Logan Steele
The heart contains specialised cardiac muscle cells called fascicles that transmit electrical impulses from the atrioventricular node (AV node) to the Purkinje fibres. These electrical impulses help the heart contract and pump blood in a coordinated way. The spatial arrangement of the muscle fascicles and intramyocardial connective tissue in the heart has been studied in the Spanish fighting bull (Bos taurus). In both ventricles, the muscle fascicles of the myocardium are arranged in 3 main directions, forming 3 muscle layers within the ventricular wall.
| Characteristics | Values |
|---|---|
| Definition | A muscle fascicle is a bundle of muscle fibers surrounded by perimysium, a type of connective tissue. |
| Presence in cardiac muscle | Yes, cardiac muscle does have fascicles. |
| Function | In the heart, fascicles transmit electrical impulses from the atrioventricular node (AV node) to the Purkinje fibers. |
| Structure | The fascicles in the heart form bundle branches, including the right fascicular branch, left anterior fascicular branch, and left posterior fascicular branch. |
| Clinical Relevance | Conditions such as bifascicular block and congenital heart disease can cause issues with the fascicles in the heart, leading to disruptions in electrical impulses and heart rhythm. |
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What You'll Learn
- The left ventricle has two fascicles, the left anterior and left posterior fascicles
- The arrangement of fascicles varies among muscles
- Fascicles are bundles of muscle fibres surrounded by perimysium
- The bundle of His splits into three bundle branches
- Heart blockages can occur in the left and right bundle branches
The left ventricle has two fascicles, the left anterior and left posterior fascicles
The left ventricle of the heart has two fascicles, the left anterior fascicle and the left posterior fascicle. These are also referred to as bundle branches, which transmit electrical impulses from the atrioventricular node (AV node) to the Purkinje fibres. The left anterior fascicle wraps around the front of the left ventricle, while the left posterior fascicle wraps around the back.
The left anterior fascicle is part of the left bundle branch, which is one of three bundle branches that originate from the bundle of His, a fascicle of fibres at the AV node. The other two bundle branches are the right fascicular branch and the left posterior fascicular branch. The arrangement of these fascicles influences the order of contraction of the muscle fascicles in different layers of the ventricle.
In a healthy heart, the anterior and posterior fascicles work together to signal the left ventricle to contract. However, in some cases, a blockage may occur in one of the fascicles, known as a fascicular block or hemiblock. A left anterior fascicular block (LAFB) occurs when there is a blockage in the anterior fascicle, causing the left ventricle to contract later than normal. Similarly, a left posterior fascicular block (LPFB) is due to a blockage in the posterior fascicle, resulting in an abnormal heartbeat.
Fascicular blocks can affect the electrical impulses in the heart, leading to arrhythmias or irregular heartbeats. In the case of LPFB, the left anterior fascicle can step in to control the contraction of the left ventricle. However, this change in the direction of the electrical impulse can cause a delay, resulting in an arrhythmia. Treatment options may include the implantation of a pacemaker to monitor and regulate the heart's electrical activity.
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The arrangement of fascicles varies among muscles
A muscle fascicle is a bundle of skeletal muscle fibres surrounded by perimysium, a type of connective tissue. The arrangement of fascicles varies among muscles. The fasciculi may be parallel to the long axis of the muscle, may spiral around the long axis, or may be at an angle to the long axis.
In the case of the heart, specialised cardiac muscle cells transmit electrical impulses from the atrioventricular node (AV node) to the Purkinje fibres – fascicles, also referred to as bundle branches. These start as a single fascicle of fibres at the AV node called the bundle of His, which then splits into three bundle branches: the right fascicular branch, left anterior fascicular branch, and left posterior fascicular branch.
The left ventricle, the heart's largest and strongest pumping chamber, has two fascicles: the left anterior (front) fascicle and the left posterior (rear) fascicle. These fascicles make up the left bundle branch, which eventually turns into Purkinje fibres, which are millions of tiny muscle fascicles.
In a bipennate muscle, the fascicles are obliquely set on both sides of a central tendon. In a multipennate muscle, the oblique fascicles converge on several tendons. Muscles that have a parallel fibre arrangement (parallel to the long axis and to each other) are designated as strap or fusiform muscles. Muscles that have a fibre arrangement oblique to its long axis are called pinnate muscles. In unipennate muscles, the obliquely set fascicles fan out on only one side of a central muscle tendon.
The spatial arrangement of the muscle fascicles and intramyocardial connective tissue has been examined in the ventricles of the heart of the Spanish fighting bull (Bos taurus). In both ventricles, the muscle fascicles of the myocardium are arranged in three main directions, forming three muscle layers within the ventricular wall. The preferentially vertical arrangement of the muscle fascicles in the superficial and deep layers suggests that these fascicles are actively involved in valvular dynamics.
