Synaptic Transmission Flashcards
1
Q
It is the major process by which 💡electrical signals are 💡transferred between cells within the nervous system (or between neurons and muscle cells or sensory receptors).
A
Synaptic Transmission
2
Q
Within the nervous system, synaptic transmission is usually conceived of as an 💡interaction between two neurons that occurs in a 💡point-to-point manner at specialized junctions called __.
A
synapses
3
Q
Two main classes of synapses
A
- electrical
2. chemical
4
Q
It is effectively a 💡low-resistance pathway between cells that allows current to flow directly from one cell to another and, more generally, allows the 💡exchange of small molecules between cells.
They are present between glial cells as well as between neurons.
LOW-PASS FILTERS
Simple and static
A
electrical synapses
5
Q
It is the 💡morphological correlate of an electrical synapse.
These junctions are 💡plaque-like structures in which the plasma membranes of the coupled cells become closely apposed and filled with electron-dense material.
A
gap junction
6
Q
Electrical synapses are __ (essentially no synaptic delay) and __ (i.e., current generated in either cell can f low across the gap junction to influence the other cell).
A
fast
bidirectional
7
Q
Slow electrical events are __ than are fast signals such as action potentials. “Low-pass filters”
A
much more readily transmitted
8
Q
One important role for neuronal gap junctions appears to be __.
A
synchronization of network activity
9
Q
It also appears that the patterns of electrical coupling by gap junctions may be __.
A
highly specific
10
Q
The properties of electrical synapses can be modulated by several factor:
A
voltage, intracellular pH, and [Ca++]
11
Q
Chemical synaptic transmission was first demonstrated between the __ and the __ by a simple experiment by Otto Loewi.
A
vagus nerve
heart
12
Q
What is the difference of the chemical synapses to electrical synapses?
A
There is no direct communication between the cytoplasm of the two cells.
13
Q
Chemical intermediaries that mediates the interaction between the cells
A
Neurotransmitters
14
Q
Chemical synapses are generally __, and thus one can refer to the presynaptic and postsynaptic elements.
A
unidirectional
15
Q
It is often the 💡terminal portion of an axon and is packed with 💡small vesicles whose exact shape and size vary with the neurotransmitter they contain.
It has regions, known as 💡active zones, of electron dense material that corresponds to the proteins involved in transmitter release.
It has 💡mitochondria and 💡rough endoplasmic reticulum.
A
presynaptic element
16
Q
It is also characterized by electron-dense material, which in this case corresponds to the 💡receptors for the neurotransmitter.
A
postsynaptic element
17
Q
Types of chemical synapses:
A
axodendritic
axosomatic
axoaxonic dendrodendritic dendrosomatic
18
Q
It is a complex synaptic arrangement that is found in the inferior olive and some other CNS regions.
It involves both chemical and electrical synapses among the participating elements.
Two dendritic spines are coupled by a gap junction.
An axon terminal packed with synaptic vesicles fills the upper right part of the panel.
A
glomerulus
19
Q
It is a complex synaptic arrangement in which cells form both electrical and chemical synapses with each other.
A
mixed synapses
20
Q
It is a complex synaptic arrangement
in which an 💡axoaxonic synapse is made onto the 💡axon terminal and influences the efficacy of that terminal’s synapse with yet a 💡third element.
A
serial synapses
21
Q
It is a complex synaptic arrangement
in which 💡both cells can release transmitter to 💡influence the other.
A
reciprocal synapses
22
Q
Synaptic transmission is initiated by arrival of the (1)__ at the (2)__. The action potential (3__ the terminal, which causes (4)__. The subsequent rise in [Ca++] within the terminal triggers the (5)__. The transmitter is then expelled into the (6)__, diffuses across it, and binds to specific receptors on the (7)__. Binding of transmitter to receptors then causes the (8)__ in the postsynaptic membrane, which in turn results in changes in the potential and resistance of the postsynaptic membrane that alter the excitability of the cell.
A
(1) action potential
(2) presynaptic terminal
(3) depolarizes
(4) Ca++ channels to open
(5) fusion of vesicles containing neurotransmitter with the plasma membrane
(6) synaptic cleft
(7) postsynaptic membrane
(8) opening (or less often, the closing) of ion channels
23
Q
The changes in membrane potential of the postsynaptic cell are termed __.
