HISTOLOGY REVIEW Nervous Tissue

Dr. Tim Ballard Department of Biology and Marine Biology

Orientation to the spinal cord

Spinal cord – cross section – silver – 4x objective dorsal horns of gray matter gray commissure central canal ventral horns of gray matter Silver stains nerve cells and unmyelinated fibers brownish-black. The white matter is lightly stained because there is so much myelin around the fibers.

Ventral motor neurons

motor neurons Spinal cord – cross section – silver – 10x objective In the ventral horn there are very large motor neurons. The brown fibers you see leaving the ventral horn are axons from these neurons.

Ventral motor neurons

Spinal cord – cross section – silver – 40x objective These much smaller cells are likely to be neuroglial cells.

neuronal cell body dendrites nucleus with a nucleolus neuronal cell body Think in three dimensions. Where would the dendritic zone or the axon be related to this two-dimensional section?

Ventral motor neurons

Spinal cord – cross section – silver – 40x objective nucleus with a nucleolus This could be an axon hillock. Compared to the other branches here, this has a larger diameter, so it could be giving rise to an axon.

Seeing Nissl substance and neurofibrils within cell bodies requires special stains. With careful fine-focusing, you may get a sense of these intracellular materials.

Look at all of the cross-hatching brown-black fibers between the cell bodies. This is the “neuropil,” all of the axons of the gray matter connecting cells.

Ventral motor neurons

Spinal cord – cross section – Nissl’s stain – 40x objective ventral motor neuron neuroglial cells Look at the differences in size between neuronal cell bodies and neuroglia.

Cerebellar cortex

Cerebellum – section – silver – 4x objective Purkinje cell layer gray matter white matter The Weigert-Weils technique stains nerve cells and unmyelinated fibers brown ish. White matter is heavily stained due to the presence of myelinated fibers.

Cerebellar cortex

Cerebellum – section – silver – 10x objective molecular cell layer Purkinje cell layer granular cell layer Look at the differences in neuronal sizes between the three layers of neurons shown above.

Cerebellar cortex

Cerebellum – section – silver – 40x objective molecular cell layer granular cell layer Purkinje cell layer Look at the differences in neuronal sizes between the three layers of neurons shown above.

Dorsal root ganglion

Spinal ganglion – section – silver – 4x objective The dorsal root ganglion consists of nothing but the cell bodies of sensory neurons.

Dorsal root ganglion

Spinal ganglion – section – silver – 40x objective Sensory neurons are pseudounipolar, so it is hard to see dendrites, axons, and central processes.

Features of nerve fibers

Nerve – longitudinal section – H&E – 4x objective The nuclei you find in this section are those of Schwann cells (neurolemmocytes).

With the H&E stain, nerve fibers don’t stain, but the Schwann cells do. Nodes of Ranvier and the myelin are much more easily seen with an osmium stain.

Features of nerve fibers

Nerve – teased fibers – osmium – 20x objective node of Ranvier Osmium stains the lipid of myelin gray-black. The segments you see are individual pieces of myelin. Between each would reside nodes of Ranvier.

Structures of a nerve in cross section

Artery, vein, and nerve – cross section – H&E – 4x objective nerve vein artery Oftentimes, an artery, its two companion veins, and a nerve will travel together bundled into a common connective tissue.

Structures of a nerve in cross section

Artery, vein, and nerve – cross section – H&E – 10x objective fascicles This nerve is formed of 4 fascicles (individual bundles of fibers)

Structures of a nerve in cross section

Perineurium – invests an individual fascicle, holding the nerve fibers together as a single fascicle Epineurium – invests all the fascicles, holding them together as a single nerve Endoneurium – extensions of the perineurium that invest each individual nerve fiber within the fascicle Artery, vein, and nerve – cross section – H&E – 10x objective This nerve is formed of 4 fascicles (individual bundles of fibers) end