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bil 360 > lecture 10b synapse > Flashcards

lecture 10b synapse Flashcards

1
Q

synapse

A

Information is transmitted either electrically or chemically at a junction between two neurons known as a

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2
Q

electrical vs chemical response

A

electrical is much faster and interacts with most to all, and has synchromous firing, bidirectional, no neurotransmitters

while chemical is slower but more controlled amd selective (larger in abundance) and has asynchromous firing, up to 0.5 sec delay

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3
Q

Electrical synapses transmit information

A

quickly
via changes in electrical potential
through relatively large pores (connexons)
across very narrow synapses (< 4nm)

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4
Q

where/when do electrical synapse occur? there are 5 places…

A

the retina
hormone secreting neurons in the hypothalamus
neuromuscular junctions involved in rapid escape response
cardiac rhythems
fight/flight

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5
Q

connexon

A

also known as a connexin hemichannel, is an assembly of six proteins called connexins that form the pore for a gap junction between the cytoplasm of two adjacent cells.

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6
Q

innexin

A

gap junction proteins expressed in invertebrates,

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7
Q

hemichannels

A

–The connexon of the presynaptic neuron fits directly onto the connexon of the post-synaptic neuron, forming two
This allows comingling of cytoplasm, and fast transmission.

may be formed by connexons of similar or different molecular composition.

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8
Q

connexin vs connexon

A

connexin is singular

connexon is plural

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9
Q

When a signal reaches an axon terminal, changes in

A

membrane potential

postsynaptic conductance

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10
Q

postsynaptic conductance

A

determine the probability that an AP

will be propagated in the postsynaptic cell.

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11
Q

Ability of synaptic input to trigger neuronal output depends on

A
  • magnitude and timing of incoming potentials
  • postsynaptic neuron morphology
  • postsynaptic neuron synapse location
  • voltage-gated channels’ locations and densities
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12
Q

postsynaptic potential (PSP)

A

membrane potential change caused by neurotransmitter binding to a postsynaptic membrane channel.

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13
Q

excitatory

A

releases excitatory neurotransmitter (e.g., glutamate)
this triggers opening of Na+ ion channels
Na+ current changes membrane potential

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14
Q

inhibitory

A

releases inhibitory neurotransmitter(s) (e.g., GABA, serotonin)
this triggers opening of K+ ion channels
K+ leaks out, Cl- leaks in
cytosol becomes relatively more negative

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15
Q

Excitatory PostSynaptic Potential (EPSP)

A

depolarizes the membrane

increases likelihood of PSP propagation.

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16
Q

Inhibitory PostSynaptic Potential (IPSP)

A

hyperpolarizes the membrane

decreases likelihood of PSP propagation

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17
Q

summation

A

A neuron has many synapses, and can receive PSPs from one or more of them that is needed to reach depolarization threshold

net eff: excitatory - inhibitory will most likely cancel out but u can usually have both for a threshold to be met

the synapses will lose amplitude over time as they travel

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18
Q

Probability of triggering an postsynaptic action potential depends on

A

the number of incoming signals
whether an incoming signal is an EPSP or an IPSP
the location of the synapse, relative to the hillock like axosomatic or axodendritic

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19
Q

axosomatic synapse

A

connect to the soma

(relatively close to the hillock) so it has greater effect with impulse

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20
Q

axodendritic synapse

A

connect to a dendrite
(relatively far from the hillock)

lose the most amplititude b/c its more far away

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21
Q

axonomic synapse

A

are passed from axon to axon

22
Q

spatial summation

A

recipient neuron sums PSPs from multiple neurons connected to it at different locations

arrive at the same time

most likrly to depolarized when summed

23
Q

temporal summation

A

recipient neuron sums PSPs from the same neuron over time

potetntials arrive at a short time after each other

24
Q

define neurotransmitters

A

chemical messengers. They send information between neurons by crossing a synapse.

synthesized in presynaptic terminal cytoplasm
stored in presynaptic terminal vesicles

25
Q

As membrane depolarization increases, what happens to the vesicles?

A

more and more of them will release neurotransmitters

26
Q

quantum (pl. = quanta)

A

The contents of one vesicle (usually several thousand molecules like neurotransmitters)

27
Q

what does the vesicle SNARE interaction mean?

