Sarcolemma (cell membrane)The cell membrane of a muscle cell.
NucleusOne nucleus lies in the middle of the cell.
Gap junctionJoins two cells so a signal can pass between them.
CaveolaeSmall pouch-like pits of the cell membrane.
Thin filament (actin)Made mostly of actin. It is fixed to a dense body or a dense plaque.
Thick filament (myosin)Made of myosin. It lies between the thin filaments.
Dense bodyA dense anchor inside the cell. Thin filaments are fixed to it.
The whole cell 2
Sarcoplasm (cytoplasm)The cytoplasm of a muscle cell, filled with filaments.
Contracted cellThe same cell after it shortens. The thin filaments pull on the dense bodies and the plaques.
Filaments and their anchors 2
Dense plaqueA dense patch on the inside of the membrane. Thin filaments are fixed to it.
Intermediate filamentStrands of desmin and vimentin that link the dense bodies.
At the membrane 1
Sarcoplasmic reticulumA network of sacs that stores calcium. It lies close under the caveolae.
How this list was compiled: Every name checked on 2026-10-01 in at least two of these, in our own words. (1) Wikipedia, Smooth muscle. (2) Kenhub, Smooth musculature. (3) Yale School of Medicine, Histology lab on muscle. (4) Popescu and others, Caveolae in smooth muscles, Journal of Cellular and Molecular Medicine, 2006. (5) Southern Illinois University School of Medicine, Histology, Smooth muscle. (6) Sit, Gutmann and Iskratsch, Costameres, dense plaques and podosomes, Journal of Muscle Research and Cell Motility, 2019. (7) North and others, Two distinct sarcolemma domains in smooth muscle, Journal of Cell Biology, 1993. (8) Gash and others, Physiology, Muscle Contraction, StatPearls, 2023. (9) Stromer and Bendayan, Desmin intermediate filaments in smooth muscle cells, Cell Motility and the Cytoskeleton, 1988. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry. Own original drawing; nothing is traced or copied. Licence: own work
How it works
This labeled diagram of a smooth muscle cell shows one spindle-shaped cell with its single nucleus, relaxed and then contracted, and a close-up of the caveolae, dense bodies and filaments just under the sarcolemma.
Read the full guide
The whole cell
A smooth muscle cell is a spindle: wide in the middle and tapering at both ends, with one nucleus in the center. It has no sarcomeres, so it shows no stripes. In most smooth muscle, gap junctions join it to its neighbors.
The close-up
Thin filaments of actin are fixed to dense bodies inside the cell and to dense plaques on the membrane. Thick filaments of myosin lie between them. Intermediate filaments link one dense body to the next. Caveolae are small pits of the membrane, with the sarcoplasmic reticulum close under them.
Questions and answers
What does a smooth muscle cell look like?
A long spindle: widest in the middle and tapering to a point at each end, with a single nucleus in the center. Unlike skeletal and cardiac muscle cells, it has no stripes.
Why is smooth muscle not striated?
It has no sarcomeres. Its thin and thick filaments are not lined up into myofibrils; they run through the cell between dense bodies and the membrane, so no bands show under the microscope.
What are dense bodies in smooth muscle?
Dense bodies are small anchor points inside the cell. Thin filaments of actin are fixed to them, and intermediate filaments link one dense body to the next. The matching anchors on the membrane are called dense plaques.
Do smooth muscle cells have gap junctions?
In most smooth muscle, yes. In the single-unit kind, found in the walls of internal organs and blood vessels, gap junctions join neighboring cells, so an electrical signal passes from cell to cell and they contract together. Multi-unit cells work independently.