Lecture 3 NS - Cells of the Nervous System Flashcards
What is a neuron and what is it supported by?
Basic structural and functional unit of the NS, information processing unit Supported by neuroglia, comprising several different cell types
How is diversity in cellular structure of neurons achieved?
All neurons have similar structures - diversity is achieved by differences in number and shape of their processes and where they project to in the brain
What is the structure of neurons?
Very large nucleus, prominent nucleolus, abundant RER, well developed GA, abundant mitochondria, highly organised cytoskeleton, highly organised metabolically active cell
What are dendrites and what is their function?
Spread from cell body and branch frequently - function: major area of reception of incoming information, as they greatly increase SA of neuron
What is the structure of dendrites?
Often covered in dendritic spines, which receive majority of synapses
What are axons and their function?
Emerge at axon hillock, ONE per cell - conduct impulses away from cell body, may branch after leaving cell body and at target
What is the structure of axons?
Prominent in microtubules and neurofilaments (intermediate filaments), can be myelinated/unmyelinated, cable properties, Nodes of Ranvier when exposed
How do paranodes help with transmission of AP?
Keeps ion channels separate to allow AP to propagate
What is the structure of axon terminals?
Either boutons or varicosities - axons often branch extensively close to target, forming synaptic terminals with target
What is the structure of a synapse?
There are synaptic densities where the vesicles fuse and release NT, and synaptic vesicles which hold the NT are packaged in GA and shipped by fast anterograde transport, w/specialised mechanisms for association to the plasma membrane MANY MITOCHONDRIA - so sensitive to O2 deprivation
How are the synapses organised?
Neurons receive multiple synaptic inputs, neurons use a diversity of chemical transmitters (excitatory and inhibitory), w/competing inputs integrating in the postsynaptic neuron (Neuronal integration)
What are the 3 types of synapse and are they often excitatory or inhibitory?
Axo-dendritic (often excitatory) Axo-somatic (often inhibitory) Axo-axonic (often modulatory)
What type of synapse is an axo-dendritic synapse?
Axon to dendritic spine
What type of synapse is an axo-somatic synapse?
Axon to cell body
What type of synapse is an axo-axonic synapse?
Axon to node of ranvier
How is the neuronal cytoskeleton arranged?
Highly organised as axons can be really long - inc. microfilaments, intermediate filaments and microtubules
What do neurofilaments do in the neuronal cytoskeleton?
They play a critical role in determining axon caliber
How does fast axonal transport occur?
It’s the transport of membrane associated materials, where vesicles with associated motors are moved down the axon Different membrane structures targeted to different compartments Retrograde moving organelles are morphologically and biochemically distinct from anterograde vesicles
What are the 4 different morphological subtypes of neurons?
Pseudounipolar, bipolar, golgi type I multipolar, Golgi type II multipolar
What does pseudounipolar morphological subtype mean?
Sensory neurons that have 2 fused processes which are axonal in structure
What does bipolar morphological subtype mean?
1 dendritic and one axonal process, such as retinal bipolar cells
What does Golgi type I multipolar morphological subtype mean?
Highly branched dendritic trees, axons extending long distances
What are some examples of Golgi type I multipolar neurons?
Pyramidal cells of the cerebral cortex, Purkinje cells of the cerebellum, anterior horn cells of the spinal cord, retinal ganglion cells
What does Golgi type II multipolar morphological subtype mean?
Highly branched dendritic trees, short axons - axons terminate quite close to cell body of origin
What is an example of a golgi type II multipolar cell?
Stellate cells of the cerebral cortex and cerebellum
What are the 3 functional classifications of neurons?
Sensory, motor and interneuron
What does an interneuron do?
Responsible for modification, coordination, integration, facilitation and inhibition of sensory input
What are neuroglia and what do they do?
Support cells of the NS, collection of random cells and have many/varied functions. They are essential for correct functioning of neurons
What are the cells that make up the neuroglia?
Astroglia, oligodendroglia, microglia, immature progenitors, ependymal cells, schwann cells, satellite glia
What are astroglia?
Have multiprocessed star-like shape and they are the most numerous cell type. Have numerous intermediate filament bundles in cytoplasm of fibrous astroglia - Gap junctions suggest astroglia signalling
What are 10 functions of astroglia?
Scaffold for neuronal migration and axonal growth during development. Formation of blood brain barrier. Transport of substances from blood to neurons. Segregation of neuronal processes. Removal of NT. Synthesis of neurotrophic factors. Neuronal-glial and glial neuronal signalling. K+ buffering. Glial scar formation.
What are the functions of neurons?
Responsible for generation and conduction of electrical signals, communicate with one another via chemicals released at synapse
What are the different types of axon terminals?
How do astrocytes interact with blood vessels?
They form an ordered arrangement of astrocytes with minimal overlap, with each cell forming a specific territory that interfaces with microvasculature
What are oligodendroglia?
Myelin forming cells of CNS - interfasicular/perineuronal oligodendroglia
What is the structure of oligodendroglia?
Small spherical nuclei, few thin processes, prominent ER and golgi, metabolically highly active
What are the functions of oligodendroglia?
Production and maintenance of the myelin sheath, of which each cell produces 1-40
What is myelin?
A lipid rich insulating membrane of up to 50 lamellae
What happens if oligodendroglia and myelin are lost?
Disastrous consequences -> diseases like MS and adrenoleucodystrophy
Where are microglia derived from?
Bone marrow during early development
What are microglia?
Resident macrophage popn of CNS
What is the role of microglia?
Involved in immune surveillance, present Ag to invading immune cells, first cells to react to infection/damage, role in tissue modelling, synaptic stripping
What do the microglia become activated to?
What are schwann cells?
They are part of peripheral NS producing myelin -> but only one sheath
What are the functions of schwann cells?
Surrounding unmyelinated axons, promote axon regeneration
How do astrocytes remove neurotransmitters?
Astrocyte processes have active transport to transport it into the cell where the NT is broken down and recycled
How do astrocytes remove K+ and why?
Remove K+ from synapse, into astrocyte processes to allow for diffusion of K+ away from the neuron
What is the difference between interfasicular and perineuronal oligodendroglia?
Interfasicular are found in the white matter and are more common than the perineuronal which are found in the grey matter
