Library · Histology
Sarcomere
Make it clearer
The sarcomere is the repeating unit inside skeletal muscle, the muscle you move at will. It is the muscle's functional unit: the smallest piece that already does what a muscle does. It is built from two kinds of filament lined up side by side, actin, the thin one, and myosin, the thick one.
Each sarcomere runs from one Z line to the next. The Z line is its border, and there a protein called alpha-actinin holds the actin filaments the way a post anchors the rails. It is a stretch of fence between two posts, with rails of two thicknesses.
Seen under an electron microscope, that stretch is not plain: you can make out the M line, the Z disc, and three bands, the H, the A, and the I.
And there is one fact that shows how the muscle changes on the inside as it works. When it contracts, the H and I bands shorten, while the A band always keeps the same length.
In brief
The sarcomere is the functional unit of the skeletal muscle fiber: an orderly arrangement of actin, the thin filament, and myosin, the thick one.
A stretch of fence between two posts, with rails of two thicknesses.
It runs from one Z line to the next, its border, where alpha-actinin anchors actin.
Under the electron microscope, the M line, the Z disc, and the H, A, and I bands stand out.
When the muscle contracts, the H and I bands shorten and the A band keeps its length.
Sources (2)
- OpenStax, Rice University10.2 Skeletal MusclePublished
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Skeletal Muscle, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated