Neurones And Glia Flashcards
(33 cards)
What are components of the cns
• Network of neurones with supporting glia
• Neurones sense changes and communicate with other neurones
– around 1011 neurones
• Glia support, nourish and insulate neurones and remove ‘waste’
– around 1012 glia
What are types of glial cells
• Astrocytes (several different types) – most abundant type of glial cell – Supporters • Oligodendrocytes – Insulators • Microglia – immune respons
What are the roles of astrocyted
• Structural support • Help to provide nutrition for neurones – glucose-lactateshuttle • Remove neurotransmitters (uptake) – control concentration of neurotransmitters (especially important for glutamate (toxic) • Maintain ionic environment – K+ buffering • HELP to form blood brain barrier
Hwo do astrocytes provide energy for neurones
• Neurones do not store or
•produce glycogen
Astrocytes produce lactate which can be transferred to neurones
• Supplements their supply of glucose
• Glucose lactate shuttle
Lactate used to produce atp
Glycogen can be stored in astrocytes. Can produce pyruvate, lactate. Transporters can transport lactate
Intense neuronal activity - need some more energy (atp) can get lactose lactate shuttel
Can operate for 10-15 min
How do astrocytes help to remove neurotransmitters
• Re-uptake
– Astrocyteshave transporters for transmitters such as glutamate
– Helps to keep the extracellular concentration low.
How do astrocytes help to buffer k+ in brain ecf
• High levels of neuronal activity could lead to a rise in [K+] in brain ECF
• Astrocytes take up K+ to prevent this
Can get build up of K= in ecf. If it gets too high will depot the surrounding Europe’s - spontaneous electrical activity - too much glutamate - toxic.
Astrocytes perm to cl-, keep memb potential very negative, so they can take upk+ - inward movement of k+ though channels and transporters - work to keep a low k+ conc
Astrocytes can be coupled. So k+ moves between them to maintain low
What are oligodendrocytes
- Responsible for myelinating axons in CNS
- Compare with PNS where Schwann cells are responsible for myelination
- Good time to revise ICPP Unit and myelination
What are microglia
• Immunocompetent cells • Recognise foreign material - activated • Phagocytosis to remove debris and foreign material • Brain’s main defence system Processes get wides when activated Mesodermal. Other glia are ectodermal a
What is the bbb
• Limits diffusion of substances from the blood to the brain extracellular fluid
• Maintains the correct environment for neurones
• Brain capillaries have
– tight junctions between endothelial cells
– basement membrane surrounding capillary
– end feet of astrocyte processes
Blood is not a suitable environment for neurones as it can have changing levels of, e.g. aas, k+, etc
Endothelial cells from tight junctions- prevents charge molecules difficusing into the brain extracellular space. (Astrocytes do not form bbb but associate)
Describe the pathways across the bbb
- Substances such as glucose and amino acids and potassium are transported across BBB.
- This allows the concentration to be controlled
Ions or small molecules rely on transporters and channels. Eg glucose in glut1. AAs are transported across - controlwhat crosses over into the brain ecf.
How is the brain immune specialised
• Does not undergo rapid rejection of allografts
• Rigid skull will not tolerate volume expansion
– Too much inflammatory response would be harmful - pressure
• Microglia can act as antigen presenting cells
• T-cells can enter the CNS
• CNS inhibits the initiation of the pro-inflammatory T-cell response
• Immune privilege is not immune isolation, rather specialisation
Descrbe neurotransmitter release at the synapse
- Depolarisation in the terminal opens voltage-gated Ca2+ channels. Ca2+ ions enter the terminal
- Vesicles fuse and release transmitter
- Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane
Descrbe the postsynaptic response
• The response depends on – nature of transmitter
– nature of receptor
• Ligand-gated ion channels
• G-protein-coupled receptors
What are the 3 chemical classes of neurotransmitters
AMINO ACIDS
glutamate, GABA, glycine
BIOGENIC AMINES
acetylcholine, noradrenalin dopamine, serotonin (5-HT), histamine,
PEPTIDES
dynorphin, enkephalins, substance P, somatostatin cholecystokinin neuropeptide Y
Descrb amino aid neurotransmitters
• excitatory amino acids – mainly glutamate – major excitatory neurotransmitter • over 70% of all CNS synapses are glutamatergic • present throughout the CNS • inhibitory amino acids – GABA – Glycine
Desribe glutamate receptors
Ionotropic
AMPA Kainate NMDA
receptors receptors receptors Na+/K+ Na+/K+ Na+/K+
and Ca2+
Ion channel - permeable to Na+ and K+ (and in some cases Ca2+ ions)
Activation causes depolarisation – increased excitability
Metabotropic
mGluR1-7
G protein-coupled receptor
Linked to either:
• changes in IP3 and Ca2+ mobilisation
• or inhibition of adenylate cyclase and decreased cAMP levels
Describe teh response at glutamate receptors
Fast excitatory responses
• Excitatory neurotransmitters cause depolarisation of the postsynaptic cell by
acting on ligand-gated ion channels.
- excitatory postsynaptic potential (EPSP)
- depolarisation causes more action potentials
What are the fucntionsof different receptors at glutamierguc synapses
• Glutamatergic synapses have both AMPA and NMDA receptors
• AMPA receptors mediate the initial fast depolarisation
• NMDA receptors are permeable to Ca2+
• NMDA receptors need glutamate to bind and the cell to be depolarised to allow ion flow through the channel
– Also glycine acts as a co-agonist
Need ampa to depolarise to activate nomad.
Descrive glutamate receptors, synaptic plasticity and excitotoxicity
• Glutamate receptors have an important role in learning and memory
– Activation of NMDA receptors (and mGluRs) can up-regulate AMPA
receptors
– Strong, high frequency stimulation causes long term potentiation (LTP)
– Ca2+ entry through NMDA receptors important for induction of LTP
• Too much Ca2+ entry through NMDA receptors causes excitotoxicity – Too much glutamate - excitotoxicity
Lip underlies leaning and memory
Calcium going in - activate downstream signalling - more ampa - more depopulated
What are the main inhibitory amino acids
• GABA is the main inhibitory transmitter in the brain
GABA
• Glycine acts as an inhibitory neurotransmitter mostly in the brainstem and spinal cord
How do gaba and glycine receptors work
• GABAA and glycine receptors have integral Cl- channels
• Opening the Cl- channel causes hyperpolarisation
– Inhibitory post-synaptic potential (IPSP)
• Decreased action potential firing
How do barbiturates and benzodiazepines affect gaba receptors
- Barbiturates and benzodiazepines bind to GABAA receptors
- Both enhance the response to GABA - Both modulate the receptors to enhance the action city
– Barbiturates - anxiolytic and sedative actions, but not used for this now
• risk of fatal overdose also dependence and tolerance
• sometimes used as anti-epileptic drugs
– Benzodiazepines
– have sedative and anxiolytic effects
– used to treat anxiety, insomnia and epilepsy
Where s glycine in high conc
Brainstem ad spinal cord
What are bogenic amines and ach
- acetylcholine
- dopamine
- noradrenaline
- serotonin (5-HT)
- mostly act as neuromodulators • confined to specific pathways
