Neuronal Anatomy

Cellular and Molecular Pathology of Neurodegenerative Diseases Course

This short document aims to summarise the anatomy of neurons with particular emphasis on features relevant to neurodegeneration.

Basic Elements

The 'classical' image of a neuron is a little misleading as it detracts from the great variety of neuronal forms that exist. Nevertheless it provides a useful starting point

Variations on a theme

Principle versus local circuit or Golgi Type II

Huge diversity: Amacrine cells with no axon, dorsal root gangion cell with split axon, cerebellar granule and Purkinje cells etc.

Appreciation of neuronal anatomy largely a function of technique used to visualise them

Cytology as demonstrated by various empirical stains

Haematoxylin and cosin: Nucleic acid blue, protein pink

Cresyl violet: Nucleic acid purple

Luxol fast blue: Myclin blue

Silver stains: Neuronal process (neurofilaments)

Golgi impregnation: Entire neuron

Lucifer yellow injection: Entire neuron

Cytology as demonstrated by enzyme histochemistry

eg:

NADPH-diaphorase

Cytochrome oxidase

Acetylcholine esterase

Cytology as demonstrated by immunohistochemical techiques

Antibodies to:

Enzymes, peptides etc: Selective populations

Pathological changes

Cytoskeletal antibodies: Variously axons, dendrites and soma

Pathological changes

Synaptic markers

Chromogranin Dense-cored vesicles

Synaptophysin Clear vesicles

Adhesion molecules

Cytology as demonstrated by electron microscopy

Massive protein synthetic machinery in perikaryon and dendrites; not axons.

Orderly cytoskeleton especially in axons

Wide range of synapses:

Type I: asymmetrical, round vesicles, excitatory Type II: symmetrical, flat vesicles, inhibitory

Structural challenges to a neuron

Maintenance of long processes with central synthetic machinery

Enormous surface area to volume ratio

Acheiving complexity of form and connectivity and maintaining plasticity