HISTOLOGY REVIEW Nervous Tissue Dr. Tim Ballard Department of Biology and Marine Biology

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

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 motor neurons

Spinal cord – cross section – silver – 40x objective Think in three dimensions. Where would the dendritic zone or the axon be related to this two-dimensional section? Ventral motor neurons neuronal cell body nucleus with a nucleolus dendrites These much smaller cells are likely to be neuroglial cells.

Spinal cord – cross section – silver – 40x objective 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 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. nucleus with a nucleolus Seeing Nissl substance and neurofibrils within cell bodies requires special stains. With careful fine-focusing, you may get a sense of these intracellular materials.

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

Cerebellum – section – silver – 4x objective 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 white matter gray matter Purkinje cell layer

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

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

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. Dorsal root ganglion

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

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

Artery, vein, and nerve – cross section – H&E – 4x objective 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 nerve artery vein

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

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