brain histology

Question 1

What is unique about the central nervous system

Answer 1

selective vulnerability of neuronal systems: degeneration of specific nuclei and connections

Mature neurons are post-mitotic cells: loss cannot be repaired, recent discovery of stem cells in the CNS

Unique anatomic/physiologic characteristics: bony enclosure, metabolic substate requirements (glucose and oxygen), no lymphatic system, presence of CSF, limited immune surveillance (physical barrier), distinctive response to injury and healing (astrocyte reaction)

Question 2

normal neurons

Answer 2

Integrating and transmitting cells of the CNS, using chemical and electrical means

Morphology varies by location

most have large nucleus with prominent nucleolus (Well defined cytoplasm containing Nissl substance), if theres nissl substance= rough endoplasmic reticulum
Branching processes (dendrites)- and longer cell process axon, axons have terminal synapses for chemical transmission to another neuron

Shape varies depending upon location in brain- pyramidal and glandular neurons in cerebral cortex, betz cells in primary motor cortex, granular neurons in hippocampus and cerebellum, purkinje cells in cerebellum, anterior horn cells in spinal cord, globoid shaped cells in deep gray nuclei (basal ganglia, thalamus, brainstem), melanin containing cells in brainstem (substantia nigra, locus ceruleus)

Question 3

Eosinophilic degeneration

Answer 3

Indicates LETHAL ischemia, hypoxia, or hypoglycemia

takes 12-24 hours to manifest at light microscope level

Morphologic criteria- shrinkage of neuronal cell body, loss of nissl with cytoplasmic eosinophilia, loss of nucleolus with nuclear pyknosis

Question 4

central chromatolysis

Answer 4

manifestation of switch from manufacture of synaptic to structural proteins in responsse to axonal damage
Reversible if axonal repair is successful
Cellular swelling with margination of nissl substance and nuvleus and accumulation of filaments and organeles

Question 5

Glial cells of the CNS

Answer 5

macroglia- all derived from neuroectoderm (90% of all CNS cells)
Astrocytes, oligodendrocytes, ependymal cells
microglia- derived from bone marrow

Question 6

AStrocytes

Answer 6

Primary replicating cell within the CNS
Round to oval nucleus (10um) with radiating cytoplasmic processes
Star shaped cytopllasm- normally invisible on H and E staining (unless reacting to injury), glial fibrillary acidic protein (GFAP)- major cytoplamsic structural protein, antibodies to GFAP help visualization of astrocytes

Functions- contribure to BBB, cytoplasmic processes end feet on blood vessel walls, control flow of macromolecules between blood CSF brain, responsible for repair and scar formation, maintain extracellular environment, metabolic buffers or detoxification and supply nutrients, structural support

Question 7

Reactive astrocytosis

Answer 7

Astrocytes activate in response to various pathologic conditions
Provides evidence of disease process, Astrocytes divide and become larger, increase in GFAP filaments reflected in visible eosinophilic cytoplasm, GFAP anitobdy will help identify the reactive astrocytes, the cytoplasm may appear starlike (fibrillary) or large and round gemistocytic

Question 8

oligodendroglia

Answer 8

responsible for myelination in the CNS, more numerous in white matter than gray matter
Smaller nucleus and fewer processes than astrocytes (round dense nucleus, perinuclear halo arterfact)

Dont synthesize GFAP, lethal injury –> demyelination

important disease involving oligodendrocytes– MS, progressive multifocal leukoencephalopathy, oligodendrogliomas

Question 9

ependymal cells- ependyma

Answer 9

cuboidal to columnar glial ciliated cells that line ventricular sufaces, Lateral surfaces have cell junctions forming CSF-brain barrier

Question 10

Choroid plexus

Answer 10

tufts of epithelium projecting into ventricles, secrete CSF, papillary architecture, cell junctions between cells ensure CSF- brain barrier

Question 11

Microglia

Answer 11

Monocyte/marcrophage-derived cells that reside in the CNS, normally inconspicuous, sparse, rod shaped nuclei without visible cytoplasm

With CNS injury may become activated- migrate to site of injury, proliferate, may differentiate into tissue macrophage (foamy clear cytoplasm), in viral infections, astrocytes and microglia form microglial nodules at sites of neuronal injury, HIV infection stimulates cellular fusion resulting in multinucleated giant cells in microglial nodules