A
excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs)
24
Q
its probability of firing action potentials
A
cell’s excitability
25
Why is the transmitter acts for only a very short time (milliseconds)?
because reuptake and degradation mechanisms rapidly clear the transmitter from the synaptic cleft
26
See anki
See anki
27
It is the signal for neurotransmitter release.
Calcium entry
28
Ca++ will enter the terminal only if there is a favorable __ to do so.
Electrochemical gradient
29
Extracellular [Ca++] is (1)__ relative to intracellular [Ca++], which favors entry into the terminal; however, during the peak of the action potential, the membrane potential is (2)__, and the (3)__ opposes the entry of Ca++ because of its (4)__. Thus, at the peak of the action potential, relatively little Ca++ enters the terminal because although the membrane is highly permeable to Ca++, the overall driving force is small.
(1) high
(2) positive
(3) voltage gradient
(4) positive charge
30
If the membrane potential is rapidly made (1)__ again (because of either the end of the action potential or by adjusting the voltage clamp), Ca++ rushes into the terminal as a result of the (2)__ (which arises instantaneously on repolarization) and the (3)__ (which remains high because it takes the Ca++ channels several milliseconds to close in response to the new membrane potential), thereby resulting in release of transmitter and a postsynaptic response
(1) negative
(2) large driving force
(3) high membrane permeability to Ca++
31
It is small round or irregularly shaped organelles that stores the neurotransmitters.
Synaptic vesicles
32
It is an action potential in a motor neuron causes a large depolarization in the postsynaptic muscle.
end plate potential (EPP) (equivalent to an EPSP in a neuron)
33
Why is the EPP amplitude is reduced under conditions of low extracellular [Ca++]?
because the presynaptic Ca++ current is reduced, leading to a smaller rise in intracellular [Ca++], and transmitter release is proportional to [Ca++]
34
It is a small spontaneous depolarizations of the postsynaptic membrane that is observed when EPP is flactuating.
miniature end plate potentials (mEPPs)
35
It is a specific site where the small vesicles that contain nonpeptide neurotransmitters only can fuse with the presynaptic membrane
active zones
36
As with other exocytotic processes, neurotransmitter release involves:
SM (sec1/Munc18-like)
SNARE (soluble N-ethyl maleimide-sensitive factor attachment protein receptor) proteins
v-SNARES in the vesicle membrane
t-SNARES in the (target) presynaptic plasma membrane
37
Example of v-SNARE
synaptobrevin
38
Examples of t-SNARES;
syntaxin and SNAP-25
39
Their 💡zipper-like interactions with the assistance of 💡SM proteins bring the vesicle membrane and the presynaptic plasma membrane close together before fusion.
synaptobrevin
syntaxin
SNAP-25
40
It is a toxin produce by 💡Clostridium botulinum that targets SNARE proteins which disrupt synaptic transmission.
Botulinum toxins
41
It is a SNARE protein that acts as the 💡Ca++ sensor and, even more specifically, that the second of its two cytoplasmic domains contains the Ca++ binding site. Its binding with calcium will trigger the 💡fusion of a docked vesicle and allowing release of its neurotransmitter.
It is degraded by botulinum toxins.
synaptotagmin
42
During synaptic transmission, __ to release their contents into the synaptic cleft.
vesicles must fuse with the plasma membrane
43
Two distinct mechanisms by which vesicles are retrieved after release of their neurotransmitter content:
endocytotic pathway
“kiss and run.”
44
It involves transient fusion of the vesicle to the synaptic membrane which will leads to the formation of a pore through which the transmitter is expelled, but there is no wholesale collapse of the vesicle into the membrane.
More rapid recycling mechanism
Kiss and run
45
Following vesicle fusion the neurotransmitter molecules are released and diffuse across the synaptic cleft (a very rapid process) and bind to receptors on the postsynaptic membrane which will lead to the opening of?
ion channels
ligand gated (opening and closing are primarily controlled by the binding of neurotransmitter)
46
It is a channel that are both ligand and voltage gated
NMDA (N-methyl-Daspartate) channels
47
“fast” synaptic transmission
ionotropic receptors
48
“slow” synaptic transmission
metabotropic receptors
49
EPSPs are always __, and IPSPs are usually __.
depolarizing potentials
hyperpolarizing
50
If acetylcholine-gated channels open when the membrane is at its (1)__, a large inward (2)__ and a small outward (3) __ will flow through the (4)__ thereby resulting in a net inward current, which acts to (5)__ the membrane.
