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Block 5 Week 1 Meg > Kenyon: Synaptic Transmission > Flashcards

Kenyon: Synaptic Transmission Flashcards

1
Q

What allows ions to move between the cells?

A

gap junctions

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2
Q

Cells connected by gap junctions are (blank). They have the same (blank).

A

electrically coupled; membrane potential.

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3
Q

A depolarization in the presynaptic neuron will be conducted directly into the (blank) neuron.

A

post-synaptic

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4
Q

T/F: The concept of “presynaptic” and “postsynaptic” may not be useful for electrical synapses. APs can go both ways.

A

True

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5
Q

Populations of cells may have synchronized electrical activity. Give a few examples of cells that exhibit this behavior.

A

particular CNS neurons **control of breathing, hormone-secreting cells in hypothalamus
cardiac muscle
smooth muscle

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6
Q

Membrane bound organelles in the presynaptic terminal containing one or several different neurotransmitters.

A

synaptic vesicles

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7
Q

A relatively wide space separating the pre- and post-synaptic neurons

A

synaptic cleft

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8
Q

List the steps in chemical neurotransmission.

A
  1. transmitter is synthesized and then stored in vesicles
  2. an AP invades the pre-synaptic terminal
  3. depolarization of presynaptic terminal causes opening of voltage-gated Ca+ channels
  4. influx of Ca+ thru channels
  5. Ca+ causes vesicles to fire with presynaptic membrane
  6. transmitter is released into synaptic cleft via exocytosis
  7. transmitter binds to receptor molecules in postsynaptic membrane
  8. opening/closing of postsynaptic channels
  9. postsynaptic current causes excitatory OR inhibitory postsynaptic potential that changes the excitability of the postsynaptic cell
  10. removal of neurotransmitter by glial cell uptake or enzymatic degradation
  11. retrieval of vesicular membrane from plasma membrane
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9
Q

What are some steps in neurotransmission that are targets for therapies?

A
  • blocking the AP via Na+ channel inhibitors
  • blocking the Ca+ influx via Ca+ channel blockers
  • blocking vesicle release via botulinum/tetanus toxin
  • inhibit or activate the receptor (curare)
  • block inactivation/uptake of neurotransmitter (prozac)
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10
Q 
What are these?
Acetylcholine
Glutamate
GABA and glycine
Biogenic amines – norepinephrine, epinephrine, dopamine, serotonin, histamine
ATP
A

small molecule neurotransmitters

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11
Q

What are these?
Brain – gut peptides (substance P, cholecystokinin octapeptide, vasoactive intestinal peptide)
Opioid peptides – enkephalin, endorphins, dynorphin
Pituitary peptides – vasopressin, oxytocin, ACTH
Miscellaneous neuropeptides

A

neuropeptides

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12
Q

What are some unconventional neurotransmitters?

A

NO
CO
endocannabinoids

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13
Q

For small molecule neurotransmitters, where are enzymes synthesized? Where does synthesis and packaging of the neurotransmitter occur?

A

enzymes are synthesized in the cell body and then transported to the nerve terminal; synthesis and packaging of the neurotransmitter is done in the terminal

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14
Q

Where are neuropeptides synthesized for packaged? What happens to loaded vesicles?

A

neuropeptides are synthesized and packaged into vesicles in the cell body; loaded vesicles are transported to the nerve terminal for release

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15
Q

So how does packaging/transport differ in small body molecules vs neuropeptides?

A

in small body molecules, enzymes are synthesized in cell body but neurotransmitter is not synthesized/packaged until it reaches the nerve terminal; in neuropeptides, the neuropeptide is synthesized and packaged while in the cell body and then transported to the nerve terminal for release

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16
Q

For unconventional neurotransmitters, where are enzymes synthesized? Where is neurotransmitter synthesized?

A

Enzymes synthesized in the cell body and then transported to the nerve terminal; synthesis of neurotransmitter done in the terminal
**like small body molecules

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17
Q

Old school vs new school way of defining a neurotransmitter:
Old school – The substance must be present (blank) in vesicles.
New school – The substance can be synthesized (blank) (unconventional neurotransmitters).

