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2.2 Brain & Behaviour > 03. Neuronal transmission I > Flashcards

03. Neuronal transmission I Flashcards

1
Q

Dendrites

A

Receive information

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2
Q

Soma / cell body

A

Main part of neuron

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3
Q

Axon

A

Send information

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4
Q

Terminal boutons

A

AKA axon terminals
- Where the axon meets a neighbouring cell’s dendrites to form a synapse

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5
Q

What is an electrical synapse?

A
  • uncommon in mammals
  • ions move freely (through proteins called ‘connexins’)
  • the junction between the neurons (gap junction) is tiny - 3nm
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6
Q

What is a chemical synapse?

A
  • most common (mammals)
  • communication done through neurotransmitters
  • junction between neurons (synaptic cleft) is 20-50nm
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7
Q

What was the first experimental evidence for chemical transmission

A

Loewi (1920s)
- vagus stimulation -> fluid removed -> injected into another creature -> slowed down their heart rate
- proved that communication can be transferred between creatures and is therefore chemical

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8
Q

In synapses, the axon can connect to 3 different places:

A
  • Axodendritic (most) -> axon connects to dendrite
  • Axosomatic -> axon connects to soma
  • Axoaxonic -> axon connects to axon
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9
Q

What are the criteria for being a neurotransmitter?

A
  • synthesised presynaptically
  • released after elec stimulation
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10
Q

Receptors have varying:

A

kinetics - rate of binding and channel gating
selectivity - what ions are fluxed
conductance - rate of flux

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11
Q

Ionotropic receptors:
Excitatory transmission

A

Ion channel opens -> influx of cations (Na+) -> depolarisation -> EPSP

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12
Q

Ionotropic receptors:
Inhibitory transmission

A

Ion channel opens -> influx of anions (Cl-) -> hyperpolarisation -> IPSP

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13
Q

Metabotropic receptors

A

Same process of inhibition and excitation, but influx of ions is triggered by the ligand-binding G-protein coupled receptor (GPCR) which causes a cascade of reactions inside the cell (second messengers)

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14
Q

Categories of neurotransmitters include:

A

Amino acids
Monoamines
Acetylcholine
Neuropeptides

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15
Q

Glutamatergic receptors include:

A

mGluR, NMDA, AMPA, Kainate

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16
Q

What is the process of glutamate production and release?

A
  • glutamate is synthesised in nerve terminate from glucose or glutamine
  • stored in vesicles
  • released by exocytosis
    (Ca2+ required)
  • acts at glutamate receptors
    (post-synaptic membrane)
  • re-uptake by EAATs (excitatory amino acid transporters) in the plasma membrane of post-synaptic cell
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17
Q

What are the agonists and antagonists for the NMDA receptor?

A

Agonist - NMDA & glutamate
Antagonist - APV

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18
Q

What are the agonists and antagonists for the AMPA receptor?

A

Agonist - AMPA & glutamate
Antagonist - CNQX

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19
Q

What are the agonists and antagonists for the Kainate receptor?

A

Agonist - Kainate & glutamate
Antagonist - CNQX

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20
Q

What are the NMDA receptor’s competitive and non-competitive agonists and antagonists? What is the co-agonist?

A

agonist: glutamate
competitive agonist: NMDA
competitive antagonist: AP5
non-competitive agonist: PCP
co-agonist: glycine

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21
Q

So how are NMDA receptors activated?

A
  • co-activation from glutamate and glycine & low enough membrane voltage
  • this allows the channel to open and Mg2+ to be moved which unblocks the channel pore.
  • glutamate alone opens the channel but doesn’t move Mg2+
22
Q

NMDA dysregulation

A
  • caused by excessive glutamate (glutamate excitotoxicity)
  • excessive Ca2+ influx, activating calcium-dependent proteases and phospholipases that break down parts of the cell
  • often after stroke or chronic stress
23
Q

AMPA vs NMDA

A
  • different kinetics: NMDA opens slower
  • NMDA channels are permeable to Ca2+, Na+ and K+
  • AMPA channels are permeable to
24
Q

What is GABA?

