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Pl. V · Centralis inversus — the spinal cord

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Pl. V · FAM. CENTRALIDAE

Centralis inversus var. interrogationis

the butterfly  ·  the spinal cord

The plate

The specimen, drawn

Pl. V

Colored-pencil field-guide plate on toned paper: a question-mark butterfly drawn in loose pencil with its wings spread, the margins deeply ragged and notched rather than smoothly curved, and the small silver question mark picked out on the hindwing. Handwritten notes say the margin is never a smooth curve and that two wings up and two wings down make four horns. Inset a, a magnified circle: a spinal cord in cross-section, a grey butterfly of grey matter on the inside with a pale rim of white matter around it and a central canal. Inset b, the same arrangement as a schematic — spinal cord.

The tissue as you will meet it on the slide.

Habitat & range

Where it lives

Body map

Body map: a simple hatched human figure on a transparent background with three numbered markers running down the trunk. Key: 1 cervical enlargement, wiring the arms; 2 lumbar enlargement, wiring the legs; 3 the cord stops near L1 — below that, roots. Where the spinal cord is found in the body.

Where this tissue is found.

Range

  • From the base of the skull down to about the first lumbar vertebra — shorter than the spine it lives in.
  • Two swellings along its length: one wiring the arms, one wiring the legs.
  • Below where it ends, a spray of roots and no cord at all.

Collection record

  • Add your slide numbers here.

Niche

What it does for a living

A two-way trunk road with its own local government. Everything going up to the brain and everything coming down from it passes through the cord in named tracts in the white matter. But the cord is not only wiring. The grey matter in the middle holds the cell bodies that fire muscles directly, and a reflex can start and finish there without the brain being consulted at all — which is why your hand is off the hot pan before you have felt anything.

field collected specimen

How to know it on sight

  • Grey on the inside, white on the outside — the exact reverse of the cerebrum.
  • The grey is a butterfly, or an H: narrow dorsal horns, blunt ventral horns.
  • A tiny central canal sitting in the middle of the crossbar.
  • A deep fissure at the front and a shallow septum at the back, which is how you tell which way is up.
A plain cross-section of the spinal cord: a darker butterfly of gray matter inside a paler rim of white matter, a pinpoint central canal, a deep notch at the bottom edge and a faint groove at the top.

Specimen 1

Low-magnification histological slide of the spinal cord with an adjacent dorsal root ganglion (DRG), stained purple. The spinal cord’s butterfly-shaped gray matter is visible in the center, surrounded by white matter. The DRG appears as an oval structure near the spinal cord, containing clusters of large neuronal cell bodies, with white myelin sheaths surrounding extending nerve fibers

Whole cord at low power, with a ganglion beside it. The butterfly is the diagnosis.

Specimen 2

Micrograph of a whole spinal cord cross-section in Masson stain: a darker bluish-gray butterfly inside a rosy rim of white matter, a deep fissure at the bottom, a thin membrane around it, and an oval dorsal root ganglion packed with round cell bodies just outside it at the upper right, its root running in toward the cord.

The same arrangement in Masson. Different stain, identical shape — the shape is what you are learning.

Specimen 3

A large spinal cord cross-section with four soft colored spots in the gray matter on one side: pink at the tip of the dorsal horn, lavender just deeper, orange at the side of the gray matter level with the central canal, and green out in the ventral horn.

The horns are inhabited: different jobs live in different corners of the grey.

Four spinal cord cross-sections drawn to the same scale. Top left, a wide oval with large gray horns and a dorsal root ganglion; top right, a smaller section with a slender gray H and thick white matter; bottom left, a rounder section filled with broad gray horns; and a small round section beside it.

People keep calling her by the wrong name

Look-alikes

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

Cerebrum

Low-magnification micrograph of the cerebrum stained with luxol fast blue, showing two broad gyri. A darker blue band of cortex follows the folded outer surface, and paler myelinated white matter fills the core of each gyrus beneath it — grey matter on the outside, white matter within.
Dense irregular connective tissue. Pink-stained collagen fibers and cells in thin skin.

This is the one that matters. Both are central nervous tissue; the cerebrum keeps its grey outside, the cord keeps its grey inside.

Dorsal root ganglion

Low-power magnification histological slide of a pink-stained dorsal root ganglion (DRG) adjacent to the spinal cord. The DRG contains large, round neuronal cell bodies surrounded by satellite cells, while the spinal cord shows a butterfly-shaped gray matter region in the center, surrounded by white matter
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.

They share a slide, so read position. The ganglion is the bump off to one side; the cord is the round thing with the butterfly in it.

Examine it yourself

The virtual slide

Find the deep fissure first and put it at the bottom. Then name the narrow horns and the blunt ones, and look for the canal in the crossbar.

Virtual slide courtesy of Histology Guide.

YOur missions

Field Notes for Future Missions

Mission 1: which way is up

Mission 2: quick check

Field notes

Why this organism

Polygonia interrogationis is named for a small silver mark on the underside of its hindwing, shaped like a question mark. But the thing that identifies it in the field is not the mark — it is the outline. The wing margins are ragged and angular, never a smooth curve, and nothing else in the northeast is shaped quite like it. The spinal cord is the same kind of problem. You do not identify it by colour or by stain; you identify it by a shape, grey horns sitting in the middle of a pale rim. Once you can see the butterfly you have the answer before you have looked at anything else on the slide.

Next · Pl. VI

Centralis trimembranatus var. arachnoideus

the three veils · the meninges.

Continue to Pl. VI →

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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

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