A

presynaptically; on demand

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18
Q

Old school vs new school way of defining a neurotransmitter:
Old school – The release of the substance must be triggered by an increase in (blank) concentration.
New school – The substance can be synthesized (blank) by Ca2+-activated enzymes and diffuse out of the presynaptic cell (unconventional neurotransmitters).

A

presynaptic Ca2+; on demand

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19
Q

T/F: All release of neurotransmitter is Ca+ dependent.

A

True

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20
Q

Old school – Specific receptors for the substance must be present on the (blank) of the postsynaptic cell.
New school – Specific receptors for the substance can be present in the (blank) of the postsynaptic cell (unconventional neurotransmitters).

A

plasma membrane; cytoplasm

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21
Q

What is this?
Vesicles bud from the endosome and fill with transmitter
Vesicles dock at release site
Vesicles fuse into the plasma membrane
Vesicle membrane retrieved by clathrin-mediated endocytosis
Vesicles uncoat
Vesicles return to the endosome.

A

traditional model for vesicle recycling

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22
Q

What step in neurotransmitter release are SNARES involved in?

A

priming of vesicle to undergo exocytosis

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23
Q

What step in neurotransmitter release is synaptotagmin involved in?

A

coating of vesicle to be endocytosed

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24
Q

Some experiments find that vesicle fusion is not complete. These results are consistent with a partial emptying of the vesicle. What is this process referred to as?

A

Kiss and run **suggests that vesicles are competent enough to release a bit at a time allowing for rapid vesicle recycling as opposed to vesicle destruction

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25
Q

What happens to neurotransmitter release if extracellular Ca+ is removed or Ca+ entry is reduced or blocked?

A

release will be reduced or locked

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26
Q

T/F: Ca2+ entry is how a voltage-change across the membrane triggers this biochemical event. It is how a voltage-change triggers contraction of cardiac and smooth muscle. Contraction of skeletal muscle is different.

A

True

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27
Q

List two different Ca+ channels that are involved in neurotransmitter release. Where are these localized?

A

Cav2.1
Cav2.2
**localized to nerve terminals and dendrites, and neuroendocrine cells

28
Q

Do neurons typically release one neurotransmitter, or several/many?

A

several/many! **co-transmission

29
Q

Neurons may release both a small molecule neurotransmitter and a neuropeptide. This is called co-transmission. What is required for the release of neuropeptide in many cases?

A

requires higher frequency of presynaptic AP and a greater elevation in intracellular Ca+

30
Q

Where are the SNAREs located? Is SNAP-25 a SNARE?

A

one SNARE in a vesicle and one in the plasma membrane; SNAP-25 is not a SNARE but regulates the assembly of the other two SNAREs

31
Q

How do SNAREs work?

A

When the vesicle docks, SNAREs pull the membrane of the vesicle toward the membrane of the neuron. Ca+ binds to SNARE, which catalyzes membrane fusion by binding to SNARE and plasma membrane.

32
Q

Why is it important to consider the action of SNAREs?

A

This is a target for drug action.

33
Q

Ion gradients contribute their (blank) to the membrane potential.

A

Nerst equilibrium

34
Q

What is the Nerst equation?

A

Ex = RT/zF ln [X]o/[X]i

35
Q

What’s the membrane potential (Ex) of K+?

A

-90mV

36
Q

What’s the membrane potential (Ex) of Na+?

A

+60 to +90mV

37
Q

What’s the membrane potential (Ex) of Cl-?

A

-88 to -35mV

38
Q

What’s the membrane potential (Ex) of Ca+?

A

+100mV

39
Q

The contribution of an ion gradient to the membrane potential is weighted by the (blank) of the cell membrane to that ion

A

permeability

40
Q

a measure of how easy it is for a molecule or ion to cross a membrane

A

permeability

41
Q

If the permeability of K+ is large, what happens to Em? If the permeability of Na+ is large, what happens to Em?

A

Em will be close to E(K); Em will be close to E(Na)

42
Q

How is permeability set?

A

by the opening and closing of ion channels

**ex: ACh binds, and ion channel opens

43
Q

What is another name for ligand-gated ion channels?

A

ionotropic

44
Q

What is another name for G-protein coupled receptors?

A

metabotropic

45
Q

If channels highly selective for Na+ open, (blank) increases, and membrane potential moves toward (blank).

