Logan Steele
The human body is composed of three major categories of muscles: smooth muscle, skeletal muscle, and cardiac muscle. Unlike skeletal muscle, which is consciously controlled by the somatic nervous system, cardiac muscle is under involuntary control. This means that the contraction of the cardiac muscle occurs without conscious awareness. This automaticity enables the heart to pump blood constantly and efficiently without requiring conscious thought.
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What You'll Learn
- Cardiac muscle is not under voluntary control
- The heart's pacemaker, the sinoatrial node, regulates its rhythmic contractions
- Cardiac muscle cells form a network in the heart
- Electrical properties of cardiac muscle cells affect the rate of heart contractions
- Cardiac muscle is striated, like skeletal muscle
Cardiac muscle is not under voluntary control
Cardiac muscle, found in the walls of the heart, is not under voluntary control. Unlike skeletal muscles, which are attached to the bones and allow us to perform movements like walking, running and jumping, cardiac muscle contracts involuntarily. This means that we have no conscious control over when it contracts and relaxes.
The somatic nervous system controls skeletal muscles, allowing us to consciously decide when to contract and relax them. This is what enables us to perform a wide range of functions and activities. Skeletal muscles are also known as striated muscles due to their striped appearance. Cardiac muscle is also striated, but this does not mean it is under voluntary control.
Cardiac muscle is under the control of the autonomic nervous system, which manages involuntary body functions. This includes vital processes such as heart rate, digestion and blood flow. The autonomic nervous system has two branches: the sympathetic and parasympathetic nervous systems. These branches coordinate different aspects of involuntary muscle activities, ensuring that critical operations occur without conscious input.
The involuntary nature of cardiac muscle is essential for maintaining an efficient and constant heartbeat throughout our lives. If the cardiac muscle were under voluntary control, we would have to consciously think about every heartbeat for the heart to pump blood efficiently around the body. Instead, the autonomic nervous system controls the continuous and rhythmic contractions of the cardiac muscle, allowing it to function without our conscious effort.
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The heart's pacemaker, the sinoatrial node, regulates its rhythmic contractions
Unlike skeletal muscle, cardiac muscle is not under voluntary control. Instead, the cardiac conduction system sends signals to the heart, telling it when to beat. The cardiac conduction system contains specialised cells and nodes that control the heartbeat, including the sinoatrial node (SA node), which acts as the heart's pacemaker.
The SA node is a small mass of specialised tissue located in the upper right chamber (atrium) of the heart. It is about 15mm long and 4mm wide, and it generates electrical impulses that set the rhythm and rate of the heart. The SA node is the heart's natural pacemaker, and it continuously generates electrical impulses, setting a healthy heart's normal rhythm and rate.
The SA node creates an excitation signal, which is an electrical signal that travels through the conduction pathway of the heart. This signal tells the different parts of the heart to relax and contract, controlling blood flow through the heart and to the rest of the body. The rate at which the heart contracts and the synchronization of atrial and ventricular contraction are dependent on the electrical properties of the cardiac muscle cells and the conduction of electrical information from one region of the heart to another.
The SA node is controlled by the autonomic nervous system, which influences the heart rate by regulating the firing of the sinus node to initiate the start of subsequent cardiac cycles. Parasympathetic input slows down the rate of action potential production, decreasing the heart rate, while sympathetic input increases the rate of action potential production, increasing the heart rate. This tight, regulated control of the sinus node allows the heart to adapt to various physiologic stressors placed on the body.
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Cardiac muscle cells form a network in the heart
Cardiac muscle cells, also known as myocardium, form a network in the heart. This network is composed of individual cardiac muscle cells joined by intercalated discs, creating long fibres. Each cell contains myofibrils, specialised protein contractile fibres of actin and myosin that slide past each other during contraction. This sliding filament theory forms the basis of muscle contraction, with actin and myosin forming cross-bridges to facilitate the process.
Cardiac muscle cells are unique in their ability to initiate electrical potentials at a fixed rate, spreading rapidly from cell to cell and triggering the contractile mechanism. This property, known as autorhythmicity, distinguishes cardiac muscle from smooth and skeletal muscle. The electrical stimulation in the form of a cardiac action potential triggers the release of calcium from the sarcoplasmic reticulum, the cell's internal calcium store. The rise in calcium causes the cell's myofilaments to undergo excitation-contraction coupling, sliding past each other and resulting in muscle contraction.
