synapses and neurotransmitters Flashcards

1
Q

what is the criteria for neurotransmitters?

A
  • 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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2
Q

what are the main classes of neurotransmitters?

A
  • amino acids
  • amines
  • peptides (made up of many amino acids)
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3
Q

evidence for neurons

A
  • golgi stain
  • physiological evidence from study of reflexes
  • final evidence from electron microscopy
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4
Q

why are synapses important?

A

they enable flexible processing and allow for specialization and integration

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5
Q

what are electrical synapses?

A

gap junctions that allow current to pass directly between neurons
they directly connect the cytoplasm of two neurons
both depolarization and hyperpolarization are transmitted

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6
Q

how to tell if neurons are connected by gap junctions?

A

physical technique - dyes can be inserted into neurons using electrodes
dyes diffuse from one neuron to the other demonstrating presence of gap junctions

electrical technique - hyperpolarizing and depolarizing stimuli are passed from one neuron to the other

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7
Q

what are electrical synapses good for?

A
  • fast communication
  • synchronizing neurons
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8
Q

what are the steps in chemical synaptic transmission?

A
  1. package neurotransmitters in vesicles and put them in pre-synaptic terminal
  2. action potential arrives - voltage-gated ca2+ channels open
  3. Ca2+ influx - vesicles fuse to membrane, neurotransmitters released
  4. neurotransmitters diffuse across the synaptic cleft, activate receptors on postsynaptic cell
  5. neurotransmitters removed from cleft
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9
Q

what are the two types of synaptic vesicles?

A

synaptic vesicles - clear, recycled by endocytosis, small molecule transmitters
dense-core secretory granules - dense, ‘one and done’, peptide neurotransmitters

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10
Q

how do vesicles fuse with the membrane?

A

v-SNAREs on the vesicle have partner t-SNAREs on the membrane
calcium binds to synaptotagmin on v-SNAREs, causing a conformational change that makes the SNAREs ‘zipper’ together

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11
Q

what are SNAREs commonly used for?

A

they are targets for toxins which cause paralyses but small amounts can be used to get rid of wrinkled (botox)

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12
Q

what are the two types of neurotransmitter receptors?

A

ligand-gated ion channels (ionotropic receptors)
G-protein coupled receptors (metabotropic receptors)

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13
Q

what are ionotropic receptors?

A

ligand-gated ion channels
binding of neurotransmitter triggers a conformational change on ion channel allowing ions to pass through

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14
Q

what are metabotropic receptors?

A

G-protein-coupled receptors (not ion channels)
binding of neurotransmitter triggers conformational change of G-protein which has more complex effects

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15
Q

how are neurotransmitters removed from synaptic cleft?

A
  • they diffuse away
  • actively taken up by transporters for recycling (into presynaptic neuron/glia)
  • destroyed in synaptic cleft by enzymes
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16
Q

differences between electrical and chemical synapses

A
  • electrical signals pass in both directions, chemical only one direction
  • electrical signals passed directly, chemical signals can be transformed (inverted, amplified etc)
  • electrical synapses are fast, chemicals are slow
17
Q

similarities between electrical and chemical synapses

A
  • both are plastic (can be modified), but chemical more so
  • allow summing up inputs by post-synaptic neuron
18
Q

features of neuromuscular junction

A
  • motor neuron action potentials always cause muscle cell action potentials
  • uses neurotransmitter acetlycholine
  • fast and reliable neurotransmission
19
Q

how does the neuromuscular junction achieve such efficient transmission?

A
  • presynaptic membrane has large number of active zones
  • postsynaptic membrane contains junctional folds densely filled with neurotransmitter receptors

active zones and junctional folds are precisely aligned

20
Q

how do neurotransmitters allow for convergence and divergence?

A
  • each transmitter can activate multiple different receptors (convergence)
  • each receptor can activate different downstream effectors
  • different transmitters or receptors can activate the same downstream effector
21
Q

how does dendritic integration work?

A

EPSPs from different neurons and dendrites summate to reach threshold, so AP generated at axon hillock, which is actively regenerated along axon

22
Q

why does it matter how excitatory and inhibitory synapses are spatially arranged?

A
  • an inhibitory synapse can block propagation of EPSP towards soma
  • GABAa receptors can decrease membrane resistance so current leaks out
  • they act by shunting inhibition
23
Q

how can inhibition act presynaptically?

A

GABA produced by 3rd party neuron can activate GABAb receptors which can close calcium channels so less neurotransmitter can be released

24
Q

how does cocaine and amphetamines affect monoamines?

A

block reuptake of dopamine, norepinephrine (noradrenaline)

25
Q

how do antipsychotics affect monoamines?

A

block dopamine receptors

26
Q

what are the main monoamines?

A

dopamine, serotonin, norepinephrine (noradrenaline), epinephrine (adrenaline)

27
Q

what are the modulatory neurotransmitters?

A

acetylcholine, monoamines

28
Q

how do antidepressants affect monoamines?

A

increasing serotonin
selective serotonin reuptake inhibitors (SSRIs)
MAO-A inhibitors (stop breakdown of serotonin)