Muscle fascicle

{{Short description|Bundle of skeletal muscle fibers}} {{Infobox anatomy | Name = Muscle fascicle | Latin = fasiculus muscularis | Image = Skeletal muscle svg hariadhi.svg | Caption = Structure of a skeletal muscle. (Fascicle labeled at bottom right.) | Image2 = | Caption2 = | System = | part_of = Skeletal muscle }}{{Distinguish|Nerve fascicle}} A '''muscle fascicle''' is a bundle of skeletal muscle fibers surrounded by perimysium, a type of connective tissue.<ref name="Damjanov-2009">{{Citation|last=Damjanov|first=Ivan|title=Chapter 21 - Skeletal Muscles|date=2009-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780323055949000210|work=Pathology Secrets (Third Edition)|pages=434–447|editor-last=Damjanov|editor-first=Ivan|place=Philadelphia|publisher=Mosby|language=en|doi=10.1016/b978-0-323-05594-9.00021-0|isbn=978-0-323-05594-9|access-date=2020-11-04|url-access=subscription}}</ref>

== Structure == Muscle cells are grouped into muscle fascicles by enveloping perimysium connective tissue.<ref name="Damjanov-2009" /> Fascicles are bundled together by epimysium connective tissue.<ref name="Damjanov-2009" /> 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.<ref>{{Citation|last1=Gandevia|first1=SIMON C.|title=CHAPTER 5 - Peripheral Motor System|date=2004-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780125476263500065|work=The Human Nervous System (Second Edition)|pages=113–133|editor-last=Paxinos|editor-first=GEORGE|place=San Diego|publisher=Academic Press|language=en|doi=10.1016/b978-012547626-3/50006-5|isbn=978-0-12-547626-3|access-date=2020-11-04|last2=Burke|first2=DAVID|editor2-last=Mai|editor2-first=JÜRGEN K.|url-access=subscription}}</ref>

== Function == In the heart, specialized cardiac muscle cells transmit electrical impulses from the atrioventricular node (AV node) to the Purkinje fibers – fascicles, also referred to as bundle branches.{{Citation needed|date=November 2020}} These start as a single fascicle of fibers at the AV node called the bundle of His that then splits into three bundle branches: the right fascicular branch, left anterior fascicular branch, and left posterior fascicular branch.

== Clinical significance == Myositis may cause thickening of the muscle fascicles.<ref name="Möller-2010">{{Citation|last1=Möller|first1=Ingrid|title=Chapter 19 - Soft Tissue Rheumatism|date=2010-01-01|url=http://www.sciencedirect.com/science/article/pii/B978143770127210019X|work=Essential Applications of Musculoskeletal Ultrasound in Rheumatology|pages=219–235|editor-last=Wakefield|editor-first=Richard J.|place=Philadelphia|publisher=W.B. Saunders|language=en|doi=10.1016/b978-1-4377-0127-2.10019-x|isbn=978-1-4377-0127-2|access-date=2020-11-04|last2=Bong|first2=David|last3=Mendieta|first3=Eugenio de Miguel|editor2-last=D'Agostino|editor2-first=Maria Antonietta|url-access=subscription}}</ref> This may be detected with ultrasound scans.<ref name="Möller-2010" />

Muscle fascicle structure is a useful diagnostic tool for dermatomyositis. Myocytes towards the edges of the muscle fascicle are typically narrower, while those at the centre of the muscle fascicle are a normal thickness.<ref>{{Citation|last1=Harati|first1=Yadollah|title=CHAPTER 4 - Myopathies|date=2010-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780323057127000040|work=Neurology Secrets (Fifth Edition)|pages=63–82|editor-last=Rolak|editor-first=Loren A.|place=Philadelphia|publisher=Mosby|language=en|doi=10.1016/b978-0-323-05712-7.00004-0|isbn=978-0-323-05712-7|access-date=2020-11-13|last2=Biliciler|first2=Suur|url-access=subscription}}</ref>

Muscle fascicles may be involved in myokymia, although commonly only individual myocytes are involved.<ref>{{Citation|last1=Ha|first1=Ainhi D. |date=2011-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780123813282000018 |volume=98|pages=1–29|editor-last=Brotchie|editor-first=Jonathan |publisher=Academic Press|language=en|doi=10.1016/b978-0-12-381328-2.00001-8|access-date=2020-11-13|last2=Jankovic|first2=Joseph|title=Pathophysiology, Pharmacology, and Biochemistry of Dyskinesia |chapter=An Introduction to Dyskinesia—The Clinical Spectrum |series=International Review of Neurobiology |pmid=21907081|isbn=9780123813282|editor2-last=Bezard|editor2-first=Erwan|editor3-last=Jenner|editor3-first=Peter|url-access=subscription}}</ref>

==See also== *Deep fascia *Endomysium *Epimysium

== References == <references />

==External links== * {{OklahomaHistology|77_04}} – "Slide 77 skeletal muscle" * {{AnatomyAtlasesMicroscopic|05|83}} – "Smooth Muscle" * [https://web.archive.org/web/20081217010216/http://www.octc.kctcs.edu/gcaplan/anat/images/Image285.gif Diagram at kctcs.edu]

Category:Muscular system