4. Histo CNS Flashcards
describe the “typical” neuron
Cell body: w/ large nucleus w/ nucleolus & nissl substance/bodies (highly metabolic area) = dense stain
Numerous dendrites: from perikaryon; a lot of branching - increase receptive area (spines are plastic)
Long axon: from axon hillock (turn into telodendria at ends)
Neurophil: network of N. fibers, their branches & synapses, all together with glial filaments
How does anterograde transport work?
directional axonal transport
Carries material from N. cell body → axon
Uses kinesin, microtubule-associated
motor protein
How does retrograde transport work? What are problems that may occur with retrograde transport?
Directional axonal transport
Carries material from axon terminal →
cell body/dendrites → cell body
Uses dynein, microtubule-associated
motor protein
= may bring toxin/virus back to cell nucleus & spread from there (ex. shingles)
What is the rate of transport for cytoskeleton elements? (usually)
slow transport: anterograde movement
0.2-4 mm/day
What are the characterisitics of fast transport?
bidirectional movement of organelles
= 20-400 mm/day
-retrograde may include endocytosed toxins & viruses
where can an axon terminal synapse?
dendrites
cell body
axons
=allow for modification of signal @ same time
T/F Synaptic transmission is bidirectional?
FALSE:
= UNIDIRECTIONAL; convert electrical signal from presyn cell to chem signal that affects postsyn cell
What are the components of a chem synapse
Presynaptic terminal bouton - mitochondria & synaptic vesicles → release NT via exocytosis
Synaptic cleft separates pre- & postsynaptic membrane (20-30 nm wide intracellular space)
Postsynaptic cell membrane: Receptors for NTs & Ion channels to initiate a new impulse
What are the components of electrical synapses
Direct, passive flow of electrical current btn neurons via gap
junctions (link pre- & postsynaptic membranes (2nm))
• Contain connexon proteins- create the gap jxns w/ pores
- pores are where the ions flow directly from one neuron to next
What is the structure that contains large number of long branches and froms a vast network of terminals contacting synapses
Astrocytes
proximal part reinforced w/ intermeidate filaments made of (glioal fibrillary acid protein)
terminal processed of single astrocyte associate with 1M+ synapses
What are the fxns of astrocytes?
- contact & loop around blood vessels to create BBB
- reuptake NT to prevent over-reactive cells
- regulate ion concentration in the environment its in
What wraps myelin in the CNS?
Oligodendrocytes
-wrap axons from multiple neurons & 1 axon could have many oligos
= small cells w/ round, condensed nuclei & unstained cytoplasm
What cells line the brain ventricles & central canal of the sp. cord? How would it present on a histological slide?
Ependymal cells
=low columnar to cuboidal cells
- apical end = cilia & long microvilli (help move CSF & used in absportion)
- joined apically via apical jxnal complexes - set boundaries to prevent CSF seeping
- no basal lamina
What are the characteristics of the choroid plexus?
=thin, folded layers of well-vascularized pia; covered by cuboidal ependymal cells
Filters ==> remove H2O from blood & release CSF
-fills ventricles, central canal of sp. cord, subarachnoid & perivascular spaces (in roof - 3rd/4th ventricle & part of lateral)
• tight junctions (zonula occludens) btn ependymal cells
–> blood-CSF barrier
What is the fxn of arachnoid villi
provide absorption path for CSF back into venous circulation
how can you identify the choroid plexus on histograph
Blood vessels that run in fronds covered by
cuboidal/columnar epithelium → villous structure
- Capillaries & vessels are large, thin-walled
- Epithelial cells rest on a basal lamina
- Long bulbous microvilli project from the epithelial cells
What is the fxn of microglia
migratory, removes damaged or unactive synapses or other fibrous components
=major mechanism of immune defense in CNS (remove mibrobial invaders)
-from monocytes
What does the sp. cord contain
Central mass of grey matter - middle area(ventral, dorsal, & lateral horns)
Central canal in central commissure of grey matter (lined by ependymal cells & contains CSF)
White matter (edges) w/ ascending tracts of sensory fibers & descending motor tracts
What are the three layers of the cerebellar cortex?
- Molecular layer: a lot of neuropil & some neuron cell (light colored)
- Purkinje cells: prominent cell body w/ dendrites thru-out molecular layer as branching baskets of N fibers (visible in H&E stain)
- Granular layer: small, densely packed neurons (ie granule cells) & little neuropil (glial cells)
=organized into folia w cerebellar medulla, located deep
What are the 5 layers of the neocortex (cerebral cortex)
- Pyramidal cells: pyramid-shaped cell bodies w/ apex directed towards the cortical surface
- Granule (stellate) cells: small neurons w/ star shaped
- Cells of Martinotti: small polygonal cells w/ few short dendrites
- Fusiform cells: spindle-shaped cells sit at right angles to the cerebral cortex
- Horizontal cells of Cajal: small & spindle-shaped; oriented parallel to the surface (least common)
What are Betz cells
Huge upper motor neurons of the motor cortex = are the largest pyramidal cells
What are the 6 cortical layers
- molecular
- external granular
- external pyramidal
- inner granular
- ganglionic
- multiform (polymorphic)
What does the molecular cortical layer contain
fibers, mostly travel parallel to surface
mostly neuroglial cells & horizontal cells of Cajal
=fewest populated area & closest to pia matter
What does the external granular cortical layer contain
small pyamidal cells & granule cells
What does the external pyramidal cortical layer contain
pyramidal cells (kinda larger and have typical pyramidal shape)
What does the inner granular cortical layer contain
many small granule cells
What does he ganglionic cortical layer contain
= internal pyramidal layer
contains pyramidal cells that are extremely large (Betz cells) in motor areas
What does the multiform (polymorphic) cortical layer contain?
cells with diverse shapes,
many are fusiform cells
= right above white matter (which has very few cell bodies)
Which neurodegenerative disease contain amyloid plaques & neurofibrillary tangles? And what are these entities?
Alzheimer’s
Amyloid (amyloid β) plaques: amorphous, pink
masses in the cortex
Neurofibrillary tangles: flame-shaped skeins formed
by abnormal accumulation of tau
What are clincal presentations of Alzheimer’s disesae
most common neurodegenerative disease (70+ age)
memory loss, then progressing to involve motor skills, speech & sensation
small portion = genetics; other etiology unknown
=Very thin gyri, esp in frontal & temporal lobes
What is the substantia nigra
Large mass of grey matter w/ multipolar neurons w/ dark pigment (neurons w/ many membrane bound granules of neuromelanin pigment)
connections w/ cortex, sp cord, corpus striatum & reticular formations
imp for control of motor fxns
What is neuromelanin
granules in substantia nigra
contain dopamine (inhibitory effect in brain areas that relate to movement)
=dark pigment on neurons
Degeneration of the substantia nigra leads to …
Parkinson’s disease
loss of substantia nigra –> loss of dopamine
present as tremors, slow movement & rigidity
What are lewy bodies?
inclusions in remaining neurons after degeneration of substantia nigra
present in Parkinson’s pts!
= round, pink stained inclusions w/ pale halo
made of clumps of alpha-synuclein & other proteins
how do you identify anterior horn vs posterior horn
anterior horn wil have pink stained cells = MN cell bodies