(1) resting potential
(2) Na+ current
(3) K+ current
(4) acetylcholine channel,
(5) depolarize
51
The net inward current that results from opening such channels is called __.
**refer to previous card
excitatory postsynaptic current (EPSC)
52
It is the potential at which there is 💡no EPSP (or EPSC).
** if the membrane potential is depolarized enough, there will be a point at which the Na+ and K+ currents through the channel are equal and opposite, and thus there is no net current and no EPSP.
Hyperpolarize
reversal potential
53
It is a 💡key criterion for demonstrating the 💡chemical-gated as opposed to the voltage-gated nature of a synaptic response because currents through voltage-gated channels do not reverse, except at the Nernst potential of the ion for which they are selective (and then only if the channel is open at that potential).
Reversal potential
54
What is the difference of IPSP to EPSP?
This difference makes IPSPs to have a reversal potential equal to the Nernst potential of the ion carrying the underlying current.
IPSP channels are permeable to only a single ionic species, either Cl− or K+.
55
The key distinction between inhibitory and excitatory synapses (and IPSPs and EPSPs) is (1)__: EPSPs (2)__ the probability, whereas IPSPs (3) the probability.
(1) how they affect the probability of the cell firing an action potential
(2) increase
(3) decrease
56
It is the ratio of 💡EPSP amplitude to the amplitude needed to reach the 💡threshold to trigger an action potential.
It quantifies the strength of the excitatory synapses.
Safety factor
57
Most synapses have __, and thus it takes the summed EPSPs of multiple active synapses to trigger an action potential in the postsynaptic neuron.
low safety factors (<1)
58
These are diseases of the neuromuscular junction where the EPPs are reduced such that the safety factor can fall below 1, and thus the EPPs sometimes fail to trigger action potentials in the muscle fibers, leading to weakness.
myasthenia gravis and Lambert-Eaton syndrome
59
It refers to the fact that EPSPs that are separated by a latency less than their duration can 💡sum.
EPSPs in response to two spikes in the same axon occurring in rapid succession
Temporal summation
60
It refers to the fact that synaptic potentials generated by 💡different synapses can interact.
Responses evoked by synapses that are 💡electrically distant from each other (1 and 3).
The combined EPSP amplitude may then reach threshold and lead to spiking of the cell.
Spatial summation
61
That is, when synapse 2 is active, channels are opened in the cell membrane, which means that it is more leaky. Therefore, when synapse 4 is also active, more of its EPSC will be lost (shunted) through the dendritic membrane, and less current will be left to travel down the dendrite to the initial segment. The result is that synapse 4 causes a smaller EPSP at the initial segment than it would have generated in isolation. Nevertheless, the combined EPSP is still larger than an EPSP caused by either synapse 2 or 4 alone.
Sublinear summation
62
Modulation of synaptic activity
Paired-pulse facilitation
Posttetanic potentiation
Synaptic depression
63
When a presynaptic axon is stimulated twice in rapid succession, it is often found that the 💡postsynaptic potential evoked by the 💡second stimulus are 💡larger in amplitude than the one evoked by the first.
Relatively rapid and short-lasting change in synaptic efficacy
paired-pulse facilitation (PPF)
64
What is the difference if PPF and temporal summation?
Temporal summation, in which two EPSPs overlap and sum to a larger response; with PPF the second EPSP itself is greater in size.
65
It is similar to PPF; however, in this case the 💡responses are compared before and after stimulation of the presynaptic neuron tetanically (tens to hundreds of stimuli at a high frequency).
Such a tetanic stimulus train causes an increase in synaptic efficacy
Posttetanic potentiation (PTP)
66
What is the similarity and difference of PTP and PPF?
PTP, like PPF, is an enhancement of the postsynaptic response, but it lasts longer
67
It is thought to reflect 💡depletion of the number of releasable presynaptic vesicles.
