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Pl. IV · Centralis corticalis — cerebrum

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Pl. IV · FAM. CENTRALIDAE

Centralis corticalis var. lichenosus

the crust  ·  cerebrum

The plate

The specimen, drawn

Pl. IV

Colored-pencil field-guide plate on toned paper: a foliose lichen drawn in loose pencil — a ruffled rosette of overlapping lobes on a ragged slab of bark, with a cut-away block at the right showing the thallus in section: a cortex on top, a layer of green algal cells beneath it, and a pale medulla of loose thread. Handwritten notes say cell bodies sit out at the surface with pale thread underneath. Inset a, a magnified circle: cerebral cortex, with crowded neuronal cell bodies and scattered triangular pyramidal cells above a clear boundary, and pale myelinated fibre below it. Inset b, a schematic of the same boundary — cerebrum.

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 two numbered markers on the head. Key: 1 the cortex — the whole folded surface; 2 the white matter packed underneath it. A closing line reads: a few millimetres thick, and all of it outside. Where cerebrum is found in the body.

Where this tissue is found.

Range

  • The entire folded surface of both hemispheres — a sheet only a few millimetres thick.
  • Folded into gyri and sulci, so that most of it is hidden down inside the folds.
  • Plus deep islands of grey, the basal nuclei, marooned inside the white matter.

Collection record

  • Add your slide numbers here.

Niche

What it does for a living

Everything that is not automatic. The cerebral cortex is where sensation becomes perception, where a movement is decided rather than executed, and where language, memory and judgement live. It is built as a sheet because a sheet lets neurons stand side by side in columns and talk to their neighbours; it is folded because the sheet is far too big for the skull it has to fit inside. Spread flat it would cover a small table.

field collected specimen

How to know it on sight

  • A darker band of cell bodies following the surface, with pale fibre underneath it.
  • That band is only a few millimetres thick, and its deep edge is surprisingly abrupt.
  • Scattered through it, triangular pyramidal cells with their points aimed at the surface.
  • Six layers if you look hard — but they shade into one another, nothing like the cerebellum’s three.
High-magnification micrograph of the cerebrum stained with luxol fast blue. Densely packed blue-stained myelinated fibres of the white matter fill the left of the field; towards the right the fibres thin out and scattered purple neuronal cell bodies of the cerebral cortex appear. The boundary between white matter and cortex runs through the middle of the field.

Specimen 1

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.

Two gyri at low power. The darker band follows the folded surface; the pale core is white matter.

Specimen 2

Very low-magnification micrograph of a slab of cerebrum stained with haematoxylin and eosin. Broad rounded gyri are separated by shallow sulci; a darker purple band of cortex follows the outer surface while paler pink white matter fills the interior — grey matter outside, white matter within.

A whole slab. Grey on the outside, white within — hold on to that and Pl. V will catch you out less.

Specimen 3

Low-magnification micrograph of a cerebral gyrus stained with haematoxylin and eosin. A purple band of cortex follows the curve of the folded surface, paler pink white matter fills the core of the gyrus, and a sulcus separates it from the neighbouring fold at the right.

One gyrus close up, with a sulcus beside it. The cortex dives down into the fold and keeps going.

A coronal slice of the brain above three brainstem sections and a spinal cord cross-section, with a pathway traced from a spinal nerve into the cord, up through each brainstem level to the thalamus, and on to the cortex; a green motor fiber leaves the front of the cord.

People keep calling her by the wrong name

Look-alikes

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

Cerebellum

Histological slide of the cerebellum showing gray matter stained dark pink and white matter stained dark purple, highlighting their structural differences.
Dense irregular connective tissue. Pink-stained collagen fibers and cells in thin skin.

Tell them apart by the row. The cerebellum has three sharp layers and a single row of giant cells; the cerebrum has neither.

Grey matter of the spinal cord

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
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 where the grey is. Here it is a band on the outside; in the cord it is a butterfly in the middle.

Examine it yourself

The virtual slide

Find the outer surface, then follow the dark band inward until it stops. That stopping point is the boundary — and it is the whole exercise.

Virtual slide courtesy of Histology Guide.

YOur missions

Field Notes for Future Missions

Mission 1: find the edge

Mission 2: quick check

Field notes

Why this organism

A foliose lichen is a crust with a cortex — and that is not a metaphor borrowed for the occasion. Cortex is the actual term for the dense protective layer on the upper surface of a lichen thallus. Cut one across and you find a tough cortex on top, a bright layer of algal cells just beneath it where all the work happens, and a pale medulla of loose fungal thread filling the middle. A slice of cerebrum reads exactly the same way: cell bodies crowded at the surface, the working layer, and pale myelinated thread underneath. Anatomy borrowed the word, and it borrowed it from something very like this.

Next · Pl. V

Centralis inversus var. interrogationis

the butterfly · the spinal cord.

Continue to Pl. V →

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