Synapses and Neurotransmitters

Question 1

what is a synapse?

Answer 1

a junction between 2 neurons allowing signals to pass from one to another.

Question 2

what is an electrical synapse?

Answer 2

are formed of gap junctions that allow current to flow directly between neurons.

Question 3

what are electrical synapses good for?

Answer 3

as they are connected by channels it allows for fast communication, and for synchronising neurons.

Question 4

what is a chemical synapse?

Answer 4

contain synaptic and secretory granules vesicles (is the usual synapse picture you see).

Question 5

what are the steps in chemical synapse transmission?

Answer 5

package neurotransmitters in vesicles at the presynaptic terminal,
action potential arrives - voltage-gated Ca2+ channels open,
Ca2+ influx causes vesicles to fuse with membrane and neurotransmitter to be released,
neurotransmitters diffuse across the synaptic cleft and activate receptors on the postsynaptic membrane,
afterwards neurotransmitter is removed from the cleft.

Question 6

what type of receptor is a ligand-gated ion channel?

Answer 6

an ionotropic receptor.

Question 7

what happens when neurotransmitter binds to ligand-gated ion channels?

Answer 7

a conformational change happens in the protein, the channel opens and allows the neurotransmitter to directly depolarise / hyperpolarise the postsynaptic cell.

Question 8

what type of receptor is a G-protein coupled receptor?

Answer 8

a metabotropic receptor.

Question 9

what happens when neurotransmitter binds to G-protein coupled receptors?

Answer 9

it activates a second messenger protein which impacts multiple areas and can open the channel.

Question 10

what happens to the neurotransmitter in the cleft afterwards?

Answer 10

taken up by reuptake transporters for recycling, or are destroyed by emzymes.

Question 11

how does the neuromuscular junction (NMJ) achieve efficient transmission?

Answer 11

on the presynaptic membrane, there are a large no. of active zones where vesicles can fuse with membrane and release acetylcholine,
on the motor end plate there are junctional folds filled with receptors aligned with the active zone to receive the signal.

Question 12

what are the types of neurotransmitter?

Answer 12

amino acids and amines, and peptides.

Question 13

what are the properties of amino acid and amine neurotransmitters?

Answer 13

they are small molecules,
stored in synaptic vesicles,
and can bind to ligand-gated ion channels or G-protein coupled receptors.

Question 14

what are the properties of peptide neurotransmitters?

Answer 14

they are larger molecules,
stored in secretory granules,
but only bind to G-protein coupled receptors.

Question 15

what is the most common excitatory neurotransmitter in the CNS?

Answer 15

Glutamate.

Question 16

what are the 3 ionotropic glutamate receptors?

Answer 16

AMPA receptors,
NMDA receptors,
Kainate receptors.

Question 17

what happens when glutamate binds to AMPA receptors?

Answer 17

it triggers Na+ and K+ currents resulting in excitatory postsynaptic potentials.

Question 18

how do NMDA receptors work?

Answer 18

they have a voltage-dependent Mg2+ block so only open when the neuron depolarises,
they let Ca2+ in leading to downstream signalling,
and they function as a coincidence detector (neuron activated right after is was already activated).

Question 19

what is the most common inhibitory neurotransmitter in the CNS?

Answer 19

GABA.

Question 20

what does GABA do?

Answer 20

produces inhibitory postsynaptic potentials via GABA-gated Cl- channels if the membrane potential is above Cl- Nernst potential.

Question 21

what does Glycine do?

Answer 21

inhibits neurons via glycine-gated Cl- channels (glycine receptors),
and binds to NMDA glutamate receptors.

Question 22

can an inhibitory synapse effect propagation?

Answer 22

it can block propagation of an excitatory postsynaptic potential (EPSP) towards the soma.

Question 23

what does Acetylcholine do?

Answer 23

it acts on nicotinic (ionotropic) receptors - nAChRs, acetylcholine-gated Na+ / Ca2+ channels found at neuromuscular junction in CNS,
and muscarinic (metabotropic) receptors - mAChRs, G-protein coupled receptors found in CNS and ANS.

Question 24

what are monoamines?

Answer 24

synthesised from amino acids packed into vesicles by vesicular monoamine transporters (VMAT).

Question 25

what are monoamines?

Answer 25

synthesised from amino acids packed into vesicles by vesicular monoamine transporters (VMAT),
they are destroyed by monoamine oxidase (MAO) and catechol-o-methyltransferase (CAMT) on postsynaptic membrane.

Question 26

what is the nigrostriatal pathway?

Answer 26

dopaminergic neurons in the substantia nigra project into the striatum, facilitates initiations of voluntary movement.

Question 27

how does Parkinson’s disease affect dopaminergic neurons?

Answer 27

dopaminergic neurons die leading to motor dysfunction (tremors, rigidity).

Question 28

what is the mesolimbic pathway?

Answer 28

dopaminergic neurons in the ventral tegmental area (VTA) project into the cortex and limbic system, initiates reward / motivation.

Question 29

what are some neurons that regulate arousal?

Answer 29

noradrenergic neurons regulate arousal.

Question 30

what are some neurons that regulate sleep / wake?

Answer 30

serotonergic neurons regulate sleep / wake and mood.

Question 31

cocaine and amphetamines block…

Answer 31

block the reuptake of dopamine, norepinephrine.

Question 32

antipsychotics block…

Answer 32

block dopamine receptors.

Question 33

what do opioid peptides (endorphins) do?

Answer 33

bind to opioid receptors (G-protein coupled receptors) and regulate pain.