Cells of the Nervous System Flashcards
What stain did early work looking at the structure of the brain use and what did this allow to be seen?
The Nissl stain which only allowed the cell body to be seen
What stain was developed and by who that allowed visualisation of the cell processes?
Golgi’s silver stain
What are the cell processes?
Dendrites and axons
What was Golgi’s reticular theory?
Golgi believed that neurites were fused together to form a reticular network
What is Cajal’s neuron doctrine?
Each neuron is a discrete cell
What is Cajal’s principle of dynamic polarisation?
that neurons transmit information in a particular direction
What is Cajal’s principle of connectional specificity?
he thought that the connections in the nervous system weren’t random (particular types of neurons connected with each-other)
How was Cajal’s theory proved right over Golgi’s?
through the development of the electron microscope
When was the electron microscope developed?
1950s
What is the human eye resolution, light microscope resolution and electron microscope resolution?
- Human eye resolution 0.1mm
- Light microscope resolution 0.1 um
- Electron microscope resolution 0.1nm
What are the advantages of the electron microscope?
- it can examine cell ultrastructure (confirmed the existence of synapses)
What is the disadvantage of the electron microscope?
The cells have to be fixed (dead)
How does immunofluorescence imaging work?
- Prepare selective antibody (or drug) tagged with fluorescent label
- Add to tissue and allow to bind strongly
- Target protein in tissue labelled with antibody
- Wash off any free labelled antibody (or drug)
- Image distribution of fluorescence (which labels antibody distribution)
How do confocal microscopes work?
- Focus a laser at different levels in a tissue that has been labelled with a fluroscent probe
- Use high sensitivity camera
- Imaging software
- You can build up a 3D image of specific cells
What are the advantages and disadvantages of confocal microscopes?
- Advantages:
- You can do this in live cells
- You can examine the physiology of cells
- Disadvantage: modest resolution, 0.1um
What is the Brainbow technique?
- Involves genetically modifying an animal so it’s cells produce random combination of dyes
- You can used it to trace the pathway of individual neurons as they will be stained with colour
What does the Clarity technique do?
- Makes brains transparent so that staining can show vastly more detail
- You need to remove the lipid bilayer using a hydrogel mesh
In the central nervous system what do glial cells do after brain injuries?
they proliferate (multiply) and this can inhibit the regeneration of damaged axons.
What do glial cells do after injury in the peripheral nervous system?
seem to promote the regrowth of neurons
What is the main role of the glia?
To act as a supporting cell
What is the original idea behind glial cells?
that glial cells ‘glued’ neurons together
What’s the glia: neuron ratio?
Outnumber neurons in some brain regions (e.g. 17:1 in thalamus; 1:1 in the cerebral cortex)
Can glial cells divide?
yes - unlike neurons
What are the different types of glial cell?
- Ependymal cells
- Oligodendrocytes
- Satellite cells (won’t worry about them)
- Astrocytes
- Microglia
- Schwann cells
Give features of astrocytes
- Majority of glia
- Star-shaped (their name means star-shaped)
- Fill space between neurons
- Regulate composition of extracellular fluid
- Astrocytes can play an important role in directing the proliferation and differentiation of neural stem cells
Give features of Oligodendrocytes and Schwann cells
- Myelinate axons of neurons
- Oligodendrocytes = CNS, provide insulation for many different axons
- Schwann cells = PNS, only insulates a single axon
Give features of Microglia
- Act as the brain scavengers
- Phagocytic/immune function
- They can migrate
Give features of Ependymal cells
- Ependymal cells line ventricles and also direct cell migration during development of the brain
- Produce CSF
- Recent research says they might be able to turn into neurons – reserve of cells for regeneration?
What type of disorder is Huntington’s disease?
a neurodegenerative disorder that develops between the age of 30 and 50
What are the symptoms and life expectancy of HD (Huntington’s disease)?
- People with HD initially show changes in personality and have problems with cognition. As the disease progresses, they start to experience random jerky movements
- The physical problems and cognitive impairments become worse over time and patients will develop dementia and exhibit rigidity and writhing movements
- Life expectancy after diagnosis is around 20 years
Why would Huntington’s occur?
- HD is an autosomal (chromosome that is not a sex chromosome) dominant disorder due to a genetic abnormality in the huntingtin gene. A section of this gene codes for a repeated sequence of glutamine residues and it’s the number of repeats of the glutamine codon that determines whether the disease will develop or not
- The single letter amino acid code for glutamine is Q, so this region is known as the polyQ region.
- If the repeat count in the polyQ region is less than 27 there is no risk of HD, if it is greater than 40 then the person will get HD, if it is in the range 36-39 then the disease may occur, repeats in the 27-35 range are unstable during cell replication and this can result in further copies being added. The risk of polyQ expansion means that a HD may occur in the offspring of a person who does not themselves develop the disease
What produces the symptoms of Huntington’s?
The mutant version of the protein the huntingtin gene codes for is not broken down correctly by cells and the result is that fragments of the protein (huntingtin) accumulate in neurons as inclusion bodies. Eventually the build up of huntingtin breakdown products will kill the cell.
What is one of the worst affected regions of the brain by Huntington’s?
The basal ganglia (a region of the brain which is vital in the control of movement and is also affected by Parkinson’s)
What happens to astrocytes and microglia due to Huntington’s?
Astrocytes and microglia also undergo changes due to Huntington’s and these changes are associated with neuroinflammation. This neuroinflammation is thought to contribute to neuronal death