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Clinical neuroscience > Cellular Physiology of the brain > Flashcards

Cellular Physiology of the brain Flashcards

1
Q

What are the major cellular components of the nervous system?

A
  • Neurones
  • Glia
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2
Q

What are the major types of glia found in the CNS?

A
  • Astrocytes (most abundant)
  • Oligodendrocytes
  • Microglia
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3
Q

What are the functions of astrocytes?

A
  • Structural support
  • Help to provide nutrition for neurones
  • Remove neurotransmitters
  • Maintain ionic environment
  • Help to form blood brain barrier
  • Can react to CNS trauma, helping to form scar tissue and to repair damage
  • Take part in synaptic function
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4
Q

How do astrocytes help provide energy for neurones?

A
  • Neurones do not store or produce glycogen
  • Rely on glucose from blood
  • When glucose delivery to neurone via blood is low, astrocytes can support neurones for a short while
  • Via glucose-lactate shuttle
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5
Q

Outline how the glucose-lactate shuttle works

A
  • Astrocytes produce lactate
  • Lactate shuttled across to neurones via MCT1/MCT2 transporters
  • Lactate is converted to pyruvate in neurones
  • Pyruvate used to release ATP
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6
Q

How do astrocytes help to remove neurotransmitters?

A
  • Have transporters for transmitters such as glutamate
  • Astrocyte processes lie very close to synaptic terminals to keep glutamate concentrations low
  • Keeps extracellular concentrations low
  • Allows termination of synaptic response
  • Cell doesn’t remain in permanently depolarised state
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6
Q

How do astrocytes help to buffer K+ in brain ECF?

A
  • When neurones are very active they fire lots of APs
  • K+ moves out into extracellular space
  • If cells are very active [K+] can get very high
  • Increased [K+] depolarises neurones and causes a positive feedback effect
  • Results in lots of unwanted activity
  • Astrocytes have a very negative cell membrane potential very close to K+ equilibrium potential
  • Ion channels and transporters allow K+ to move into astrocytes e.g. Na+/K+ ATPase
  • Astrocytes are coupled to one another and ions move between them
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6
Q

What is the function of oligodendrocytes?

A
  • Responsible for myelinating axons in CNS
  • Schwann cells are responsible for myelinating PNS
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7
Q

What is the function of microglia?

A
  • Immunocompetent cells
  • Have long dendrites
  • When microglia recognise foreign material, they become activated
  • Dendrites swell and cells become phagocytic
  • Remove debris and foreign material
  • Brain’s main defence system
  • Can also act as antigen presenting cells
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8
Q

What forms the blood brain barrier?

A
  • Endothelial cells of capillaries
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9
Q

What does the blood brain barrier do?

A
  • Limits diffusion of substances from blood to brain extracellular fluid
  • Maintains correct environment for neurones
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10
Q

Describe the structure of brain capillaries

A
  • Tight junctions between endothelial cells - prevents molecules from freely diffusing across capillaries
  • Basement membrane surrounding capillary
  • End feet of astrocyte processes
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11
Q

What pathways exist across the blood brain barrier?

A
  • H2O, CO2 and O2 can freely diffuse across the BBB
  • Substances such as glucose, amino acids, potassium are transported across
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12
Q

Why do we need to control ion concentration across the blood brain barrier?

A
  • Exercise can increase K+ levels in blood
  • Don’t want K+ to cross BBB
  • Otherwise it will cause unwanted neuronal activity
  • Also need to limit amino acids from crossing BBB as these can act as neurotransmitters
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13
Q

Why is the CNS immune privileged?

A
  • Rigid skull will not tolerate volume expansion
  • Too much inflammatory response would be harmful
  • Microglia can act as antigen presenting cells
  • T cells can enter CNS
  • CNS inhibits initiation of pro-inflammatory T cell response
  • CNS is immune specialised, not isolated
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14
Q

What are the four main sections of a typical neurone?

A
  • Cell soma
  • Dendrites
  • Axon
  • Terminals
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15
Q

Outline what happens after neurotransmitter is released

A
  • Depolarisation in terminal
  • Voltage-gated Ca2+ channels open
  • Ca2+ enter terminal
  • Vesicles fuse and release transmitter
  • Neurotransmitter diffuses across synaptic cleft
  • Binds to receptors on post-synaptic membrane
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16
Q

Outline the post-synaptic response

A
  • Depends on nature of transmitter and nature of receptor (ligand-gated or GPCR)
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17
Q

What are the three classes of neurotransmitters?

