Cells of the nervous system Flashcards
What is a neurone?
Main informational processing unit of the nervous system.
It is responsible for the generation and conduction of electrical signals. They are used to communicate with one another via chemicals that are released at the synapse.
Neurones are supported by neuroglia, comprising of different cell types.
What characteristics differ between neurones?
Differences in number (abundance) and the shape of their processes (location as well)
It is this diversity that makes them less vulnerable to degredation in CNS conditions like Alzheimer’s, Parkinsons, MS and ALS (amyotrophic lateral sclerosis)
What are the characteristics of neurones?
- Large nucleus
- Prominent nucleolus
- Abundant RER and free ribosomes
- Well developed golgi- high levels of protein trafficking via the secretory pathway
- Abundant mitochondria
- Highly organised cytoskeleton
- In general, it is a highly organised metabolically active cell
What are the dendrites?
Dendrites are input to neurones from other neurones. Spread from cell body and branch frequently have tree structure to increase SA of neurone.
Thin dendrite protrusions (an actual lump sticking out from the main bit) called dendritic spines recieve the majority of the synapses. Dendritic spines can have multiple synapses.
Large pyramidal neurones can have 30,000-40,000 spines.
Describe a pyramidal cell
The centre is like a triangle (pyramid).
Primary dendrites come off the vertices (corners) of the pyramid.
There are secondary dendrites branching off the primary
Tertiary dendrites branch off the secondary
THERE IS ONLY 1 AXON
Dendrites have over 80,000 spines per cell
Which type of neurones are present in the cerebellum?
The purkinje neurones
Dendrite have an enormous number of spines (80,000) and the human cerebellum has approx 15 mill purkinje cells.
What are the axons? - what is their function?
They conduct impulses away from cell body- they emerge at the axon hillock. There is usually only ONE axon per cell.
They may branch a little after leaving the cell body and at the target- form axon collaterals.
Contains abundant intermediate filaments and microtubules- the intermediate filaments are needed for tensile strength as the cells are very long.
Axons can be myelinated or unmyelinated- exposed bits of myelinated axons are called nodes of ranvier.
Why is it important that the axon remains the same diameter all the way down?
In order to maintain the same speed of transmission of AP.
Describe the segregation of axons into different bits
Paranode- the area where the ends of the myelin are bound to the axon to form tight junctions- this prevents leakage of current under the myelin sheath.
Juxtaparanode- an area adjacent to the paranode where you find VGKC and VGCC.
NB- about the fluorescent labelling- a fluorescent antibody has been used against a protein involved in binding ends of the myelin to the axon to form tight junctions.
What are the 2 types of axon terminals and describe them
Axons will often branch extensively close to the target (terminal arbor) and they form synaptic terminals with the target.
They can either be:
- Boutons- the classic one on one pre-synaptic to post-synaptic
- Varicosities- this is when the synapse with many smooth muscle cells as it passes- there are multiple swellings containing neurotransmitter.
Characteristics of synapses
- Abundant mitochondria- 45% of tot energy consumption is needed for ion pumping and synaptic transmission- its is a process that is sensitive to oxygen deprivation.
- Synaptic vesicles are packaged in the golgi and shipped by fast anterograde transport.
- Specialised mechanisms for association of synaptic vesicles with the plasma membrane
- Competing inputs are integrated in the post-synaptic neurone- neuronal integration
Describe this with respect to the densities
Under the microscope, you have synaptic vesicles (neurotransmitter) and mitochondria. Synaptic density (increased number of protein), important for control of the mechanism of the synapse
What is synaptic organisation?
Neurones recieve input from multiple places.
Each synapse uses a diversity of chemical transmitters, excitatory and inhibitory.
How are synapses organised?
Synapses can form by attaching to different areas.
They are named based on which parts of the 2 neurones synapses:
- (a) axo-dendritic= often excitatory
- (b) axo-somatic = often inhibitory
- (c) axo-axonic= often modulatory
What is the neuronal cytoskeleton?
Axons can range in length- from micrometers to meters.
Neuronal filaments play a critical role in determining axon caliber.
Microtubules are abundant in the nervous system
What is involved in fast axonal transport?
Vesicles associated with motors are moved down the axon at 100-400mm per day.
Proteins are packaged into a vesicle and then the vesicle is targeted down towards the presynaptic membrane. The microtubules are polarised so the vesicles can only move in one direction.
Retrograde transport- moving vesicles back to the cell body. The transport travels in 2 directions but down two different microtubules.
What is the axonal damage in MS?
If there is a restriction to the axon (e.g. traumatic injury or inflammatory disease) you begin to see SWELLINGS
SWELLINGS - vesicles of neurotransmitter keep being transported down the axon and they accumulate because they have no where to go.
What are the different morphological subtypes of neurones?
- PSEUDOUNIPOLAR- sensory neurones have 2 fused process which are axonal in structure (one axon splits into 2). The signal recieved passes into the axonal terminal without going to the soma.
- BIPOLAR- (like retinal bipolar cells) involved in white matter of the cerebral cortex.
- Golgi type 1 multipolar
- Golgi type 2 multipolar
Describe golgi type 1 multipolar
- Highly branched dendritic trees
- axons extend long distances
Examples:
- Pyramidal cells of the cerebral cortex
- Purkinje cells of the cerebellum
- Anterior horn cell of the spinal cord
- Retinal ganglion cells
Golgi type 2 multipolar cells
Highly branched dendritic trees, short axons.
The axons terminate quite close to the cell body of origin
E.g. stellate cells of the cerebral cortex and cerebellum.
What are the functional classifications of neurones?
- Sensory neurones
- Motor neurones
- Interneurones (responsible for modification, coordination, integration, facilitation and inhibition of sensory input)
What are neuroglia?
Neuroglia: glue of the nervous system
They are the support cells with varied functions. They are essential for functioning of neurones.
They include the following:
Astroglia
Oligodendroglia
Microglia
Immature progenitors
Ependymal cells
Schwann cells
Satellite glia
describe astroglia
Multiprocessed- star shaped
Most abundant cell type in the brain- numerous intermediate filament bundles in cytoplasm (GFAP)- give axons their tensile strength. They signal to each other by gap junctions. In grey matter, they appear as fuzzy balls- protoplasmic because of overlapping processes.
What are the functions of astroglia?
- Scaffold for neuronal migration and axon growth during development.
- Formation of blood-brain barrier. They have feet onto the blood vessels. Ordered arrangement of astrocyes with minimal overlap- some have contact with blood vessels, others have contact with neurones.
- Transport of substances from blood to neurons.
- Segregation of neuronal processes (synapses). They need to be separated between one another.
- Removal of neurotransmitters.
- Synthesis of neurotrophic factors.
- Neuronal-glial and glial neuronal signalling
- Potassium ion buffering
- Glial scar formation
