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==Normal histology==
==Normal histology==
===Normal cells===
{{main|Neurohistology}}
*Neuron:
This is a big topic. It is covered in a separate article called ''[[neurohistology]]''.
**Abundant cytoplasm - '''key feature'''.
**Often very large cells, with angled edges.
**Prominent nucleolus.
**Nissl substance (granular perinuclear material - rough ER).
*Glial cells.
**Oligodendrocyte.
***Small round nuclei (lymphocyte-like nucleus) - '''key feature'''.
***May resemble a ''fried egg'' on H&E (clear cytoplasm, central nucleus).
**Astrocyte.
***Irregular non-ovoid nucleus - '''key feature'''.
***Nuclei less dense than in oligodendrocyte.
***Close to blood vessels.
***Form blood-brain barrier.
***Cytoplasm normally ''not'' visible.
***Image: [http://embryology.med.unsw.edu.au/histology/endocrine/pin42he.jpg astrocyte (med.unsw.edu.au)] (in [http://embryology.med.unsw.edu.au/notes/endocrine12.htm endocrine development]).
**Microglia - macrophage of the brain (derived from monocyte).
***May be large.
***May have vesicles.
***Rarely seen in normal tissue.
*Ependyma.
**Simple ciliated cuboidal epithelium.
**Image: [http://www.stonybrookmedicalcenter.org/sbumcfiles/images/221-001.jpg Ependyma (stonybrookmedicalcenter.org)].
 
====Normal cellular constituents in a table====
{| class="wikitable"
|
|Key feature
|Other features
|Image
|-
|Neuron
| cytoplasm
| Nissl substance (prominent<br> RER), "sharp" corners <br>in cell membrane, nucleolus <br>- usu. prominent<ref name=Ref_PSNP16>{{Ref PSNP|16}}</ref>
| [http://commons.wikimedia.org/wiki/File:Alzheimer_type_II_astrocyte_high_mag_cropped.jpg red neurons (WC)]
|-
|Astrocyte
| non-ovoid nucleus
| no cytoplasm
| [http://embryology.med.unsw.edu.au/histology/endocrine/pin42he.jpg (unsw.edu)]
|-
|Oligodendrocyte
| round small nucleus
| peri-nuclear clearing
|
|-
|Microglia
| rod-like shape,<br> may have "bent" nucleus
| rarely seen in normal tissue
| [http://missinglink.ucsf.edu/lm/ids_104_cns_injury/Response%20_to_Injury/Microglia.htm (ucsf.edu)],[http://www.pathology.vcu.edu/WirSelfInst/neuro_medStudents/glialpath.html (vcu.edu)]
|-
|}
 
====Neurons====
There are many types of 'em.  Broadly, they can be classified as:
#Pyramidal - have a pyramidal shape.
##Dentrites go to molecular layer.
##Axons go to outside of cortex.
#Non-pyramidal.
 
Motor neurons:
*Coarse Nissl substance - '''key feature'''.
**Nissl described as having a ''tigroid appearance''.<ref>URL: [http://www.stonybrookmedicalcenter.org/pathology/neuropathology/chapter1 http://www.stonybrookmedicalcenter.org/pathology/neuropathology/chapter1]. Accessed on: 5 July 2010.</ref>
*Polygonal shape.
*Send dendrites in all directions.
 
Image: [http://www.stonybrookmedicalcenter.org/sbumcfiles/images/238-002.jpg Motor neuron (stonybrookmedicalcenter.org)].
 
===Histology - where===
====Subependyma====
Features:<ref>Half-day. 28 June 2010.</ref>
*Ependyma (simple ciliated cuboidal epithelium).
*Subependymal plate - connective tissue with blood vessels.
 
====Pons====
Features:
*Looks like bacon.<ref>Half-day. 28 June 2010.</ref>
*Image: [http://www.stonybrookmedicalcenter.org/sbumcfiles/images/243-scout.jpg Pons (stonybrookmedicalcenter.org)].
 
====Caudate====
Features:
*Neurons with adjacent ependymal lining.<ref>URL: [http://www.stonybrookmedicalcenter.org/pathology/neuropathology/chapter1 http://www.stonybrookmedicalcenter.org/pathology/neuropathology/chapter1]. Accessed on: 2 July 2010.</ref>
**The caudate forms lateral wall of lateral ventricle.
 
====Putamen====
Features:
*Histologically identical to the ''caudate'' - but not adjacent to a ventricle, i.e. an ependymal lining.
*Striatopallidal fibers [[AKA]] ''pencils of Wilson'' - bundles of blue fibres (on H&E LFB).
**Image: [http://frontalcortex.com/?page=oll&topic=24&qid=760 Pencils of Wilson (frontalcortex.com)].
 
====Globus pallidus====
Features:
*Histologically distinct from caudate and putamen.
 
