Cardiac Muscles

What Are Cardiac Muscles?

Cardiac muscles are striated muscle fibres existing in the heart only. They are special because they are rhythmically and involuntarily contracting in nature. This is because the primal function is meant for pumping blood throughout the body. Cardiac muscle cells, also known as cardiomyocytes, interdigitate through special structures called intercalated discs, which enable synchronised contractions of the cardiomyocyte to maintain a brisk heartbeat.

Understanding cardiac muscles is important in an attempt to understand how the heart operates and therefore supports and maintains circulation in the body. Research about the physiology of cardiac muscles enables the diagnosis and treatment of many conditions relating to the heart, including arrhythmias, heart attacks, and heart failures. Levels of information regarding cardiac muscle functioning help in the development of treatments and interventions geared at enhancing heart health and the general functionality of the cardiovascular.

Overview Of Cardiac Muscles

Cardiac muscles are explained below-

General Characteristics Of Cardiac Muscles

Cardiac muscles, also the myocardium, are muscle tissues that are unique to the heart. They are characterised by being striated and not under control, with the feature of rhythmical contraction. The cardiac muscles are active without stopping and control by the mind because the force of contraction is provided by intrinsic electrical excitation. They demonstrate intercalated discs with facilities to generate synchronised contractions.

Differences And Similarities Between Cardiac, Skeletal, And Smooth Muscles

Compared to the skeletal muscles, cardiac muscles are striated but are involuntary, unlike the voluntary control of skeletal muscles. They also differ from smooth muscles in being striated and, in contrast to the non-striated smooth muscles controlling involuntary movement of the organs, exist to work continuously and rhythmically for the pumping of blood.

Cardiac muscles assume properties for continuous, regular contractions which are crucial for the pumping of blood, whereas the skeletal muscles have the responsibility of supporting movement and the smooth muscles managing internal processes.

Histology Of Cardiac Muscles

The histology of Cardiac muscles are explained below-

Microscopic Structure

Cardiac muscle cells (cardiomyocytes)

The cardiomyocytes are the basic unit of functional cardiac muscle, they are cylindrical, striated muscle cells, generally with one nucleus. They are connected by intercalated discs which allow transmission of electrical signals so that the heart muscle can contract in unison.

Striations and intercalated discs

The striations in cardiac muscle are due to the arrangement of filaments made of actin and myosin. Intercalated discs are specialised attachments between the ends of cardiomyocytes. They contain gap junctions, through which the action potential conduction is very fast, and desmosomes, which impart mechanical strength.

Types Of Cells In Cardiac Muscle Tissue

Pacemaker cells

Cardiac tissue consists of pacemaker cells and contractile cells. Pacemaker cells occur mainly in the sinoatrial node, the points that generate electric impulses for the sustention of a heartbeat, while the contractile cells are responsible for the mechanical contraction of the heart.

Staining techniques and histological slides

Specific ways of staining are needed for histological studies of cardiac muscle to bring out the different components. Stains like hematoxylin and eosin can identify the striations, nuclei, and intercalated discs. Special stains and electron microscopy will give information about cellular structures and their junctions in detail.

Structure Of Cardiac Muscles

The structure of Cardiac muscles is explained below-

Sarcolemma

The sarcolemma is the membrane of the cell coat, and the sarcoplasm is the cytoplasm, including myofibrils responsible for the cell's contraction. The sarcolemma corresponds to the plasma membrane of cardiomyocytes. It encloses the cell, thus providing the cell with its structure. More importantly, it is responsible for passing action potentials and maintaining the necessary ionic balance for muscle contraction.

Sarcoplasm

Sarcoplasm is the cytoplasm of the cardiomyocyte containing a large number of myofibrils, mitochondria, and other organelles. The nucleus contains the constituents necessary for the processes of muscle contraction and the production of energy, including enzymes and stored glycogen.

Nucleus

Each cardiomyocyte contains one nucleus, which is centrally located. The nucleus controls cellular activities and gene expression necessary for the maintenance of cardiac muscle health and function.

Mitochondria

The number of mitochondria in cardiomyocytes is very great, indicative of the high energy requirements of these cells. Mitochondria are the site of ATP production via aerobic respiration and thus are crucial for maintaining cardiac muscle contraction.

Special Features Of Cardiac Muscle Cells

Intercalated discs

These are specialised junctions between the cardiomyocytes that facilitate the mechanical and electrical coupling of adjacent cells. This ensures contractions are synchronised and therefore efficient.

Gap junctions

Gap junctions in the intercalated discs create a pathway for the rapid movement of electrical impulses from one cell to another which makes it possible to co-ordinate contraction that enables the heart to be an efficient pump.

Desmosomes

Desmosomes were discussed as adhesive structures of the cardiomyocytes. They aid in holding tissues together to withstand the forces during contraction.

Arrangement Of Myofibrils And Sarcomeres

The myofibrils within the cardiomyocyte are further arranged into a sarcomere, and this arrangement is essentially the generic term for the basic contractile unit. This overlapping arrangement between the thick and thin filaments is responsible for the striated appearance and is the very essence of muscle contractility.

Function Of Cardiac Muscles

The function of Cardiac muscles are explained below-

Role In The Circulatory System

Pumping blood

The cardiac muscle contracts and propels blood from the heart's chambers into the arteries. In effect, the process is very crucial in the maintenance of the pressure of blood, hence facilitating circulation effectively.

Maintaining blood pressure

The pressure generated by the force of the cardiac muscle with its multiple contractions maintains the blood pressure within the arterial system, hence enabling the distribution of it to all tissue parts.

The cardiac cells contract starting from impulse conduction by pacemaker cells and, finally, the interaction of actin and myosin filaments by sliding in the sarcomeres.

Mechanism Of Contraction

Excitation-contraction coupling

Excitation-contraction coupling is the process by which the action potential, or electrical excitation, of the heart muscle, leads to its mechanical contraction.

Role of calcium ions

Calcium ions are must-haves for cardiac muscle contraction. They combine with troponin molecules, activators that interact with the actin and myosin filaments. Add to this effect is the sliding over each other of the filaments, hence muscle contraction.

Action potential propagation

Action potentials developed in the sinoatrial node get propagated through the conduction system of the heart—the atrioventricular node, the bundle of His, and the Purkinje fibres. The spread is well-coordinated, and this brings forth a well-synchronized contraction of the heart chambers.

Differences In Contraction Compared To Skeletal And Smooth Muscles

Contractions in cardiac muscle are both involuntary and rhythmic; this is in contrast to the voluntary contractions of skeletal muscles. This property of the cardiac muscles also differs from those of smooth muscle, where contraction and relaxation are sustained with a slower rhythm. The contraction of the cardiac muscles, occurring via the electrical conduction system of the heart, is coordinated for effective pumping.

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