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Clinical Pharmacology > Neurones and Glia > Flashcards

Neurones and Glia Flashcards

1
Q

What 2 main components make up the CNS and what are the functions of each component?

A

Neurones - sense changes and communicae with other neurones

Glia - support, nourish and insulate neurones and remove waste

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2
Q

How many neurones/ glia cells are there in the brain?

A

Neurones ~1011

Glia ~1012 (x10 more then neurones)

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3
Q

What are the 3 types of glial cells?

A
  1. Astrocytes
    • most abundant
    • supporters
  2. Oligodendrocytes
    • insulators
  3. Microglia
    • immune response
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4
Q

What is the role of astrocytes?

A
  • Structural support
  • Help provide nutrition for neurones (glucose-lactate shuttle)
  • Remove neurotransmitters (uptake)
  • Maintain ionic environment (K+ buffering)
  • Help form blood brain barrier
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5
Q

Explain the glucose-lactate shuttle of astrocytes

A
  • Neurones do not store or produce glycogen
  • Glucose enters astrocytes by GLUT1 transporter
  • Astrocytes produce lactate from glycolysis that can be transported into neurones by MCT1 transporter
  • In the neurone, Lactate converted to pyruvate which can be used for energy
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6
Q

Why do astrocytes need to re-uptake neurotransmitters?

A
  • Astrocytes have transporters for transmitters e.g glutamate (major excitatory neurotransmitter)
  • Helps to keep extracellular concentration low so a second response can occur
  • Too much glutamate causes excito-toxicity to neurones as too much Ca2+ is released
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7
Q

Why is it necessary for astrocytes to buffer K+ in the brain ECF?

A
  • High levels of neuronal activity leads to a rise in [K+] in brain ECT
  • Too much K+ causes neurones to depolarise → inadvertantly activating neurones
  • The resting membrane potential is more negative and can therefore buffer K+ from ECF
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8
Q

What is the role of oligodenrocytes?

A

Responsible for myelinating multiple axons at once within the CNS

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9
Q

What are microglia?

A

Immunocompetent ‘macrophages’ of the brain

Recognise foreign material, once activated dendrites get thicker and become phagocytotic

Remove debris and foreign material - brains main defence system against plaques and dead material

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10
Q

What is the function of the the blood brain barrier?

A
  • Limits diffusion of substances from the blood to the brain ECF
  • Maintains correct environment for neurones
  • Brain capillaries have
    • tight junctions between endothelial cells
    • basement membrane surround capillary
    • end feet of astrocyte processes
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11
Q

Which substances can be transported across the blood brain barrier?

A
  • Glucose - transported
  • Amino acids- transported
  • K+ - transported
  • Lipid soluble move freely e.g CO2 and O2
  • Ions and small molecules can’t move across due to very tight junctions allowing for tight junction
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12
Q

Explain what is meant by ‘The CNS is immune priveleged’

A
  • The brain does not undergo rapid rejection of allografts
  • Rigid skull will not tolerate volume expansion- too much inflammatory response would be harmful
  • Microglia can act as APCs
  • T Cells can enter the CNS but the CNS inhibits the pro-inflammatory T cell response
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13
Q

Identify the dendrites, soma, axon, terminals, internodes and myelin sheath

A
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14
Q

How is neurotransmitter released at the synpase?

A
  • Action potential arrives at the pre-synaptic terminal
  • Depolarisation of the terminal opens VGCC
  • Ca2+ ions enter the terminal
  • Vesicles fuse with pre synaptic membrane and transmiter is released
  • Transmitter diffuses across the cleft and binds to receptors post-synaptically
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15
Q

What does the postsynaptic response depend on?

A
  • nature of transmitter
  • nature of receptor
    • ligand gated ion channel
    • GPCR
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16
Q

What are the 3 main chemical classes of neurotransmitter?

A
17
Q

What are the main amino acid neurotransmitters?

A

Excitatory - mainly Glutamate major excitatory neurotransmitter (70% of all CNS synapses are glutamatergic)

Inhibitory - GABA and Glycine

18
Q

What are the main types of Glutamate receptors?