Synaptic Depression
68
A postsynaptically related cause of synaptic depression can be __ in the postsynaptic membrane.
desensitization of the receptors
69
Both potentiation and depressive processes can occur at the same synapse.
True
70
Presynaptic receptors can be either ionotropic or metabotropic.
True
71
The activation of presynaptic (1) __ will (2)__ alter the electrical properties of the presynaptic terminal and cause rapid transient (millisecond time scale) changes in the probability of vesicle release (although they too can have much longer lasting effects).
(1) ionotropic receptors
| (2) directly
72
It refers to occasions when binding of presynaptic receptors leads to a 💡decrease in release of transmitter
Presynaptic inhibition
73
Presynaptic inhibition mechanisms:
1. opening of channels decreases membrane resistance and creates a current shunt.
2. change in membrane potential caused by the opening of presynaptic ionotropic channels.
74
Opening of channels decreases membrane resistance and creates a current shunt.
shunt acts to divert the current
lessens the depolarization of the active zone
less activation of Ca++ channels, less Ca++ entry, and less release of transmitter
75
Change in membrane potential caused by the opening of presynaptic ionotropic channels.
small depolarization
inactivation of voltage-gated Na+ channels
lessening of the action potential–associated current and transmitter release
76
It is a process where 💡repetitive stimulation of certain synapses in the brain can also produce more 💡persistent changes in the efficacy of transmission at these synapses.
long-term potentiation or long-term depression.
77
T he increased synaptic efficacy that occurs in long-term potentiation probably involves both presynaptic (greater transmitter release) and postsynaptic (greater sensitivity to transmitter) changes, in contrast to the short-term changes that involve changes only in presynaptic function.
True
78
It is an early step required for initiating the changes that result in long-term enhancement of the response of the postsynaptic cell to neurotransmitter.
Entry of calcium into the postsynaptic region
79
Entry of calcium occurs at the post synaptic region is through:
NMDA receptors
| AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors
80
It is activated by 💡calcium entry at post synaptic region.
It is a multifunctional 💡protein kinase that is present in very high concentrations in postsynaptic densities.
It is believed to phosphorylate proteins that are essential for the induction of long-term potentia-tion.
Ca++-calmodulin kinase II
81
These are the substances that 💡mediate chemical signaling between neurons.
Neurotransmitters
82
For a substance to be considered a neurotransmitter, it must meet several generally recog-nized criteria;
1. the substance must be demonstrated to be present in the presynaptic terminal
2. the cell must be able to synthesize the substance
3. It should be released on depolarization of the terminal.
4. Finally, there should be specific receptors for it on the postsynaptic membrane
83
It is a general term to describe 💡both synaptic and nonsynaptic signaling between cells.
Neurotransmission
84
3 major categories of the neurotransmitters:
1. small-molecule transmitters
2. peptides
2. gaseous transmitters
85
These are the small-molecule neurotransmitters
acetylcholine, amino acids, biogenic amines, and purines.
86
PNS: neuromuscular junctions, at sympathetic and para-sympathetic ganglia, and of the postganglionic fibers from all parasympathetic ganglia and a few sympathetic ganglia.
CNS: It is the trans-mitter at neurons in some brainstem nuclei, in several parts of the basal forebrain (septal nuclei and nucleus basalis) and basal ganglia, and in the spinal cord.
Acetylcholine
87
It a form of dementia in which memory function is gradually and progressively lost due to degeneration of cholinergic neurons from the basal forebrain.
Alzheimer’s disease
88
It is an enzyme that synthesizes acetylcholine.
choline acetyltransferase
89
Two precursors of acetylcholine:
acetyl coenzyme A and choline
90
It is an enzyme that terminates the action of acetylcholine.
acetylcholinesterase (highly concentrated in the synaptic cleft)
91
It is the 💡product of acetylcholine hydrolysis that is taken up by an 💡Na+ symporter in the presynaptic membrane for the 💡resynthesis of acetylcholine.
Choline
92
It is a drug that interfere with 💡acetylcholinesterase and thereby enhance the action of acetylcholine by prolonging its presence at its synapses.