The coordination of cardiac muscle cell contraction is essential for efficient blood pumping from the heart. Gap junctions between adjacent cardiomyocytes allow for the propagation of coordinated action potentials, ensuring synchronised contraction. Cardiac muscle cells have a single central nucleus, similar to smooth muscle, and are rectangular in shape. They are highly resistant to fatigue due to the presence of numerous mitochondria, which provide the energy required by the cell in the form of adenosine triphosphate (ATP).
The discovery of adult endogenous cardiac stem cells has raised the possibility of using stem cell lineages to treat heart failure. However, the functionality of newly formed or repaired cardiac muscle cells remains a challenge, and further research is needed to unlock the full potential of stem cell therapy for improving cardiac function after a heart attack.
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Electrical properties of cardiac muscle cells affect the rate of heart contractions
Cardiac muscle, found in the walls of the heart, is under the control of the autonomic nervous system. The contraction of cardiac muscle is involuntary, strong, and rhythmic. The heart's pumping action is facilitated by cardiac muscle cells, which undergo twitch-type contractions with long refractory periods followed by brief relaxation periods. This relaxation is essential for the heart to fill with blood before the next cycle.
There are two major types of cardiac muscle cells: myocardial contractile cells and myocardial conducting cells. The contractile cells, which make up 99% of the cells in the atria and ventricles, are responsible for conducting impulses and contractions that pump blood through the body. The conducting cells, on the other hand, form only 1% of the cells and are similar in function to neurons. They initiate and propagate the electrical impulse that travels through the heart, triggering contractions.
The electrical properties of these cardiac muscle cells are critical in maintaining the rate of heart contractions. Myocardial conducting cells play a key role in this process by generating and transmitting electrical impulses. These impulses trigger the contractions that propel blood through the body. The ability of the conducting cells to initiate and propagate these electrical signals ensures the coordinated contraction of the heart muscle.
Additionally, the inherent rate of individual cardiac muscle cells comes into play. When independently beating embryonic cardiac muscle cells are placed together, the cell with the faster inherent rate sets the pace. The electrical impulse spreads from the faster to the slower cells, triggering a contraction. As more cells are joined, the fastest cell retains control of the rate. This phenomenon is observed in the fully developed adult heart, where the cardiac conduction system generates its own electrical impulse, guided by the fastest cells.
In summary, the electrical properties of cardiac muscle cells, particularly the myocardial conducting cells, are essential for regulating the rate of heart contractions. Their ability to generate and transmit electrical impulses ensures the coordinated contraction of the heart, facilitating the pumping of blood through the body.
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Cardiac muscle is striated, like skeletal muscle
There are three types of muscle tissue in the human body: cardiac, smooth, and skeletal. Cardiac muscle, found in the walls of the heart, is under the involuntary control of the autonomic nervous system. This means that it works without conscious thought. The cardiac muscle cell has one central nucleus and is rectangular in shape. Importantly, it is striated, like skeletal muscle.
Skeletal muscle is the most common type of muscle in the body and is under voluntary control. Skeletal muscles are attached to the bones and consist of flexible muscle fibres. They are also striated, or striped, in appearance, and are often referred to as striated muscles. Skeletal muscles serve a variety of functions, including chewing and swallowing, as well as expanding and contracting the chest cavity to enable breathing.
Cardiac muscle, like skeletal muscle, is made up of sarcomeres that allow for contractility. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, and proteins. The cardiac muscle must contract with enough force to pump blood into circulation and meet the metabolic demands of the entire body.
The striated appearance of cardiac and skeletal muscles is due to the presence of sarcomeres, which consist of thick and thin filaments of the proteins myosin and actin, respectively. These filaments interact to form the basis of the sliding filament theory, which explains muscle contraction. The sliding filament theory highlights the key role of these striated muscles in generating the necessary force for their respective functions.
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Frequently asked questions
No, cardiac muscle is not under voluntary control. Its rhythmic contraction is regulated by the sinoatrial node of the heart, which acts as the heart's pacemaker.
Cardiac muscle is one of the three major muscle types, found only in the heart.
Skeletal muscle is under voluntary control, whereas cardiac muscle is not. Cardiac muscle is also regulated by the autonomic nervous system.
Cardiac muscle pumps blood throughout the body and maintains blood pressure.
Cardiac muscle cells form a network in the heart and are connected by intercalated discs, which control the synchronised contraction of cardiac tissues. The contraction of these muscles produces force and shortening in the bands of muscle, resulting in a decrease in heart chamber size and the ejection of blood into the pulmonary and systemic vessels.
