Neuro: Neurones and Glia Flashcards
1
Q
How do you fix a tissue sample?
A
- Fixated with paraformaldehyde
- It is then either embedded paraffin or it can also be frozen.
2
Q
How do you section a tissue sample?
A
- using a microtome: you embed the brain in wax, then you mount it in the microtome and slice it
- using a cryostat: you freeze the brain, then slice it in the cryostat
3
Q
Describe the Nissl stain.
A
- Comprised of a basic dye (e.g. cresyl violet)
- Stains nuclei and Nissl bodies by staining the RNA
- Can help differentiate between neurones and glial cells.
4
Q
Describe the Golgi stain.
A
- Use of a silver chromate solution that stains neurones (including their cell bodies) and their projections.
- Allows us to see neurones in much greater detail than Nissl stain
5
Q
Describe light microscopy.
A
- Has a limit due to properties of the microscope lenses and physical light.
- Standard light microscopy has a limit of resolution of 0.1 uM
- Space between neurons approximately 0.02 uM (or 20 nM)
6
Q
Describe electron microscopy.
A
- Uses an electron beam instead of light to form images. This increases it’s resolving power.
- Resolution of 0.1 nM (1000x better than a standard light microscope)
7
Q
How can we seen different brain regions in much more detail?
A
Fluorescence microscopy and genetic manipulation techniques (e.g. Cre-Lox)
8
Q
Describe a prototypical neurone.
A
Highly specialised for the conduction and transmission of electrical and chemical signals.
- Cell Body (Soma) - this is home to the neurones organelles
- Axon - highly specialised neuronal projection that conducts nerve impulses or action potentials
- Dendrites - highly specialised neuronal projections that receive synaptic input from other neurones
Together the axon and dendrites are collectively termed neurites.
9
Q
What does the cell body (soma) comprised of?
A
- Nucleus - enclosed in nuclear envelope. Contains chromosomes which contain DNA and genes and is the site of gene transcription
- Rough endoplasmic reticulum (RER) - membrane bound organelle with ribosomes attached to its outer surface. Major site of protein synthesis in neurones.
- Smooth endoplasmic reticulum (SER) - similar to RER but no ribosomes. Heterogenous - preforms different functions in different locations. E.g. some SER is continuous with the RER and can act as a site of where proteins are carefully folded to give them their 3D structure.
- Golgi apparatus - complex organelle resembling a stack of membrane enclosed discs. Site of post translational modification. Chemical modification and subsequent sorting of proteins that are destined for different parts of the neurone e.g. into axons or dendrites.
- Mitochondrion - site for cellular respiration ATP production
10
Q
Describe the neuronal cytoskeleton
A
- Internal ‘scaffolding’ that give neurons their shape.
- Microtubules (20nm) - comprised of polymers of tubulin (protein). Run longitudinally down axons and dendrites. They are important in axoplasmic transport.
- Microfilaments (5nm) - comprised of polymers of actin. They are found throughout the neurone but are particularly abundant in axons and dendrites.
- Neurofilaments (10nm) - unique to neurons and consist of multiple protein subunits wound together in a rope-like structure. This makes neurofilaments strong. Abundant in axons and are important in regulation of axonal shape.
- Neurofilaments are a promising biomarker for several neurodegenerative disorders e.g. Alzheimer’s (where levels of neurofilament in CSF are elevated upon neuronal degeneration and neuronal cell death)
11
Q
Describe axons.
A
- Conduct nerve impulses (action potentials) over long distances within the nervous system
- Axon begins with a region called the Axon hillock. This tapers away from the soma to form the initial segment of the axon.
- Diameter of the Axon ‘proper’ ranges from 1um-25um
- Speed of nerve impulse depends on axon diameter
- Can branch to form axon collaterals which can travel long distances to communicate with different parts of the nervous system. Occasionally an axon collateral can return to communicate to the same cell - this is termed a recurrent axon collateral.
- The axon terminal is the site at which the axon comes into contact with other neurons at a synapse.
- Cytoplasm of the axon terminal differs in several ways to axon proper. E.g. microtubules found in the axon proper do not extend into the axons terminal. Also, the axon terminal contains a pool of synaptic vesicles available for neurone to neurone communication across a synapse and is rich in proteins and mitochondria due to higher energy demand at the axon terminal site.
- Specific types of glial cells myelinate axons which speeds up the propagation of nerve impulses down an axon. Nodes of Ranvier (gaps) highly enriched in voltage-gated Na+ ion channels, allowing the nodes of Ranvier to propagate an action potential.
12
Q
Describe dendrites.
A
- Receive synaptic inputs from other neurons such as axon terminals
- Dendrites of some neurons are covered with specialised ‘dendritic spines’ - small sacs of membrane that protrude from the dendrites of some cells to receive synaptic input. Can be described as filopodia shaped, cup shaped and mushroom shaped.
- 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) during adolescence and adulthood. Highlights importance of dendritic spine number in neuronal communication.
13
Q
Describe the classification of neurones.
A
- Total number of projections (neurites) - unipolar, bipolar, multipolar. Most neurones in the human brain are multipolar.
- Structure of the dendritic trees and dendritic spines - e.g. Stellate cells (star shaped) and Pyramidal cells (pyramid shape). Can be spiny (have dendritic spines) or aspinous (no dendritic spines)
- Connections - sensory neurones (sensory surfaces), interneurons (other neurones), motor neurones (control movement)
- Axon length - Golgi type I neurones (axons extend from one part of the brain to another), Golgi type II neurones (axons don’t extend beyond cell body vicinity)
- Neurotransmitter they use e.g. cholinergic, GABAergic, glutamatergic
14
Q
Describe glial cells.
A
Glial cells are the ‘support cells’ within the nervous system and can be classified into four categories based on structure and function.
- Astrocytes
- Microglia
- Ependymal cells
- Oligodendricytes and Schwann cells
15
Q
Describe astrocytes.
A
- Star-shaped glial cells
- Most common glial cell within the human brain
- Regulate chemical content of the extracellular environment in the brain e.g. by enclosing synaptic junctions and actively removing neurotransmitters from the synaptic cleft. Restricts diffusion of neurotransmitters which otherwise would interfere with normal neuronal function.