It is used to treat myasthenia gravis.
anticholinesterases
93
It is an 💡autoimmune disease in which 💡antibodies bind to acetylcholine receptors at the neuromuscular junction, thereby disrupting their functionality and causing them to be more rapidly degraded.
The eduction in receptors leads to severe weakness and ultimately paralysis.
Myasthenia gravis
94
Three most important amino acids that acts as a neurotransmitter.
glutamate, glycine, and GABA
95
It is the neurotransmitter at the overwhelming majority of 💡excitatory synapses throughout the CNS.
It has a key role in multiple metabolic pathways, and it is a 💡precursor to GABA.
It is the 💡major excitatory CNS neurotransmitter
It is a potent 💡neurotoxin at high concentrations
Glutamate
96
What is the action of glutamate to cells?
It causes depolarization
97
It is the major inhibitory transmitter throughout the nervous system.
GABA
98
It is an enzyme that catalyze the synthesis of GABA from glutamate.
glutamic acid decarboxylase
99
Most notable brain regions that contain large numbers of 💡GABAergic projection neurons.
spiny neurons of the striatum
| Purkinje cells of the cerebellar cortex
100
It is a neurotransmitter that functions as an 💡inhibitory neurotransmitter in a much more 💡restricted territory (predominantly at spinal cord).
It acts as a 💡co-transmitter at excitatory 💡NMDA-type glutamate receptors.
Glycine
101
Fluctuations in glycine levels may also be an important modulator of NMDA-mediated synaptic transmission.
True
102
After GABA and glycine are released from the presynaptic terminal, they are taken back up into the nerve terminal and neighboring glia by __.
high-affinity Na+-Cl−–coupled membrane transporters (solute carrier 6 (SLC6) family)
103
Transport of the GABA and glycine into the cell is accomplished by (1)__ with (2)__ Na+ and (3)_ Cl− ion.
(1) symport
(2) two
(3) one
104
Biogenic amines
Cathecholamines:
dopamine
norepinephrine (noradrenaline)
epinephrine (adrenaline)
serotonin (5-hydroxytryptamine [5-HT])
histamine
105
-
Dopamine
106
-
Norepinephrine
107
-
Epinephrine
108
-
Serotonin
109
-
Histamine
110
```
Tyrosine
(1)
L-dopa
(2)
Dopamine
(3)
Norepinephrine
(4)
Epinephrine
```
1. tyrosine hydroxylase
2. dopa-decarboxylase
3. dopamine β-hydroxylase
4. phenylethanolamineN-methyl transferase
111
```
Tryptophan
(1)
5-hydroxytryptophan
(2)
Serotonin
```
1. tryptophan 5-hydroxylase
| 2. aromatic L-amino acid decarboxylase
112
It catalyze the conversion of histidine to histamine.
histidine decarboxylase
113
Glutamate inside the presynaptic terminal is packaged into synaptic vesicles by a second set of glutamate transporters known as __.
vGLUTs (vesicular glutamate transporters)
114
Transport of glutamate into synaptic vesicles by vGLUT is driven by the __, the electrochemical gradient for which having been established by an H+-ATPase in the vesicle membrane.
countertransport of H+ ions
115
Removal of synaptically released biogenic amines is generally accomplished by reuptake into glia and neurons via transporters belonging to the
Na+-Cl−–dependent transporter family
116
These are enzymes that degrades catecholamines.
monoamine oxidase and catechol Omethyltransferase
117
It has the potential to act as a transmitter or cotransmitter at synapses in the peripheral and central nervous systems.
It is found in all synaptic vesicles and thus is co-released during synaptic transmission.
It has its own receptors, which like standard neurotransmitters, are coupled to ion channels, but it can also modify the action of other neurotransmitters with which it is co-released, including norepinephrine, serotonin, glutamate, dopamine, and GABA.
ATP
118
ATP is broken down by __ and __ to adenosine, which can be taken up again by the presynaptic terminal.
ATPases
5-nucleotidase
119
It inhibit 💡dopamine receptors on postsynaptic membranes and thus diminish the effects of dopamine released from presynaptic nerve terminals.
Overdoses of such antipsychotic drugs can produce a temporary 💡parkinsonian-like state.
