Digital Neuroanatomy

LM NEUROHISTOLOGY

George R. Leichnetz, Ph.D. Professor, Department of Anatomy & Neurobiology Virginia Commonwealth University 2004

Press the Å and Æ keys on your keyboard to navigate through this lecture There are three morphological types of neurons in the nervous system: unipolar, bipolar, and multipolar. While all three types can be found in the PNS, the CNS only contains multipolar neurons. CNS multipolar neurons vary greatly in morphology: eg. spinal cord motor neurons, pyramidal cells of cerebral cortex, Purkinje cells of cerebellar cortex. The supportive cells of the CNS are neuroglia: astrocytes, oligodendrocytes, and microglia. Oligodendrocytes myelinate CNS axons, while Schwann cells myelinate PNS axons. Protoplasmic astrocytes predominate in CNS gray matter, while fibrous astrocytes predominate in CNS white matter. The ventral horn of the spinal cord Lumbar Spinal Cord contains multipolar motor neurons.

Dorsal White Horn Matter Gray Matter Ventral Kluver- Horn Barrera Stain (LFB & CV) Cell bodies of motor neurons

Dendrite

Gray Matter Dendrite

Perineuronal H & E oligodendrocyte Stain Nucleus, nucleolus Abundant Nissl substance Dorsal root

Dorsal root ganglion

Ventral root

Gray Matter: contains White Matter: cell bodies of neurons contains x-sections of myelinated axons

Multipolar motor neurons Silver Stain of the ventral horn Large multipolar motor neurons of the spinal cord ventral horn: see nucleus, nucleolus, abundant Nissl substance, multiple tapering processes (dendrites). The axon hillock (origin of axon from cell body) lacks Nissl.

Nucleus Axon hillock

dendrites

Nucleolus

Nissl substance (RER)

Kluver-Barrera Stain (Luxol Fast Blue and Cresyl Violet) Thoracic Spinal Cord The nucleus dorsalis of Clarke, located in the base of the dorsal horn of the thoracic spinal cord, contains multipolar neurons whose nucleus is eccentric and Nissl around the periphery of the cell body (as if it were chromatolytic).

Nucleus dorsalis H & E of Clarke Stain Lateral horn

Oligodendrocytes Intermediolateral Cell Lateral horn Column (Lateral Horn) Thoracic Spinal Cord contains multipolar preganglionic sympathetic neurons.

Oligodendrocyte nucleus Protoplasmic astrocyte nucleus The cerebral cortex (gray matter on the surface of the cerebrum) contains multipolar pyramidal neurons.

Subcortical white matter

Cerebral cortex

Oligodendrocyte nucleus

Protoplasmic Lamina III astrocyte nucleus pyramidal neurons Pyramidal neurons of the cerebral cortex. The neuroglia of the cortex are protoplasmic astrocytes (euchromatic) and perineuronal and juxtavascular oligodendrocytes (heterochromatic, small dense spheroidal nuclei)

Apical dendrite Pyramidal neurons Apical dendrite

Perineuronal oligodendrocyte nucleus Basal Protoplasmic astrocyte nucleus dendrites

Axon

Perineuronal oligodendrocyte nucleus The cerebellar cortex contains multipolar Purkinje neurons.

Molecular layer

Cerebellum Purkinje cell layer

Cell body of Granular layer Purkinje cell Primary dendrite

Abundant dendritic spines on dendrites Dendrites

Cell body of Purkinje H & E Axon Cerebellar Cortex neuron The spinal cord white matter contains myelinated tracts, abundant fibrous astrocytes and interfascicular oligodendrocytes. Cross-sections of myelinated axons Dural sac (dura mater)

Dorsal Column

Lateral column

Ventral column

H & E Stain Thoracic Spinal Cord Fibrous astrocyte Interfascicular nucleus oligodendrocyte nucleus The spinal cord white matter is divided into columns: dorsal, lateral and ventral columns. Each contains ascending and descending tracts of myelinated axons. Interfascicular oligodendrocytes myelinate more than 50 axons. Dorsal column

