Synaptic Transmission Flashcards by Michelle Chen

What is anther name for electrical synapses?

Gap junctions

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T or F: gap junctions are voltage gated

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What are the protein structures that make up a gap junction called.

Connexons

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Connexons are comprised of proteins called ___

connexins

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T or F: connexins are multiunit structures

F - connexons are multiunit structures

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How many connexins make up 1 connexon

6 (hexamer)

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Which glial cell are known for making gap junctions?

Astrocytes

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T or F: astrocytes are the only cells that make gap junctions

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What is a gap junction comprised of?

Several (a patch of them) connexons on one cell connecting to connexons on another cell.

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Which microscopy method allows you to see gap junctions?

Electron microscopy (EM)

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T or F: neurons can only make gap junctions with other neurons

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How many transmembrane domains does a connexon have?

24 - each connexin has 4 transmembrane domains and each connexon has 6 connexins

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Name a method used to view gap junctions. Describe

Live staining - label connexins with fluorophores

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At electrical synapses, how are postsynaptic cells depolarized?

Na entering axon terminus due to AP reaching axon terminus (on presynaptic cell) will flow through gap junctions into the dendrites of the postsynaptic cell

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T or F: the magnitude of the Vm does not change between the pre and postsynaptic cell at an electrical synapse. Explain

F - gap junctions act as resistors which reduce the Vm at the postsynaptic cell

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T or F: gap junctions are selective pores

F - non-selective

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List 4 things that a gap junction will allow through

Ions (current)
IP3
cAMP
ATP 
The last 3 are signalling molecules - i.e. gap junctions pass current and signalling molecules

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Give 2 properties of the postsynaptic Vm after current/ions (Na) pass through the gap junction

slightly attenuated magnitude

2. slightly delayed in reaching its peak

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T or F: glia can pass Na through gap junctions

F - glial cells do not depolarize

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Give a strategy to determine whether cells are gap-junctioned together

inject fluorescent dyes into axon terminal of 1 cell - if the dyes are small enough, they will pass through the gap junctions and light up adjacent cells

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T or F: the neurons in a fetus are mostly connected via electrical synapses

T - early in dvlpmt, cells are initially gap-junctioned, then switch over to chemical synapses

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T or F: gap junctions are prevalent in early dvlpmt

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Where are gap junctions located on the presynaptic cell?

Close to soma

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T or F: pre and postsynaptic terminals are very similar

F - each side is very specialized to release NT or receive NT

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What type of signal is an AP - chemical or electrical?

Electrical - mediated by ions

T or F: chemical transmission is fast

F - chemical signalling at (chemical) synapse takes longer than signalling at gap junction

What is the dominant type of signalling in the brain?

Chemical

T or F: synapses are held together by proteins

T - synapses are tightly attached to each other; can isolate synaptosomes

What is Sherrington known for?

Observing that basket cells cup and make contact with Purkinje cells

T or F: Loewi hypothesized that electrical signals propagate from one cell to the next

F - hypothesized that chemical signals propagate from 1 cell to the next

Vagus nerve is part of the ____ nervous system

parasympathetic

stimulating the vagus nerve increases or decreases heart rate?

decreases

Which ion channel does TTX inhibit?

VG Na channels

T or F: Applying TTX at the presynaptic terminal reduces/blocks depolarization from occurring at the postsynaptic cell

F - release of NT doesn't depend on Na, but Ca, so depolarization of the postsynaptic cell still occurs

What were scientists trying to figure out by using the squid giant axon?

Which ion is involved in causing chemical transmission at the synapse/which ion is involved in releasing NT from vesicles

T or F: applying TEA at the presynaptic terminal doesn't affect depolarization from occurring in the postsynaptic cell

Which ion channel does TEA block?

VG K channels

Which part of the neuron is Ca signalling limited to?

At the synapses

Chemical neurotransmission is ion-dependent. Which ion?

T or F: synapses in central nervous system are large

List 3 things that define a NT.

1. Must be present w/in presynaptic neuron 2. Must be released in depolarization and Ca dependen fashion 3. Must have specific receptors on post synaptic neuron

Where are the VG Ca channels located on the presynaptic membrane with respect to the NT receptors on the postsynaptic membrane?

Directly across from the postsynaptic membrane

What signal causes vesicles to fuse with plasma membrane?

Ca influx due to AP opening VG Ca channels in the presynaptic terminal

T or F: Synaptic vesicle trafficking is no different from general vesicle trafficking

F - synaptic vesicles wait for a signal to fuse with membrane; whereas other vesicles don't need a signal to fuse with membrane

Explain how dyes are used to study vesicle cycling

- add dye around outside of neuron/synapse, then stimulate axon to release NT - new vesicles made have some dye in them - dye is only present in vesicles - stimulating the axon again releases dyes out of vesicles - shows that vesicles go through a cycle where they are made, packaged with NT, then fuse with membrane to release NT

Is vesicle cycling a fast or slow process?