Chlorpromazine
120
When neuropeptides are co-released with other transmitters, they may act synergistically or antagonistically.
True
121
In the spinal cord, these neuropeptides act 💡synergistically with 💡glutamate and with 💡substance P 💡to enhance the action of serotonin and they 💡antagonize norepinephrine’s action at other synapses.
tachykinins and calcitonin gene–related peptide (CGRP)
122
The slower release and lack of rapid reuptake mean that neuropeptides can act for long durations, diffuse over a region of brain tissue, and affect all cells in that region (that have the appropriate receptors) rather than just acting at the specific synapse at which it was released.
True
123
These are drugs derived from the juice of the 💡opium poppy.
Opiates
124
Compounds that are not derived from the opium poppy but that exert direct effects by binding to opiate receptors are called __.
They inhibit neurons in the brain involved in the 💡perception of pain.
They are the most potent 💡analgesic (pain-relieving)
opioids
125
Opioids are defined as compounds whose effects are stereospecifically antagonized by a morphine derivative called __.
naloxone
126
These are three major classes of endogenous opioid peptides in mammals:
enkephalins, endorphins and dynorphins
127
These are the simplest opioids; they are pentapeptides.
Enkephalins
128
These are somewhat 💡longer peptides that contain one or the other of the 💡enkephalin sequences at their N-terminal ends.
Dynorphins and endorphins
129
It is a peptide consisting of 11 amino acids.
It is involved in 💡pain transmission and has a powerful effect on smooth muscle.
it is the transmitter used at synapses made by 💡primary sensory neurons (their cell bodies are in the dorsal root ganglia) with spinal interneurons in the dorsal horn of the spinal column, and thus it is an example of a peptide acting as a 💡primary transmitter at a synapse.
Substance P
130
These are opioids that act to decrease the release of 💡substance P at these synapses and thereby 💡inhibit the pathway for pain sensation at the first synapse in the pathway.
Enkephalins
131
These are 💡neither packaged into synaptic vesicles nor released by exocytosis.
Instead, these are 💡highly permeant and 💡simply diffuse from synaptic terminals to neighboring cells after synthesis, their synthesis being triggered by depolarization of the nerve terminal (the influx of Ca++ activates synthetic enzymes).
Gas neurotransmitters
132
Examples of gaseous neurotransmitters.
nitric oxide (NO) and carbon monoxide (CO)
133
It is a 💡transmitter at synapses between inhibitory motor neurons of the enteric nervous system and gastrointestinal smooth muscle cells
It also functions as a neurotransmitter in the CNS.
It functions as a 💡cellular signal transduction molecule (by regulating guanylyl cyclase) both in neurons and in nonneuronal cells
nitric oxide (NO)
134
It is an enzyme that 💡catalyzes the production of NO as a product of the oxidation of 💡arginine to citrulline.
NO synthase
135
NO synthase is stimulated by an increase in __.
cytosolic [Ca++]
136
Neurotransmitter receptors are members of one of two large groups or families of proteins:
Ligand-gated ion channels (ionotropic receptors) and G protein-coupled receptors (metabotropic receptors )
137
Almost all classic neurotransmitters and neuropeptides have at least one metabotropic-type receptor. Many of the classic neurotransmitters also have at least one ionotropic receptor.
True
138
These are protein complexes that both have an extracellular binding site for the transmitter and form an 💡ion channel (pore) through the cell membrane.
Ionotropic receptors
139
Binding of the neurotransmitter alters (usually increases) the probability of the ion channel being in the open state and thus typically results in postsynaptic events that are rapid in both onset and decay, with a duration of several milliseconds.
True
140
See anki
See anki
141
These receptors mediate postsynaptic phenomena that have a 💡slow onset and that may persist from hundreds of milliseconds to minutes.
metabotropic receptors
142
Two major group of acetylcholine receptors:
Nicotinic receptors (ionotropic cys-loop family)
muscarinic receptors (metabotropic family of receptor proteins)
143
These are acetylcholine receptor that mediate 💡synaptic transmission at the neuromuscular junction.
These receptor contains a relatively 💡nonselective cationic channel, so binding of acetylcholine produces an EPSP.
nicotinic receptors
144
The junctional receptors (nicotinic) all use the __, whereas centrally located receptors (nicotinic) use one of the α subunits between __.
