Histology Of The CNS Flashcards
What does the cell body of a typical neuron have?
Well developed nucleolus and Nissl substance
What are Nissl Substances?
Basically rER of neurons
Where do dendrites of a typical neuron extend from?
From perikaryon
What increases the receptive area of a typical neuron?
Numerous dendritic spines that are plastic
What is a neuropil?
Dense network of nerve fiber and their branches and synapses, together with glial filaments
What is a multipolar neuron?
Many dendrites
One axon
What is a bipolar neuron?
One dendrite
One axon
What is a pseudo-unipolar neuron?
One cell process w/ branches, single axon, single dendrite
Where would you find a multipolar axons?
Spinal motor neurons in cns and autonomic ganglia
Where would you find bipolar neurons?
Sensory neurons in olfactory epithelium, retina, ganglia of vestibulocochlear n.
Where would you find pseudo-unipolar neurons?
Sensory neurons in the PNS
Dorsal root ganglia
How are neurons in the PNS myelinated?
Satellite cells surround soma
Schwann cells wraps itself around the axons and form myelin
How does a Schwann cell myelinate?
1 cell to 1 neuron?
What is a myelin sheath in the PNS made of?
Mostly made of phospholipids
How are axons myelinated in the CNS?
Oligodendrocytes myelinates and warps a cell process around the axon
1 cell to many neurons
How do synapses communicate?
Unidirectional
Coverts electrical signal (nerve impulses) from presynaptic cell
To chemical signal
To postsynaptic cell
And most release NTRs
What comprises a chemical syanpse?
Presynaptic bouton/terminal
Synaptic cleft
Postsynaptic membrane
What does the presynaptic bouton contain?
What does it do?
Mitochondria
Synaptic vesicles
Release NTRs via exocytosis
What is the synaptic cleft
A 20-30 NK wide intercellular space that separates pre and post synaptic membranes
What does the postsynaptic membrane contain?
Receptors for NTRs
Ion channels to initiate a new impulse
What is an electrical synapse
Direct, passive flow of electrical current between neurons using gap junctions
What is contained in the electrical synapse?
Connexon proteins
What do connexon proteins do?
Link pre and post synaptic membranes and allow for ions to flow thru
Where are electrical synapses found?
Retina
Olfactory bulb
Inferior Olivary nucleus
What do the different axon connections allow for?
I.e. axon to cell body, axon to axon, axon to dendrite
Allows for modulation of different signals coming in at same time
What is anterograde transport in axons?
Transport from nerve cell body to axon
How does anterograde transport happen?
Utilizes kinesiology, microtubule-associated motor protein
What is retrograde transport in axons?
Transport from axon terminal to cell body/dendrites
How does retrograde transport occur?
Uses dynein- a microtubule associated motor protein
What uses retrograde transport?
Example?
Endocytosed toxins and viruses
-shingles
What uses slow transport?
Speed of slow?
Anterograde movement of substances usually cytoskeleton elements
.2-4.0 mm/day
What uses fast transport?
Speed?
Both retrograde and anterograde (bidirectional) movement of organelles
20-400 mm/day
What are astrocytes
Type of glial cells with large number of long,branching processes
What are the proximal regions of astrocytes reinforced with?
What are these made of?
Reinforced with intermediate filaments
Made of glial fibrillary acid protein (GFAP)
What do the intermediate filaments of astrocytes do?
Forms network of terminals connecting synapses and other structures
How many synaptic sites do the terminal processes of a single astrocytes typically associate with?
Over 1 million synaptic sites
What is the function of Astrocytes
Establish BBB with their endfeet
Regulate immediate microenvironment around cell in terms of ion concentration
Reuptake NTRs
Assists with neuronal development
Replicates to occupy space of dying neurons
What are oligodendrocytes?
Glial cells that extend processes to wrap nearby axons in myelin in the CNS
Histologically, how do oligodendrocytes appear?
Small cells with rounded, condensed nuclei and unstained cytoplasm
What are microglia?
Migratory glial cell that removes damaged or inactive synapses or other fibrous components
Which glial cell is a major mechanism of immune defense in the CSF?
Microglia - remove any microbial invaders
What do microglial cells originate from?
Monocytes
What is the funciton of microglial cells?
Phagocytize invaders moving thru CNS
Protect CNS by engulfing infectious agents and other potential harmful substances
What are ependymal cells?
Cells that line brain ventricles and central canal of SC
Histologically, how do ependymal cells appear?
Columnar or cuboidal cells
Apical end may have cilia and long microvilli
No basal lamina present
What do the cilia and long microvilli of ependymal cells do?
Facilitate movement of CSF
Involved in absorption
How do ependymal cells create fluid boundary?
Joined apically by apical junctional complexes
What are the functions of ependymal cells?
Lines ventricles of brain and central canal of SC
Assists in production and circulation of CSF
Where are choroid plexus cells found?
In roofs of 3rd and 4th ventricles and parts of lateral ventricular walls
Histologically, how do choroid plexus cells appear?
Thin, elaborate folded layer of well vascularized pia mater
Covered by cuboidal ependymal cells
What do choroid plexus cells do?
Remove water from blood and release it as CSF
What is contained in chorodi plexus cells?
Na, k, and CL (took it out so CSF doesn’t have it)
Some proteins
Sparse lymphocytes
What does the CSF fill?
