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] 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.
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.[4]
Muscle fascicles may be involved in
myokymia, although commonly only individual myocytes are involved.[5]