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Introduction to neuroscience > Synapses + neurotransmitters > Flashcards

Synapses + neurotransmitters Flashcards

1
Q

What are the two kinds of synapse?

A

Electrical- gap junctions that allow electrical current to pass directly between neurons
Chemical- neurotransmitters released by exocytosis and then bind to specific receptors

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2
Q

How do you distinguish an electrical synapse from a chemical one?

A

Small molecules like dyes diffuse from one to the other
deleting connexin gene shakB2 will stop the passing of depolarization and hyperpolarization from one neuron to another in electrical synapses

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3
Q

What are the differences between chemical and electrical synapse transmission?

A

Electrical- signals pass in both directions, signals are passed directly so can only be attenuated, faster
chemical- signals pass in only one direction, signals can be radically transformed, slower

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4
Q

Steps in chemical synapse transmission

A

Package neurotransmitters and move them into presynaptic terminal > AP arrives so voltage gated Ca2+ channels open > Ca2+ influx means v SNAREs and t SNAREs zip together > vesicles fuse to membrane > neurotransmitters released by exocytosis > diffusion across synaptic cleft > activate receptors on postsynaptic cell triggering further signalling > neurotransmitters removed from cleft

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5
Q

What are the properties of synaptic vesicles?

A

Clear and small
small molecule neurotransmitters
filled by transporter proteins at the presynaptic terminal
recycled by endocytosis

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6
Q

What are the properties of dense-core secretory vesicles

A

Dense and large
Peptide neurotransmitters
Created and filled by ER/golgi secretory apparatus
One and done/ destroyed after use

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7
Q

Differences between ionotropic and metabotropic receptors

A

Ionotropic- directly depolarize or hyperpolarize the postsynaptic cell
Metabotropic- more complex effects such as enzyme cascades and secondary messengers

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8
Q

What three ways can a neurotransmitter be removed from the synaptic cleft?

A

Diffusing away
Actively being taken up by transporters for recycling
Destroyed in synaptic cleft by enzymes

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9
Q

Similarities between chemical and electrical synapses

A

They are both plastic (can be modified) but chemical more so than electrical
both allow summing up inputs by the postsynaptic neuron

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10
Q

Features of a neuromuscular junction

A

Fast and reliable transmission
Motor neuron APs always cause muscle cell APs
Uses ACh as neurotransmitter

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11
Q

What makes neuromuscular junctions efficient?

A

One of the largest synapses in the body with a large number of active zones in the presynaptic neuron
Postsynaptic cell contains junctional folds which are densely packed with receptor sites
Active zones and junctional folds are also precisely aligned for transmission

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12
Q

What are the criteria for determining if a molecule is acting as a neurotransmitter?

A 
Neurotransmitters must:
be present in presynaptic terminals
be released in response to stimulation 
act on the postsynaptic neuron
\+ blocking the neurotransmitter should prevent synaptic transmission
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13
Q

Features of amino acid and amine neurotransmitters

A

Small molecules
Stored in synaptic vesicles
Can bind to both ligand gated ion channels or G-protein coupled receptors

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14
Q

Features of peptide neurotransmitters

A

Large molecules
Stored in secretory granules
Only bind to G-protein coupled receptors

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15
Q

What is a co-transmitter?

A

A small molecule that neurons release along side a peptide neurotransmitter

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16
Q

Glutamate

A

Most common excitatory neurotransmitter in the CNS
Amino acid so found in all neurons
3 ionotropic receptors based on their agonists- AMPA, NMDA, Kainate
Action is terminated by selective uptake by presynaptic cells and glia

17
Q

AMPA receptors

A

Mediate fast excitatory transmission

Triggers Na+ and K+ currents triggering EPSPs

18
Q

NMDA receptors

A

Often co-exist with AMPA receptors
Have a voltage dependent Mg2+ blocks
so they only open when the membrane is already depolarized
Function as a coincidence detector- when a neuron is activated after just being activated this makes learning possible
Let in Ca2+ which causes downstream signalling

19
Q

What are examples of metabotropic glutamate receptors? What do these do?

