Histology of the CNS

Question 1

What do you call the small expansions at the end of an axon?

Answer 1

Terminal Bouton

Question 2

Where the soma extends into the axon?

Answer 2

Axon Hillock

Question 3

Central region of cytoplasm around the nucleus crowded with organelles

Answer 3

Perikaryon

Question 4

Cytoplasm of neurons contain granules callde?

Answer 4

Nissl Bodies

Question 5

Smallest Filaments in the Cytoskeleton of Neurons

Answer 5

Actin Filaments (3-4 Nanometers)

Question 6

Most prominent filaments of Neurons

Answer 6

Microtubules (24-28 Nanometers)

Question 7

What are the most important of the filaments?

Why?

Answer 7

The microtubules

They are the pathways of neurotransmitters from cell to cell

Question 8

Terminal Portion of an Axon

Answer 8

Motor End-Plate

Question 9

What is Myelin called outside the CNS?

Inside the CNS?

Answer 9

Inside: Oligodendroglia
Outside: Schwann Cells

Question 10

Types of Neurons According to Polarity (4)

Answer 10

1. Unipolar
2. Pseudo-Unipolar
3. Bipolar
4. Multipolar

Question 11

Where are Unipolar Neurons found?

Describe features (Soma, Axon, Dendrites)

Answer 11

Only embryos, not in adults

Soma and axon only, no dendrites

Question 12

Describe a Pseudo-unipolar Neuron (Axon, Dendrites, Sensory/Motor)

Answer 12

Very long axon and dendrites

Mostly sensory neurons

Question 13

Bipolar Neuron Features (Axon, Dendrite)

Answer 13

Axon on one side, dendrites on the other

Two processes at opposite ends of soma

Question 14

Where are Bipolar Neurons found?

Answer 14

Retinal Cells and Olfactory Epithelium

Question 15

Describe Multipolar Neurons

Answer 15

Most common neurons

Many cytoplasmic processes but only one axon per cell

Question 16

Examples of Multipolar Neurons

Answer 16

Pyramidal Cells

Purkinje Cells

Question 17

Subtypes of Multipolar Neurons

Answer 17

Golgi Type 1: Long projecting axons

Golgi Type 2: Axons project locally (Do not leave the grey matter of the cerebral hemisphere)

Question 18

3 Types of Neurons According to Function

Answer 18

1. Afferent Neurons
2. Efferent Neurons
3. Interneurons

Question 19

[Afferent Neurons]

1. Sensory or Motor?
2. Where does it carry impulses from and where does it go?
3. What type of neurons are they?

Answer 19

Sensory/Receptor Neurons
Carry impulses from sensory towards CNS
Pseudounpilar type of neuron

Question 20

[Efferent Neurons]

Where does it carry information from and to where?

Answer 20

From CNS -> Muscles/Glands

Question 21

[Interneurons]

Function

Answer 21

Relay information between sensory and motor neurons

Question 22

What are the most abundant type of neurons in the CNS?

Answer 22

Interneurons

Question 23

[External Granular Layer]

Contains what kind of neurons?

Answer 23

Stellate Neurons

Question 24

[External Pyramidal Layer]

Contains what kind of neurons?

Main source of?

Answer 24

Small pyramidal neurons

Cortical-Cortical Efferent Fibers

Question 25

[Multiform Layer] Characteristics

Answer 25

* 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

Question 26

Layers of the Cerebral Cortex

Answer 26

1. Molecular 2. External Granular 3. External Pyramidal 4. Internal Granular 5. Internal Pyramidal 6. Multiform

Question 27

How are Astrocytes stained?

Answer 27

Glial Fibrillary Acidic Protein

Question 28

What do Astrocytes envelope?

Answer 28

Synapses

Question 29

2 Kinds of Astrocytes

Answer 29

1. Fibrous | 2. Protoplasmic

Question 30

Where are Fibrous astrocytes found? | End feet attached to what?

Answer 30

Found in the white matter | Attached to capillary walls

Question 31

Where are Protoplasmic astrocytes found? | End feet attached to what?

Answer 31

Found in gray matter | End feet envelope synapses

Question 32

Functions: Astrocytes (9)

Answer 32

* 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

Question 33

Tumors that arise from Astrocytes

Answer 33

Astrocytomas

Question 34

Differentiate a normal neuron from an astrocytoma

Answer 34

Normal: Pale staining nuclei Astrocytoma: Dark nuclei

Question 35

Function: Oligodendrocytes

Answer 35

Responsible for myelination of nerve fibers within the CNS

Question 36

Ratio of Oligodendrocyte :: Myelinated Axons

Answer 36

1 : 50

Question 37

Myelination starts at what age?

Answer 37

6-9 Years Old

Question 38

Define: Nodes of Ranvier

Answer 38

Gaps between myelin sheaths which propagate electrical impulses faster (Saltatory Conduction: Node->Node)

Question 39

Trivia: How big is the node of Ranvier

Answer 39

1mm

Question 40

Cause: Cerebral Palsy (Periventricular Leukomalacia)

Answer 40

Damage to developing oligodendrocytes | Damaged by excessive release of glutamate

Question 41

Cause: Oligodendroglioma

Answer 41

Tumors affecting glial cells

Question 42

Effect: JC Virus

Answer 42

Can affect oligodendrocytes causing progressive multifocal leukoencephalopathy (PML)

Question 43

Microglia cells are similar to what leukocytes?

Answer 43

Macrophages

Question 44

Microglia originate from?

Answer 44

Myeloid Progenitor Cells

Question 45

First line of defense against infection within the BBB?

Answer 45

Microglia

Question 46

Functions: Microglia (10)

Answer 46

• 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)

Question 47

Function: Ependymal Cells

Answer 47

Involved in CSF Production | Absorb and recycle neurotransmitters

Question 48

What kind of cells make up Ependymal Cells?

Answer 48

Columnar and Cuboidal with Cilia

Question 49

Modified Ependymal Cells + Capillaries =?

Answer 49

Choroid Plexuses

Question 50

Schwann Cells are like?

Answer 50

Oligodendrocytes in the PNS but only 1:1 ratio | This is important in regeneration of damaged axons