Download Smooth muscles

ADULOJU IRETIOLUWA M.
14/MHS01/010
MEDICINE AND SURGERY
HISTOLOGY OF THE MUSCLE TISSUE AND ITS TYPES
Muscle tissue is a soft tissue that composes muscle in animal bodies,
and gives rise to muscles’ ability to contract. This is opposed to other
components or tissues in muscle such as tendons or perimysium. It is
formed during embryonic development through a process known as
MYOGENESIS. Muscle tissue varies with function and location in the
body.
In mammals, there are three types. Theyare;
 Skeletal or striated muscle
 Smooth or non-striated muscle
 Cardiac or semi-striated muscle

Skeletal muscles
Contractions move part of the skeleton. Also called voluntary
because usually the contractions are under your control. They
have a stripy appearance, because of the repeating structure of
the muscle; there are many myofibrils (fibers), each one of which
is made up of repeating units called muscle sarcomeres. Each
sarcomeres is 2.5mm long. Connective tissue elements surround
muscle fibers. Individual muscle fibers are surrounded by a
delicate layer of reticular fibers called the endomysium. Groups of
fibers are bundled into fassicles by thicker CT layer called the
perimysium. The collection of fassicles that constitutes one
muscle is surrounded by a sheath of dense CT called the
epimysium, which continues into the tendon. Blood vessels and
nerves are found in the CT associated with muscles. The
endomysium contains only capillaries and the finest neuronal
branches.
Cardiac muscles
They make up the muscular walls of the heart (myocardium). They
are involuntary because their contractions are not under our control.
However, they have a similar ultrastructural organization to skeletal
muscle. So, they also have a stripy appearance because of the repeating
units called muscle sacromeres. Cardiac muscle cells are joined to one
another in a linear array. The boundary between two cells abutting one
another is called an intercalated disc. Intercalated discs consist of
several types of cells junctions whose purpose is to facilitate the
passage of an electrical impulse from cell to cell and to keep the cells
bound together during constant contractile activity.
 Smooth muscles
They are found in the walls of most blood vessels and tubular
organs such as the intestine. They are also involuntary. However,
they do not have a stripy appearance, because they do not have
repeating sarcomeres. The contractile proteins, myosin and actin
are much more randomly arranged than in skeletal or cardiac
muscle. Smooth muscle fibers are generally arranged in bundles
or sheets. Each fiber 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 fiber. Fibers 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 (tapered part of
one fibre over thicker part of another). In longitudinal sections, it
is often not possible to distinguish the fibre boundaries, and
smooth muscle may closely resemble connective tissue (bundles
of collagen). Where smooth muscle bundles are interlaced with
bundles of connective tissue (e.g in the uterus), one can
distinguish the smooth muscle by the orientation of the nuclei (all
oriented in the same direction), and the greater abundance of
nuclei per unit area (every smooth muscle cell has a nucleus,
fibroblast nuclei are more scattered in bundles of CT). Also
smooth muscle nuclei often have a corkscrew shape in
longitudinal section due to contraction of the muscle fibre during
fixation. In cross section, smooth muscle appears as profiles of
various sizes, depending on whether the cut went through the
thick central part or tapered end of any individual fibre. Nuclei are
seen only in the thicker profiles.
One distinguishing physiological feature of smooth muscle is its
ability to secrete connective tissue matrix.
Skeletal and cardiac are also called striated because they have dark and
light bands running across the muscle width when they are looked at
under the microscope.