Central Nervous System

666 Spinal Cord—Spinal Medulla

Cross-section of the cervical part (C5)—cervical intumescence.

The spinal medulla is traversed lengthwise by the columnar gray matter (substantia grisea). It is completely enveloped by the white matter (substantia alba, medullary sheath). The columnar gray matter displays a butterfly or H-pattern in cross-sections. There is a deep anterior median fissure (fissura mediana anterior), the dorsal median fissure is not as deep (sulcus medianus posterior). The gray matter forms extensions, which look like horns in crosssections. They are therefore named cornua. Both halves of the spinal medulla feature a larger anterior horn (cornu anterius, columna anterior) and a slender posterior horn (cornu posterior, columna posterior). Both sides are connected via the central intermediary matter, which is joined in the center (commissura grisea) with the central canal. The figure reveals that the posterior horns extend to the surface in the proximity of the posterior root of the spinal nerves. The tissue next to the spinal cord (stained brown) represents the rootlets of the posterior root of the spinal nerves (fila radicularia). The darker stained medullary sheath shows a clear substructure. This sheath contains the longitudinal, mostly myelinated nerve fibers of the various afferent and efferent projection tracts.

The surface of the spinal cord is covered by the spinal pia mater (stained soft yellow).

Stain: medullary sheath preparation—Weigert carmine; magnification: × 8

667 Spinal Cord—Spinal Medulla

Cross-section of the thoracic part (T6). Note the delicate anterior and posterior horns of the gray matter. The gray matter protrudes slightly to the sides (cornu laterale).

Stain: medullary sheath preparation—Weigert carmine; magnification: × 8

668 Spinal Cord—Spinal Medulla

Cross-section of the lumbar part (L6)—lumbosacral intumescence.

The gray matter (anterior and posterior horns) is prominently expressed because the nerves for the extremities exit here.

Stain: medullary sheath preparation—Weigert carmine; magnification: × 8

669 Spinal Cord—Spinal Medulla

Cross-section of the sacral part (S3).

Massive posterior horns are characteristic of the sacral spinal medulla. There is a broad interface to the anterior horns. Note the very narrow medullary sheath.

Stain: medullary sheath preparation—Weigert carmine; magnification: × 8

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Central Nervous System

Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy © 2003 Thieme All rights reserved. Usage subject to terms and conditions of license.

Central Nervous System

670 Spinal Cord—Spinal Medulla

Cross-section of the white matter (substantia alba) of the spinal medulla. The medullary sheath consists predominantly of longitudinal myelinated nerve fibers. Their myelin sheaths 1 are colorless in this preparation and show a wide range of diameters. The dark spots inside the colorless (white) areas are silver impregnated axons 2 . Unmyelinated or sparsely myelinated axons occur sporadically. Delicate vascularized connective tissue septa 3 start at the surface and traverse the spinal white matter. This causes a subdivision of the medullary sheath into parcels.

1 Myelin sheaths

2 Axons (neurites)

3 Vascularized connective tissue septa

Stain: Bielschowsky-Gros silver impregnation; magnification: × 500

671 Spinal Ganglion

Spinal ganglia are spindle-shaped nodes with a diameter of 5–8 mm. They are located in the posterior roots of the spinal nerves immediately before posterior and anterior roots merge. Each spinal ganglion is enveloped by a strong collagen fiber capsule 1 (= constituent of the spinal dura mater). Distally, it continues in the perineurium of the spinal nerve. Each ganglion is traversed by a delicate vascularized connective tissue (endoneurium of the spinal nerve), which is continuous with the connective tissue of the capsule. Embedded in this loose connective tissue are pseudounipolar nerve cell bodies and their satellite cells (= peripheral glial cells) as well as the axons of these primary sensory neurons of the spinal nerves (cf. Figs. 256, 672–674).

1 Connective tissue capsule

2 Posterior root of the spinal nerve Stain: azan; magnification: × 12

672 Spinal Ganglion

Vertical section of a spinal ganglion which is part of the posterior root of the spinal nerve (radix posterior) immediately before it merges with the anterior root and forms the spinal nerve. The anterior root of the spinal nerve is not shown. The figure shows fiber tracts, i.e., axon bundles of different sizes, which build the posterior root 1 or the posterior branch of the spinal nerve 2 , respectively. The black spots with different diameters represent pseudounipolar ganglia cells 3 . The spinal ganglion is encased by a vascularized connective tissue capsule 4 , which is continues with the spinal dura mater (cf. Figs. 66, 256, 671, 673, 674).

