Fascicles

A fascicle is a small bundle or cluster of fibers, cells, or other structures. The term comes from the Latin fasciculus, meaning “a little bundle,” and it is used across biology, medicine, and related fields to describe organized groupings that function together.

In anatomy, a fascicle refers to a bundle of skeletal muscle fibers surrounded by a connective tissue sheath called the perimysium. Several fascicles compose a whole muscle, which is enclosed by the epimysium. Nerves also contain fascicles, with each fascicle wrapped by the perineurium; multiple fascicles form the nerve, whose outer layer is the epineurium. The term highlights the hierarchical organization of muscle and nerve tissue.

In botany, fascicle describes a bundle of leaves, needles, or flowers arranged along a short axis or stalk. For example, pine needles are commonly grouped into fascicles of two to five. The concept can apply to other plant structures that occur in clustered arrangements.

In publishing and taxonomy, a fascicle is an independently published installment of a book, periodical, or monograph, intended to be bound with the remainder later. Historically, fascicles facilitated distribution of multi-volume works and large catalogs before the final compilation was issued.

In neuroanatomy, the related term fasciculus (or fascicle) denotes a tract or bundle of nerve fibers within the central nervous system. Examples include various named fasciculi and fiber pathways. Across fields, fascicles denote structurally integrated bundles that serve coordinated functions.