MUSCULAR
SYSTEM
Muscle cells are specialized contractile cells , also called
fibres.
There 3 types of muscle tissues are
1.
Smooth muscle
2.
Cardiac muscle
3.
Skeletal muscle
SMOOTH MUSCLE :
1.
Smooth muscle (involuntary or non-straited )
muscle is not under conscious control .
2.
The cells are small , have one nucleus and are
spindle shaped .
3.
Smooth muscle forms sheets in the walls of
hollow organs and tubular structures to regulate diameter and propel substances
through tracts.
4.
Some smooth muscle units have the ability to
initiate their own contraction independently of nerve stimulation , cardiac
muscle has this property too.
]me hormones and local metabolites may influence
contraction. E.g Adrenaline (epinephrine ) from the adrenal medulla dialates
the airways.
5.
Smooth muscle do not exhibit cross-striations
under microscope,being plan and smooth in form and their uniform appearance
when viwed under a microscope has led to the term smooth muscle which is in contrast with striated
appearance of skeletal and cardiac muscles.
6.
They are supplied by autonomic nerves and
therefore, are not under voluntary control and respond slowly to stimuli.
therefore, are not under voluntary control and respond slowly to stimuli.
7.
They provide motor power for regulating the
internal environment related to digestion, circulation, secretion and excretion.
8.
Smooth muscles are less dependent on nervous
control, being capable of contracting automatically, spontaneously ,and often
rhythmically and each muscle fibre is an elongated, spindle-shaped cell,with a
single nucleus placed centrally; the myofibrils show longitudinal striations.
9.
Muscles of the blood vessels, and the arrector
pili or erector pili muscles of the skin are examples of smooth muscles.
CARDIAC MUSCLE :
1.
This type of muscles are found in the heart.
2.
It is intermediate in structure, being striated
and at the same time involuntary.
3.
It is meant for automatic and rhythmic –contractions
and each muscle fiber.
4.
These fibers have a single nucleus placed
centrally which branches and anastomoses with the neighboring fibers at
intercalated discs.
5.
The cross- strations are less prominent than
those in the skeletal muscle.
6.
These muscles are found only in the heart and
are responsible for pumping blood .
7.
Cardiac muscle are also called as “involuntary
muscles”.
8.
Cardiac muscle is unique as it stimulates itself
to contract by virtue of pacemaker which is also made of cardiac muscle tissue.
9.
The cells of cardiac muscle tissue are striated –that
is , they appear to have light and dark stripes when viwed under a light
microscope, the arrangement of protein fibres inside of the cells causes these
light and dark bands. Striations indicate that a muscle cell is very strong,
unlike visceral muscles.
10.
The cells of cardiac muscle are branched X or Y
shaped cells tightly connected together by fingerlike projections from two
neighboring cells (intercalated discs) that interlock and provide a strong bond
between the cells.
11.
The branched structure and intercalated discs
allow the muscle cells to resist high blood pressures and strain continuous working.
This features also help to spread electrochemical signala quickly from cell to
cell so that the heart can beat as a unit.
SKELETAL
MUSCLES:
1.
Skeletal muscles are type of muscle which are
most abundant and are found attached to skeleton. They are also called as
Striped, striated, somatic or voluntary muscles.
2.
They exhibit cross-striations under microscope,
and are considered to be best differentiated form of muscle.
3.
They are supplied by somatic (cerebrospinal)
nerves and therefore are under voluntary control ,with certain exceptions.
4.
They respond quickly to stimuli, being capable
of rapid contractions, and help in adjusting the individual to
external environment. They also get fatigued very easily.
5.
Each muscle
fibre of skeletal muscle is a multinucleated cylindrical cell, containing
groups of myofibrils. Myofibrils are made up of myofilaments of three types (myosin,actin
and tropomysin). These are the actual contractile elements of the muscle.
6.
Sleletal muscle are under highest nervous
control of cerebral cortex.
7.
Examples of these types of muscles are muscles
of limbs and body wall,and bronchial muscles are examples of skeletal.
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