1 Posterior root of the spinal nerve

2 Posterior branch of the spinal nerve

3 Group of ganglia cells

4 Connective tissue capsule

Stain: Bielschowsky-Gros silver impregnation; magnification: × 7

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673 Spinal Ganglion

Detail from Fig. 671. The round or ellipsoid cell bodies 1 are of different sizes, their diameters vary from 20 to 120 μm. Spinal ganglia cells are among the largest cells in the body. They contain large, round nuclei with nucleoli, which show strong affinity to stains (cf. Figs. 1, 66, 256). The cytoplasm contains Nissl bodies. Note the corona of small satellite cells (lemmocytes) and the loose, vascularized connective tissue (endoneurium) (stained light blue). The cytoplasmic processes form T-shaped dendritic peripheral branches and a central axon (not seen in this figure). The axon (radix posterior, see Fig. 672) ends at the inner cells of the spinal medulla. The center of the figure shows a bundle of myelinated nerve fibers 2 (cf. Figs. 674).

1 Spinal ganglia cells (perikarya of pseudounipolar neurons)

2 Myelinated nerve fibers Stain: azan; magnification: × 80

674 Spinal Ganglion

Detail from Fig. 656. Vertical section of myelinated nerve fibers from the posterior root of the spinal nerve. The preparation has been treated with lipophilic solvents (alcohol, xylene). This has led to a separation of the myelin sheaths. The lipids have been extracted from the myelin sheath, and only a protein precipitate, the neurokeratin skeleton, has remained. Note the delicate loose connective tissue (stained blue), which corresponds to the endoneurium of peripheral nerves. The larger nuclei (stained red) are part of Schwann cells. The smaller, spindle-shaped nuclei belong to fibrocytes.

Stain: azan; magnification: × 200

Central Nervous System

675 Cerebral Cortex

The neurons of the cerebral cortex (gray matter) are arranged in horizontal layers (laminae). One type of neuron predominates in each layer. The borders of the vertical layers are diffuse. This figure shows the cytoarchitecture (Nissl image) of the parietal lobe of the isocortex and its layers. The preparation depicts only nerve cell perikarya and glial nuclei. The outer layer I (molecular or plexiform layer) is cell sparse containing only scattered horizontal cells. Layer II, the external lamina granulosa, consists of granular cells. The external pyramidal layer III contains pyramidal cells of varying sizes together with scattered nonpyramidal neurons (cf. Figs. 676, 677). There are densely packed granular cells in the internal granular layer, the lamina granularis interna IV. The internal pyramidal layer V and spindle layer VI, the lamina multiformis , are relatively narrow in the parietal lobe. Apart from vertically running vessels (cut in various planes), there are also smaller vessels, which run in horizontal direction (cut longitudinally).

Stain: cresyl violet; magnification: × 30

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676 Cerebral Cortex

Detail from a vertical section of the isocortex with internal pyramidal layer (lamina pyramidalis interna or ganglionaris), layer V, and the internal granular layer (lamina granularis interna), layer VI. The pyramidal cells reach a height of 120 μm and a width of 80 μm. The cell bodies 1 are stained brown in this preparation. Pyramidal cells send out long ascending dendrites 2 . A strong axon extends from the basal cytoplasm of the pyramidal cells. The axons of these Betz giant cells are part of the pyramidal tract (cf. Figs. 675, 677).

1 Cell bodies of pyramidal cells

2 Dendrites

Stain: Bielschowsky-Gros silver impregnation; magnification: × 300

Central Nervous System

677 Cerebral Cortex

Section of the isocortex, primary motor cortex, area 4 (precentral gyrus, Brodmann’s area 4).

Pyramidal cells of the internal pyramidal cell layer (layer V) are stained using Golgi’s silver impregnation technique. The cell bodies and all cell processes of the nerve cells are stained.

Pyramidal cells are type 1 Golgi cells. Axons, which end in extracortical tissue, are one of their characteristic features. The cell bodies of the pyramidal cells have diameters between 10 and 70 μm. The largest pyramidal cells are the Betz giant cells and the Meynert cells. The pyramidal cell owes its name to the roughly triangular faces of its cell body. The basis of the pyramid usually points toward the medulla. The branching apical dendrites run from the tip of the pyramid to the cortical surface. There are also dendrites at the basal plasma membrane. These run predominantly in a horizontal direction. The axon exits the pyramidal cell at the basal axon hillock and extends toward the medulla. Apical and basal dendrites are densely covered with spikes. Collaterals split from the axon shortly after it exits the pyramidal cell at the axon hillock. The collaterals either ascend or run in horizontal direction (cf. Figs. 2, 20, 248–253, 675, 676).

Stain: Golgi silver impregnation; magnification: × 500

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Central Nervous System

678 Cerebellar Cortex

Central sagittal section of the cerebellar vermis.