A
  • gamma aminobutyric acid
  • inhibitory transmitter
  • activates GABAA (ionotropic) and GABAB (metabotropic)
25
GABAA receptor
- ionotropic - ligand-gated Cl- channel
26
GABAB receptor
- metabotropic - GPCR coupled to K+ or Ca2+ - slow IPSPs
27
Too much GABA...
- leads to over-inhibition, which can cause sedation and coma - means that drugs that increase GABA transmission can treat epilepsy
28
What is GHB (gamma-hydroxybutyrate)?
A date rape drug Metabolism converts it into GABA This leads to unconsciousness and even coma
29
What can alcohol cause?
Unconsciousness, coma, and death (although often one passes out before ingesting lethal dose)
30
What drugs bind at the GABAA receptor and compete with GABA?
Agonists - Muscimol Antagonists - bicuculine, picrotoxin
31
What drugs bind at the GABAA receptor and don't compete with GABA?
Agonists - Alcohol - Barbiturates Indirect agonist - Benzodiazepines (BDZ) (also anti-convulsant) - Drugs decreasing GABA activity increase anxiety (anxiogenic) (result: more Cl- current, more inhibition, stronger IPSPs) Antagonist - Flumazenil (can reverse sedation from BDZ overdose)
32
What do drugs that increase GABA activity do?
Reduce anxiety Change the kinetics of the GABA receptor
33
Benzodiazepines history
Discovered in the 1960s First one was chlordiazepoxide (Librium), which was replaced with diazepam (Valium) to treat anxiety
34
What do Benzodiazepines do?
They act as: - Anxiolytic - Anticonvulsant - Sedative - Muscle relaxant - Amnestic They are fast-acting but may cause dependence Effects are strengthened by alcohol
35
What is a neuromodulator?
A type of neurotransmitter that affects the neuronal response to other neurotransmitters They do not carry any primary info themselves
36
Examples of neuromodulators include:
- dopamine - serotonin - histamine - neuropeptides
37
What is the Dopaminergic system?
Dopamine neurons are found in the midbrain. They project into the forebrain. Here are some of the systems in the Dopaminergic system: - Nigrostriatal - Mesolimbic - Mesocortical
38
What does the nigrostriatal system do (1) and what area is it found in (2)?
1. has a role in movement - dysfunction causes Parkinson's & Huntington's disease 2. projections from the substantia nigra to neostriatum (caudate and putamen)
39
What does the mesolimbic system do (1) and what area is it found in (2)?
1. reinforcement/reward (so has a role in addiction) 2. projections from the ventral tegmental area to nucleus accumbens (NAcc))
40
What does the mesocortical system do (1) and what area is it found in (2)?
1. working memory/planning (dysfunction: schizophrenia) 2. projections from the VTA to prefrontal cortex
41
What is the process of dopamine synthesis?
Tyrosine (essential amino acid obtained in diet) -> catalyzed by tyrosine hydroxylase (TH) (rate limiting step) -> L-Dopa -> catalyzed by dopa decarboxylase -> Dopamine It is then stored in vesicles
42
What drugs affect dopamine synthesis?
Reserpine - impairs vesicle storage (empty vesicles -> no neurotransmission)
43
What is the process of dopamine release?
Presynaptic membrane depolarises -> influx of Ca2+ (through voltage-gated channels) -> Ca2+ causes exocytosis of vesicles
44
What is the process of dopamine reuptake/metabolism?
Transmission is terminated by transporters that respond to electrochemical gradient (Dopamine transporters (DATs)) -> in the cytoplasm dopamine reloaded into vesicles or metabolised
45
Drugs that affect dopamine release and reuptake
Cocaine, Amphetamine and Methylphenidate (Ritalin) - psychostimulants - block reuptake of monoamines, inc. dopamine Selegiline – Monoamine oxidase B inhibitor (prevents breakdown of catecholamines)
46
What is the Serotonergic system?
Nine raphe nuclei (in brain stem), each projecting to a different part of the brain Descending projections to cerebellum and spinal cord (pain) The dorsal and medial raphe project throughout the cerebral cortex. Functions: mood, sleep, pain, emotion, appetite
47
What is the process of serotonin synthesis?
Tryptophan (dietary amino acid) -> converted via tryptophan hydroxylase (rate limiting) -> makes 5-HTP -> converted via aromatic amino acid decarboxylase -> Serotonin It is then stored in vesicles
48
What is the process of serotonin release?
Ca2+ dependent exocytosis
49
What is the process of serotonin reuptake/metabolism?
- transmission terminated by SERTs (serotonin transporters) - serotonin is degraded by MAOs in the cytoplasm
50
What drugs affect serotonin reuptake?
Fluoxetine (Prozac) is an SSRI and blocks reuptake of serotonin MDMA (ecstasy) causes increased empathy and euphoria and makes serotonin transporters (SERT) work in reverse - more serotonin is released Monoamine oxidase inhibitors boost monoamines

2.2 Brain & Behaviour (15 decks)

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