A

IONOTROPIC - integral ion channels

  • AMPA receptors (Na+/K+)
  • Kainate receptors (Na+/K+)
  • NMDA receptors (Na+/K+ and Ca2+)

Activation causes depolarisation increasing excitability → AMPA and NMDA mainly at synapses causing fast neurotransmission

METABOTROPIC - GPCR

  • mGluR1-7
  • Linked to either IP3 and Ca2+ mobilisation
  • or inhibition of AC and decreased cAMP
19
Q

Glutamergic synspases have both AMPA and NMDA receptors. Explain how the two cause a response

A
  • AMPA receptors mediate the initial fast depolarisation
  • NMDA receptors permeable to Ca2+
  • NMDA receptors need glutamate to bind to depolarise the cell and allow ions to flow through the channel
    • GLYCINE acts as a co-agonist
    • Glutamate alone not enough as Mg2+ ions block the pore
    • Activation of AMPA receptors causes Mg2+ to move out of the pore
20
Q

How are glutamate receptors involved in learning and memory?

A
  • Activation of NMDA receptors (and mGluRs) can up-regulate AMPA receptors
  • Strong, high frequency stimulation causes long term potentiation
  • Ca2+ entry through NMDA receptors important for induction of LTP
  • However, too much calcium through NMDA can cause excitotoxicity
21
Q

What are the 2 inhibitory amino acid neurotransmitters?

A
  • GABA - main inhibitory in brain
  • Glycine acts as inhibitor mainy in the brainstem & spinal cord
22
Q

Describe the type of receptors for GABAA and Glycine

A

Both have integral Cl- channels

Opening the channel causes hyperpolarisation → decreased action potential firing

23
Q

How do barbiturates and benzodiazepines elicit their effects at GABAA receptors?

A

Both bind to GABAA enhancing the response to GABA → don’t open the channel themselves but get a bigger and longer response when GABA is present

Barbiturates - anxiolytic and sedative action (rarelt used as risk of fatal overdose, dependence and tolerance)

Benzodiazepines - have sedative and anxiolytic effects, used to treat anxiety, insomnia and epilepsy

24
Q

What is the role of glycinergic interneurones in the spinal cord and brainstem?

A

Involved in reflexes e.g. patellar jerk reflex

Every contraction needs a relaxation

25
Q

Where is ACh mainly released as a neurotransmitter?

A
  • neuromuscular junction
  • ganglion synapse in ANS
  • postganglionic release in parasympathetics
  • also nicotinic and muscarinic recepors in the brainstem
26
Q

Describe the cholinergic pathways in the CNS

A
  • Neurones originate in the basal forebrain and brainstem
  • There are diffuse projections to many parts of the cortex and hippocampus
  • Local cholinergic interneurones in the corpus straitum
  • Responsible for arousal, learning and memory
27
Q

What is the link between the cholinergic pathways in the CNS and Alzheimer’s disease?

A

Nucleus basalis neurones are the 1st to die in Alzheihmers

Drugs inhibiting AChesterase can slow progression by alleviating symptoms (no long term effect)

28
Q

Which dopaminergic pathway is involved in motor control?

A

The Nigrostriatal pathway

29
Q

What dopaminergic pathways are involved in mood, arousal and reward?

A

Mesocortical pathway and Mesolimbic pathways

30
Q

Name some conditions associated with dopamine dysfunction

A
  • Parkinson’s
    • loss of DA neurones
    • substantia nigra mainly
    • can be treate with levodopa
  • Schizophrenia
    • due to release of too much DA
    • amphetamine similar effect produces schizophrenic like behaviour
    • antipsychotic drugs are D2 receptor antagonists
31
Q

Explain why L-DOPA is given alongside Carbidopa in treatment of Parkinson’s

A
  • L-DOPA transported across BBB by LNAA (large neutral amino acid transporter)
  • In the brain it is converted to Dopamine by AADC
  • Caribdopa inhibits AADC but cannot cross BBB
    • it lmits the increase of dopamine in the periphery to avoid unwanted side effects
32
Q

Which receptors does noradrenaline act on?

A

GPCR alpha and beta adrenoreceptors

33
Q

Where are cell bodies containing noradrenaline neurones mainly located?

A

In the brainstem (pons and medulla)

The Locus Coerelus main cell body

34
Q

What is the role of locus ceruleus in behavioural arousal?

A
  • Most NA in brain comes from the locus ceruleus
  • LC is inactive during sleep but activity increases during behavioural arousal
  • Amphetamines increase the release of NA and DA increasing wakefulness
35
Q

What is the link between depression and and NA?

A

Depression may be associated with a deficiency of NA

36
Q

What functions are Serotoning (5-HT) incolved in?

A
  • Sleep /wakefulness
  • Mood

Clinical Pharmacology (25 decks)

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