Session 2: The Role of Neurones and Glia Flashcards
Types of glial cells.
Astrocytes
Oligodendrocytes
Microglia
Functions of oligodendrocytes
Insulators providing the myelin sheath for axons
Functions of the microglia.
Immune response
The role of the astrocytes.
Structural support for neurons
Help to provide nutrition for neurones via the glucose-lactate shuttle.
Removal of neurotransmitters by taking up glutamate.
Maintain ionic environment by K+ buffering.
Help to form the blood brain barrier.
Explain the energy provision to neurones by astrocytes.
Can be either by a direct pathway where glucose goes from blood into neuron directly.
or
By glucose lactate shuttle where glucose enters the astrocyte and is formed into glycogen.
The glycogen then turns into pyruvate and then into lactate.
The lactate then is transported out of the astrocyte and into the neuron where the lactate is transformed into pyruvate again.
Explain astrocytes removal of neurotransmitters.
They have transporters for transmitters and especially glutamate.
Glutamate is toxic in high concentrations which means that it needs to be taken up somehow and that is done via the astrocytes.
This helps to keep the extracellular concentration low.
Explain how astrocytes work as buffers for K+ in the brain ECF.
As neuronal activity increases in the brain there will be an influx of Na+ and to combat that influx there is an efflux of K+.
This leads to a rise of K+ extracellularly and hyperkalaemia can ensue. In order to compensate for this rise in K+ the astrocytes will take up K+.
How does myelination increase conduction velocity?
By a large increase in membrane resistance
By a large decrease in membrane capacitance
What is capacitance?
The membrane’s ability to store charge
Explain the role of microglia.
Immunocompetent cells which recognise foreign material.
This causes phagocytosis to remove debris.
This is the brain’s main defence.
Explain the purpose of the blood brain barrier.
Limits the diffusion of substances from the blood to the brain ECF.
It maintains the correct environment for the neurones.
Explain the relation between the brain capillaries and the blood brain barrier.
There are tight junctions between the endothelial cells.
There is also a basement membrane surrounding the capillaries.
And end feet of astrocyte processes.
Give examples of substances that can be transported across the BBB.
Glucose
Amino acids
Potassium
CO2
Explain the typical neuronal structure.
Four main sections:
Cell soma
Dendrites
Axon
Terminals
Briefly explain the neurotransmitter release at the synapse.
Depolarisation causes Ca2+ ions to enter the terminal.
The Ca2+ causes the vesicles to fuse with the membrane and release the transmitters.
The neurotransmitters diffuses acrsos the synaptic cleft and binds to receptors on the postsynaptic membrane causing an action potential.
What does the postsynaptic response depend on?
The neurotransmitter
The receptor (ligand-gated or g-protein)
What are the main groups of neurotransmitters in the CNS?
Amino acids
Biogenic amines
Peptides
Give example of NT amino acids.
Glutamate
GABA
Glycine
Give examples of NT biogenic amines.
ACh
NA
Dopamine
Serotonin
Histamine
Give examples of NT peptides
Substance P
Somatostatin
Cholecystokinin
Neuropeptide Y
Give examples of excitatory amino acids as NTs.
Mainly glutamate
Give examples of inhibitory amino acids NTs.
GABA
Glycine
Give examples of the main glutamate receptors.
Ionotropic receptors
Metabotropic receptors
Give the subreceptors of ionotropic glutamate receptors.
AMPA receptors
Kainate receptors
NMDA receptors
Explain how the ionotropic receptors work.
They are ion channels receptors and cause an increase in the permeability of Na+ and K+ (also Ca2+ in the case of NMDA receptors).
This causes depolarisation and increased excitability.
Explain how the metabotropic receptors work.
G-protein coupled receptors
Ip3 and Ca2+ increase
or
inhibition of adenylate cyclase and decreased cAMP.
Explain the fast excitatory reponses.
Excitatory neurotransmitters cause depolarisation of the postsynaptic cleft by acting on ligand-gated ion channels (ionotropic).
This causes excitatory postsynaptic potential (EPSP) and the depolarisation causes more action potentials
What kind of receptors are found on glutamatergic synapses?
They have both AMPA and NMDA receptors.
The AMPA receptors mediate the initial fast depolarisation and the NMDA receptors are permeable to Ca2+.
Explain how the GABA and glycine receptors work.
They have integral Cl- channels which when they open causes hyperpolarisation and an inhibitory post-synaptic potential and a decrease in action potential firing.
Explain briefly the cholinergic pathways in the CNS.
They originate in the basal forebrain and brainstem.
They then give diffuse projections to many parts of the cortex and hippocampus.
E.g. Septohippocampal pathway.
Explain how Alzheimer’s disease relate to cholinergic pathways.
Degeneration of cholinergic neurones in the nucleus basalis.
Main function of the mesolimbic pathway.
Involved in mood, arousal and reward.
Why does carbidopa not convert L-DOPA into Dopamine in the brain?
Because it cannot cross the BBB
Briefly explain the noradrenergic pathways in the CNS.
Cell bodies of NA containing neurones are found (arise) from the brainstem and specifically pons and medulla.
There is then a diffuse release of NA throughout the cortex, hypothalamus, amygdala, and cerebellum.
Explain glycine’s role in the patellar tendon reflex.
Hitting the patellar tendon causes spindle fibres to activate and afferents activate with glutamate as their NT. This produces an excitatory response of the quadriceps to jerk the knee upwards (knee extension).
Glutamate also excites an interneuron in order to activate it and produce glycine at another synapse which will inhibit the hamstring muscle causing it to relax in order to not produce the opposing force.
