A muscle fascicle is a bundle of

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

fibers surrounded by

perimysium Perimysium is a sheath of connective tissue that groups muscle fibers into bundles (anywhere between 10 and 100 or more) or fascicles. Studies of muscle physiology suggest that the perimysium plays a role in transmitting lateral contractile ...

, a type of

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

Structure

Muscle cells A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a mus ...

are grouped into muscle fascicles by enveloping

. Fascicles are bundled together by

epimysium Epimysium (plural ''epimysia'') (Greek ''epi-'' for on, upon, or above + Greek ''mys'' for muscle) is the fibrous tissue envelope that surrounds skeletal muscle. It is a layer of dense irregular connective tissue which ensheaths the entire muscle ...

connective tissue. Muscle fascicles typically only contain one type of muscle cell (either type I fibres or type II fibres), but can contain a mixture of both types.

Function

In the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

specialized

cardiac muscle cell Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle tha ...

s transmit electrical impulses from the

atrioventricular node The atrioventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart. The AV node lies at the lower back section of t ...

(AV node) to the

Purkinje fibers The Purkinje fibers (; often incorrectly ; Purkinje tissue or subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium. The Purkinje fibers are specia ...

– fascicles, also referred to as bundle branches. These start as a single fascicle of fibers at the AV node called the

bundle of His The bundle of His (BH) or His bundle (HB) ( "hiss"Medical Terminology for Health Professions, Spiral bound Version'. Cengage Learning; 2016. . pp. 129–.) is a collection of heart muscle cells specialized for electrical conduction. As part of t ...

that then splits into three bundle branches: the right fascicular branch, left anterior fascicular branch, and left posterior fascicular branch.

Clinical significance

Myositis Myositis is a rare disease that involves inflammation of the muscles. This can present with a variety of symptoms such as skin involvement (i.e., rashes), muscle weakness, and other organ involvement. Systemic symptoms such as weight loss, fatigue ...

may cause

thickening A thickening agent or thickener is a substance which can increase the viscosity of a liquid without substantially changing its other properties. Edible thickeners are commonly used to thicken sauces, soups, and puddings without altering thei ...

of the muscle fascicles. This may be detected with ultrasound scans. Muscle fascicle structure is a useful diagnostic tool for

dermatomyositis Dermatomyositis (DM) is a long-term inflammatory disorder which affects skin and the muscles. Its symptoms are generally a skin rash and worsening muscle weakness over time. These may occur suddenly or develop over months. Other symptoms may inc ...

. Myocytes towards the edges of the muscle fascicle are typically narrower, while those at the centre of the muscle fascicle are a normal thickness. Muscle fascicles may be involved in

myokymia Myokymia is an involuntary, spontaneous, localized quivering of a few muscles, or bundles within a muscle, but which are insufficient to move a joint. One type is superior oblique myokymia. Myokymia is commonly used to describe an involuntary eye ...

, although commonly only individual myocytes are involved.

References

External links

* – "Slide 77

" * – "Smooth Muscle"
Diagram at kctcs.edu
Muscular system {{muscle-stub

Structure

Function

Clinical significance

See also

References

External links