L20 - synapses and neurotransmission

Question 1

synapse

Answer 1

point where electrical signals move from one neurone to another

Question 2

electrical synapse

Answer 2

pre and post SN directly connected by gap junctions (2nM)

Question 3

chemical synapse

Answer 3

• pre and post SN physically separated by cleft
• pre SN release chemical transmitter from their axon terminals
• NT binds to receptors on post

Question 4

gap junctions in electrical synapses

Answer 4

• 2nM
• formed by connexons
• direct passage of ions + small molecules through these channels
• quick signals

Question 5

features of chemical synapsis

Answer 5

• pre SN
• post SN
• synaptic cleft
• pre S terminal has vesicles with NT

Question 6

3 types of synapses in CNS

Answer 6

1. axo- dendritic
2. axo- somatic
3. axo- axonal

Question 7

axo-dendritic synapse

Answer 7

one neuron’s axon sends signals to another neuron’s dendrite

Question 8

axo-somatic

Answer 8

when one neurones axon sends signals to another cell body

Question 9

axo-axonal

Answer 9

when one neurones axon sends signals to another neurones axon

Question 10

describe pre sn

Answer 10

vesicles arranged at active zones

Question 11

describe post SN

Answer 11

• specialised
• contains clusters of NT receptors and signalling molecules

Question 12

what is a NT?

Answer 12

chemical messenger

Question 13

what are NT released by?

Answer 13

1. when A.P reaches terminal, there is influx of sodium ions causing depol
2. activates calcium channels
3. strong electrochemical gradient which moves calcium to terminal
4. ca2+ enters cell and interacts with synaptotagmin, which interacts with snare proteins
5. vesicles fuse with pre membrane
6. exocytosis
7. enter cleft
8. bind to receptors

Question 14

what happens to unbound NT or after job is done?

Answer 14

1. degradation
2. diffusion away from receptor
3. reuptake via pre sn
4. enzymatically transformed into inactive substances

Question 15

what can NT’s be classified into?

Answer 15

1. amines
2. a.a
3. peptides
4. purines

Question 16

2 types of NT receptors?

Answer 16

• ionitropic
• metabotopic

Question 17

describe ionitropic receptors

Answer 17

• ligand (transmitter) gated ion channel- e.g ACh, GABA, dopamine
• transmembrane proteins open for ions like Na+
• excitatory or inhibitory

Question 18

describe metabotropic receptors

Answer 18

• G protein coupled receptors
• ligand binds
• G protein activates second messenger cascade

Question 19

cholinergic transmission at neuromuscular junction

Answer 19

• synapse between motor neurone and skeletal muscle
• junction is motor endplate
• uses ACh as NT

Question 20

suffix -ergic

Answer 20

applies to neurone that release NT (e.g dopaminergic neurone)

Question 21

synthesis and degradation of ACh

Answer 21

• ACh is synthesised in pre SN by choline acetyltransferase
• metabolised by acetylcholinesterase

Question 22

what does ACh act on?

Answer 22

nicotinic (ion channels) and muscarinic receptors (GPCR)

Question 23

glutamate

Answer 23

• main excitatory transmitter in CNS
• activates inotropic and metabotropic receptors

Question 24

GABA

Answer 24

• main inhibitory transmitter in CNS
• activates small family of ionotropic and metabotropic receptors

Question 25

what is an excitatory postsynaptic potential?

Answer 25

- EPSP - makes neurone more likely to generate A.P

Question 26

what is an inhibitory postsynaptic potential?

Answer 26

- IPSPs - result of flow of negative ions into cell or positive ions out of cell - less likely to generate A.P

Question 27

synaptic integration

Answer 27

1. temporal summation: adding up potentials at same synapse but at different times 2. spatial summation: adding up potentials that occur at different sites on the neurone

Question 28

what can happen if excitatory and inhibitory potential of the same size happens at same time and place?

Answer 28

cancel each other out so memb potential may not change