A

PNa; ENa **NOT necessarily TO ENa, but close!! The larger the PNa, the closer to ENa

46
Q

If channels highly selective for K+ open, (blank) increases, and membrane potential moves toward (blank).

A

PK; EK

47
Q

Suppose channels open that allow both Na+ and K+ through the membrane. These are commonly called (blank).
Both PNa and PK will increase. What will happen to the membrane potential??

A

nonselective channels; the membrane potential will move toward a potential in between ENa and EK. Toward zero!!

48
Q

Electrophysiologists call the potential that channels are moving the potential toward the (blank) or Erev

A

reverse potential

49
Q

The reversal potential is the (blank) potential associated with the opening of a particular channel.

A

target

50
Q

Opening a channel will shift the membrane potential towards (blank).
The more channels you open the closer the membrane potential will move to (blank)

A

Erev; Erev

51
Q

Suppose the membrane potential is -65 mV (i.e. a normal RP). What happens if one opens nonselective channels?

A

the membrane potential will become LESS negative

52
Q

Suppose a physiologist has hooked the cell to a device that shifts the membrane potential to +65 mV*. What happens if one opens nonselective channels?

A

the membrane potential will become MORE negative

53
Q

Suppose a physiologist has hooked the cell to a device that shifts the membrane potential to 0 mV. What happens if one opens nonselective channels?

A

The membrane potential will move toward 0 mV, i.e. it will not change. This is the “reversal potential” or Erev.

54
Q

T/F: The reversal potential is the target potential associated with the opening of a particular channel.
For a highly selective channel Erev is the Nernst equilibrium potential of the chosen ion.
For a poorly or non-selective channel Erev will be between the Nernst equilibrium potentials of the ions that pass through the channel.

A

True

55
Q

What is the general rule for Erev?

A

The general rule…is that the action of a neurotransmitter drives the postsynaptic potential toward Erev (the target potential) for the particular ion channels being activated.”

**The value of Erev is determined by the relative permeability of the channels to Na+, K+, Ca2+, Cl

56
Q

The main channels activated by neurotransmitters to generate receptor potentials are (blank) for monovalent cations or (blank) for Cl- or for Ca+. Channels activated by neurotransmitters that are highly selective for K+ and Na+ are (blank).

A

nonselective; selective; rare

57
Q

If Erev (target potential) is positive to threshold the event is a (blank) making the postsynaptic neuron (blank) likely to fire an action potential.

A

excitatory postsynaptic potential (EPSP); more

58
Q

If Erev (target potential) is negative to threshold the event is a (blank) making the postsynaptic neuron (blank) likely to fire an action potential.

A

inhibitory postsynaptic potential (IPSP); less

59
Q

T/F: If Erev (target potential) is negative to threshold the event is an inhibitory postsynaptic potential (IPSP) making the postsynaptic neuron less likely to fire an action potential. **Even if Erev is positive to the resting potential!

A

True

60
Q

Opening channels to allow for an inhibitory potential (usu Cl- channels) stabilizes the membrane potential near (blank) making it harder to get to threshold.

A

Erev (negative to threshold)

61
Q

Ion channels nonselective for cations or selective for Ca2+ mediate (blank) (Erev positive to threshold)
Ion channels selective for K+ mediate (blank) (Erev negative to threshold)
Ion channels selective for Cl- mediate (blank) if ECl is negative to threshold or (blank) if ECl is positive to threshold.

A

EPSPs;
IPSPs;
IPSPs;
EPSPs

62
Q

If two action potentials arrive at the same time, what does this lead to? Is timing important?

A

summation **generates larger AP

Yes, timing is important - APs must arrive at about the same time

63
Q

EPSPs and IPSPs are additive, but are they always linear?

A

No; may cause a decrease in the AP when they sum

64
Q

T/F: The summation of EPSPs and IPSPs is not linear

A

TRUE

65
Q

Postsynaptic neurons can signal back to the presynaptic neuron. What is this called? What are some examples of transmitters that can exhibit this behavior?

A

retrograde signaling; NO, CO, endocannabinoids, prostaglandins

66
Q

T/F: Receptors on the presynaptic terminal can regulate release and inhibition of release.
It is common for a neurotransmitter to inhibit its own release.
The neurotransmitters can come from the neuron itself or other neurons.

A

True

Block 5 Week 1 Meg (8 decks)

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