Neurophysiology Flashcards
(25 cards)
What are the four classes of neuroglial cells?
Astrocytes, oligodendrocytes, microglia, ependymal
What are the functions of neuroglia cells?
All serve specialised functions, generalised as “housekeeping” - regulation of environment, regulation of energy provision, regulation of synaptic function, facilitating action potential transmission, waste disposal, injury protection and repair
What are the general characteristics of glial cells
Do not have axons,
do not generate or propagate APS,
Negative resting membrane potential (due to K+ distribution)
Electrically dynamic, closely associated with CNS microvasculature
Can divide and multiply
What is the key role of astrocytes?
Developing and mature CNS, they contribute to the integrity of the BBB - create a high resistance junction between brain capillary endothelial cells.
Regulate external chemical environment, store and disperse excessive ion concentrations in extracellular fluid
Key component of the tripartite synapse, regulating synaptic transmission
Where are astrocytes found?
In grey matter as protoplasmic astrocytes, often describes and tiling tissue
And as white matter, as fibrous astrocytes.
What is the tripartite synapse?
A functional unit in the brain that includes a pre-synaptic neuron, a post-synaptic neuron, and an astrocyte. Used sense neurotransmitter release and modulate calcium levels in the pre- and post-synaptic neurons, and even releasing neurotransmitters themselves.
What diseases occur in astrocytes?
Reactive astrocytosis on tissue damage: multiply, increase process length, change staining properties, become phagocytic.
Abnormal proliferation leads to tumours (astrocytomas - 2nd most common in children)
What are oligodendrocytes?
Form myelin sheath around nerve axons (insulates and increases spread of current speeding up AP conduction), resemble Schwann Cells.
They also have a structural role surrounding other fibres without forming sheaths
Important in inhibition of neuronal growth
What are disorders in the oligodendrocytes?
Central demyelination (MS), auto immune, plaques on myelin, inflammation, 2:1 female:male, and tumours (oligodendrogliomas)
How does adaptive myelination support learning?
Mice using knockout of myelin regulatory factor - in adult mice preventing the formation of myelinating oligodendrocytes, these mice are slower to learn a complex wheel-running task
where are microglia found
Present in white and grey matter
What are microglia for ?
Resident macrophages of the CNS, phagocytic and important in mediating immune response within CNS, act as antigen presenting cells and interact with T-helper cells
What are ependymal cells responsible for
Lining cavities and ventricles, involved in CSF production in choroid plexus, facilitate movement of CSF, ciliated columnar epithelial cells, disorders include tumours (ependymomas)
Describe the paracrine signalling for astrocytes
Diffusion the chemical signal in interstitial fluid to the neighbour cells. (Probably the oldest mechanism).
Describe the autocrine signalling for astrocytes
Released signalling molecule acts on the cell, which has released it (a mechanism for feedback). For astrocytes the best documented case in ATP, which astrocytes release upon various stimuli, including mehchanical disturbance of their membranes and which then act on the P2 receptors on the surface of the same astrocyte
What do astrocytes contain and then export to neurons
Precursors for biosynthesis of key neurotransmitters: glutamine, both glutamate and GABA are taken up by astrocytes where they are converted to glutamine which is then transferred back to neurons and used to re-syntehesis either glutamate or GABA.
Energy substrates - lactate, used to support their energy generation (converted into pyruvate and then consumed by mitochondria)
Biosynthetic and energy substrates - glucose form blood first enters astrocytic end feet and only then is transferred to neurons.
What are the signalling molecules used
ATP - ADP - AMP - Adenosine
Lactate (as signalling molecule)
Cytokins (short signalling peptides)
D-serine and glycine (co-agonist on NMDA glutamate receptors)
Possibly tonic release go GABA or even glutamate
What is the concept of lactate shuttle?
General idea is that astrocytes overproduce lactate which they then release into extracellular space, while neurons take it up and use for energy production after conversion into pyruvate.
What is the mechanism between astrocytes and adenosine
The link between neurones and astrocytes is adenosine signalling via adenosine 2A type of receptors highly expressed by astrocytes. Widely known that neuronal activity leads to generation of adenosine in extracellular space (direct release or conversion of ATP). By acting on A2B receptors adenosine activated adenylate cyclase, PKA and this leads to release of an array of molecules, including lactate.
What is the proposed theory for astrocytes as interoreceptors
They sense some changes in the environment, release gliotransmitters, meaning that they sense some changes in the environment, release gliotransmitters and this modulates the activity of the local neuronal networks.
What are some examples of astrocytes acting as intero-receptors?
Role of astrocytes in central chemo-sensitivity and regulation of breathing
And the role of astrocytes in maintenance of central perfusion pressure via their intrinsic mechnano-sensitivty. Sensing changes in the environment
How do astrocytes help maintain stable breathing patterns in response to fluctuating blood gas levels?
Astrocytes are sensitive to changes in pH, elevated CO2 leads to lower pH, astrocytes particularly in the medullary and pontine regions of brainstem detect these changes via acid-sensing ion channels (ASICs).
What are ion channels?
Ion channels are everywhere, in nervous, muscle, epithelial cells. Electrical activity of a neutron is determined by the flow of ions through an ion channel. Typically required 4-6 similar protein molecules to assemble a pore between them. The subunit composition varies from one type e of channel to the next which determined their different properties. The nature of the R groups lining the pore decodes the ion selectivity
How is the equilibrium (reverse) potential calculated?
The Nernst equation
Eion = 61.5 mV / Z Log10 (C out/C in).
