Histology of the CNS Flashcards
Neuropil
Dense network of nerve fibers and their branches and synapses, together with glial filaments
Anterograde transport
Carries material from the nerve cell body to axon
Utilizes kinesin, microtubule associated motor protein
Retrograde transport
Carries material from axon terminal to cell body or from dendrites to cell body
Utilizes dynein, microtubule associated motor protein
Slow transport
Anterograde movement of substances such as cytoskeletal elements
Fast transport
Bidirectional movement of organelles such as endocytosed toxins and viruses
Electrical synapse
Direct, passive flow of electrical current between neurons via gap junctions made of connexon
Astrocytes
Many long, branches processes, typically associated with 1 million+ synaptic sites
Proximal regions reinforced with intermediate filament made of glial fibrillary acid protein GFAP
Form vast network of delicate terminals connecting synapses and other structures
Contribute to BBB
Oligodendrocytes
Extend processes that wrap nearby axons in myelin
Wrap multiple axons
Small cells with rounded, condensed nuclei and unstained cytoplasm
Ependymal cells
Columnar or cuboidal cells that line the brain ventricles and the central canal of the spinal cord
Apical end my have cilia and long microvilli, facilitate production, movement of CSF and involved in absorption
Joined apically by apical junctional complexes, no basal lamina
Choroid plexus
Found in the roofs of the 3rd and 4th ventricles and parts of lateral ventricular walls
Thin, elaborated folded layer of vascularized pia mater covered by cuboidal ependymal cells
Removes H2O from blood and releases it as CSF
Large bulbous microvilli project from epithelial cells resting on basal lamina
Tight junctions b/w epithelial cells contribute to blood-CSF barrier
Microglia
Less numerous than oligodendrocytes or astrocytes
Migratory, will remove damaged or unactive synapses or other fibrous components
Major mechanism of immune defense in the CNS, removing any microbial invaders
Originate from monocytes
Spinal cord
Central mass of grey matter has the shape of a butterfly
Ventral, dorsal and lateral horns
Central canal lies in the central commissure of grey matter- lined by ependymal cells and contains CSF
White matter consists of ascending tracts of sensory fibers and descending motor tracts
Cerebellar cortex
Molecular layer- has much neuropil and scattered neuronal cell bodies
Purkinje cells- extend dendrites throughout the molecular layer as a branching basket of nerve fibers
Granular layer- contains various very small, densely packed neurons (i.e. granule cells) and little neuropil
Organized into folia with the cerebellar medulla located deep
Cerebral cortex
Biologically older parts of cortex are arranged into three layers and known as archicortex
Most of the cortex is called neocortex and consists of 6 layers
Cells of the neocortex
Pyramidal cells- largest known pyramidal cells are huge upper motor neurons called Betz cells
Granule/stellate cells- small neurons with a cell body the shape of a star (look like granules in micrographs)
Cells of Martinotti- small polygonal cells with a few short dendrites
Fusiform cells- spindle shaped cells oriented at right angles to the surface of the cerebral cortex
Horizontal cells of Cajal- small spindle shaped but oriented parallel to the surface (least common)
Also contains supporting glia
Cortical layers
Molecular layer- consists largely of fibers, most which travel parallel to surface & mostly neuroglial cells and horizontal cells of Cajal
External granular layer- consists mainly of small pyramidal cells and granule cells
External pyramidal layer- pyramidal cells are somewhat larger and possess a typical pyramidal shape, not sharply demarcated from layer two
Inner granular layer- characterized by the presence of many small granule cells
Ganglionic layer- internal pyramidal layer contains pyramidal cells are extremely large (Betz cells) I motor areas
Multiform (polymorphic) layer- contains cells with diverse shapes, many are fusiform cells
Alzheimer’s disease
Striking thinning of gyri, particularly those of the frontal and temporal lobes
Plaques, neurofibrillary tangles and neuronal loss are identified on sections
Amyloid beta plaques- amorphous, pink masses in the cortex
Neurofibrillary tangles- flame shaped skeins formed by abnormal accumulation of tau
Substantia niagra
Connections with the cortex, spinal cord, corpus striatum and reticular formation
Important role in fine control of motor function
Neurons contain numerous membrane-bound granules of neuromelanin pigment
Neuromelanin contains dopamine- inhibitory effects in brain areas dedicated to movement
Parkinson’s disease
Clinical features of tremor, slow movement and rigidity from degeneration of neurons in the substantia niagra causing loss of dopamine
Distinctive inclusions known as Lewy bodies are seen in the remaining neurons
Rounded, pink staining inclusions w/ pale halo
Composed of aggregates of protein alpha-synuclein and other proteins
What type of transport results in shingles sometimes
Retrograde transport picks up viral particles and transports them back to cell body
