments interact with a second set of actin filaments which insert into
intracytoplasmatic dense bodies. From these dense bodies further actin filaments extend to interact
with yet another set of myosin filaments. This sequence is repeated until the last actin filaments of
the bundle again insert into attachment plaques.
ORIGIN
Smooth muscle cells arise from undifferentiated mesenchymal cells. These cells differentiate first
into mitotically active cells, myoblasts, which contain a few myofilaments. Myoblasts give rise to
the cells which will differentiate into mature smooth muscle cells.
TYPES
1..The multi unit
type
represents functionally independent smooth muscle cells which are often innervated by a single
nerve terminal and which never contract spontaneously (e.g smooth muscle in the walls of blood
vessels.
2..The visceral type represents bundles of smooth muscle cells connected by GAP junctions,
which contract spontaneously if stretched beyond a certain limit(e.g in the walls of the intestines.
THE SKELETAL MUSCLE
© They consist of very long tubular cells,which are called muscle fibres.
© The fibres contain many peripherally placed nuclei.
© The fibres show in many preparations characteristic cross-striations.
© They are innervated by the somatic nervous system.
© They make up the voluntary muscles.
STRUCTURE
Muscle fibres in skelatal muscle occur in bundles,fascicles, which make up the muscle. The
muscle is surrounded by a layer of connective tissue,the epimysium, which is continuous with the
muscle fascia. Connective tissue from the epimysium extends into the muscle to surround
individual fasicles (perimysium). A delicate network of loose connective tissue composed of fine
(endomysium) is found between the muscle fibres of a fascicle. Finally, each muscle fibre is
surrounded by a basement membrane.
ORIGIN
The myoblast of all skeletal muscle fibres originate from the paraxial mesoderm. Myolasts
undergo frequent divisions and coalesce with the formation of a multinucleated,syncytical muscle
fibre or myotube. The nuclei of the myotube are still located centrally in the muscle fibre. In the
course of the nuclei are gradually displaced to the periphery of the cell.
TYPES
Fibre types are determined by the pattern of stimulation of the fibre,which,in turn,is determined by
the type of neuron which innervates the muscle. The types are:
#Type I fibres (red fibres)
Red muscles contain predominantly red muscles cells. Red muscle fibres are comparatively thin
and contain large amounts of myoglobin and mitochondria. Red fibres contain an isoform of
myosin with low ATPase activity. Contraction is slow and are used when sustained production of
force is necessary e.g in the control of posture.
Type II fibres
White muscles cells, which are predominantly found in white muscles ,are thicker and contain less
myoglobin. ATPase activity of the myosin isoform in white fibres is high, and contraction fast.
Type IIA fibres(red) contain many mitochondria and are available for both sustained activity and
short-lasting, intense contractions .
CARDIAC MUSCLE
®Here the myocardium, consists of muscle cells,cardiomyocytes ,with one centrally placed
nucleus.
®Their cells exhibit cross-striations.
®The cells excitation is mediated by rhythmically active modified cardiac muscle cells.
®It is innervated by the autonomic nervous system ,which adjusts the force.
®They are also called involuntary striated muscles .
STRUCTURE
The ultrastructure of the contractile appaaratus and the mechanism of contraction largely
correspond to that seen in skeletal muscle cells. Although equal in ultrastructure to skeletal
muscle , the cross-striations in cardiac muscle are less distinct, in part because rows of
mitochondria and many lipid and glycogen droplets are found between myofibrils.
THE
BAND
S AND
LINES OF THE MUSCLE
SACROMERE
A sacromere is the basic unit of striated muscle tissue. Skeletal muscles are composed of tubular
muscle cells(myocytes called muscle fibers) which are formed by a process known as myogenesis.
Muscle fibres are composed of tubular myofibrils. Sacromeres are composed of long, fibrous
proteins as filaments that slide past each other when a muscle contracts or relaxes.
Two important proteins are myosin and actin.
Myosin: long, fibrous tail and a globular head which binds to actin and ATP also.
Actin: are bound to z-line, which forms the borders of the sacromere.
** A sacromere is defined as the segment between two Z-lines(which appears as a series of dark
lines
** Surrounding the Z-line is the region of the I -band(for isotropic). It is the zone of thin filaments
that is not superimposed by thick filaments.
** Following the I-band is the A-band(for anisotropic). An A-band contains the entire length of a
single thick filament.
** Within the A-band is a paler region called the H-zone.H-band is the zone of thick filaments that
is not superimposed by thin filaments.
** inside the H-zone is a thin M-line formed of cross connecting elements of the cytoskeleton.
THE
RELATIONSHIP BETWEEN PROTEINS AND THE REGIONS OF THE SACROMERE
Actin filaments, the filaments are the major components 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 extends from the Z-line of the sacromere, where it binds to the thick filament
system, to the M-band where it is thought to interact with the thick filaments.
.