Download NAME: SAFIA BELLO MIKAILU MATRIC NO: 14/MHS01/035

NAME: SAFIA BELLO MIKAILU
MATRIC NO: 14/MHS01/035
DEPARTMENT: MEDICINE AND HEALTH SCIENCES
THE HISTOLOGY OF MUSCLE AS A TISSUE
The muscle or rather muscle tissue is composed of cells that are highly specialized to
shorten in length by contractility. This muscle tissue is made of cells that are called
myocytes. These myocytes are specialized for contraction with apparatus of actin and
myosin proteins. Elongated in one direction are the muscle fibers. These muscles function
in: contraction for locomotion and skeletal movement, for propulsion and for pressure
regulation. Morphologically, muscle tissues are of two (2) types: (i) striated (ii) non-striated.
Functionally, there are also two (2) types of muscle tissue; (i) voluntary (ii) involuntary.
Histologically, the muscle tissue is of three (3) types: (i) skeletal muscle (ii) cardiac muscle
(iii) smooth muscle.
However, the skeletal muscle is a striated and voluntary muscle, present mainly in
limbs and in relation to body wall. It is formed by fusion of multiple myoblasts during
embryonic life and mostly originates from somatic mesoderm. The basic unit of the skeletal
muscle is long, cylindrical fiber. Microscopically, the skeletal muscle fibers are arranged
parallel to each other having alternate dark and light bands (cross striations). The skeletal
muscle is multinucleated, placed peripherally beneath the sarcolemma. It has the myofibrils
as the contractile elements and the sarcomere as its fundamental contractile unit. The
myofilaments contain thick myosin and actin filaments. Each thick filament of this skeletal
muscle is surrounded by six (6) thin filaments in hexagonal fashion. It has accessory proteins
necessary for proper contraction: titin, alpha, actinin, nebulin, tropomodulin, dystrophin.
The motor fibbers and the sensory fibbers are the nerve supply to the skeletal muscle.
Sensitive stretch receptors called neuromuscular spindles are present within nearly all
skeletal muscles. These spindles consist of a connective tissue capsule, in which are found
modified muscle fibers called intrafusal fibers and numerous nerve endings, surrounded by
a fluid-filled space. The neuromuscular spindles monitor the changes (distension) in the
muscle lengths and activate complex reflexes to regulate muscle activity. Skeletal muscle is
surrounded by a dense, irregular connective tissue layer called epimysium.From epimysium,
a less dense irregular connective tissue layer, called perimysium, extends inward and
divides the interior of the muscle into smaller bundles called fascicles; each fascicle is thus
surrounded by perimysium. A thin layer of reticular connective tissue fibers, called
endomysium, invests individual skeletal muscle fibers. An illustration of the skeletal muscle
is shown below.
More so, the cardiac muscle is striated and involuntary, present exclusively in the
heart. It originates in the splanchnopleuric mesoderm. The cardiac muscle is supplied by the
autonomic nervous system. Microscopically, the cardiac muscle consists of long and thick
branching muscle fibers which may appear as Y shaped. It also consists of centrally placed
single oval nucleus, faint transverse striations and also A and I bands along with Z discs
present. The terminal ends of adjacent cardiac muscle fibers show characteristic and densestaining, end-to-end junctional complexes called intercalated disks. These disks are special
attachment sites that cross the cardiac cells at irregular intervals in step like fashion.
Located in the intercalated disks are the gap junctions that enable ionic communication and
continuity between adjacent cardiac muscle fibbers. An illustration of the cardiac muscle is
shown below.
Furthermore, the smooth muscles have a wide distribution and are found in
numerous hollow organs; gastro-intestinal walls, blood vessels, urinary bladder, ureter,
uterine tube, arrector pili muscle of hair follicles, etc. Smooth muscle fibers also contain
contractile actin and myosin filaments; however, they are not arranged in the regular, crossstriated patterns that are visible in both the skeletal and cardiac muscle fibers. As a result,
these muscle fibers appear smooth or non-striated. Smooth muscle fibers are also
involuntary muscles and are, therefore, under autonomic nervous system and hormonal
control. Microscopically, smooth muscle consists of elongated spindle shaped fibers,
centrally placed single elongated nucleus. Its adjacent cells are in contact with each other
through gap junctions. As shown below;
REFERENCES:
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