Histology of the CNS

Question 1

Neuropil

Answer 1

Dense network of nerve fibers and their branches and synapses, together with glial filaments

Question 2

Anterograde transport

Answer 2

Carries material from the nerve cell body to axon

Utilizes kinesin, microtubule associated motor protein

Question 3

Retrograde transport

Answer 3

Carries material from axon terminal to cell body or from dendrites to cell body
Utilizes dynein, microtubule associated motor protein

Question 4

Slow transport

Answer 4

Anterograde movement of substances such as cytoskeletal elements

Question 5

Fast transport

Answer 5

Bidirectional movement of organelles such as endocytosed toxins and viruses

Question 6

Electrical synapse

Answer 6

Direct, passive flow of electrical current between neurons via gap junctions made of connexon

Question 7

Astrocytes

Answer 7

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

Question 8

Oligodendrocytes

Answer 8

Extend processes that wrap nearby axons in myelin
Wrap multiple axons
Small cells with rounded, condensed nuclei and unstained cytoplasm

Question 9

Ependymal cells

Answer 9

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

Question 10

Choroid plexus

Answer 10

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

Question 11

Microglia

Answer 11

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

Question 12

Spinal cord

Answer 12

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

Question 13

Cerebellar cortex

Answer 13

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

Question 14

Cerebral cortex

Answer 14

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

Question 15

Cells of the neocortex

Answer 15

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

Question 16

Cortical layers

Answer 16

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

Question 17

Alzheimer’s disease

Answer 17

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

Question 18

Substantia niagra

Answer 18

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

Question 19

Parkinson’s disease

Answer 19

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

Question 20

What type of transport results in shingles sometimes

Answer 20

Retrograde transport picks up viral particles and transports them back to cell body