Download Cardiac muscle

NAME: ADEBAYO OLUWABUKUNMI
MATRIC NO: 14/MHS02/001
DEPARTMENT: MEDICINE AND SURGERY.
Assignment: Write an essay on muscle as a tissue and state its types.
ANSWERS
Muscle
Muscle is a soft tissue that composes muscles 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 the
three types are: skeletal or striated muscle; smooth or non-striated muscle; and
cardiac muscle, which is sometimes known as semi-striated. Smooth and
cardiac muscle contracts involuntarily, without conscious intervention. These
muscle types may be activated both through interaction of the central nervous
system as well as by receiving innervation from peripheral plexus or endocrine
(hormonal) activation. Striated or skeletal muscle only contracts voluntarily,
upon influence of the central nervous system. Reflexes are a form of nonconscious activation of skeletal muscles, but nonetheless arise through
activation of the central nervous system, albeit not engaging cortical structures
until after the contraction has occurred.
The different muscle types vary in their response to neurotransmitters and
endocrine substances such as acetyl-choline, noradrenalin, adrenalin, nitric
oxide and among others depending on muscle type and the exact location of the
muscle.
Muscle tissue has a ability to relax and contrast and so bring about movement
and mechanical work in various parts of the body. There are other movements
in the body too which are necessary for the survival of the organism such as the
heart beat and the movements of the alimentary canal.
There are different types of muscle. We have the skeletal muscle, cardiac
muscle and smooth muscle.
Smooth muscle
This is a muscle tissue that lacks cross striations, that is made up of elongated
spindle-shaped cells having a central nucleus, and that is found especially in
vertebrate hollow organs and structures (as the small intestine and bladder) as
thin sheets performing functions not subject to direct voluntary control. It is also
called an unstraited muscle and sometimes called an involuntary muscle due to
its inability to control its movements. Smooth muscle is found in the walls of
hollow organs such as the Stomach, Esophagus, and Bronchi and in the walls of
blood vessels. This muscle type is stimulated by involuntary neurogenic
impulses and has slow, rhythmical contractions used in controlling internal
organs, for example, moving food along the Esophagus (Peristalsis) or
constricting blood vessels during Vasoconstriction. The function of smooth
muscle includes:
(a) It controls slow and involuntary movements such as the contraction of the
smooth muscle in the walls of the stomach and intestine.
(b) The muscles of the arteries contracts and relaxes to regulate the blood
pressure and the flow of blood.
DIAGRAM
Skeletal muscle
Skeletal muscle is that which is usually attached to bones and have their main
function of contracting to facilitate the movement of our skeletons and is also
the most abundant muscle. They are also known as striated muscles and a
voluntary muscle due to its appearance and man ability to control its movement
through nervous impulses from our brains sending messages to the brain. This
muscle has the ability to contract and still return to their original shape, they
contain bands of actin and myosin which forms the sacromere found within the
myofibrils which causes their stripy appearance. The whole muscle, such as the
biceps, is enclosed in a sheath of connective tissue, the epimysium. This sheath
folds inwards into the substance of the muscle to surround a large number of
smaller bundles, the fasciculi. These fasciculi consist of still smaller bundles of
elongated, cylindrical muscle cells, the fibres. Each fibre is a syncytium, i.e. a
cell that have many nuclei. The nuclei are oval in shaped and are found at the
periphery of the cell, just beneath the thin, elastic membrane (sarcolemma). The
sarcoplasm also has many alternating light and dark bands, giving the fibre a
striped or striated appearance (hence the name striated muscle). With the aid of
an electron microscope it can be seen that each muscle fibre is made up of many
smaller units, the myofibrils. Each myofibril consists of small protein filaments,
known as actin and myosin filaments. The myosin filaments are slightly thicker
and make up the dark band (or A-band). The actin filaments make up the light
bands (I-bands) which are situated on either side of the dark band. The actin
filaments are attached to the Z-line. This arrangement of actin and myosin
filaments is known as a sacromere
During the contraction of skeletal muscle tissue, the actin filaments slide
inwards between the myosin filaments. Mitochondria provide the energy for this
to take place. This action causes a shortening of the sacromeres (Z-lines move
closer together), which in turn causes the whole muscle fibre to contract. This
can bring about a shortening of the entire muscle such as the biceps, depending
on the number of muscles fibres that were stimulated. The contraction of
skeletal muscle tissue is very quick and forceful. The function of skeletal
muscle includes:
(a) Skeletal muscle helps to bring about the co-ordinate movements of the
limbs, trunk, jaws, eyeballs, etc.