A

mGluR1, mGluR2

They allow glutamate to sometimes be inhibitory, like in the retina

20
Q

GABA

A

Most common inhibitory neurotransmitter in the CNS
y-amino butyric acid
Synthesized from glutamate by the enzyme glutamic acid decarboxylase
Action is terminated by selective uptake into presynaptic neurons and glia

21
Q

GABA A receptors

A

Causes IPSPs via GABA gated chloride channels

if the membrane potential is > chloride’s Nernst potential

22
Q

Why is the right amount of inhibition by GABA important?

A

Too much- coma, loss of consciousness

Too little- seizures

23
Q

What drugs can modulate GABA A receptors and what effects do they have?

A

They have no effect unless GABA is also bound so they are all allosteric drugs
Ethanol- alcohol
Benzodiazepines- treat anxiety
Barbituates- sedatives and anti-convulsants
Neurosteroids- metabolites of steroids

24
Q

GABA B receptors

A

G-protein couples receptors that act in diverse ways
Can open K+ channels, close Ca2+ channels, trigger secondary messengers like cAMP
Often presynaptic or auto-inhibitory

25
Q

Glycine

A

Major inhibitory NT is the brain stem + spinal cord
Acts via Glycine receptors which are glycine-gated chloride channels
Also binds to NMDA glutamate receptors

26
Q

Formation of ACh

A

Choline + Acetyl CoA > Acetylcholine
Uses enzyme cholineacetyltransferase ChAT
This is a good marker for cholinergic neurons
Acetyl CoA is produced by cellular respiration in mitochondria

27
Q

nAChRs

A

ACh gated Na+/K+ receptors
Neuromuscular junctions + CNS
Agonist- nicotine
Antagonist- curare

28
Q

mAChRs

A 
5 types of GPCRs 
CNS + autonomic nervous system
M1, 3, 5- excitatory via Gq
M2, 4- inihibitory via Gi/o
Agonist- muscarine
Antagonist- atropine
29
Q

What chemicals block the release of ACh?

A

Botulinum toxin

Black widow spider venom

30
Q

What chemicals block acetylcholinesterase?

A

Nerve gas
Organophosphate pesticides
Alzheimer’s treatments

31
Q

What chemicals activate ACh receptors? (agonists) and what chemicals block ACh receptors? (antagonists)

A

Nicotine and muscarine
Neonicotinoid pesticides
Curare and atropine

32
Q

What are monoamines and catecholamines?

A

Monoamines are synthesized by amino acids and include: serotonin and catecholamines (dopamine, adrenaline and noradrenaline)
Receptors are mostly G-protein coupled receptors

33
Q

Storage and removal of monoamines

A

Packaged into vesicles using vesicular monoamine transporters (VMAT)
Removed from synaptic cleft by re-uptake transporters, particular ones for each monoamine
Destroyed by monoamine oxidase (MAO) and catechol-O-methyltransferase on the postsynaptic cell (catecholamines only)

34
Q

What role does dopamine play in motor control?

A

Dopaminergic neurons in the substantia nigra project to the striatum
nigrostriatal pathway allows for the initation of voluntary movement
In Parkinson’s disease it is these neurons that die and cause motor dysfunction

35
Q

What role does dopamine play in motivation and reward?

A

Dopaminergic neurons in the ventral tegmental area (VTA) project to the cortex and limbic system
mesolimbic pathway mediates reward and motivation
Intra-cranial self-stimulation of the mesolimbic pathway is extremely rewarding and so is a target for addiction

36
Q

What role does noradrenaline play in arousal?

A

Small number of noradrenergic neurons in the locus coeruleus innervate the whole brain
Controls: sleep/wake, attention, arousal, mood, memory, anxiety, pain etc
Distinct from the role of noradrenaline in the autonomic NS

37
Q

What do seratonergic neurons regulate? Where are they located?

A

Sleep/wake and mood’

In the Raphe nuclei which project all over the brain

38
Q

What drugs affect monoamines?

A

Cocaine and amphetamines block the re-uptake of dopamine and noradrenaline
Anti-psychotics block dopamine receptors
Anti-depressants- tri-cyclics block the re-uptake of NE + serotonin, selective serotonin re-uptake inihibitors (SSRIs), MAO-A inhibitors

39
Q

Other neurotransmitters

A

ATP
Opioid peptides or endorphins
Endocannabinoids
Nitric oxide

Introduction to neuroscience (8 decks)

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