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Pl. III · Laevis fusiformis — smooth muscle

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3–4 minutes

Date Last Modified

Pl. III · FAM. LAEVIDAE

Laevis fusiformis var. strangulans

the slow squeeze  ·  smooth muscle

The plate

The specimen, drawn

Pl. I

[ plate drawing to come · the strangler fig ]

Habitat & range

Where it lives

Body map

[ body map to come — needs the BioRender export ]

Range

  • The muscularis externa of the whole gut, from the middle of the esophagus to the anus.
  • The wall of every artery and vein, wrapped circularly as the tunica media.
  • The airways, all the way down to the terminal bronchioles.
  • The bladder, the ureters, the uterus and the ductus deferens.
  • The iris and ciliary body of the eye — and the tiny muscles that stand your hair up.

Collection record

  • Add your slide numbers here.

Niche

What it does for a living

Slow, cheap and tireless. Smooth muscle narrows tubes and empties hollow organs, and it does the work on a budget: it can hold a contraction for hours on a fraction of the ATP striated muscle would burn through, and it can be stretched enormously and still pull. It also never takes an order from you. Autonomic nerves, circulating hormones and the stretch of the organ wall itself all get a vote, and the sheet answers as one piece because the cells are wired to each other by gap junctions rather than each waiting for its own nerve.

field collected specimen

How to know it on sight

  • No striations anywhere — the cytoplasm is an even pink.
  • Cells spindle-shaped: fat through the middle, tapering to a point at both ends.
  • One central nucleus to a cell, and in a good longitudinal section the nuclei look staggered, because the fat middles do not line up with each other.
  • Sheets rather than bundles — usually two layers lying at right angles to one another.
Comparison of Circular and Longitudinal Layers of smooth muscle of the muscularis externa

Specimen 1

Histological cross section of smooth muscle

Ureter. The even pink with no cross-stripes anywhere is the diagnosis; the nuclei are inside the pink, one to a cell.

Specimen 2

Interface of longitudinally and transversely sections smooth muscle fibers

Detrusor. Two layers meet in this field — one cut lengthwise into long spindles, one cut across into circles.

Specimen 3

Histological cross section of smooth muscle

Esophagus, cut across. Each cell is a small pink polygon, and only the ones sliced through the middle show you a nucleus at all.

Two halves. Left, labeled single-unit, visceral: a sheet of pink spindle-shaped cells lying side by side, with one autonomic nerve fiber running across it and a string of yellow beads along it, labeled varicosities; a note says sheets of cells joined by gap junctions, the whole sheet contracts as one; below, the intestines, labeled gut wall. Right, labeled multiunit: three separate spindle cells, each reached by its own branch of one nerve ending in a bead; a note says each cell has its own nerve ending, cells contract separately; below, a pair of eyes labeled iris and a hair follicle with its small slanting muscle, labeled arrector pili.

People keep calling her by the wrong name

Look-alikes

Two plates. Read the line underneath each one before you decide.

Dense regular connective tissue

Photomicrograph of dense irregular connective tissue of plantar skin, intensely stained with hematoxylin and eosin (H&E). Thick bundles of eosinophilic collagen fibers are arranged in a non-parallel, interwoven pattern, dominating the field. Scattered elongated nuclei are seen within the collagen matrix, representing fibroblasts. The H&E staining highlights the protein-rich collagen as pink and the cell nuclei as darker shades.
Dense irregular connective tissue. Pink-stained collagen fibers and cells in thin skin.

Tell them apart by where the nuclei sit. Smooth muscle nuclei are inside the pink; tendon nuclei lie in rows in the gaps between the bundles.

Cardiac muscle

A magnified view of cardiac muscle tissue as seen on a histological slide. The image exhibits striated muscle fibers running horizontally across the frame, purple-stained nuclei are squished between sarcolemma.
Micrograph of kidney tissue displaying tubular structures lined by simple cuboidal epithelium. The cells manifest as circular or elliptical forms with centrally positioned, round, blue-stained nuclei.

Tell them apart by the stripes and the fork. Cardiac is striated and branches; smooth is evenly pink and never branches.

Examine it yourself

The virtual slide

Find a patch where the cells are cut lengthwise and look for the tapered ends. Then find a patch cut across, and notice that only some of the cells show a nucleus.

Virtual slide courtesy of Histology Guide.

YOur missions

Field Notes for Future Missions

Mission 1: find the spindles

Mission 2: quick check

Field notes

Why this organism

A strangler fig begins as a seed dropped in the crown of another tree, sends roots down around its host, and over decades tightens until the tree inside it is gone. Nothing about that is fast and nothing about it is voluntary. Smooth muscle does the same thing to a tube: a slow, sustained, entirely unhurried squeeze that costs almost nothing to hold and that you cannot argue your way out of. It is why you cannot simply decide to stop a cramp.

Return · Ordo Musculi

Frontispiece

the three specimens, and the key that tells them apart.

Back to the Frontispiece →

Hop to:

← Epithelial Tissues: A Guided Journey

All plates — The Tissue Field Guide: Epithelium

Frontispiece Ordo Epithelia (main page)
Pl. I · Simple squamous
Pl. II · Simple cuboidal
Pl. III · Simple columnar
Pl. IV · Stratified squamous
Pl. V · Stratified cuboidal
Pl. VI · Stratified columnar
Pl. VII · Transitional
Pl. VIII · Pseudostratified columnar
Epithelial Identification Game

All Modules
  1. Anatomical Language, Membranes & Homeostasis
  2. Just Enough Chemistry
  3. The Cell & Its Transport
  4. Making Cells & Proteins
  5. The Integumentary System
  6. The Skeletal System
  7. The Muscular System
  8. Nervous Tissue & the Senses
  9. The Spinal Cord
  10. The Brain & the Blood–Brain Barrier
  11. The Autonomic Nervous System
  12. The Special Senses
  13. The Endocrine System
  14. Blood
  15. The Heart
  16. Blood Vessels
  17. The Digestive System
  18. The Respiratory System
  19. The Urinary System
  20. Fluids, Electrolytes & Acid–Base Balance
  21. The Reproductive System
  22. The Immune System

List of terms