(b) It also helps in the breathing process.
DIAGRAM
Medical application
 Myasthenia gravis is an autoimmune disorder characterized by
progressive muscular weakness caused by a reduction in the number of
functionally active
acetylcholine receptors in the sarcolemma of the myoneural junction. This
reduction is caused by circulating antibodies that bind to the acetylcholine
Receptors in the junctional folds and inhibit normal nerve-muscle
communication. As the body attempts to correct the condition, membrane
segments with
Affected receptors are internalized, digested by lysosomes, and replaced by
newly formed receptors. These receptors, however, are again made
unresponsive to acetylcholine by similar antibodies, and the disease follows its
progressive course
 The variation in diameter of skeletal muscle fibers depends on factors
such as the specific muscle and the age and sex, state of nutrition, and
physical
training of the individual. It is a common observation that exercise enlarges the
musculature and decreases fat depots. The increase in muscle thus
obtained is caused by formation of new myofibrils and a pronounced growth in
the diameter of individual muscle fibers. This process, characterized by
increased of cell volume, is called hypertrophy. Tissue growth by an increase in
the number of cells is termed hyperplasia, which takes place most readily in
smooth muscle, whose cells have not lost the capacity to divide by mitosis.
Cardiac muscle
This type of muscle is found solely in the walls of the heart. It has similarities
with skeletal muscles in that it is striated and with smooth muscles in that its
contractions are not under conscious control. However this type of muscle is
highly specialized. It is under the control of the autonomic nervous system,
however, even without a nervous impute contractions can occur due to cells
called pacemaker cells. Cardiac muscle is highly resistant to fatigue due to the
presence of a large number of mitochondria, myoglobin and a good blood
supply allowing continuous aerobic metabolism. (Myocardium), found only in
the heart, is a striated muscle similar in structure to skeletal muscle but not
subject to voluntary control.
Cardiac and skeletal muscles are "striated" in that they contain sacromere and
are packed into highly regular arrangements of bundles; smooth muscle has
neither. While skeletal muscles are arranged in regular, parallel bundles, cardiac
muscle connects at branching, irregular angles (called intercalated). Striated
muscle contracts and relaxes in short, intense bursts, whereas smooth muscle
sustains longer or even near-permanent contractions. This is a unique tissue
found only in the walls of the heart. Cardiac (Heart) Muscle Tissue shows some
of the characteristics of smooth muscle and some of skeletal muscle tissue. Its
fibres , like those of skeletal muscle, have cross-striations and contain numerous
nuclei. However, like smooth muscle tissue, it is involuntary. Cardiac muscle
differ from striated muscle in the following aspects: they are shorter, the
striations are not so obvious, the sarcolemma is thinner and not clearly
discernible, there is only one nucleus present in the centre of each cardiac fibre
and adjacent fibres branch but are linked to each other by so-called muscle
bridges. The spaces between different fibres are filled with areolar connective
tissue which contains blood capillaries to supply the tissue with the oxygen and
nutrients. Function of cardiac muscle:
(a) Cardiac muscle tissue plays the most important role in the contraction
of the atria and ventricles of the heart
(b) It causes the rhythmical beating of the heart, circulating the blood and
its contents throughout the body as a consequence.
DIAGRAM