====Hippocampus====
Hippocampal formation:<ref>URL: [http://www.stonybrookmedicalcenter.org/pathology/neuropathology/chapter1 http://www.stonybrookmedicalcenter.org/pathology/neuropathology/chapter1]. Accessed on: 2 July 2010.</ref>
#Dentate gyrus.
#*"Dense" thin layer of nuclei.
#*Quasi "U-shaped"; "open" (top) portion of "U" is superolateral.
#*Image: [http://www.stonybrookmedicalcenter.org/sbumcfiles/images/225-001.jpg Dentate gyrus (stonybrookmedicalcenter.org)].
#Hippocampus proper ([[AKA]] ''Ammon's horn'') - this is subdivided:
#*CA3 - superior.
#*CA1 - inferior (next to subiculum).
#*CA2 - in between CA3 and CA1, lateral.
#*CA4 - medial (closest to dentate gyrus; CA4 sits in "open" part of "U").
#Subicular complex.
 
Images:
*[http://en.wikipedia.org/wiki/File:Brainmaps-macaque-hippocampus.jpg Hippocampus - frontal section (WP)].
*[http://commons.wikimedia.org/wiki/File:Hippocampus_%28brain%29.jpg Hippocampus - good schematic (WC)].
*[http://www.ajnr.org/cgi/content-nw/full/28/5/958/F1 Hippocampus (ajnr.org)].
*[http://edoc.hu-berlin.de/dissertationen/schubert-stephan-nicolas-2003-09-26/HTML/schubert_html_21d219b1.png Hippocampus and subiculum (hu-berlin.de)].
*[http://spinwarp.ucsd.edu/NeuroWeb/Text/br-800epi/br-800epi1.gif Hippocampus - crappy schematic (ucsd.edu)].
 
Important note:
*CA1 - weak link, dies in ischemia, affected by hypoglycemia.
*CA2 - resistant to ischemia.
 
DDx of ischemia-like changes in the hippocampus:
*Toxins.
 
====Cerebellum====
Main components:
*Cortex (superficial) - branches (Christmas tree-like).
*Dentate nucleus (deep) - looks like the bite impression of a molar.
**Image: [http://www.stonybrookmedicalcenter.org/sbumcfiles/images/227-scout.jpg Cerebellum, cortex & dendate nucleus - low power (stonybrookmedicalcenter.org)].
 
Cerebellar cortex:
*Layers (superficial to deep) - mnemonic ''MPG'':<ref>URL: [http://www.stonybrookmedicalcenter.org/pathology/neuropathology/chapter1 http://www.stonybrookmedicalcenter.org/pathology/neuropathology/chapter1]. Accessed on: 2 July 2010.</ref>
*#Molecular layer -- "very pink" on H&E.
*#*Inhibitory interneurons: stellate cells, basket cells.
*#Purkinje cell layer.
*#*One cell layer thick - hueuege cells (~50-80 micrometers<ref name=Ref_PSNP16>{{Ref PSNP|16}}}}</ref>).
*#**Very large nucleus (~4x RBC diameter =~ 4x the size of granule cell).
*#***Large nucleolus (~1x RBC diameter =~ size of granule cell).
*#Granule cell layer -- "very blue" on H&E.
*#*Granule cells (many), interneurons (Golgi cells --few in number). (???)
*Images:
**[http://www.stonybrookmedicalcenter.org/sbumcfiles/images/227_001.jpg Cerebellar cortex - micrograph (stonybrookmedicalcenter.org)].
**[http://upload.wikimedia.org/wikipedia/commons/7/7c/Gray706.png Cerebellar cortex - schematic (Gray's Anatomy - WC)].
 
Notes:
*''Bergmann glia'' are found between the molecular layer & granular layer.  They are normally not seen.  They are increased & prominent in pathologic states (e.g. ischemia); "Bergmann gliosis".<ref name=Ref_PSNP18>{{Ref PSNP|18}}</ref>
 
====Cerebral cortex====
Layers (superficial to deep):
#Molecular layer.
#*Empty appearing.
#Outer granular layer.
#*Higher cell density & smaller cells than pyramidal layer.
#Outer pyramidal layer.
#Inner granular layer.
#*Not prominent in frontal cortex.
#*Where the thalamic axons end.
#*Divided in three (''a'', ''b'', ''c'') in the calcarine cortex due to two white matter bands (external band of Baillarger, internal band of Baillarger) than are grossly identified as the ''line of Gennari''.<ref name=Ref_PSNP24>{{Ref PSNP|24}}</ref>
#Inner pyramidal layer.
#*Location of ''Betz neurons'' - large motor neurons of cerebral cortex.
#Multiforme layer (Polymorphic layer).
 
Images:
*[http://commons.wikimedia.org/wiki/File:Cajal_cortex_drawings.png Cajal drawings - different areas (WC)].
*[http://www.ruf.rice.edu/~lngbrain/cglidden/Lab8_fig1.gif Different stains (rice.edu)].
*[http://williamcalvin.com/bk7/img/bk7p31.jpg Cerebral cortex (williamcalvin.com)].
*[http://www.benbest.com/science/anatmind/anatmd5.html Cerebral cortex (benbest.com)].


==Histopathology==
==Histopathology==
Michael
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