Central Nervous System - Histology

Introduction

The Central Nervous System (CNS) is composed of the brain and the spinal cord and it is from the CNS that the Peripheral Nervous System (PNS) is derived. This page is specifically focussed on the histologic appearence of both the brain and spinal cord and therefore the anatomy of both structures will not be provided in depth. Instead, links to the relevant anatomy and physiology pages for each structure will be given below.

Anatomy & Physiology Links

Please use the links below to familiarise yourself with the anatomy and physiology of the different aspects of the CNS as an aid to utilising and understanding the CNS histology images below;

CNS Development
Forebrain
Midbrain
Hindbrain
Cranial Nerves
Spinal Cord

Histology of the Spinal Cord

The spinal cord is composed to two discrete parts; the white matter which is the outer part of the cord and the grey matter which is the inner portions of the cord. The white matter is given this name due to its appearance in unfixed histological specimens in which the white nature of the tissue is caused by the myelination of ascending and descending nerve fibres. The grey matter is also named after its unfixed histological appearance and contains the cell bodies of neurons as well as nerve fibres.

Within the spinal cord the grey matter forms an H-shape where the ventral horns of the H are broader than the dorsal horns. The grey matter shape has also been likened to that of a butterfly. The grey matter also has a histologically visible central canal running through it. The ventral horns of the grey matter contain the cell bodies of motor neurones whilst the dorsal horns contain sensory neurons where the cell bodies are found in the dorsal root ganglia. Please see sensory pathways for further information on the composition of nerve fibres within the spinal cord. The relative size of the grey matter is dependant on the number of motor cells related to controlling limbs and therefore the size varies along the length of the spine. Around the areas of the fore and hindlimbs the grey matter is considerably larger.

Spinal Cord - © John Bredl

The above image shows a complete cross-sectional histology of a spinal cord. In this particular stain the grey matter can be seen in a slightly darker shade than the white matter. The relative size of the grey matter is small compared to the white matter and therefore the level of the cross-section is unlikely to be around the level of any limbs. The dorsal horns and be seen to extend near to the dorso-lateral surface of the spine. The slide also contains small elements of the dorsal and ventral roots leaving the spinal cord. The connecting element of the grey matter which is immediately ventral to the central canal is called the grey commissure (GC). The stained areas found around the edge of the spinal cord are fibrous material that is the pia mater. This pia mater follows the contours of the spinal cord and also folds into the ventral fissure. At the ventral aspect of the ventral fissure some small blood vessels can be seen present in the pia mater.

Spinal Cord 2 - © John Bredl

The above image shows a higher magnification view of the grey matter of the spinal cord which is clearly surrounded by white matter. The ventral horn has a number of processess which extend into the white mater. The image displays a number of multipolar cells that are relatively large compared to the nerve fibres which surround these cells. Although at this magnification it is not possible to definitively identify these cells but it is likely that they are cell bodies of neurons. The surrounding nerve fibres are likely to be neuroglial cells, although the cytoplasm of these cells is not visible. The seemingly poor organisation of the tissues surrounding these neurons is often referred to as neuropil.

Spinal Cord 3 - © John Bredl

This image shows a further magnified view which displays the central canal and ependymal cell layers. The surrounding tissue is similar to that of the grey matter neuropil seen in the previous image above. Within the central canal vessel some remnants of CSF can be seen. Within the neuropil tissues some cell bodies can be seen.

Rabbit Spinal Cord

Rabbit Spinalcord at 40x Magnification

This image shows a moderately magnified image of the outer edge of the spinal cord. The bulk of the histological appearence is made up by white matter which is predominantly nerve fibres and myelin sheaths. This histological image clearly shows the different layering of protection around the outside of the spinal cord and how closely associated this protection is. The outer layer is the dura mater and then continuing to move towards the spinal cord there is the sub-dural space leading to the arachnoid mater. Inside the arachnoid space is the sub-arachnoid space and then the pia mater which is closely bound to the underlying neural tissues.

Histology of the Brain

Cerebrum section

The cerebrum contains the cell bodies of nerves both receiving and sending sensory information involved in controlling voluntary movement via motor activity and in the integration and coordination of other nerves. The cerebrum is also involved in memory functions.

In a full thickness histological image of the cerebrum it would be possible to distinguish numerous layers including the pia mater on the outer edge of the brain, the plexiform layer, pyramidal layer, granular layer and a polymorphic cell layer innermost, prior to the white matter towards the centre of the brain. The plexiform layer consists of mainly fibrous material which run in parallel to the surface of the brain. This layer contains relatively few cells, mainly neuroglial cells. The pyramidal cell layers mainly consist of small, medium and large pyramidal shaped cells which generally become larger as they become closer to the white matter of the cerebrum. Finally the pleopmorphic layer contains cells of very doverse shapes, a majority of which have a spindle shape. These cells are often called fusiform cells.

Cerebrum - © John Bredl

The histologic image above displays a very clear high magnification image displaying cell bodies with dendrites and axons extending from them. It should be noted that such a clear image of the nerve cells within the cerebrum

Cerebellum section

Cerebellum

Cerebellum - © John Bredl

Other Histology

Choroid Plexus Histology 40x