Synaptic Transmission

Question 0

What are 3 roles of electrical synapses?

Answer 0

1) network activity (synchronization of electrical activity/info across many neurones)
2) communication between glia
3) coordination of growth in embryonic development (Bear et al)

Question 1

What protein forms a gap junction?

Answer 1

Connexin (6 subunits from a connexon = hemichannel)

Question 2

Which type of synapse has a role in epilepsy?

Answer 2

Electrical

Question 3

Which type of synapse is the most common form of communication in the CNS?

Answer 3

Chemical

Question 4

Chemical synapses occur between a presynaptic element, most commonly _______, and postsynaptic elements such as ________

Answer 4

Axon terminals

Dendrites, soma, axon terminals

(I.e. Axoaxonic, axosomatic, axodendritic)

Question 5

Why is chemical transmission greatly flexible?

Answer 5

Many different NTs and receptors
Can modulate expression of NT and receptors
=> huge modulatory activity

Question 6

What is the distance across the synapse for a) electrical synapses?
and b) chemical synapses?

Answer 6

Electrical - 0.35nm

Chemical - 30-50nm

Question 7

What is the synaptic delay at:

a) electrical synapse?
b) chemical synapse?

Answer 7

a) none

b) min 0.3ms, usually 1-5ms

Question 8

What is the direction of transmission for chemical and electrical synapses?

Answer 8

Chemical - unidirectional

Electrical - bidirectional

Question 9

What are the 4 types of major NT?

Answer 9

Ach
Amines
AAs
Peptides

Question 10

Small molecule NTs are synthesised in______ and stored in _____?

Answer 10

Synaptic terminal using enzymes from cell body

Small clear vesicles (40-60nm)

Question 11

Large NTs are synthesised in _____ and stored in _____?

Answer 11

Cell body using RER and Golgi

Large dense core vesicles (90-250nm)

Question 12

Where does Ca enter the presynaptic terminal?

Answer 12

Active zone

Question 13

What is a MEPP?

Answer 13

Miniature end plate potential

=> spontaneous release of a single vesicle (quanta) (not due to AP)

Question 14

What is/what causes an EPP?

Answer 14

Multiple MEPPs due to AP dependent release of many vesicles

Question 15

Are axo-dendritic synaptic connections usually inhibitory or excitatory?

Answer 15

Excitatory

Question 16

Are axo-somatic synaptic connections usually inhibitory or excitatory?

Answer 16

Inhibitory

Question 17

Synapses where influence neurone firing the greatest?

Answer 17

At the initial segment / axon hillock

Question 18

Which type of synaptic connection is modulatory and controls NT release?

How does it control NT release?

Answer 18

Axo-axonic

Controls Ca influx in presynaptic neurone

Question 19

What is the name of the axo-axonic connection that increases NT release?

Answer 19

Presynaptic facilitation

Decreases K+ current, increases Ca current

Question 20

What is integration?

Answer 20

Summation of all EPSPs and IPSPs

Question 21

Where does integration occur?

Answer 21

Axon hillock

Question 22

What is convergence?

Answer 22

Many neurones synapse onto one neurone

Question 23

What is divergence?

Answer 23

One neurone communicates with many via axon collaterals

Question 24

What is temporal summation?

Answer 24

Summation of PSPs arriving in quick succession (only needs one synaptic input)

Question 25

What is spatial summation?

Answer 25

Summation of PSPs from different inputs across membrane surface

Question 26

How does frequency affect NT release?

Answer 26

Increased frequency = increased release

Question 27

What NTs require higher frequency APs for release?

Answer 27

Peptides

Question 28

Why is an AP?

Answer 28

Self-propagating wave of depolarization

Question 29

What is the normal direction of an AP?

Answer 29

Orthodromic

Question 30

Synaptobrevin is what type of SNARE and what does it do?

Answer 30

V-SNARE Binds T-SNAREs: SNAP-25 and syntaxin forming SNARE complex (docking and priming)

Question 31

Which SNARE protein is a Ca sensor? What does it trigger?

Answer 31

Synaptotagmin SNARE complex formation and Fusion (Ca dependent)

Question 32

What do synapsins do?

Answer 32

Restrain vesicles - bind NT to cytoskeleton

Question 33

How are vesicle released from synapsins?

Answer 33

Ca dependent phosphorylation of synapsin

Question 34

What occurs in targeting and docking?

Answer 34

Vesicle moves towards and binds to active zone

Question 35

What is priming?

Answer 35

Vesicles are prepared for fusion

Question 36

What is fusion?

Answer 36

Pore opening

Question 37

What is the process (each step) of NT release from vesicles?

Answer 37

1) vesicles restrained (synaspsin) 2) targeting + docking 3) priming 4) fusion 5) exocytosis 6) endocytosis

Question 38

How long does it take for vesicles to be recycled after release?

Answer 38

30-60 sec

Question 39

What is the role of Clathrin proteins and dynamin?

Answer 39

Endocytosis; - Clathrin binds and distorts vesicle membrane, pulls it into cell - once fully invaginated dynamin "pinches off" vesicle (Energy dependent GTP -> GDP)

Question 40

What do zinc endonucleases and clostridium toxins do?

Answer 40

Cleave SNARE proteins actively involved in fusion

Question 41

What are clostridium toxins?

Answer 41

Botulinum and tetanus

Question 42

Which toxins is synaptobrevin cleaved by?

Answer 42

Tetanus and botulinum B, E, F + G

Question 43

Which toxins are snap-25 and syntaxin cleaved by?

Answer 43

Snap25: botulinum A + E Syntaxin: botulinum C

Question 44

What does botulinum toxicity cause?

Answer 44

Blocks neuro transmission at peripheral Cholinergic synapses

Question 45

Do vesicle transporters have high or low specificity?

Answer 45

LOW (many NTs use same transporter)

Question 46

Do membrane tansporters have high or low specificity?

Answer 46

High (each NT has dif transporter)

Question 47

What are vesicular transporters? What else do they require to function?

Answer 47

Proton dependent antiporters (NT in, H+ out) ATPase: transports H+ into vesicle creates electro chem gradient

Question 48

What is a membrane transporter? Which NTs have these?

Answer 48

Na- dependent symporter Choline, 5-HT, DA, GABA, glutamate

Question 49

What is disinhibition?

Answer 49

Inhibition of inhibitory neurones Generation of excitation by transient inhibition of a tonically active neurone

Question 50

Describe how disinhibition works in the basal ganglia to excite the motor cortex

Answer 50

1) striatum excited (by excitatory input from cortex) 2) increased inhibition of globes pallidus 3) decreased inhibition of VL/VA of thalamus (it is disinhibited) 4) allows excitation of motor cortex