Flashcards in Module 1: Cellular and Development Neurobiology Deck (364)
What is the difference between CNS and PNS Neurons?
Peripheral Neurons have their cell bodies outside the brain or spinal cord
Central Neurons have their cell bodies inside the brain or spinal cord
Some central neurons have axons that extend extensively into the peripheral nervous system (e.g. motor neurons). Because their CELL bodies are in the CNS they are no doubt central neurons
Some PNS neurons have axons that project into the CNS (e.g. dorsal root ganglion sensory neurones). Because their cell bodies are in the PNS, they are nevertheless peripheral neurons.
What are the features of neurons and their diversity?
- Basic structural and functional unit of the nervous system
- information processing unit
- responsible for the generation and conduction of electrical signals
- communicate with one another via chemicals released at the synapse
- enormous heterogeneity
- supported by neuroglia, comprising of several different cell types
What are the cellular features of a neuron?
- large nucleus
- prominent nucleolus
- abundant rough ER
- well developed Golgi
- abundant mitochondria
- highly organised cytoskeleton
- HIGHLY ORGANISED METABOLICALLY ACTIVE CELL
What is the classification of neurons based on their morphology?
What are the types of neurons? (Morphology)
- Motor neuron
- Pyramidal neuron
- Purkinje cell
- Retinal neuron
- Olfactory neuron
- Touch and Pain Sensory neuron
- Amacrine cell
What is the classification of neurons based on their function?
- Sensory neurons (afferent neurons) (e.g. in skin, ear, tongue) transmit information about the surrounding environment to the central nervous system neurons.
- Motor neurons (efferent neurons) innervate muscle and stimulate muscle contraction.
- Interneurons are CNS neurons that communicate with other CNS neurons
What is the organisation of neuronal circuits?
- Divergence: a mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS.
- Convergence: a mechanism providing input to a single neuron from multiple sources
- Serial processing: neurons or pools work in a consequential manner
- Parallel processing: individual neurons or neuronal pools process information simultaneously
- Reverberation: a feedback mechanism that may be excitatory or inhibitory
Why must the axonal compartment be kept separate from the somato-dendritic compartment?
- Certain proteins, complexes and cargo must be delivered to particular regions of the neuron
What are somato-dendritic specific components?
- Microtubule stabilising protein: MAP2B
- All the neurotransmitter receptors, post-synaptic density (PSD) scaffolding and signalling proteins required at post-synapse
What are some features of dendrites?
- major area of reception of incoming information
- spread from cell body and branch frequently
- greatly increase the surface area of a neuron
- location of branches determines the origin of incoming signals
- often covered in protrusions called spines
What are axon specific components?
- Neurofilaments, only present in axons where they are important for strength
- Microtubule stabilising protein tau
- Cell adhesion molecules L1 (NgCAM), TAG-1
- All the neurotransmitters, growth factor receptors, SNARE complexes etc, required at the pre-synapse
What are some features of axons?
- conduct impulses away from the cell body
- emerge at the axon hillock
- usually one per cell
- may branch after leaving cell body and at target
- prominent microtubules and neurofilaments
What are some structural features of axons?
- axons contain abundant intermediate filaments and microtubules
- axons can be myelinated or unmyelinated
- axonal membrane of myelinated fibre only exposed at node of Ranvier
- has cable properties to maintain constant speed of conduction
- large numbers of mitochondria required to maintain action potential
How is the axonal membrane organised in specific domains?
Soma - Axon initial segment - Myelinated axon - Axon terminal
Within myelinated axon:
Juxtaparanode - paranode - node - paranode - juxtaparanode
What are the different types of synapses?
- Synapses with other neurons
What are some structural features of a synapse?
- Synaptic vesicles packaged in the Golgi and shipped by fast anterograde transport
- specialised mechanisms for association of synaptic vesicles with the plasma membrane (active zone)
- voltage gated Ca2+ channels enriched
- abundant mitochondria - around 45% of total energy consumption is required for ion pumping and synaptic transmission - sensitivity to O2 deprivation
What is the organisation of synapses?
- neurons receive multiple synaptic input
- neurons use a diversity of neurotransmitters, inhibitory and excitatory
- most synapses are axo-dendritic which are usually excitatory
- axo-somatic and axo-axonic synapses are usually inhibitory or modulatory
- competing inputs are integrated in the postsynaptic neuron (neuronal integration)
- axon potential generated at the axon hillock
What are some features of synaptic diversity?
- Some neurotransmitters REDUCE THE LIKELIHOOD OF ACTION POTENTIAL FIRING by the target neuron (Decrease depolarisation e.g. GABA, dopamine)
- Some neurotransmitters INCREASE THE LIKELIHOOD OF ACTION POTENTIAL FIRING by the target neuron (Increase depolarisation e.g. glutamate, acetycholine)
What are some features of synaptic diversity? (cont)...
- Each synapse has multiple receptors e.g. 11 glutamate receptor proteins, 3 GABA receptors, 5 dopamine receptors, 14 5HT receptors etc
What is the structure of Astrocytes?
- 40% cells in human brain
- Many thin processes around capillaries (left), synapses, surface of neurons.
- Cytoskeleton - GFAP (Glial fibrillary acidic protein), microtubules, actin.
- Expression of vimentin
- glycogen granules
- Rough ER, Golgi apparatus
- Large nucleus
- Light cytoplasm
What may astrocytes come into contact with?
- Capillary endothelial cells (round BV)
- Neuronal cell bodies
- Initial segment
- Axon (at nodes)
- Ependymal cells lining the ventricles
- Pial surface of the brain
What are different types of astrocytes?
What are functions of astrocytes?
Modulation of synaptic function:
synaptogenesis and synaptic pruning
• Metabolic function: production of cholesterol
• Maintenance of the BBB
• Regulation of blood flow
• Neuroprotective: release of growth factors
• Recycling of neurotransmitters
• Production of anti-inflammatory cytokines
What are some dysfunctions of astrocytes?
• Increased glutamate cytotoxicity
• Increased levels of Calcium and ATP release
• Increased production of nitric oxide
• Accumulation of superoxide dismutase
• Formation of glial scar
Why is the BBB essential?
It is essential for controlling entry of molecules and ions from the general circulation into the nervous system
What forms the BBB?
- A tight association of brain capillary endothelial cells
- Astrocytic endfeet enwrap enthodelial cells providing a gateway of nutrients etc into the CNS and the removal of metabolites out of the CNS
How is AQP4 involved in the BBB?
- Regulation of extracellular space volume
- Potassium buffering
- CSF circulation
- interstitial fluid resorption
- metabolic waste clearance
- Ca2+ signalling
Astrocytes express a large array of:
- transport proteins for nutrients (e.g. glucose) and metabolites
- neurotransmitters (e.g. GABA and glutamate)
- neurotransmitter receptors
- neuronal trophic factors (e.g. GDNF, FGF, IGF)
How are astrocytes associated with synapses?
- Well placed to interact with released transmitters and to respond to synaptic activation
- well placed to modulate neuronal function via transmitter removal and also release
- regulation of synaptic pruning