Synaptic Transmission

Question 1

Is synaptic transmission unilateral?

Answer 1

Yes

Question 2

What are the two types of synaptic transmission and which one is faster?

Answer 2

Electric transmission is faster than chemical

Question 3

What do chemical synapses generate that add to create an action potential?

Answer 3

PSP (postsynapticpotentials)

Question 4

What are the channel cells composed of in electric gap junctions?

Answer 4

6 connexins

Question 5

What is the mechanism of electric synapse transmission?

Answer 5

It is the flow of ions directly from cytoplasm to cytoplasm

Question 6

What does the PSP of an electric synapse look like after one presynaptic action potential?

Answer 6

It slightly depolarises

Question 7

What kind of junction established principles of synaptic transmission?

Answer 7

The Neuromuscular Junction

Question 8

What are 4 types of CNS synapse based off of connectivity?

Answer 8

Axodendritic - to dendrite
Axoaxonic - to another axon
Axosomatic - to cell body
Dendrodendritic - dendrite to dendrite

Question 9

What are characteristics of the two Gray’s types of chemical synapse?

Answer 9

Type 1 - Asymmetrical membrane differentiations, excitatory

Type 2 - Symmetrical membrane differentiations, inhibitory

Question 10

When a synapse lands on a dendritic spine, does the post synaptic neuron fire an action potential?

Answer 10

Not necessarily!

Question 11

What depolarization is required for an action potential?

Answer 11

-40mV

Question 12

How many mV is an EPSP roughly?

Answer 12

0.5mV

Question 13

How did Otto Loewi contribute to the understanding of NTs in 1932?

Answer 13

He injected saline from an electrically generated slow heart frog heart that slowed down the heart of another without electrical stimulation

Question 14

What are the 7 steps of chemical synapse transmission?

Answer 14

1. Neurotransmitter synthesis
2. Loading of NTs into vesicles
3. Fusion of vesicle to membrane at presynaptic nerve terminal
4. Release of NT into synaptic cleft
5. Binding of NT to postsynaptic receptors
6. Postsynaptic response
7. Removal of NTs from synaptic cleft

Question 15

Why is it important that receptors have low affinities for their NTs?

Answer 15

Because they should only be activated by high concentrations of NT

Question 16

What are the three types of NT? What are they (with popular examples)?

Answer 16

Amino Acids - Small Amino Acids (GABA, glutamate)
Amines - Small amino acids (dopamine, acetylcholine)
Peptides - short amino acid chains (dynorphin)

Question 17

Where are NTs synthesized?

Answer 17

Amino acids + amines = enzymes at nerve terminals
Peptides = The ER/packaged in the Golgi apparatus

Question 18

What ion stimulates exocytosis?

Answer 18

Intracellular Ca2+

Question 19

What is the nature of Ca2+ gates?

Answer 19

They are voltage gated, but slower than Na+ gates

Question 20

Describe the two types of vesicle content emptying into the synapse

Answer 20

1. Kiss and run, energetically favorable that creates a small opening that connects the vesicle and presynaptic membrane
2. Full collapse into the presynaptic membrane

Question 21

What process recovers vesicle membranes?

Answer 21

Endocytosis

Question 22

What does the stochastic nature of transmitter release entail?

Answer 22

Most of the time there are actually synaptic failures, and nothing happens after an action potential in terms of NT release, and sometimes NT release has different effects on the PSP

Question 23

What is the quantal unit of NT transmission?

Answer 23

Vesicles

Question 24

What is the quantal hypothesis of NT release?

Answer 24

Based off of the amplitude of the end-plate potentials, we can assign probabilities of single, double, etc. quantal events

Question 25

In a NMJ, how many synaptic vesicles would be released for an EPSP of how much?

Answer 25

Roughly 200 vesicles woul dbe released for an EPSP of roughly 40mV

Question 26

What direction does voltage go in an EPSP or IPSP?

Answer 26

EPSP - Voltage depolarizes + IPSP - Voltage polarizes -

Question 27

In a CNS synapse, what happens in an EPSP?

Answer 27

One vesicle is released for a change of only a few tenths of a milivolt

Question 28

What is an ionotropic receptor?

Answer 28

It is a transmitter-gated ion channel

Question 29

What is the full formula for the current of an EPSP?

Answer 29

I (epsp) = N(total number of channels) * p0 (probability they’re open) * y(conductance of one) * (vm - Eepsp)(driving force)

Question 30

Why is the reversal potential for Vepsp and Iepsp zero?

Answer 30

Because both Na and K channels flux with voltage changes

Question 31

What are the 4 mechanisms of NT recovery/degradation?

Answer 31

1. Diffusion away from the synapse 2. Reuptake into the presynaptic axon terminal 3. Enzymatic destruction in the synaptic cleft or terminal cytosol 4. Desensitization, ie. Enzyme deactivates a NT

Question 32

What do receptor antagonists do? What is an example of this?

Answer 32

Inhibit neurotransmitter receptors (curare)

Question 33

What do receptor agonists do? What is an example of this?

Answer 33

Mimic naturally occurring NTs e.g. Nicotine

Question 34

What is the root cause of neurological and psychiatric disorders?

Answer 34

It is defective neurotransmission

Question 35

What is synaptic integration?

Answer 35

It is the process where multiple synaptic potentials combine in one postsynaptic neuron

Question 36

What are the three types of EPSP summation that allow for sophisticated computations?

Answer 36

Integration - EPSPs added together Spatial - Coordinated EPSPs at different areas Temporal - EPSPs generated at the same synapse in rapid succession

Question 37

How do dendrites contribute to synaptic integration?

Answer 37

Depolarization falls off with increasing distance of the dendrite

Question 38

What is the formula for the depolarization of the membrane based off of the length of the dendrite?

Answer 38

Vx = V0/e^(x/y(dendritic length constant))

Question 39

Why are dendrites considered excitable?

Answer 39

They have voltage gated channels as well, and can act as amplifiers

Question 40

How can dendrites carry signals in the opposite direction?

Answer 40

Their sodium channels

Question 41

What is the difference between an IPSP and a shunting inhibition?

Answer 41

IPSP = Membrane potential less an -65mV Shunting inhibition = Current flow inhibited from soma to axon hillock