4. Histo CNS

Question 1

describe the “typical” neuron

Answer 1

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

Question 2

How does anterograde transport work?

Answer 2

directional axonal transport

Carries material from N. cell body → axon

Uses kinesin, microtubule-associated
motor protein

Question 3

How does retrograde transport work? What are problems that may occur with retrograde transport?

Answer 3

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)

Question 4

What is the rate of transport for cytoskeleton elements? (usually)

Answer 4

slow transport: anterograde movement

0.2-4 mm/day

Question 5

What are the characterisitics of fast transport?

Answer 5

bidirectional movement of organelles

= 20-400 mm/day

-retrograde may include endocytosed toxins & viruses

Question 6

where can an axon terminal synapse?

Answer 6

dendrites

cell body

axons

=allow for modification of signal @ same time

Question 7

T/F Synaptic transmission is bidirectional?

Answer 7

FALSE:

= UNIDIRECTIONAL; convert electrical signal from presyn cell to chem signal that affects postsyn cell

Question 8

What are the components of a chem synapse

Answer 8

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

Question 9

What are the components of electrical synapses

Answer 9

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

Question 10

What is the structure that contains large number of long branches and froms a vast network of terminals contacting synapses

Answer 10

Astrocytes

proximal part reinforced w/ intermeidate filaments made of (glioal fibrillary acid protein)

terminal processed of single astrocyte associate with 1M+ synapses

Question 11

What are the fxns of astrocytes?

Answer 11

1. contact & loop around blood vessels to create BBB
2. reuptake NT to prevent over-reactive cells
3. regulate ion concentration in the environment its in

Question 12

What wraps myelin in the CNS?

Answer 12

Oligodendrocytes

-wrap axons from multiple neurons & 1 axon could have many oligos

= small cells w/ round, condensed nuclei & unstained cytoplasm

Question 13

What cells line the brain ventricles & central canal of the sp. cord? How would it present on a histological slide?

Answer 13

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

Question 14

What are the characteristics of the choroid plexus?

Answer 14

=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

Question 15

What is the fxn of arachnoid villi

Answer 15

provide absorption path for CSF back into venous circulation

Question 16

how can you identify the choroid plexus on histograph

Answer 16

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

Question 17

What is the fxn of microglia

Answer 17

migratory, removes damaged or unactive synapses or other fibrous components

=major mechanism of immune defense in CNS (remove mibrobial invaders)

-from monocytes

Question 18

What does the sp. cord contain

Answer 18

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

Question 19

What are the three layers of the cerebellar cortex?

Answer 19

1. Molecular layer: a lot of neuropil & some neuron cell (light colored)
2. Purkinje cells: prominent cell body w/ dendrites thru-out molecular layer as branching baskets of N fibers (visible in H&E stain)
3. Granular layer: small, densely packed neurons (ie granule cells) & little neuropil (glial cells)

=organized into folia w cerebellar medulla, located deep

Question 20

What are the 5 layers of the neocortex (cerebral cortex)

Answer 20

1. Pyramidal cells: pyramid-shaped cell bodies w/ apex directed towards the cortical surface
2. Granule (stellate) cells: small neurons w/ star shaped
3. Cells of Martinotti: small polygonal cells w/ few short dendrites
4. Fusiform cells: spindle-shaped cells sit at right angles to the cerebral cortex
5. Horizontal cells of Cajal: small & spindle-shaped; oriented parallel to the surface (least common)

Question 21

What are Betz cells

Answer 21

Huge upper motor neurons of the motor cortex = are the largest pyramidal cells

Question 22

What are the 6 cortical layers

Answer 22

1. molecular
2. external granular
3. external pyramidal
4. inner granular
5. ganglionic
6. multiform (polymorphic)

Question 23

What does the molecular cortical layer contain

Answer 23

fibers, mostly travel parallel to surface

mostly neuroglial cells & horizontal cells of Cajal

=fewest populated area & closest to pia matter

Question 24

What does the external granular cortical layer contain

Answer 24

small pyamidal cells & granule cells

Question 25

What does the external pyramidal cortical layer contain

Answer 25

pyramidal cells (kinda larger and have typical pyramidal shape)

Question 26

What does the inner granular cortical layer contain

Answer 26

many small granule cells

Question 27

What does he ganglionic cortical layer contain

Answer 27

= internal pyramidal layer

contains pyramidal cells that are extremely large (Betz cells) in motor areas

Question 28

What does the multiform (polymorphic) cortical layer contain?

Answer 28

cells with diverse shapes,

many are fusiform cells

= right above white matter (which has very few cell bodies)

Question 29

Which neurodegenerative disease contain amyloid plaques & neurofibrillary tangles? And what are these entities?

Answer 29

Alzheimer’s

Amyloid (amyloid β) plaques: amorphous, pink
masses in the cortex

Neurofibrillary tangles: flame-shaped skeins formed
by abnormal accumulation of tau

Question 30

What are clincal presentations of Alzheimer’s disesae

Answer 30

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

Question 31

What is the substantia nigra

Answer 31

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

Question 32

What is neuromelanin

Answer 32

granules in substantia nigra

contain dopamine (inhibitory effect in brain areas that relate to movement)

=dark pigment on neurons

Question 33

Degeneration of the substantia nigra leads to …

Answer 33

Parkinson’s disease

loss of substantia nigra –> loss of dopamine

present as tremors, slow movement & rigidity

Question 34

What are lewy bodies?

Answer 34

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

Question 35

how do you identify anterior horn vs posterior horn

Answer 35

anterior horn wil have pink stained cells = MN cell bodies