α1 subunit
α2 and α10
145
These five known muscarinic subtypes of acetylcholine receptors:
M1 to M5
146
These are muscarinic subtypes of acetylcholine receptors that are coupled to 💡pertussis toxin–insensitive G proteins
M1, M3, and M5
147
These are muscarinic subtypes of acetylcholine receptors that are coupled to 💡pertussis toxin–sensitive G proteins.
M2 and M4
148
Glycine-mediated inhibitory synapses are common in the __, whereas GABAergic synapses make up the majority of inhibitory synapses in the __.
spinal cord
brain
149
Both glycine and GABA have ionotropic receptors that are members of the cys-loop family, each of these receptors has a Cl− channel.
True
150
Glycine receptors are pentamers and may be heteromers of α and β subunits (3 : 2 ratio) or homomers.
The β subunit seems to bind to an intracellular scaffold protein called that appears to help localize receptors to the postsynaptic site.
gephyrin
151
T he α subunit contains the glycine binding site, and there are four genes coding for distinct α subunits (and splice variants of each).
True
152
GABA has two separate ionotropic receptors coded for by distinct sets of genes.
GABA(A) and GABA(C)
153
These are GABA ionotropic receptors that is being targeted by the drugs: 💡benzodiazepines and barbiturates which enhance opening of the receptors’ Cl− channels in response to GABA.
GABA(A) receptors
154
These are GABA ionotropic receptors that are structurally similar to GABA(A) receptors but have a distinct pharmacological profile (e.g., they are 💡not affected by benzodiazepines) and are coded for by a separate set of genes (ρ1, ρ2, and ρ3).
GABA(C) receptors
155
These are GABA 💡metabotropic receptors where binding of GABA to this receptor activates a heterotrimeric GTPbinding protein which leads to 💡activation of K+ channels and hence 💡hyperpolarization of the postsynaptic cell, as well as 💡inhibition of Ca++ channels (when located presynaptically) and thus a reduction in release of transmitter.
GABA(B) receptor
156
Glutamate has both ionotropic and metabotropic receptors.
True
157
These are ionotropic receptor subtypes of glutamate:
These are excitatory and contain a cationic-selective channel and are permeable to 💡Na+ and K+, but 💡only a subset allow Ca++ to pass.
AMPA, kainate, and NMDA
158
These are formed from GluR1 to GluR4 subunits.
AMPA receptors
159
These require either KA1 or KA2 and GluR5 to GluR7 subunits.
kainate receptors
160
These all have NR1 subunits plus some combination of NR2 and NR3 subunits.
NMDA receptors
161
AMPA and kainate receptors behave as classic ligand-gated channels
True
162
NMDA channels are different. First, they require 💡binding of both glutamate and glycine to open. Second, they display 💡voltage sensitivity as a result of Mg++ blockade of the channel. That is, at resting (or more negative) membrane potentials, a 💡Mg++ ion blocks the entrance to the channel so that even when glutamate and glycine are bound, no current flows through the channel. If the cell is depolarized the Mg++ block is relieved and current can flow through the channel.
True
163
Purines have two receptor families:
These receptors form a cationic channel that is permeable to Na+, K+, and Ca++.
an ionotropic (P2X) and a metabotropic (P2Y) family
164
These are coded for by 10 genes, but only 6 are expressed in the human CNS.
They have the typical features of G protein–coupled receptors and are known to 💡activate K+ currents and 💡modulate both NMDA and voltage-gated Ca++ currents.
They predominate on astrocytes.
Metabotropic purine receptors (P2Y receptors)
165
Receptors for the various biogenic amines [except one class of serotonin receptors (5-HT3)] are all 💡metabotropic-type receptors. Thus, these neurotransmitters tend to act on relatively long time scales by generating slow synaptic potentials and by initiating second messenger cascades.
Biogenic Amine Receptors: Serotonin, Dopamine, Noradrenaline, Adrenaline, Histamine
Neuropeptide Receptors
166
NO and CO do not bind to receptors. One way they do affect cell activity is to activate enzymes involved in second messenger cascades, such as guanylyl cyclase.
Gas Neurotransmitter Receptors
