Neurones and gila

Question 1

What is the brain comprised off?

Answer 1

The human brain is comprised of both neurons and glial cells - these are broad categories, comprising numerous cell types with different structures and functions.

Question 2

Describe the premise of the reticular theory versus the neuron doctrine

Answer 2

• Camillo Golgi (1843-1926) - Golgi proposed that neurons were fused together to form a continuous reticulum (or network) - Reticular theory
• Santiago Ramon y Cajal (1852-1934) - Cajal proposed that neurons were not continuous but communicated by neuron-neuron contact - Neuron doctrine

Question 3

In terms of neural tissue and staining what is: fixation, sectioning?

Answer 3

Fixation
Brain tissue is fixed for preservation and subsequently embedded (e.g. paraffin, frozen)

Sectioning
Amicrotome can cut slices from a block of embedded brain tissue

Question 4

What does the Nissl stain and the Golgi stain show?

Answer 4

Nissl stain
The Nissl stain – comprised of a basic dye (e.g. cresyl violet) – stains the nuclei and Nissl bodies of neurons

Golgi stain
The Golgi stain – comprised of a silver chromate solution – stains neurons and their projections

Question 5

Compare the light and electron microscope

Answer 5

Light microscopy
• Standard light microscopy has a limit of resolution of 0.1 𝝻M
• Space between neurons approximately 0.02 𝝻M (or 20 nM)
Electron microscopy
• Electron microscopy has a limit of resolution of 0.1 nM
• Our insights into the fine structure of neurons have come from electron microscopy

Question 6

Are neurones continuous?

Answer 6

Neurons are not continuous but are discrete individual units

Question 7

What do Fluorescence microscopy and genetic manipulation techniques allow us to see?

Answer 7

• Fluorescence microscopy and genetic manipulation techniques (e.g. Cre-Lox) allow us to see brain regions and individual neurons/glial cells in breath-taking detail

Question 8

What is a neurone and what does it comprise of?

Answer 8

Neurons are the information processing cells within the nervous system, highly specialised for the conduction and transmission of electrical and chemical signals.

At its simplest, a prototypical neuron comprises:

1. Cell body (soma)
2. Axon
3. Dendrites

Question 9

What organelles does the soma contain?

Answer 9

The cell body (or soma) of a neuron contains the same organelles found in all human cells including:

1. Nucleus
2. Rough endoplasmic reticulum (RER)
3. Smooth endoplasmic reticulum (SER)
4. Golgi apparatus
5. Mitochondrion

Question 10

What is the cytoskeleton and what is it comprised off?

Answer 10

The cytoskeleton is the internal ‘scaffolding’ that gives a neuron its characteristic shape. It is comprised of microtubules, microfilaments and neurofilaments.

Question 11

Describe the structure of the microtubules, microfilaments and neurofilaments

Answer 11

Microtubules
• A polymer of the protein tubulin – located in axons and dendrites and important in axoplasmic transport
Microfilaments
• A polymer of the protein actin – found throughout the neuron but particularly abundant in axons and dendrites
Neurofilaments
• A type of intermediate filament – particularly abundant in axons and important in regulating axonal shape
• Promising biomarker for neurodegenerative disorders (e.g. Alzheimer’s)

Question 12

What are axons and what are they comprised off?

Answer 12

Axons are highly specialised neuronal projections that conduct nerve impulses (or action potentials) within the nervous system – comprised of various regions:
Axons are comprised of:

1. Axon hillock – tapers away from the soma to form the initial segment of the axon
2. Axon ‘proper’ – axon can branch to form axon collaterals (and recurrent collaterals)
3. Axon terminal – site at which the axon comes into contact with other neurons at a synapse

Question 13

What is myelin?

What are the gaps in myelin?

Answer 13

1. Myelin is a membranous sheath that wraps around and insulates axons
2. Gaps in myelin sheath are Nodes of Ranvier – highly enriched in voltage-gated Na+ ion channels

Question 14

What are dendrites?

What are the dendrites of one neurone called?

What are they covered with?

Answer 14

• Dendrites are highly specialised neuronal projections that receive synaptic inputs from other neurons
• Dendrites of a single neuron are collectively termed a ‘dendritic tree’
• Dendrites of some neurons are covered with specialised structures termed ‘dendritic spines’ – small sacs of membrane that protrude from the dendrites of some cells to receive synaptic input
• Dendritic spine structure is sensitive to type and amount of synaptic activity

A number of conditions have been associated with abnormal dendritic spine number (e.g. Alzheimer’s disease, schizophrenia).

Question 15

What is neurotransmission?

Answer 15

Neurotransmission is the fundamental process that drives information transfer between neurons and their targets.

Question 16

How can we classify neurones?

Answer 16

Neurons can be classified based on neuronal structure and gene expression:
Number of projections
Neurons can be classified by the total number of projections (or neurites):

Dendrites
Neurons can be classified by their dendritic trees and dendritic spines:

Classification of neurons: neuronal structure
Neurons can be classified based on neuronal structure and gene expression:
Connections
Neurons can be classified by their connections – sensory, motor and interneurons:

Axon length
Neurons can be classified by axon length – Golgi type I and Golgi type II:

Neurons can be classified based on neuronal structure and gene expression:
Gene expression
Neurons can also be classified by the neurotransmitter that they use – these differences arise due to the differential expression of proteins involved in neurotransmitter synthesis, storage and release.

Question 17

What are gilal cells?

Answer 17

Glial cells are the “support cells” within the nervous system and can be classified into four categories based on structure and function.

Question 18

What are astrocytes and where are they located?

Answer 18

Astrocytes are star-shaped glial cells that function to regulate – in a number of ways – the extracellular environment of the brain.

• Astrocytes are the most numerous type of glial cell within the human brain
• Astrocytes regulate the extracellular environment in the brain by, for example, enclosing synaptic junctions and actively removing neurotransmitters from the synaptic cleft

Question 19

What are microglia and what is there function?

Answer 19

Microglia are a type of glial cell that function as phagocytes within the nervous system to remove neuronal and glial debris.

Microglia – which account for approximately 5-15% of total CNS cell number depending on anatomical region – are broadly distributed in the brain and spinal cord

Microglia have been shown to function in:
• Phagocytosis of neuronal and glial debris (e.g. sites of injury)
• Synaptic connection remodelling
• Directing neuronal migration during brain development

Question 20

What are Ependymal cells and what are there function?

Answer 20

Ependymal cells are a type of glial cell that provide the lining of the ventricular system of both the brain and spinal cord.
Ependymal cells line the ventricular system and act as a physical barrier separating brain tissue from cerebrospinal fluid (CSF)
Ependymal cells have been shown to function in:
• Osmotic regulation of cerebrospinal fluid
• Flow of cerebrospinal fluid
• Directing cell migration during brain development
Accordingly, deficits in ependymal cell function have been linked with the severe neurological condition hydrocephalus

Question 21

What are Oligodendrocytes and Schwann cells?

Answer 21

Oligodendrocytes and Schwann cells are glial cells that function to provide myelin – a membranous sheath around axons – to neurons in the nervous system.

Oligodendrocytes and Schwann cells differ in their location and in some other characteristics:
Oligodendrocytes
Oligodendrocytes (pictured) are situated in the central nervous system (CNS)

Schwann cells
• Schwann cells are situated in the peripheral nervous system (PNS)
• One oligodendrocyte contributes myelin to several axons, whilst Schwann cells myelinate only a single axon