3. Neurones And Glia Flashcards
Give 4 roles of astrocytes
Structural support. Help provide nutrition for neurones. Remove neurotransmitters. Maintain ionic environment. Help to form the blood brain barrier.
How do astrocytes provide energy for neurones?
Astrocytes produce lactate which can be transferred to neurones - glucose lactate shuttle.
How do astrocytes help remove neurotransmitters?
Astrocytes have transporters for transmitters eg glutamate. Glutamate is broken down to glutamine in the astrocytes and transported back to the presynaptic terminal.
Why do astrocytes need to help provide energy for neurones?
Neurones do not store glycogen so the lactate supplements their supply of glucose.
Why do astrocytes need to help remove neurotransmitters?
To help keep the extracellular concentration of neurotransmitters low as they can be toxic at high concentrations eg glutamate.
Why are astrocytes needed to help buffer K+ in the brain?
High levels of neuronal activity can lead to a rise in [K+] in the brain ECF. Increased [K+] causes depolarisation of neurones. Inappropriate firing of neurones can lead to epilepsy.
What are oligodendrocytes?
Cells responsible for myelinating axons in the CNS. Myelinate many neurones at once
What are microglia? What do they do?
Immunocompetent cells which recognise foreign material, become activated and phagocytose to remove debris and foreign material.
What 3 cels/structures form the blood brain barrier?
Tight junctions between epithelial cells.
Basement membrane surrounding capillary.
End feet of astrocytes processes.
Describe neurotransmitter release at axon synapses.
Depolarisation in the terminal opens voltage-gated Ca2+ channels. Ca2+ ions enter the terminal. The increased [Ca2+] causes the vesicles to fuse with the membrane at the presynaptic terminal and release the transmitter.
What does the postsynpatic response at a synapse depend on?
The nature of the transmitter.
Nature of the receptor eg ligand-gated ion channels or GCPR.
What are the 3 chemical classes of neurotransmitters in the CNS?
Amino acids.
Biogenic amines.
Peptides.
Glutamate is the main excitatory amino acid neurotransmitter in the CNS. What are the two types of receptors?
Ionotropic - is ligand gated.
Metabotropic - is a GCPR.
What are the 3 types of ionotropic glutamate receptors and what ions are each permeable to?
AMPA - Na/K+.
Kainate - Na+/K+.
NMDA - Na+/K+ and Ca2+.
What is the one type of metabotropic glutamate receptors and how do they work?
mGluR1-7 - linked to either changes in IP3 and Ca2+ mobilisation of inhibition of adenylate cyclase and decreased cAMP.
How do excitatory transmitters such as glutamate cause fast excitatory responses?
Excitatory neurotransmitters cause depolarisation of the postsynaptic cell by acting on ligand-gated ion channels. This causes an excitatory postsynaptic potential and depolarisation causes more action potentials.
How do glutamate receptors have an important role in learning and memory?
Activation of NMDA receptors can up-regulate AMPA receptors. Strong, high frequency stimulation causes long term potentiation. Ca2+ entry through NMDA receptors is important for induction of the long term action potential.
What does too much Ca2+ entry through the NMDA receptors cause? Give an example of when this can occur.
Excitotoxicity, as causes the release of too much glutamate. Eg stroke.
Give 2 examples of inhibitory amino acid neurotransmitters - one in the brain and one in the brainstem and spinal cord.
Brain - GABA.
Brainstem and spinal cord - glycine.
Describe the action of GABA and glycine (inhibitory amino acid neurotransmitter) receptors
Have integral Cl- channels. Opening of Cl- channel causes hyperpolarisation, this is an inhibitory post-synaptic potential, which results in decreased action potential firing.
What are benzodiazepines, which bind to GABA receptors, used to treat?
Have sedative and anxiolytic effects so are used to treat anxiety, insomnia and epilepsy.
Degeneration of cholinergic neurones in the nucleus basalis is associated with what disease? And so what can be used to alleviate the symptoms?
Alzheimer’s disease.
Cholinesterase inhibitors.
What 3 functions of the brain are cholinergic pathways involved in?
Arousal.
Learning and memory.
Motor control.
Where do neurones in the cholinergic pathways of the CNS originate and project to?
Originate in the basal forebrain and the brainstem.
Give diffuse projections to parts of the cortex and hippocampus.
Similar to the cholinergic pathways in the CNS, there are also dopaminergic pathways. What are the 3 pathways and what functions are each associated with?
Nigrostriatal pathway - motor control.
Mesocortical pathway and mesolimbic pathway - mood, arousal and reward.
What changes in the CNS is Parkinson’s disease associated with and so what can be used to treat it?
Associated with loss of dopaminergic neurones, and substantia nigra input to the corpus striatum.
Can be treated with levodopa.
What changes in the CNS may cause schizophrenia and so what class of drugs are antipsychotics?
Increased amphetamine in the brain leading to increased dopamine and noradrenaline release in the dopaminergic and noradrenergic pathways of the CNS.
Antipsychotic drugs are antagonists at dopamine D2 receptors.
Through what receptors does noradrenaline operate?
Alpha and beta GCPRs in both the ANS and CNS.
Where do noradrenergic pathways in the CNS originate from?
Cell bodies of noradrenaline containing neurones are located in the brainstem, in the locus ceruleus.
What happens to noradrenaline release in the CNS when asleep and during behavioural arousal?
Sleep - locus ceruleus neurones are inactive.
Arousal - locus ceruleus neurones activity increases. Amphetamines increase release of noradrenaline and dopamine and increase wakefulness.
What condition may be associated with a deficiency of noradrenaline?
Depression
What are the functions of serotonergic pathways in the CNS and so what class of drugs can be used in treatment of depression and anxiety disorders?
Sleep/wakefulness and mood.
SSRIs (serotonin selective reuptake inhibitors).