A
  • Amino acids
  • Biogenic amines
  • Peptides
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18
Q

What are some examples of amino acid neurotransmitters?

A
  • Glutamate - excitatory
  • GABA - inhibitory
  • Glycine - inhibitory
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19
Q

What are the two basic classes of glutamate receptors?

A
  • Ionotropic
  • Metaboptropic
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20
Q

What are the different types of ionotropic receptors?

A
  • AMPA receptors (Na+/K+)
  • Kainate receptors (Na+/K+)
  • NMDA receptors (Na+/K+ and Ca2+)
  • Ion channel permeable to Na+ and K+ (and in some cases Ca2+ ions)
  • Activation causes depolarisation - increased excitability
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21
Q

What is the metabotropic receptor for glutamate like?

A
  • G protein coupled receptor
  • Linked to either: changes in IP3 and Ca2+ mobilisation
  • Or inhibition of adenylate cyclase and decreased cAMP levels
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22
Q

Outline fast excitatory responses

A
  • Excitatory neurotransmitters
  • Allows cations to influx into cells
  • Causes depolarisation in postsynaptic terminal
  • This is an excitatory postsynaptic potential (EPSP)
  • Depolarisation causes more action potentials
23
Q

What happens if an EPSP exceeds the threshold potential?

A
  • Action potentials are triggered
  • Large amounts of transmitter in synapse cause increased magnitude of of EPSP and increased frequency of APs
24
Q

What are glutamatergic synapses like?

A
  • Very important, particularly in learning and memory
  • AMPA and NMDA receptors work together
25
Q

How do glutamatergic synapses work?

A
  • Glutamatergic synapses have both AMPA and NMDA receptors
  • AMPA receptors mediate initial fast depolarisation
  • Glutamate activates these receptors
  • This allows removal of Mg2+ ion from pore of NMDA receptor
  • Makes them permeable to Ca2+
  • Glycine acts as a co-agonist
26
Q

What is long term potentiation?

A
  • If synapse is strongly activated, lots of glutamate is released and additional AMPA receptors are inserted into postsynaptic membrane
  • Ca2+ entry through NMDA receptors important for induction of LTP
  • Extra AMPA means that synapse will transmit more readily
  • Molecular basis for learning and memory
27
Q

What happens if too much Ca2+ enters through NMDA receptors?

A
  • Causes excitotoxicity
  • Also, if all synapses were to strengthen, they would rapidly reach saturation and information could not be stored
28
Q

How do we prevent too much Ca2+ enters through NMDA receptors?

A
  • Long-term depression
  • Actively downregulates strength of glutamatergic synapses
  • May contribute to forgetting
29
Q

What are the inhibitory amino acid neurotransmitters?

A
  • GABA is main inhibitory transmitter in brain
  • Glycine acts mostly in brainstem and spinal cord
30
Q

What are the GABA receptors?

A
  • Ionotropic - GABAA
  • Metabotropic - GABAB (GPCR with modulatory roles)
31
Q

How do the GABAA receptors work?

A
  • Permeable to Cl- (have integral Cl- channels)
  • Opening Cl- channels leads to influx into cell
  • Hyperpolarisation
  • Causes inhibitory postsynaptic potential
  • Leads to decreased action potential firing
32
Q

Which drugs bind to GABAA receptors?

A
  • Barbiturates
  • Benzodiazepines
  • Enhance response to GABA
33
Q

What are the uses of barbiturates?

A
  • Rarely used nowadays
  • Risk of fatal overdose, dependence and tolerance
  • Sometimes used as anti-epileptic drugs
34
Q

What are the uses of benzodiazepines?

A
  • Used as sedatives and anxiolytics
  • Addictive
  • Treat anxiety, insomnia, epilepsy
35
Q

Outline what glycine is like as a neurotransmitter

A
  • Inhibitory
  • Less widespread than GABA
  • Released in spinal cord during REM sleep, causing paralysis
  • Receptors are same as GABA receptors
36
Q

What is the role of other neurotransmitters in the CNS?

A
  • Have a more modulatory role
  • Involved in discrete pathways
37
Q

Give examples of biogenic amines and acetylcholine

A
  • Acetylcholine
  • Dopamine
  • Noradrenaline
  • Serotonin
  • Mostly act as neuromodulators
  • Confined to specific pathways
38
Q

Where is ACh found in the CNS?

