Dominic Stone
The human heart is a vital organ that pumps blood throughout the body, and its functions are regulated by the autonomic nervous system. The autonomic nervous system controls involuntary body functions such as heart rate, digestion, and blood flow. The heart is innervated by sympathetic and parasympathetic fibres from the autonomic branch of the peripheral nervous system, and this network of nerves is known as the cardiac plexus. This complex system ensures that the heart contracts rhythmically and continuously, maintaining a consistent heartbeat without any conscious effort. Thus, the cardiac muscle is considered an involuntary muscle.
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What You'll Learn
- Cardiac muscle is a specialised type of muscle found only in the heart
- The heart is innervated by sympathetic and parasympathetic fibres
- The network of nerves supplying the heart is called the cardiac plexus
- Injury to the cardiac plexus can impair the function of the heart
- The autonomic nervous system controls involuntary body functions
Cardiac muscle is a specialised type of muscle found only in the heart
Cardiac muscle, also called myocardium, is one of three major categories of muscles found within the human body, the others being smooth muscle and skeletal muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart.
The heart is made up of three layers—the pericardium, myocardium, and endocardium. The cardiac muscle forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The myocardium found in the ventricles is thick to allow for forceful contractions, while the myocardium in the atria is much thinner. The cardiac muscle is responsible for the contractility of the heart and, therefore, its pumping action. The pumping action of the heart is 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 cardiac muscle cells are connected to each other via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium (also known as the visceral pericardium). The inner endocardium lines the cardiac chambers, covers the cardiac valves, and joins with the endothelium that lines the blood vessels that connect to the heart. On the outer aspect of the myocardium is the epicardium, which forms part of the pericardial sac that surrounds, protects, and lubricates the heart. The cardiac muscle forms both the atria and the ventricles of the heart. The individual myocytes that make up the myocardium also differ between cardiac chambers. Ventricular cardiomyocytes are longer and wider, with a denser T-tubule network.
The innervation of the heart refers to the network of nerves that are responsible for the functioning of the heart. The network of nerves supplying the heart is called the cardiac plexus. It receives contributions from the right and left vagus nerves, as well as the sympathetic trunk. These nerves are responsible for influencing heart rate, cardiac output, and contraction forces of the heart. Injury to the cardiac plexus or any of its contributories can impair the function of the heart.
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The heart is innervated by sympathetic and parasympathetic fibres
The heart is innervated by a network of nerves called the cardiac plexus, which is made up of sympathetic and parasympathetic fibres from the autonomic branch of the peripheral nervous system. This network of nerves is responsible for the functioning of the heart, including influencing heart rate, cardiac output, and contraction forces.
The sympathetic part of the cardiac plexus is composed of fibres from the sympathetic trunk, which arise from the upper segments of the thoracic spinal cord. These fibres reach the cardiac plexus via cardiac nerves, with preganglionic fibres branching from the upper thoracic spinal cord and synapsing in the lower cervical and upper thoracic ganglia. Postganglionic fibres then extend from the ganglia to the cardiac plexus. Sympathetic stimulation of the heart increases heart rate, inotropy, and conduction velocity, with sympathetic fibres increasing heart rate and contractility through the release of norepinephrine.
The parasympathetic portions of the cardiac plexus, on the other hand, receive contributions from the right and left vagus nerves, also known as the tenth cranial nerve. The right vagus nerve primarily innervates the SA node, while the left vagus innervates the AV node, although there may be overlap in the anatomic distribution. The vagus nerve plays a crucial role in the parasympathetic nervous system, which is responsible for regulating various involuntary bodily functions. Parasympathetic stimulation of the heart has the opposite effect of sympathetic stimulation, slowing the heart rate, prolonging AV conduction, and reducing myocardial contractility during heightened sympathetic activity.
Damage to the vagus nerves can affect the ability to decrease the heart rate, leading to tachycardia. Similarly, injury to the sympathetic fibres contributing to the cardiac plexus can impair the ability to increase heart rate, resulting in bradycardia. Therefore, the balance between sympathetic and parasympathetic innervation is crucial for maintaining proper heart function.
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The network of nerves supplying the heart is called the cardiac plexus
The cardiac plexus is generally divided into two parts: the superficial part and the deep part. The superficial part is located below the arch of the aorta, in front of the right pulmonary artery, and between the arch and the pulmonary trunk. It is formed by the superior branches of the left sympathetic nerves and the lower superior cervical branches of the left vagus nerve. The deep part of the cardiac plexus is situated in front of the bifurcation of the trachea, above the point of division of the pulmonary artery, and behind the aortic arch. It is formed by the cardiac nerves arising from the cervical ganglia of the sympathetic trunk, and the cardiac branches of the vagus and recurrent laryngeal nerves.
