Neurons and Glia Flashcards
What is contained within the nerve cell body?
Cell body contains the cell nucleus, the protein forming apparatus and endoplasmic reticulum etc.
What is the significance of dendrites on the nerve cell?
Dendrites grow out of the cell body-long thin extensions form the dendritic tree
These are the receptive surfaces of the nerve cell, and form a large enough SA for 100s of synaptic inputs
Describe the axon of the nerve cell
Axon is a single branching structure terminating in boutons (synaptic terminals)
Explain why nerve cells are so well perfused
Nerve cells are very metabolically active - have a large supply of capillaries
What brain section thickness is required to be seen under a microscope?
Need thin sections (typically 40-100μm for light microscopy of brain)
Nerve cells are seen through a hyper microscope
What main structure hinders the vew of brain details?
RBC are dark and will obscure details – they need to be removed
Explain how RBCs are removed from a brain section
- Remove blood (RBCs) by washing through with saline
solution - Add formaldehyde fix to form a solid sample
- Solid brain tissue formed - easier to cut
What are the 2 techniques used to slice a thin brain section?
- Microtome (wax embedded)
- Cryostat (frozen)
Outline how a microtome is produced
In order to section the sample we can embed it in wax (holds it all together)
The wax segments stick together edge to edge so a whole strip can be lifted together in one piece ready for the microscope slide
Why may a cryostat be the preferred slicing technique over a microtome?
The wax can get in the way off many histochemical techniques
How do we overcome a pale and opaque brain section?
Sample is quite pale and opaque as the brain tissue is full of myelin and fats
Using a strong solvent render it transparent
Why do we need to stain the brain sample before viewing under a microscope?
Brain tissue no longer visible on microscope as transparent and featureless due to strong solvent
What are the different methods of making brain sections visible?
- Franz Nissl (late 19th Century)
- Camillo Golgi (late 19th Century)
- Intracellular injection of a label
- Small extracellular injections of tracer
- Electron microscopy
- Genetic manipulation
How does nissl staining work?
Certain stains bind to the protein making apparatus in the nerve cell bodies - labels RNA Darker areas (cerebral cortex) have more cell bodies Paler areas (white matter) is where the nerve cell axons are running along
What is the significance of Nissl staining?
Nissl staining enables us to see arrangement patterns within the cell bodies
Using this technique brogman (classical neuroscientist) was able to split the brain up into different functional areas
Outline how Camilo Golgi staining works
silver chromate could create a dense black stain, which labelled a small % of the cells present in their entirety - labels some cell bodies
Enables us to see not only the cell body but also the dendritic tree
We may also be able to see the beginning of the axons
What are multipolar neurons?
Many dendrites coming off the cell body
What is a stellate cell?
Different dendrites coming off cell body in all different directions evenly
What are pyramidal cells?
Triangular cell bodies, skirt of dendrites and an apical dendrite
What is meant by ‘spiny’ nerve cells?
Some cells are spiny others are non-spiny
Spines are the site of fast excitatory synaptic connections – inhibitory and modulatory synapses are found on the dendritic shafts in between, and the cell body itself.
What is the significance of spines?
Spines are plastic, changing in ways that strengthen or weaken the synaptic link, allowing neural circuits to embed new skills and memories.
Give an example of a pseudo-unipolar axon in the body
Pseudo-unipolar - axon from toe → brainstem
At the toe has an arborization with sensitive nerve endings
In the brain has arborizations with synaptic endings and the cell body is sitting in the dorsal root ganglion
This is a typical sensory neuron from the somatic sensory system
Evaluate the use of golgi staining
Golgi stain allowed classification but still unable to view much of the axon
What is the benefit of using an intracellular label injection?
Gives a more complete picture
Can visualise the tracer
The same histochemical techniques can highlight multiple features in the same tissue and can be combined with physiological measurements of the living cell
How does intracellular injection work?
Cells are labelled with a small, soluble molecule (eg biocytin) which is made
visible via a chemical reaction.
Explain how intracellular injection of a label is carried out
Done using a finely drawn pipette, starting off with a capillary glass. Can infuse the cell with a tracer if done accurately
What is biotin?
A vitamin that helps cells produce energy and boost nerve function in high doses
How is biotin visualised using intracellular label injection?
Expose the sections to antibodies with binding sites for biotin
More antibodies are raised against those antibodies
The latter can be linked to a fluorescent protein (visible under appropriate illumination)
OR
Horseradish peroxidase (HRP) an enzyme catalysing the conversion of the soluble molecule into a dark, dense insoluble
What is the purpose of small extracellular tracer injections?
Can see the dendritic pattern, shape and morphology
What structures take up the small intracellular tracer injection?
Taken up by cells and synaptic cells
Transported by axons and taken up by axon terminals - transported retrogradely to the cell body