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NAME-ADIGHIJE CLAUDIA CHISOM
COURSE-HISTOLOGY OF BASIC TISSUES
COURSE CODE-ANA 203
DEPARTMENT- PHYSIOLOGY
DIRECT ENTRY
TOPIC-HISTOLOGY OF THE MUSCLE AS A TISSUE
THE MUSCLE
The muscle is a contractile form of tissue which organisms use to
effect movement. It is composed of cells that are differentiated for
the optimal use of the universal cell property called contractility.
Microfilaments and associated proteins together generate the
forces necessary for cellular contraction, which drives movement
within certain organs and body as a whole. Almost all muscle cells
are of mesodermal origin and they differentiate mainly by a
gradual process of cell lengthening with simultaneous synthesis of
myofibrillar proteins.
MUSCLE FUNCTIONS
1) Contraction for locomotion and skeletal movement
2) Contraction for propulsion
3) Contraction for pressure regulation
Muscles can however be classified based on structure and
based on functions. There are two types of muscles based on
structure and they are
1) Striated muscle- Here, the muscle tissue in which the
contractile fibrils in the cells are aligned in parallel
bundles, so that their different regions form stripes visible
in a microscope. Muscles of this type are attached to the
skeletons by tendons and are under voluntary controls.
They are usually the skeletal muscles because it is
attached mainly to the bones and skin and it is responsible
for the mobility of the body and limbs. Striated muscles
are dense and fibrous tissues whose primarily function is
to allow the body to move by repeated contraction and
relaxation.
2) UNSTRIATED MUSCLE
This is a smooth thin and muscle that is not controlled
voluntarily. It is a muscle tissue that contracts without
conscious control, having the form of thin layers or sheets
made up of spindle shaped, unstriated cells with single
nuclei and found in the walls of the internal organs, such
as the stomach,intestine,bladder,and blood vessels,
excluding the heart.
The two classifications of muscles based on functions are
1) Voluntary muscles- This is a muscle whose action is
normally controlled by an individual’s will; mainly
skeletal muscle composed of parallel bundles of
striated muscles except the heart, whose action is
normally controlled by individual volition.
2) Involuntary muscles- This is a muscle that contract
without conscious control and found in walls of internal
organs such as stomach and intestine and bladder and
blood vessels excluding the heart.
TYPES OF MUSCLES
There are mainly three mainly three types of muscles;
1) SMOOTH MUSCLES
Smooth muscle is the intrinsic muscle of the
internal organs and blood vessels. It is also found in the
iris and ciliary body of the eye and associated with hair
follicles. No striations are present in smooth muscle
due to the different arrangement of actin and myosin
filaments. Smooth muscles are intrinsically contractile
but responsive to autonomic and hormonal stimuli.
They are specialized for slow and prolonged
contraction.
PROPERTIES OF SMOOTH MUSCLES
Smooth muscle fibres are generally arranged in bundles
and sheets. Each fibre is fusiform in shape with a
thicker central portion and tapered at both ends. The
single nucleus is located in the central part of the fibre.
Its fibres do not branch. They range enormously in size
from 20 (in wall of small blood vessels) to 500 (in wall
of uterus during pregnancy) micrometers. Smooth
muscle fibres lie over one another in a staggered
fashion.
SKELETAL MUSCLE
Skeletal muscle constitutes the muscle that is attached
to the skeleton and controls motor movement and
posture. There are a few instances where this type of
muscle is restricted i.e. soft tissues like the tongue,
pharynx, diaphragm and the upper part of the
oesophagus. Skeletal muscle fibre cells are actually a
multinucleated syncytium formed by the fusion of
individual small muscle cells or myoblasts, during
development. They are filled with longitudinally
arrayed subunits called myofibrils. The myofibrils are
made up of the myofilaments myosin and actin. Skeletal
muscle fibres however bear obvious striations, have
many peripherally located nuclei, are of the same
thickness throughout their length and do not branch.
CARDIAC MUSCLE
The cardiac muscle is a type of muscle found in the
heart, and at the base of the venae cava as they enter
into the heart. Cardiac muscle is intrinsically contractile
but is regulated by autonomic and hormonal stimuli.
They exhibit striations because it also has myosin and
actin filaments arranged into sarcomeres.Generally,
these striations do not appear as well defined as in
skeletal muscles. Cardiac muscle cells however have
only one or two nuclei which are centrally located.
These muscle cells are joined together in a linear array,
therefore they branch and anastomose with other
fibres and they are also joined together by intercalated
discs .