Histology of the Central Nervous System (Dennis)

Question 1

Typical neuron:

Answer 1

Cell body with large nucleus, well developed nucleolus and nissi substances/bodies (ribosomal activity since neurons are very active)

Question 2

Dendrites:
Axon:

Answer 2

-Extend from perikaryon (extensive branching)
Has numerous dendritic spines that increase the receptive surface area
-Long axon emerges from the axon hillock

Question 3

What is a neuropil?

Answer 3

Dense network of fibers and their branches and synapses together with glial filaments

Question 4

Anterograde axonal transport:

Answer 4

Cell body > axon

Uses kinesin, microtubule associated motor protein

Question 5

Slow transport

Fast transport

Answer 5

• Anterograde movement of substances (0.2-4mm/day) and typically cytoskeletal elements
• bidirectional movement of organelles (20-400 mm/day), may include endocytosed toxins and viruses

Question 6

How does synaptic communication work?

Answer 6

Nerve impulse transmitted from one neuron to effector cells (unidirectional)
Electrical signal from presynaptic cell converted to chemical signal that affects postsynaptic cell (via neurotransmitters)

Question 7

Presynaptic terminal:

Answer 7

Bouton contains mitochondria and synaptic vesicles > release NT via exocytosis

Question 8

Modularities of synapses:

Answer 8

Dendrites are not the only place neurons contact each other. Can be axon to cell body, axon to axon etc. Allows different signals to come in at the same time

Question 9

What is electrical synapse?

Answer 9

Flow of electrical current between neurons via gap junctions and links pre and postsynaptic neurons
Contains connexon proteins that form gap junctions that link the pre and postsynaptic membranes. Allows ions to pass through the junctions.

Question 10

Astrocytes

Answer 10

Has large number of long branching processes

Proximal regions have intermediate filaments made of GFAP (glial fibrillary acid protein)

Question 11

Functions of astrocytes:

Answer 11

Has perivascular feet that loop around blood vessels to establish BBB
Also reuptake NTs to keep neurons from firing often
Also regulate ionic environment around the cell

Question 12

What do oligodendrocytes do?

Answer 12

Wrap axons in myelin via extended processes in the CNS

Wraps axons from multiple neurons (promiscuous, numerous contacts)

Question 13

What are ependymal cells?

Answer 13

• Columnar cuboidal cells lining the ventricle and central canal of spinal cord
• Apical end may have cilia and microvilli that facilitate movement and absorption of CSF
• Joined apically by apical junctional complexes to create boundary for the fluid

Question 14

Choroid plexus:

Answer 14

Thin layer of cuboidal ependymal cells + vascular pia mater
Found on roofs of 3rd and 4th ventricles
Start to filter things from the blood and release the filtrate as CSF

Question 15

Functions of the choroid plexus

Answer 15

Removes H2O from blood and releases it as CSF

CSF fills the ventricles, central canal of SC, subarachnoid and perivascular spaces

Question 16

Features of the choroid plexus

Answer 16

• Blood vessels have a branching system with fibrous core and cuboidal/columnar epithelium
• Epithelial cells rest on basal lamina with long bulbous microvilli projecting from them
• Tight junctions connect the epithelial cells contributing to the blood CSF barrier. Basically helps the BBB formed by astrocytes.

Question 17

Functions of microglia:

Answer 17

CNS monocytes. Behave like macrophages
Remove damaged or unactive synapses or other fibrous components
Immune defense against microbial invaders in CNS

Question 18

Spinal cord

Answer 18

Central mass of gray matter; butterfly shape

Contains the Ventral, dorsal and lateral horns.

Question 19

Central canal of spinal cord

Answer 19

Lies in the central commissure lined with ependymal cells and contains CSF

Question 20

3 layers of the cerebellar cortex

Answer 20

Molecular layer - has neuropil and neuronal cell bodies
Purkinje cells - has dendrites
Granular layer - small densely packed neurons (granule cells)

Cerebellar medulla located deep to this

Question 21

What is the old layer of cerebral cortex?

Answer 21

Archicortex

Question 22

What makes up most of the cerebral cortex?

Answer 22

Neocortex consisting of 6 layers

Question 23

Cells of the neocortex:

Answer 23

Pyramidal cells - pyramid shaped cell bodies
Granule (stellate) cells - small neurons with star shaped cell bodies
Cells of Martinotti - small polygons with few short dendrites
Fusiform cells - spindle shaped cells oriented perpendicular to surface
Horizontal cells of Cajal - spindle shaped cells oriented parallel to surface

Question 24

What are the cortical layers of the cerebral cortex?

Answer 24

Molecular layer - fibers, neuroglial cells and horizontal cells of Cajal
External granular layer - small pyramidal cells/granule cells
External pyramidal layer - larger pyramidal cells
Inner granular layer- small granule cells
Ganglionic layer - extremely large pyramidal cells (Betz cells)
Multiform (polymorphic layer) - diverse shaped cells

Question 25

Alzheimer’s disease:

Answer 25

Memory failure, eventually motor skills, speech and sensation
Characterized by thinning of gyri especially frontal and temporal lobes

Question 26

Histology of alzheimers:

Answer 26

Plaque, tangles and neuron loss
Amyloid B plaques - amorphous, pink masses in the cortex
Neurofibrillary tangles - flame skeins formed by abnormal accumulation of tau

Question 27

Substantia nigra:

Answer 27

• Large mass of grey matter containing dark pigmented multipolar neurons
• Neurons have neuromelanin pigment which contains dopamine which inhibits brain areas dedicated to movement
• Important role in fine control of motor function

Question 28

Parkinson’s clinical features:

Answer 28

Tremor, slow movement, rigidity from degeneration of neurons in the substantia nigra > loss of dopamine

Question 29

Histology of Parkinson’s disease:

Answer 29

Lewy bodies are rounded pink-staining inclusions w pale halo

Aggregates of alpha synuclein