The cerebellar cortex is the about 1-mm thick folded layer of gray matter overlying the cerebellar surface. Grooves subdivide the gray matter in many small coils. The medullary layer of white matter consists of thin medullary layers 1 . In a medullary sheath preparation, the cerebellar cortex shows an outer molecular layer (stratum moleculare) (stained yellow) 2 and an inner granular layer (stratum granulosum) (stained brownish) 3 . The layer between the inner and outer layers is the wide stratum ganglionare (stratum neuronorum piriformium gangliosum) 3 . This layer is easily recognized. It consists of large Purkinje cells (Purkinje cell layer) (cf. Figs. 5, 254, 681, 682). Remnants of the soft pia mater 4 are visible on the surface of this section.

1 Medullary layer

2 Molecular layer

3 Stratum ganglionare, Purkinje cell layer

4 Pia mater

Stain: medullary sheath stain (modified Weigert hematoxylin stain); magnification: × 5

679 Cerebellar Cortex

Staining clearly differentiates between the granular layer 1 and the molecular layer 2 , which contains few cells and appears pale. The molecular layer is 430 μm thick, the granular layer measures about 350 μm at the turn of the coils. The layer is clearly thinner in the grooves. Numerous densely packed cells form the granular layer 1 . The granular structure is based on the crowded presence of small cells. In general staining procedures, only the cell nuclei are clearly rendered (see Fig. 680). The Purkinje cells of the stratum ganglionare (stratum neuronorum piriformium) are located between the granular and molecular layers (see Figs. 5, 681, 682). The medullary layer 3 contains the myelinated nerve fibers of the cerebellar tracts.

1 Granular layer

2 Molecular layer

3 Medullary layer with laminae

4 Pia mater

Stain: Weigert medullary sheath staining; magnification: × 10

680 Cerebellar Cortex

Detail from a center sagittal section of the cerebellar vermis (cf. Figs. 678, 679). The figure shows the result of Nissl staining of the nerve and glial cells (Nissl image). The cell-rich granular layer 1 is rendered particularly well, while the molecular layer is only slightly tinged with a grayish blue hue. The laminae of the medullary layer 3 have remained unstained.

1 Granular layer

2 Molecular layer

3 Medullary layer, laminae

4 Pia mater

Stain: Nissl stain; magnification: × 10

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681 Cerebellar Cortex

The perikarya of the Purkinje cells in the stratum ganglionare are about 30 μm thick. They are arranged in a row. Purkinje cells appear striking even with general staining methods because they are by far the largest neurons of the cerebellum (cf. Fig. 254).

The round or rounded Purkinje cell bodies are darkly stained in this preparation. From their somata ascends an elaborately branched dendritic tree into the molecular layer and the glial external limiting membrane. The usually strong primary dendrites branch into secondary and tertiary dendrites. They form an espalier-like configuration in the molecular layer. The territories of individual Purkinje cells may overlap. There are fiber tracts in the lower third of the molecular layer immediately over the cell body of the Purkinje cells, which run parallel to the granular layer and vertical to the dendritic trees of the Purkinje cells. These fiber tracts are axons of basket cells, which are often called tangential fibers. There are many small astrocytes and basket cells in the molecular layer (stained black). The lower edge of the figure shows the granular layer, which is tightly packed with small granular cells. The axons of the Purkinje cells (not sectioned) end as sole efferent fibers of the cerebellar cortex adjacent to the neurons of the cerebellar nuclei.

Stain: Bielschowsky-Gros silver impregnation; magnification: × 200

Central Nervous System

682 Cerebellar Cortex

Purkinje cells from the cerebellar cortex of a rhesus monkey, vermis, lobulus II.

The primary dendrite of a Purkinje cell 1 ascends to the molecular layer and forms secondary and tertiary dendritic branches in this layer. The nuclei of granular cells 2 from the granular layer are located adjacent to the body of the Purkinje cell. A layer of cross-sectioned myelinated nerve fibers 3 in the lower third of the molecular layer follows. These are myelinated parallel fibers, which are abundant in some parts of the cerebellum. Only the very large myelinated fibers in the plexus supraganglionare represent retrogressive collaterals of the Purkinje cell axons. At the magnification, the very fine parallel fibers are not visible in this figure in the upper two thirds of the molecular layer. There is a cross-sectioned capillary at the lower edge of the figure. The oligodendrocyte 4 next to it was identified by its dense cytoplasm.

1 Cell body of a Purkinje cell

2 Nucleus of a granular cell

3 Myelinated axons

4 Oligodendrocyte

5 Capillary

Semi-thin section; stain: methylene blue-azure II; magnification: × 630

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