B&b Week 5: Cns Micro-Anatomy

Front 1

Now CNS Microanatomy

Back 1

*Coverings *Neurons -structure, function, neocortical organization, ischemic and degenerative changes *Glial cells -Astrocytes: structure, function, reactive and neoplastic changes -Oligodendrocytes: structures, function, myelin, demyelinating and neoplastic changes -ependyma and choroid plexus *Deep gray matter *Superficial Gray Matter: MTL and hippocampus *Cerebellum

Front 2

Dura Mater

Back 2

Most superficial layer -Two layers of connective tissue with venous sinuses where they meet -Penetrated by arachnoid villi Arterial bleeding can separate the dura from inner skull surface: an epidural hematoma

Front 3

Arachnoid Mater

Back 3

Middle Layer -Fibroblasts and arachnoidal cells -mostly fused to the dura, but easily interrupted by minor injuries to veins causing subdural bleeding -Arachnoidal cells fiund in clusters with prominent whorls and occasional psammoma bodies: AC's are the origin of meningiomas

Front 4

Pia Mater

Back 4

-Tightly affixed to the brain matter -Delicately anchored to the arachnoid mater by strands of arachnoid trabeculae -Collagen deposition causes gradual opacification -Subarachnoid space is frequently involved in meningitis, neoplastic infiltration and hemmorhages (lots of blood vessels -The Virchow Robin space around the small blood vessels is the site for these pathologies

Front 5

6 cellular layers of the cerebral neocortex

Back 5

1) a relatively acellular outer molecular layer, (2) external granular layer comprised of small round darkly staining neurons (3) external pyramidal layer comprised of larger triangular shaped neurons (4) internal granular layer (5) internal pyramidal layer (6) a polymorphous or multiform layer with a mixed populations of neurons, including large pyramidal type cells.

Front 6

Accumulation of lipfuscin in neurons

Back 6

-normal age-related process. -Oxidized fatty acids from membrane breakdown accumulate as a fine light brownish retractile material, typically located along the perikaryal edge.

Front 7

Ischemic changes to neurons

Back 7

“red” neuron. -shrunken cell body -intense cytoplasmic eosinophilia with complete loss of Nissl basophilia. -Dark nucleus without an evident nucleolus.

Front 8

Degenerative neuronal inclusions -Alzheimers -Parkinsons

Back 8

Neurfibrillary tangles in Alzheimers -Slightly basophilic and “flame shaped” -extend out along the apical dendritic process when involving pyramidal cells. -Special stains, including silver preparations, can highlight them. Lewy bodies in Parkinsons -Round eosinophilic inclusion that displaces the cytoplasmic neuromelanin and has a clear halo. -intensely labeled with antibodies for synuclein.

Front 9

Astrocytes normal histology

Back 9

-Extend foot processes towards the pial surface (glia limitans), the basement membrane of blood vessels, and non-synaptic regions of neurons. -But visualized as of bareunremarkable nuclei in contrast to the much larger neuronal and the densely hyperchromatic oligodendroglial nuclei. -Lots of intermediate filament known as glial fibrillary acidic protein (GFAP). Immunohistochemical stained

Front 10

Astrocyte reactive changes to brain injury

Back 10

Two components to this rapid response: *Hypertrophy: changes include accumulation of GFAP that can be demonstrated with immunohistochemical staining. *Hyperplasia: GFAP staining may also highlight the increased numbers of astrocytes and their processes.

Front 11

Astrocytomas????

Back 11

?????

Front 12

Oligodendroctyes

Back 12

-found both in gray and white matter. -only be identified histologically by their dense darkly stained nuclei and lack of conspicuous cytoplasm. -found in small groups of 2-3 cells in close proximity to neurons (satellitosis). -predominate type of glial cell in the white matter. -can be identified as individual andoccasionally rows of, nuclei between fascicles of myelinated fiber tracts. -One oligodendrocyted can myelinate up to 50 axons that may belong to the same or different fiber tracts.

Front 13

????Demyelinating Changes???

Back 13

?????

Front 14

????Oligodendrocytomas????

Back 14

?????

Front 15

Epenydma

Back 15

-line the ventricles of the brain and the central canal of the spinal cord. -They are cuboidal with elongated nuclei, microvilli -Like other epithelial cells, bound together by junctional complexes at their luminal surfaces. But no basement membrane -Instead, the base of ependymal cells breaks up into fine branches that interdigitate with an underlying layer of astrocytic processes. -Specialized ependymal cells have elongated processes that extend to the subependymal vasculature, thus linking the ventricular, vascular and intraparenchymal compartments of the CSF. -A similar pattern in ependymoma that often have prominent perivascular processes.

Front 16

Choroid Plexus

Back 16

-most epithelial of the glial-derived CNS structures. -cuboidal cells with round nuclei that rests on a basement membrane and are organized around a fibrovascular core. -Typically, choroid plexus is found throughout the ventricles -produces CSF. -The choroid plexus may develop from modified ependyma. -can give rise to both benign and malignant neoplasms.

Front 17

Deep Gray Matter

Back 17

group of deep subcortical nuclei that include the basal ganglia, thalamus and hypothalamus. The basal ganglia are further subdivided into the caudate, putamen, globus pallidus and subthalamic nucleus. All of the deep gray structures have in common a non-laminar architecture containing mixed populations of neurons and myelinated fibers. From a histologic perspective the basal ganglia are readily divided into the corpus striatum (caudate and putamen) and the globus pallidus. The structures of the corpus striatum have a similar histologic appearance, being composed of large and medium sized neurons packed moderately densely within a neuropil containing distinctive tracts of myelinated fibers (so called “pencil fibers”). This is in marked contrast to the globus pallidus (literally the “pale globe”) which contains a less densely packed population of large polygonal neurons embedded within a neuropil rich in myelinated fibers, lending a pale appearance to this region on gross examination. In contrast, the thalamus and hypothalamus are microscopically heterogeneous with marked variation in neuronal type and size, as well as the amount and prominence of myelinated fibers.

Front 18

Superficial Gray Matter

Back 18

most frequently encountered in the medial temporal lobe and hippocampus where there is a three-layered subiculum and a single pyramidal layer hippocampal formation. This is a phylogenetically more ancient part of the cerebrum that is characterized by the presence of Ammon’s horn (hippocampus proper) and the dentate gyrus, and the subiculum, a three-layered cortex that connects the hippocampus to the parahippocampal gyrus. The abbreviation cornu ammonis (CA) is routinely used for the hippocampus. This structure is comprised of four regions based on the cytoarchitecture of the single layer of pyramidal cells that comprise it, and their interconnections. The CA1 region (a.k.a. Sommer sector) is the most sensitive to various insults including ischemia, seizures and the degenerative changes of Alzheimer’s disease.

Front 19

Cerebellum

Back 19

Like the cerebrum, the cerebellum also has a convoluted surface (folia) that creates a large surface area to accommodate as many neurons as possible. Each folia is comprised of a relatively hypocellular outer molecular layer (ML) that contains the complex dendritic processes of Purkinje cells (P); the greatest number of neurons are actually contained in the densely packed granular layer (GL) that contains small round neurons with inconspicuous processes. Silver staining or neurofilament immunohistochemistry can be used to highlight the dendritic processes of the Purkinje cells that project into the molecular layer. Synaptophysin immunohistochemistry or silver staining may also highlight process that surround and synapse on the individual Purkinje cells.