The sympathetic part of the cardiac plexus is composed of fibres from the sympathetic trunk, arising from the upper segments of the thoracic spinal cord. Fibres from the sympathetic trunk reach the cardiac plexus via cardiac nerves. The parasympathetic portions of the cardiac plexus receive contributions from the vagus nerve. The preganglionic fibres, branching from the right and left vagus nerves, reach the heart and enter the cardiac plexus by synapsing with ganglia within this plexus and the walls of the atria.
Injury to the cardiac plexus or its contributories can impair the function of the heart. Damage to the vagus nerves will affect the ability to decrease the heart rate, leading to tachycardia. Similarly, damage to the sympathetic fibres contributing to the cardiac plexus can reduce the ability to increase heart rate, causing bradycardia.
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Injury to the cardiac plexus can impair the function of the heart
The cardiac plexus is a large network of nerves located around the base of the heart. It is composed of both sympathetic and parasympathetic nerves, which are responsible for influencing heart rate, cardiac output, and contraction forces of the heart. The cardiac plexus is split into two parts: the superficial part and the deep part. The superficial part is located below the arch of the aorta and in front of the right pulmonary artery. The deep part lies between the aortic arch and the tracheal bifurcation.
Injury to the cardiac plexus or any of its contributaries can impair the function of the heart. Damage to the vagus nerves, which provide parasympathetic innervation to the heart, will affect the ability to decrease the heart rate, leading to tachycardia. Similarly, damage to the sympathetic fibres contributing to the cardiac plexus can reduce the ability to increase heart rate, resulting in bradycardia.
The sympathetic fibres that contribute to the cardiac plexus arise from the upper segments of the thoracic spinal cord. These fibres reach the cardiac plexus via cardiac nerves, with preganglionic fibres branching from the upper thoracic spinal cord and synapsing in the lower cervical and upper thoracic ganglia. Postganglionic fibres then extend from these ganglia to the cardiac plexus.
The cardiac plexus plays a crucial role in regulating the activity of the heart, blood pressure, and blood flow to the face. It helps prevent fainting during periods of anxiety and can be used in acupuncture to relax muscles. In addition, the cardiac plexus is involved in electrophysiological functions, with right-sided nerves supplying the sinoatrial (SA) node and left-sided nerves supplying the atrioventricular node.
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The autonomic nervous system controls involuntary body functions
The autonomic nervous system is a network of nerves that controls involuntary body functions. It is always active, even when we sleep, and is essential to our survival. The autonomic nervous system is part of the peripheral nervous system, which also includes the somatic nervous system. Unlike the somatic nervous system, which includes the muscles we can control, the autonomic nervous system connects our brain to our internal organs, managing processes that occur without conscious thought, such as breathing, the heartbeat, blood pressure, and digestion.
The autonomic nervous system has two main divisions: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system activates processes that help us in times of stress or danger, such as the "`fight-or-flight'" response. On the other hand, the parasympathetic nervous system does the opposite, inhibiting processes and promoting "rest-and-digest" functions. For example, it slows the heart rate, decreases blood pressure, and stimulates the digestive tract.
The heart, in particular, is innervated by both sympathetic and parasympathetic fibres from the autonomic nervous system, forming a network of nerves called the cardiac plexus. The cardiac plexus receives contributions from the right and left vagus nerves and the sympathetic trunk. These nerves influence heart rate, cardiac output, and the contraction forces of the heart. Damage to the vagus nerves, for instance, can impair the ability to decrease the heart rate, leading to tachycardia.
Disorders of the autonomic nervous system can disrupt these vital functions. Autonomic disorders may result from damage to autonomic nerves or parts of the brain that control body processes. Symptoms of autonomic dysfunction include orthostatic intolerance, which can cause light-headedness, blurred vision, head pressure, palpitations, and difficulty breathing when a person stands up. Autonomic dysfunction has also been observed in patients with COVID-19.
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Frequently asked questions
Cardiac muscles are involuntary muscles.
Cardiac muscles are unique tissues located only in the heart. They show characteristics of both smooth and skeletal muscles. Cardiac muscle cells can be branched, unlike skeletal and smooth muscles.
Cardiac muscles are composed of a syncytium connected by intercalated discs to support the synchronized contraction of cardiac tissue.
The innervation of the heart refers to the network of nerves responsible for the functioning of the heart. The heart is innervated by sympathetic and parasympathetic fibres from the autonomic branch of the peripheral nervous system.
The network of nerves supplying the heart is called the cardiac plexus. It is composed of sympathetic and parasympathetic systems. It receives contributions from the right and left vagus nerves and the sympathetic trunk.
