Lecture 5: Synaptic Transmission Flashcards

1
Q

What is synaptic modulation?

A

Changes in synaptic function, allowing both robust function and higher complexity (learning, memory, etc.)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Gap junction structure

A

6 connexin transmembrane proteins form a connexon hemi-channel. Pairs of hemi-channels cross both cell membranes. Arrays of these pairs form a gap junction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Properties of gap junctions

A

-Channels can be modulated open/closed
-Post-synaptic response is very fast, <1 ms
-Transmitted signal depends on relative size/electrical properties of pre/post synaptic neurons + gap junctions
-No amplification or polarity reversal possible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How do botulinum toxins paralyze?

A

Botulinum cleaves SNARE proteins, inhibiting the release of NTs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is 1 quantum of neurotransmitter?

A

1 quantum of NT = 1 vesicle, which contains 1000s of NT molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Miniature End Plate Potential (MEPP)

A

The post-synaptic potential caused by spontaneous (not induced) fusion and release of 1 NT vesicle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

End Plate Potential (EPP)

A

The summation of the many MEPPs stimulated in response to an action potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How many vesicles are released per action potential?

A

Vesicles per action potential depend on how much Ca2+ influx occurs. At the neuromuscular junction, 1 AP = ~150 vesicles, much more than enough to trigger post-synaptic firing. In the CNS, 1 AP = 1-4 vesicles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Different types of neurotransmitter receptors

A
  1. Ionotropic (1 NT opens 1 channel directly)
  2. Metabotropic (GPCR or other secondary messenger)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Ionotropic receptor

A

One type of post-synaptic receptor. Ligand gated ion channel that opens when 1 NT binds, fast response

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Metabotropic receptor

A

One type of post-synaptic receptor. GPCR that can open many ion channels in response to 1 NT, amplifying the signal. Response can be ~100 ms to minutes; plays role in modulating function or sustained effects.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Chemical synapse properties

A

Neuronal tuning, synaptic strength modulation, signal amplification, excitatory/inhibitory signals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Neuromuscular junction properties

A

No summation occurs; 1 action potential = 1 muscle activation (strong synapse)

1 AP -> ~150 vesicles, creating EPP up to 70 mV; ensures 1:1 transmission with 1.5-4 safety factor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Typical EPSP value

A

~0.2-0.4 mV on average; ~25 summed for 10 mV threshold change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Synapse

A

Anatomically specialized junction between 2 neurons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Convergence

A

A single post-synaptic cell can receive signals from 100s or 1000s of synapses

17
Q

Divergence

A

1 pre-synaptic cell can branch to synapse on many post-synaptic cells

18
Q

What affects the excitability of a post-synaptic cell?

A

Number of active synapses and number of excitatory/inhibitory signals received

19
Q

Types of synapses

A
  1. Electrical
  2. Chemical
20
Q

Electrical synapse

A

Gap junction joining plasma membranes of 2 neurons, allowing local currents from arriving APs to flow directly through

21
Q

Chemical synapse

A

Synaptic vesicles containing NTs (can be multiple different) are released to the synaptic cleft and bind to the post-synaptic cell, stimulating a post-synaptic potential via ion channels. Prevents direct current propagation but permits signal summation.

22
Q

EPSP

A

Excitatory Post-Synaptic Potential. Created by opening Na+/K+ nonselective channels, allowing Na+ influx/small K+ efflux and local depolarization

23
Q

IPSP

A

Inhibitory Post-Synaptic Potential. Created by opening K+ or Cl- channels, reducing chance of reaching AP threshold. K+ hyperpolarizes. If Cl- is actively exported, Cl- influx hyperpolarizes. If not, Cl- stabilizes resting membrane potential and counters positive ion movement.

24
Q

Post-synaptic density

A

The post-synaptic membrane adjacent to the axon terminal is a specialized area with a high density of membrane proteins

25
How are neurotransmitters stored and released?
1. NTs stored in vesicles docked at active zones or dispersed in axon terminal 2. AP opens voltage-gated Ca2+ channels, allowing Ca2+ influx. 3. Ca2+ binds synaptotagmins, causing SNARE protein conformational changes -> membrane fusion and NT release.
26
Post-fusion vesicle fates
1. Endocytosis recycling beyond active zone. 2. "Kiss and run" fusion; resealing/withdrawal after brief fusion. Common in high frequency neurons.
27
What happens to NTs after receptor binding?
Unbound NTs are removed by: 1. Reuptake; active transport and recycling to pre-synaptic axon. 2. Transport to nearby glial cells for degradation. 3. Diffusion away from receptors. 4. Enzymatic inactivation (some reused).
28
Types of summation
1. Temporal 2. Spatial
29
Temporal summation
Summation based on input frequency, where a new PSP is added on before the previous graded potential leaks away.
30
Spatial summation
Summation of 2 inputs arriving simultaneously at different locations on the cell.
31
Axon hillock
Most responsive area of neuron due to higher density of voltage-gated Na+ channels, = more negative threshold vs. dendrites or cell body. Synapses closer to the hillock will induce a greater EPSP.
32
How long do post-synaptic potentials last?
Always longer than 1 AP duration; neuronal responses almost always come in bursts, not as single events.