Histology of the CNS Flashcards
What do you call the small expansions at the end of an axon?
Terminal Bouton
Where the soma extends into the axon?
Axon Hillock
Central region of cytoplasm around the nucleus crowded with organelles
Perikaryon
Cytoplasm of neurons contain granules callde?
Nissl Bodies
Smallest Filaments in the Cytoskeleton of Neurons
Actin Filaments (3-4 Nanometers)
Most prominent filaments of Neurons
Microtubules (24-28 Nanometers)
What are the most important of the filaments?
Why?
The microtubules
They are the pathways of neurotransmitters from cell to cell
Terminal Portion of an Axon
Motor End-Plate
What is Myelin called outside the CNS?
Inside the CNS?
Inside: Oligodendroglia
Outside: Schwann Cells
Types of Neurons According to Polarity (4)
- Unipolar
- Pseudo-Unipolar
- Bipolar
- Multipolar
Where are Unipolar Neurons found?
Describe features (Soma, Axon, Dendrites)
Only embryos, not in adults
Soma and axon only, no dendrites
Describe a Pseudo-unipolar Neuron (Axon, Dendrites, Sensory/Motor)
Very long axon and dendrites
Mostly sensory neurons
Bipolar Neuron Features (Axon, Dendrite)
Axon on one side, dendrites on the other
Two processes at opposite ends of soma
Where are Bipolar Neurons found?
Retinal Cells and Olfactory Epithelium
Describe Multipolar Neurons
Most common neurons
Many cytoplasmic processes but only one axon per cell
Examples of Multipolar Neurons
Pyramidal Cells
Purkinje Cells
Subtypes of Multipolar Neurons
Golgi Type 1: Long projecting axons
Golgi Type 2: Axons project locally (Do not leave the grey matter of the cerebral hemisphere)
3 Types of Neurons According to Function
- Afferent Neurons
- Efferent Neurons
- Interneurons
[Afferent Neurons]
- Sensory or Motor?
- Where does it carry impulses from and where does it go?
- What type of neurons are they?
Sensory/Receptor Neurons
Carry impulses from sensory towards CNS
Pseudounpilar type of neuron
[Efferent Neurons]
Where does it carry information from and to where?
From CNS -> Muscles/Glands
[Interneurons]
Function
Relay information between sensory and motor neurons
What are the most abundant type of neurons in the CNS?
Interneurons
[External Granular Layer]
Contains what kind of neurons?
Stellate Neurons
[External Pyramidal Layer]
Contains what kind of neurons?
Main source of?
Small pyramidal neurons
Cortical-Cortical Efferent Fibers
[Multiform Layer]
Characteristics
- Few large pyramidal neurons
- Many spindle-like neurons and multiform neurons • Difficult to distinguish under a light microscope
- Reciprocal connection to and from the thalamus
Layers of the Cerebral Cortex
- Molecular
- External Granular
- External Pyramidal
- Internal Granular
- Internal Pyramidal
- Multiform
How are Astrocytes stained?
Glial Fibrillary Acidic Protein
What do Astrocytes envelope?
Synapses
2 Kinds of Astrocytes
- Fibrous
2. Protoplasmic
Where are Fibrous astrocytes found?
End feet attached to what?
Found in the white matter
Attached to capillary walls
Where are Protoplasmic astrocytes found?
End feet attached to what?
Found in gray matter
End feet envelope synapses
Functions: Astrocytes (9)
- Structural support
- Metabolic support (provide glucose to neurons)
- Regulate extracellular K+ concentration
- Regulate oligodendroctye myelinating activity
- Minimal role in maintaining BBB
- Reuptake and release of neurotransmitters
- Help regulate blood flow
- Nervous system repair (glial cell formation or gliosis)
- Fillers after injury to brain
Tumors that arise from Astrocytes
Astrocytomas
Differentiate a normal neuron from an astrocytoma
Normal: Pale staining nuclei
Astrocytoma: Dark nuclei
Function: Oligodendrocytes
Responsible for myelination of nerve fibers within the CNS
Ratio of Oligodendrocyte :: Myelinated Axons
1 : 50
Myelination starts at what age?
6-9 Years Old
Define: Nodes of Ranvier
Gaps between myelin sheaths which propagate electrical impulses faster (Saltatory Conduction: Node->Node)
Trivia: How big is the node of Ranvier
1mm
Cause: Cerebral Palsy (Periventricular Leukomalacia)
Damage to developing oligodendrocytes
Damaged by excessive release of glutamate
Cause: Oligodendroglioma
Tumors affecting glial cells
Effect: JC Virus
Can affect oligodendrocytes causing progressive multifocal leukoencephalopathy (PML)
Microglia cells are similar to what leukocytes?
Macrophages
Microglia originate from?
Myeloid Progenitor Cells
First line of defense against infection within the BBB?
Microglia
Functions: Microglia (10)
• First line of infection in blood brain barrier
• ‘Janitors’ for dead neurons
o Constantly moving, clearing dead neurons and debris
• ‘Alarm’
o Sensitive to slightest form of inflammation or infection
• Have unique K+ channels in their membrane which makes them
sensitive to smallest changes in potassium ion concentration
• Phagocytosis of foreign bodies/invaders
o Significant in patients with TB: bacteria could be swallowed but cannot be broken down so it persists in the brain and could cause TB meningitis
• Cytotoxicity: hydrogen peroxide, nitrous oxide, proteases, glutamate, aspartate (chemical warfare with collateral damage)
• Part of antigen presentation
• Pruning of synapses (removing of bad immature behaviours or
childishness)
• Promotion of repair
• Extracellular signalling (cytokines)
Function: Ependymal Cells
Involved in CSF Production
Absorb and recycle neurotransmitters
What kind of cells make up Ependymal Cells?
Columnar and Cuboidal with Cilia
Modified Ependymal Cells + Capillaries =?
Choroid Plexuses
Schwann Cells are like?
Oligodendrocytes in the PNS but only 1:1 ratio
This is important in regeneration of damaged axons
