NEURO: Neurons and Glia Flashcards
Why do we have to get rid of red blood cells to examine a nerve cell under a microscope?
because red blood cells are dark and will obscure details, therefore, they need to be removed
What important step is needed in order to slice/section the brain?
It needs to be stored and firmed up by paraformaldehyde.
Without it, the brain is a similar softness to raw chicken (if we put a bit of pressure on it, it deforms, so we can’t get clean slices).
What are two ways in which we can slice brains?
The two ways are:
- using a microtome: you embed the brain in wax in a particular orientation, then you mount it in the microtome and slice it (Sectioning)
- using a cryostat: you freeze the brain, then slice it in the cryostat or embedded in paraffin (fixation)
What does the Nissl stain label?
Disadvantage?
Stains the nuclei and Nissl bodies of neurons
Nissl stain allowed Brodmann to divide the brain into what he thought were different functional areas because they had different stripe patterns within the cortex
A disadvantage of the Nissl stain: nerve cells were just seen as little coloured blobs
What does the Golgi stain label?
disadvantage?
The silver chromate labels the cell body of some neurons and their projections (dendritic tree) and, to some extent, the beginning of the axons
It’s not too effective.
much of the axon could not be seen
How do we visualise individual neurons today?
Fluorescence microscopy and genetic manipulation techniques (e.g. Cre-Lox)
How are intracellular structures visualised?
electron microscopy:
- uses a beam of electrons and a camera
- ultrathin sections, typically 3-60nm
- magnification>100,000x
- resolution to <0.5nm
What is found in a cell Body?
*largest cell body is ~40um in scale
the same organelles found in all human cells including: Nucleus Rough endoplasmic reticulum (RER) Smooth endoplasmic reticulum (SER) Golgi apparatus Mitochondrion
What is the cytoskeleton?
The cytoskeleton is the internal ‘scaffolding’ that gives a neuron its characteristic shape. It is comprised of microtubules, microfilaments and neurofilaments.
Microtubules:
A polymer of the protein tubulin – located in axons and dendrites and important in axoplasmic transport
What is an axon?
single long fibre extending from the cell body and terminates in boutons (synaptic terminals), which are the chemical communication points between different nerve cells across a synapse
highly specialised neuronal projections that conduct nerve impulses
Axon is comprised of: Axon hillock – tapers away from the soma to form the initial segment of the axon Axon ‘proper’ – axon can branch to form axon collaterals (and recurrent collaterals) Axon terminal – the site where axon comes into contact with other neurons at a synapse
What are all the glial cells made from?
neural tube
-by the same stem cells that make nerve cells, but later in development, they switch over from nerve cells to glial cells
Glial cells function
Glial cells are able to myelinate axons:
-Myelin is a membranous sheath that wraps around and insulates axons
-Gaps in myelin sheath are Nodes of Ranvier – highly
enriched in voltage-gated Na+ ion channels
What are all the types of glial cells?
4 glial cells:
- astrocytes
- oligodendrocytes
- neurolemmocytes (Schwann cells)
- Ependymal cells
What do Astrocytes (astroglia) do?
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
Myelinating Glia (neurolemmocytes and oligodendrocytes)
· neurolemmocytes each myelinate a single axon running down a peripheral nerve
· oligodendrocytes myelinate multiple axons within the central nervous system (e.g. white matter in the brain)
-underneath this membrane the actual nerve cell itself does not introduce channel proteins into its own extracellular membrane underneath the myelin, ensuring that the axon is well insulated and that it does not leak ions, helping to speed action potentials
Microglia
function as phagocytes within the nervous system
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
Why are microglial cells not considered glial cells?
because they arise from the mesoderm and not from the neural tube
Difference between microglial cells and other immune cells
other immune cells can’t get into the nervous system due to the blood-brain barrier
Ependymal
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 CSF
- Flow of CSF
- Directing cell migration during brain development
deficits in ependymal cell function have been linked with the severe neurological condition hydrocephalus
Describe the Cre/Lox technology in targeting specific cells.
Cre recombinase is an enzyme that recognises loxP sites. Different genetic modifications take place depending on the loxP location/orientation.
Dendrites
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 the the 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
conditions have been associated with abnormal dendritic spine numbers (e.g. Alzheimer’s disease, schizophrenia).
what is neurotransmission?
the fundamental process that drives information transfer between neurons and their targets.
What are the different ways in which we classify neurones?
based on their structure, and based on their gene expression.
STRUCTURE:
- number of neurites (axons and dendrites)
- dendrites (dendritic tree formation, presence of spines)
- connections (primary sensory neurones, motor neurones, interneurons)
- axon length
GENE EXPRESSION:
- types of protein
- types of neurotransmitter
- GFP can be tagged to a certain protein and neurones expressing that protein are then revealed
Nerve cell classifications
Multipolar
-many dendrites coming off from cell body
Bipolar
-two extensions from cell body (one axon and one dendrite)
Pseudounipolar
-single axon splits into two branches; one branch runs to peripheral tissues and other to CNS
List the kind of membrane proteins that are found on the different membranes.
Ligand-gated ion channels and G-protein coupled receptors are found mainly on the dendritic membrane.
Voltage-gated ion channels are mainly found on the axonal membrane.
What are the two types of synaptic boutons that we can have?
Terminal boutons: where they synapse at the end of an axon
A bouton en passant: when the synapse is along the length of an axon
Describe some differences between neurones and glia.
NEURONES:
- easy to measure responses
- can see they have a difference in voltage across their membranes
- can see that they fire action potentials
- thought to be the main players
GLIA:
- difficult to measure responses
- they seem to communicate in slow waves of calcium concentrations (which are difficult to detect)
- thought to play a supporting role
How do we visualise individual neurons today?
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