A
  • Neuromuscular junction
  • Ganglion synapse in ANS
  • Postganglionic parasympathetic
  • Also a central neurotransmitter
39
Q

What is the role of ACh in the CNS?

A
  • Central neurotransmitter
  • Acts at both nicotinic and muscarinic receptors in brain
  • Mainly excitatory
  • Receptors often present on presynaptic terminals to enhance release of other transmitters
40
Q

Outline the key pathways involving ACh in the CNS

A
  • Arousal - anticholinergic drugs may cause drowsiness
  • Learning and memory - cholinesterase inhibitors treat Alzheimer’s
  • Motor control - cholinergic drugs treat Parkinson’s
41
Q

Outline the cholinergic pathways in the CNS

A
  • Discrete groups of neurones originate in basal forebrain and brainstem (nucleus basalis)
  • Give diffuse projections to many parts of cortex and hippocampus
  • Also local cholinergic interneurons e.g. in corpus striatum, thalamus, substantia nigra
42
Q

What is associated with Alzheimer’s disease?

A
  • Degeneration of cholinergic neurones in nucleus basalis
  • Cholinesterase inhibitors are used to alleviate symptoms of Alzheimer’s
43
Q

Which key pathways involve dopamine (DA)?

A
  • Nigrostriatal
  • Neocortical
  • Mesolimbic
44
Q

Outline the nigrostriatal pathway

A
  • DA
  • From substantia nigra to striatum
  • Important for motor control
  • Degeneration of this pathway causes Parkinson’s
45
Q

Outline the neocortical pathway

A
  • DA
  • From midbrain to cerebral cortex
  • Mood, arousal and reward
46
Q

Outline the mesolimbic pathway

A
  • DA
  • From midbrain to limbic system
  • Mood, arousal and reward
  • Overactivity in this pathway may contribute to schizophrenia
  • Amphetamines release dopamine and noradrenaline - produce schizophrenic like behaviour
47
Q

How can Parkinson’s disease be treated?

A
  • Levodopa - converted to dopamine by aromatic amino acid decarboxylase (AADC)
48
Q

How do antipsychotic drugs work on?

A
  • As antagonists at dopamine D2 receptors
49
Q

How does levodopa interact with the BBB?

A
  • L-DOPA is converted to dopamine by AADC in brain
  • L-DOPA crosses BBB readily via Large Neutral Amino Acid transporter (LNAA)
  • L-DOPA can also be converted in periphery by AADC
  • High levels of dopamine cause side effects affecting heart, GI tract and urinary system
  • Carbidopa is co-administered
  • Inhibits peripheral AADC
  • Does not cross BBB so production of dopamine from L-DOPA is not affected
50
Q

How does noradrenaline (NA) operate?

A
  • Released by sympathetic postganglionic terminals
  • Operates through GPCRs (adrenoceptors) - similar both in brain and periphery
51
Q

Which key pathways involve noradrenaline?

A
  • Cell bodies are found in brainstem
  • Project to widespread areas including cortex, limbic system and cerebellum
  • Involved in behavioural arousal
52
Q

Where does most NA in the brain come from?

A
  • Locus coeruleus
  • Locus coeruleus neurones inactive during sleep
  • Activity increases during behavioural arousal
  • Amphetamines increase release of NA and increase wakefulness
  • Low levels of NA are associated with depression
53
Q

Outline the serotonergic pathways in the CNS

A
  • Serotonin, 5-HT
  • Similar distribution to NA neurones - originates from raphe nuclei of brainstem
  • Involved in sleep and wakefulness and regulation of mood
  • Low levels of serotonin cause depression
54
Q

What do SSRIs do?

A
  • Selective serotonin reuptake inhibitors increase levels of serotonin in brain
  • Can help with depression and anxiety disorders
55
Q

What is the role of histamine in the CNS?

A
  • Has a role in sleep and wakefulness
  • Stimulates cortex, maintains wakefulness
  • Some antihistamines can cause drowsiness by antagonising this action
56
Q

Outline the role of peptides in the CNS

A
  • Diffuse slowly
  • Sometimes widespread
  • Often alongside other transmitters, modulatory action
  • Dynorphin and encephalins involved in pain transmission

Clinical neuroscience (19 decks)

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