Fast - 1 min per cycle

Is fusion of vesicles to membrane a fast or slow process?

Fast - 1 ms

T or F: outer surface of synaptic vesicle is covered with proteins

What proteins help vesicles load NT?

NT-specific transporters on the surface of the vesicles | ex. GABA transporters load GABA into the vesicle

Name 3 basic SNARE proteins

SNAP-25 Synaptobrevin Syntaxin

What is the shape/structure of the SNARE proteins?

Long, alpha-helical

T or F: Munc proteins are SNARE proteins required for release of NT at synapse

What does synaptotagmin do?

It is a Ca sensor that binds to Ca

T or F: synaptotagmin is the only SNARE protein that binds/responds to Ca

What are V-SNAREs?

SNARE proteins located on vesicles

What are T-SNAREs?

SNARE proteins on presynaptic plasma membrane

Which proteins are involved in docking?

V-SNAREs and T-SNAREs bind to each other; tight binding | Munc 13 and 18 hep coordinate this event

Which step in the vesicle cycle is Synaptotagmin involved in?

Fusion - not involved in docking or priming

What is the reserve pool?

There are many more vesicles present than the number that will be released. The vesicles that are not released are sequestered in a reserve pool

Which is the correct order of events: a) docking, fusion, priming b) priming, docking, fusion c) docking, priming, fusion

c) docking, priming fusion

V-SNARE and T-SNARE binding to each other are part of which event? a) docking b) priming c) fusion

a) docking

T or F: synaptotagmin is part of the SNARE complex

F - it binds to the SNARE complex after the complex forms

T or F: priming is a GTP-dependent event

F - ATP-dependent

Which event do tetanus and botulinum toxins disrupt?

docking

T or F: Paralysis caused by tetanus and botulinum toxins is reversible

T or F: The priming event is energy dependent

T - requires ATP

What is synapsin involved in?

reserve pool

Which SNARE protein can be used as a marker for the presynaptic terminal?

Synapsin bc there are good Ab developed for it

Which protein is responsible for maintaining vesicle size as the vesicle forms off the plasma membrane?

Dynamin - it cleaves vesicle from the membrane

What is clathrin-mediated endocytosis and what step of the vesicle cycle is it involved in?

As new vesicles are made/bud from the plasma membrane, they are coated by clathrin. They're involved in the coating, budding, and uncoating event

T or F: release of NT from small clear vesicles and dense cor vesicles are both Ca dependent

List 4 NT that are packaged into small clears

glutamate GABA ATP ACh

T or F: small clear vesicles are made in the cell body and transported to the axon terminal

Where are dense core vesicles made?

Soma (vesicles made and filled with NT in soma)

T or F: more than 1 type of NT may be released from 1 synapse

T - bc some synapses can have both small clears and dense core vesicles

NT release due to AP is most likely caused by which type of vesicle?

Small clears, because the Ca channels are located right next to where they dock

Are dense core vesicles near Ca channels?

Are dense core vesicles more or less sensitive to Ca compared to small clears?

More sensitive

T or F: The synaptotagmin in an axon terminal containing both small clears and dense core vesicles have different affinities to Ca

T - synaptotagmin (Ca sensor) associated with dense core vesicles have higher affinity to Ca

Name 2 methods to remove NT from synaptic cleft

1. degradation | 2. reuptake

What happens if pumps involved in NT reuptake are blocked?

Prolonged NT signalling

Which enzyme degrades ACh in the NMJ?

cholinesterase

What are the 2 major classes of NT receptors?

Metabotropic receptors - GPCRs | Ionotropic receptors - ligand gated ion channels

What is the signal that ionotropic receptors respond to/cause ionotropic receptors to open?

A ligand -ie. the NT - binding to the receptor

List 3 properties of ionotropic receptors

1. can be inactivated 2. have some ion selectivity 3. conductance may be modified

List 2 ways in which the conductance of ionotropic channels may be modified

1. phosphorylation | 2. having more ionotropic receptors

T or F: Both N and C terminals of the connexin are on the cytoplasmic side of the cell

Describe how glutamate is removed from the synapse

They are moved via reuptake pumps, not by enzymatic degradation. Reuptake pumps are present on neighboring glia (some can be on neurons) Neighboring glia take up glutamate, degrade it into glutamine, release glutamine into ECS Neurons pump in glutamine and converts it back to glutamate

Synaptic Transmission Flashcards

(88 cards)