A

(Soluble N-Ethylmaleimide-sensitive factor) Attachment REceptor

28
Q

synapsin

A

it attaches the vesicle to the actin fillaments

when phosphorylated, it releases the vesicle

29
Q

step 1 of SNARE is Tethering but what occurs

A
  1. Vesicle is attached to actin filaments by synapsin.
  2. Phosphorylation of synapsin causes it to release the vesicle.
  3. Vesicle migrates to a terminal membrane active zone.
  4. The vesicle is reversibly tethered to the active zone.
    (syntaxin is held in an inactive configuration by Munc18)
30
Q

Step Two: Docking

A

occurs when synaptobrevin binds to syntaxin and SNAP-25.

This step is irreversible.

31
Q

step three: stabilization

A

Complexin protein stabilizes the vesicle at the active zone.

32
Q

step 4: vesicle priming

A
  1. Ca+2 ions enter the cell via voltage-gated channels
    xxxin response to an action potential.
  2. The ions bind to synaptotagmin.
33
Q

step 5: vesicle fusion

A
  1. The synaptagmin-Ca+2 complex binds to the SNARE proteins.
  2. This displaces complexin and triggers formation of a fusion pore.
  3. Neurotransmitter passes through the pore and into the synapse.
34
Q

when the snare complex diassembles what happens?

A

the vesicles are released from the terminal membrane

35
Q

name 2 types of vesicle recycling

A

classical and kiss/run

36
Q

classical recycling

A

Clathrin proteins interact to form a lattice
around the membrane to be removed.
They facilitate the “pinching off” of the vesicle from the membrane.

spiky appearance and gets recycled as well

37
Q

kiss/run

A

opens just enough (think of not tongue kissing but just a little open ) then pinches off and recycles

38
Q

diff btwn snare and recycling vesicles

A

snare is exocytosis

39
Q

3 types of neurotransmitter removals

A

diffusion

enzymatic degradation

neurotransmitter reuptake

40
Q

diff for neurotransmitters

A

Neurotransmitter molecules simply diffuse away from the synaptic cleft

41
Q

enzymatic degradation

A

Specialized enzymes may be employed to break down specific neurotransmitters that are in synaptic cleft
For example, acetyocholinesterase breaks down acetylcholine at neuromuscular junctions.
Breakdown products can be recycled into the presynaptic neuron
to be used as raw materials to build new neurotransmittters.

42
Q

neurotransmitter reuptake

A

mainly reabsorbs the neurotransmitters back into the presynaptic

allows recycling of neurotransmitters
allows regulation of neurotransmitter concentration in the synapse
this can determine how long the signal lasts

43
Q

ionotropic receptor

A

ligand-gated ion channels
opened by neurotransmitter binding
allows ions into postsynaptic neuron
produce a rapid, transient effect

44
Q

metabotropic receptor

A

G-protein coupled receptors
triggered by neurotransmitter binding
initiates a signalling cascade in the postsynaptic cell
produce a slow, longer-lasting effect
effect can be more widespread throughout the cell than ionotropic effect

45
Q

agonist

A

substance that binds to receptors

and mimics the effects of a neurotransmitter.

46
Q

antagonist

A

substance that blocks the receptor,

preventing the effects of a neurotransmitter.

47
Q

inverse agonist

A

binds to receptors and elicits an effect opposite that of the appropriate neurotransmitter.

48
Q

neuromodulator

A

substance that can act locally or at a distance,
increasing or decreasing the effect of neurotransmitters.
The neuromodulator itself does not initiate depolarization.

49
Q

Slow (metabotropic) synaptic transmissions

A

operate by opening G-protein coupled (metabotropic) channels
may be either excitatory or inhibitory
are mediated by biogenic amine and peptide neurotransmitters and involve
second messengers
cleaving of proteins
cleavage of high-energy phosphate bonds
usually take many biochemical steps to complete.
take hundreds of milliseconds to affect target cells

50
Q

Fast (ionotropic) synaptic transmissions

A

operate by opening ligand-gated (ionotropic) ion channels may be either excitatory or inhibitory
are mediated by specific neurotransmitters, for example:
glutamate (excitatory)
GABA (inhibitory)
affect their target cells in less than a millisecond

51
Q

Most fast EPSPs are triggered by

A

glutamate

52
Q

Most fast IPSPs are triggered by

A

GABA and glycine

bil 360 (11 decks)

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