Ventricles, central canal of SC, and perivascular spaces
What are villous structures?
Branching system of blood vessels that run in fronds
What are fronds composed of?
Fibrous core covered by cuboidal/columnar epithelium
What does the epithelial cells of the choroid plexus cells rest on?
What projects from them?
Basal lamina
Long bulbous microvilli
What is found between epithelial cells of the choroid plexus?
Zona occludens (tight junctions) that contribute tot he blood-CSF barrier
What is the dorsal (posterior) horn of the spinal cord for?
Sensory info
What is the ventral horn of the spinal cord function?
Assoc. motor neurons
What is in the center of the spinal cord?
Grey matter shaped like a butterfly
How can you tell apart dorsal and ventral horns?
Dorsal = smaller wing
Ventral = will see motor neurons in it
Where is the central canal of the Spinal cord?
What is it lined with? What does it contain?
In central commissure of grey matter
Lined w/ ependymal cells
Contains CSF
What does the white matter of the Sc contain?
Ascending sensory tracts
Descending motor tracts
What are the three layers of the cerebellum?
Molecular
Purkinje
Granule cell
What is found in the molecular layer of the cerebellum?
Where is this layer in relation to the others?
Many neuropil and scattered neuronal cell bodies
Most superficial layer
What characterizes the purkinje layer of the cerebellum?
Extend dendrites thru-out the molecular layer
“branching baskets of nerve fibers”
What is contained in the granule cell layer of the cerebellum?
Where is this layer in relation to the others?
Very small, densely packed neurons
Little neuropil
Deepest layer
Where and what is the cerebellar medulla?
Located deep to all the layers
White matter of the cerebellum
How many layers of the cerebral cortex are there?
Six
What 5 cell types are there in the neocortex?
Pyramidal cells Granule cells (aka Stellate) Cell of martinotti Fusiform cells Horizontal cells of Cajal
+supporting glia
How many layers are the older parts of the cortex arranged into? What is this called?
3 layers
Archicortex
What are two types of pyramidal cells?
Pyramid shaped cell bodies
Betz cells
What is the apex of pyramid shaped cell bodies directed toward?
Cortical surface
What are Betz cells?
Largest pyramidal cells
Upper motor nuerons of the motor cortex
What are granular cells?
What is another name for them?
Small neurons w/ a cell body in the shape of a star
Stellate cells
How will granular cells appear in micrographs
As granules
Not stars
What are cells of martinotti?
Small polygonal cells w/ few short dendrites
What are fusiform cells?
Spindle shaped cells at right angle to the surface cerebral cortex
What are the horizontal cells of Cajal?
Small and spindle shaped
Oriented parallel to the surface
Which cell type is least common in the cerebral cortex
Horizontal cells of Cajal
What are the six layers of the cerebral cortex?
- Molecular layer
- External granular layer
- External pyramidal layer
- Inner granular layer
- Ganglionic layer
- Multiform (polymorphic) layer
What does the molecular layer consist of?
Which layer is it?
Layer 1
Consists largely of fibers traveling parallel to the surface
Neuroglia cells and horiz. Cells of Cajal
What does the external granular layer consist of?
Which layer is it?
Second layer
Consists mainly of small pyramidal cells and granule cells
What does the inner granular layer consist of?
Which layer is it?
Layer 4
Many small granule cells
What does the Ganglionic layer consist of?
Which layer is it?
Fifth layer
Internal pyramidal layer
Large pyramidal cells (Betz cells) in motor areas
What does the Multiform (polymorphic) layer consist of?
Which layer is it?
Layer 6
Contains cells w/ diverse shapes
many fusiform cells
What is the most common neurodegenerative disease?
Alzheimer’s disease
When does Alzheimer’s typically present? What does incidence increase with?
~70 y.o.
Increase w/ age
What are the symptoms of Alzheimer’s disease?
Memory failure
Progressing steadily to involve motor skills, speech and sensation
What is the etiology of Alzheimer’s disease?
Unknown
Small population has genetic assoc.
What happens to the gyri as a result/cause of alzheimers?
Thinning of gyri
Especially those of frontal and temporal lobes
Histologically, what do we see for Alzheimers?
Amyloid beta plaques
Neurofibrillary tangle
Neuronal loss
How do amyloid beta plaques look histologically?
Amorphous, pink masses in cortex
Look like circular discs
What do neurofibrillary tangles look like histologically?
What are they formed by?
Flame shaped skeins
Abnormal accumulation of tau protein
What is substantia nigra? What is its role?
Mass of grey matter with multipolar neurons w/ dark pigment
Role in fine control of motor function
What does substantia nigra have connections with?
Cortex
SC
Corpus striatum
Reticular formation
What do the neurons of substantia nigra contain?
Membrane bound granules of neuromelanin pigments
What will neuromelanin produce?
Dopamine
What is Parkinson’s disease?
Degeneration of neurons in the substantia nigra leading to loss of dopamine
What are the clinical features of Parkinson’s disease?
Slow movement, tremor, rigidity
What is the etiology of Parkinson’s disease?
Unknown
What are the remaining neurons of the substantia nigra called In Parkinson’s?
Lewy bodies
How do Lewy bodies appear histologically?
What are they composed of?
Have distinctive inclusion s
Rounded pink staining w/ pale halo
Composed of aggregates of alpha-synuclein protein + others
