Synaptic Transmission

Question 1

What is the difference between electrical and chemical synapses?

Answer 1

electrical synapse:
- extremely fast
- bi-directional
- one-to-one
- exchange of small molecules
chemical synapse:
- a bit of a delay
- one-directional
- tuneable transmission
- variety of neurotransmitters

Question 2

What is the contact point called between two neurons?

Answer 2

The synapse

Question 3

What is the function of an electrical synapse and a chemical synapse?

Answer 3

electrical synapse: synchronisation of cells in a network, fast responses
chemical synapse: regulated activity, plasticity

Question 4

name 2 different neurotransmitter receptors and whether they are ionotropic or metabotropic

Answer 4

1. Ligand-gated ion channels (ionotropic)
2. G-protein-coupled (metabotropic)

Question 5

What properties should a neurotransmitter have?

Answer 5

• should be present/ stored in the presynaptic neuron
• should be released upon depolarisation and calcium influx
• should be only temporary present outside the cell, the signal must be stopped
• should be specifically detected by receptors on the postsynaptic neuron

Question 6

How is synaptic transmission through chemical synapses tuneable?

Answer 6

• amplification of signals
• suppression of signals
• alteration of signals
  (plasticity)

Question 7

Where do the neurotransmitter vesicles originate from?

Answer 7

the RER and the Golgi

Question 8

What is the main difference between small clear core vesicles vs dense core vesicles?

Answer 8

SV are recycled, whereas DCV are not as quick

Question 9

Why are SV recycled?

Answer 9

Neurotransmitter vesicles can travel a distance of 40 cm/day which means it would take 3 days before the neurotransmitter vesicle from the neuron cell body has reached the synapse

Question 10

What is a synapse?

Answer 10

A contact point between two neurons

Question 11

Explain the experiment of Heuser and Reese in which they showed that neurotransmitter vesicles are recycled.

Answer 11

They labeled the outside of the neurons with a dark colour. Then they watched whether the colour would be seen inside of the synapse

Question 12

Name the different stages of fusion of synaptic vesicles and what happens

Answer 12

1. Docking; attachment of the vesicle to the release site
2. priming; vesicles are prepared for fast release.
3. calcium sensing: calcium influx triggers the fusion of the synaptic vesicle membrane with the plasma membrane, releasing the neurotransmitters into the synaptic cleft.

Question 13

name the key proteins of the fusion of synaptic vesicles and whether they are part of the SV or the plasma membrane

Answer 13

SNARE
- Synaptobrevin on the SV
- Syntaxin and SNAP-25 on the plasma membrane
Calcium sensor
- synaptotagmin on the SV

Question 14

Name the different steps in the fusion of synaptic vesicles

Answer 14

1. synaptobrevin on the vesicle make a connection with Syntaxin and SNAP-25 on the plasma membrane
2. these will form a complex and the vesicle will dock
3. Synaptotagmin on the SV will bind to the SNARE complex
4. the negative charge of the phospholipids of the 2 membranes is a repulsive barrier for fusion
5. Entering CA2+ from the plasma membrane binds to synaptotagmin, leading to a more positive charge
6. membranes come together and fusion starts

Question 15

Synaptic vesicle fusion is coupled to ….. influx

Answer 15

Synaptic vesicle fusion is coupled to CALCIUM influx

Question 16

How does an ionotropic receptor work?

Answer 16

Upon binding of the selective neurotransmitter, this receptor increases the
permeability of the plasma membrane of specific ions. This can result in an ionic
current

Question 17

What is Ohm’s law

Answer 17

V (Voltage)
————–
I (current) * R (resistance)

Question 18

What is the formula to calculate the current of an ion?

Answer 18

C ion = g x (V m - E rev)
C ion : current of an ion
g: permeability (0 or 1)
V m: membrane potential
E rev: reversal potention of an ion

Question 19

What is the equilibrium potential?

Answer 19

A balance between the diffusion forse and electrical forse. No net movement of K+ ions, electrochemical equilibrium

Question 20

How do you calculate the driving force of an ion?

Answer 20

Vm – E rev ion
V m: membrane potential
E rev: reversal potention of an ion

Question 21

What does positive\ negative EPC mean?

Answer 21

End-plate current
-Positive EPC is a loss of positive ions or a
gain of negative ions to the cytoplasm, e.g.
the influx of Cl - at 0V .
-Negative EPC signifies a gain of positive
charge or a loss of negative charge to the
cytoplasm of the cell,
e.g. the influx of Na+ at 0V

Question 22

What happens to the reversal potential if you elevate the extracellular concentration of K+?

Answer 22

Higher external shifts reversal potential to the right. A decreased concentration gradient outward for K+ thus the reversal potential becomes more positive

Question 23

Name excitatory neurotransmitters and channels

Answer 23

glutamate, Na+, Ca2+ channels

Question 24

Name inhibitory transmitter and channels

Answer 24

Gaba and CL- channels

Question 25

what is the difference between excitation and inhibition

Answer 25

The reversal potential is higher then the threshold for an action potential: excitation
the reversal potential is lower then the threshold for an action potential: inhibition