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Fascicles are bundles of muscle fibres surrounded by perimysium
A muscle fascicle is a bundle of muscle fibres surrounded by perimysium, a type of connective tissue. Fascicles are bundled together by epimysium connective tissue. Each muscle fibre within a fasciculus is surrounded by endomysium, a thin, delicate network of connective tissue strands that also contains the microcirculation network.
The arrangement of fascicles varies among muscles. They may be parallel to the long axis of the muscle, spiral around it, or be at an angle to it. In the heart, for example, the muscle fascicles of the myocardium are arranged in three main directions, forming three muscle layers within the ventricular wall. This arrangement suggests that these fascicles are actively involved in valvular dynamics.
Fascicles typically only contain one type of muscle cell (either type I or type II fibres) but can contain a mixture of both types. The number of type 1, 2A, and 2B fibres is roughly comparable in commonly biopsied muscles, but the percentages of each fibre type vary with the specific muscle studied, as well as sex, age, and physical state.
In bipennate muscles, the fascicles are obliquely set on both sides of a central tendon, while in multipennate muscles, the oblique fascicles converge on several tendons.
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The bundle of His splits into three bundle branches
The bundle of His, also known as the atrioventricular bundle, is a vital component of the heart's electrical conduction system. It is a collection of heart muscle cells that transmit electrical impulses from the atrioventricular node to the ventricles of the heart. The bundle of His splits into three bundle branches: the left bundle branch, the right bundle branch, and the left posterior fascicular branch.
The left bundle branch is larger than the right, reflecting the size difference between the two ventricles. It supplies the left ventricle, which is more muscular and requires stronger contractions to pump blood to the body. The right bundle branch supplies the right ventricle. These bundle branches carry electrical impulses that stimulate the ventricles to contract, facilitating blood circulation.
The bundle branches are a part of the electrical system of the heart, which controls the heartbeat. The electrical impulses travel through the bundle branches to the Purkinje fibers, which provide electrical conduction to the ventricular muscle, causing the cardiac muscle of the ventricles to contract at a paced interval. This entire process takes about 25 milliseconds, allowing the heart to function effectively.
The bundle of His and its branches play a critical role in maintaining the heart's rhythm and ensuring synchronized contractions of the ventricles. Disorders affecting the bundle of His or its branches can lead to "bundle branch blocks," which limit the heart's ability to coordinate the activities of the atria and ventricles, resulting in decreased efficiency in pumping blood.
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Heart blockages can occur in the left and right bundle branches
Cardiac muscle cells transmit electrical impulses from the atrioventricular node (AV node) to the Purkinje fibres, via fascicles, also referred to as bundle branches. These start as a single fascicle of fibres at the AV node, called the bundle of His, which then splits into three bundle branches: the right fascicular branch, left anterior fascicular branch, and left posterior fascicular branch.
Heart blockages can occur in these left and right bundle branches, resulting in a bundle branch block (BBB). This is a blockage or disruption to the electrical signal that causes the heartbeat. BBB can affect the right ventricle (right bundle branch block), left ventricle (left bundle branch block), or both ventricles. In the case of a right bundle branch block, the right side of the heart beats slightly later than the left side, and vice versa for a left bundle branch block.
A bundle branch block can be caused by a heart attack, which can result in scar tissue that may damage the left or right bundle branch. Other causes include congenital heart disease, dilated cardiomyopathy, heart disease (coronary artery disease), heart failure, heart infection (myocarditis), heart valve disease, high blood pressure (hypertension), and hypertrophic cardiomyopathy. People with underlying health problems, especially heart conditions, are at a higher risk of bundle branch block.
The condition often presents no symptoms and requires no treatment unless there are underlying heart conditions. However, in some cases, it can lead to dizziness, fainting, shortness of breath, and an irregular heartbeat. Diagnosis of BBB is typically done through an electrocardiogram (EKG) or echocardiogram.
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Frequently asked questions
Cardiac muscle fascicles are specialized heart muscle cells that transmit electrical impulses from the atrioventricular node (AV node) to the Purkinje fibers.
Cardiac muscle fascicles play a crucial role in the heart's pumping action by conducting electrical impulses to the heart's lower chambers (ventricles). These electrical signals help the heart contract and pump blood in a coordinated manner.
A blockage in the cardiac muscle fascicles, known as a bifascicular block, can cause a delay or interruption in the transmission of electrical signals between the left and right bundle branches. This disruption affects the heart's lower pumping chambers, leading to arrhythmia or a slow heart pump.