Lateral column

Ventral column

Silver Stain The white matter columns (or funiculi) of the spinal cord contain myelinated axons (black dots). The lighter area (donut) around each axon cylinder was occupied by myelin. Groups of axons (tracts) ascend or descend See cross sections of axons (black dots) in the white matter. surrounded by myelin sheath (donut). The white matter under the cerebral cortex (subcortical white matter) contains myelinated axons going to and from the cortex, and contains abundant fibrous astrocytes and interfascicular oligodendrocytes.

Subcortical white matter

Interfascicular oligodendrocyte nuclei

Fibrous astrocyte nucleus The neuroglia of the cerebral cortex are predominantly protoplasmic astrocytes and perineuronal oligodendrocytes. The “perineuronal” oligodendrocytes myelinate the first segment of the neuron closest to the cell body.

Pyramidal neurons Protoplasmic astrocyte nuclei Perineuronal oligodendrocyte nuclei

Pyramidal neurons In the PNS, dorsal root ganglia contain sensory unipolar neurons surrounded by supportive elements, the satellite cells.

Dorsal root ganglion

The larger cell bodies are somatic sensory; smaller are visceral sensory Within the dorsal root ganglion, there (Pseudo-) unipolar are satellite cells and neuron cell bodies fibroblast nuclei between the unipolar neurons. (Fibroblasts are associated with connective tissue in the ganglion.) Spheroidal cell Satellite cell nuclei Nucleus, nucleolus bodies with central nucleus H & E The single process Stain divides into a peripheral process that goes to sensory receptor in skin or muscle and central Single “pole” process that goes of neuron thru dorsal root into Fibroblast the CNS. nuclei In the PNS, bipolar neurons Organ of Corti in are found in special sensory cochlea contains hair ganglia, like the cochlear cell receptors for hearing (spiral) ganglion in the cochlea of the inner ear. Spiral (Cochlear) ganglion

The bipolar neurons send one process to the hair cell receptor and the central process into the auditory nerve (CN. VIII) to CNS, which travels centrally into the brain. Bipolar neurons in the vestibular ganglion typically have an ovoid cell body. Its central and peripheral processes extend from the ends of the cell body. The peripheral process goes to hair cells in the vestibular end organs. The central process goes to the vestibular complex in the brainstem. The retina contains bipolar neurons. The rods and cones are specialized receptors on the peripheral processes of neurons that have their bipolar cell bodies in the outer nuclear layer of the retina.

Pigmented epithelium

Rods Rods Cone Cone

Cell bodies of bipolar neurons of the rods and cones Protoplasmic astrocytes, located in gray matter (seen here in cerebral cortex), have a bushy appearance.

Protoplasmic astrocyte

Apical Protoplasmic Pyramidal dendrite astrocytes neuron Basal dendrites Axon Pyramidal neurons Fibrous astrocytes (seen here in subcortical white matter) have long willowy processes and are less highly branched than protoplasmic astrocytes.

Astrocytes send processes to capillaries Fibrous astrocytes

Capillary Fibrous astrocytes in the subcortical white matter, stained with a special silver stain, show long processes to capillaries which end in perivascular end feet.

Fibrous astrocyte Capillary

Capillary

Capillary Capillary In the PNS, peripheral nerves are surrounded with epineurium. Fascicles within the nerve are surrounded with perineurium, and individual fibers are surrounded with endoneurium. This connective tissue is produced by fibroblasts. The myelin sheath around each axon is produced by Schwann cells. Thus the nuclei seen within peripheral nerves belong to fibroblasts and Schwann cells. Perineurium Pale violet axons are surrounded by space (donut) of myelin sheath

Epineurium Endoneurium

Perineurium

Schwann cell nuclei are plump, euchromatic; fibroblast nuclei are cigar-shaped