1/5 Britton Synaptic Transmission Flashcards
(120 cards)
1
Q
Neuronal action potentials (APs) are the ___ signals
A
Electrical
2
Q
APs propagate along:
A
the membrane of the nerve axon
3
Q
How do APs propagate from 1 cell to another?
A
They communicate at synapses
4
Q
____ is a site of cellular communication
A
Synapse
5
Q
The _____ is the site where electrical information (action potential) is transmitted from one cell to another
A
Synapse
6
Q
In an _____ synapse, electrical information is transmitted as an electrical signal
A
Electrical
7
Q
In a ____ synapse, the electrical information is transmitted as a chemical signal
A
Chemical
8
Q
_____ allow electrical current to flow from one excitable cell to the next
A
Electrical synapses
9
Q
Current flows via channels between the cells called ______
A
Gap junctions
10
Q
What are gap junctions?
A
Intercellular channels that directly connect the cytoplasm of adjacent cells and allow the movement of ions
11
Q
Gap junctions allow cells to be:
A
Electrically coupled
12
Q
Where are gap junctions commonly found?
A
- cardiac muscle
- some types of smooth muscle (bladder, uterus)
13
Q
Why are gap junctions unique?
A
They span 2 plasma membranes
14
Q
Each cell contributes to ____ of the gap junction channel
A
Half
15
Q
Each half of the gap junction channel is known as a:
A
connexon or hemichannel
16
Q
Connexons are ____ and each unit is called a _____
A
hexameric; connexin
17
Q
A chemical synapse transmits APs from one cell to another via release of:
A
Chemical neurotransmitters
18
Q
Chemical synapses occur where?
A
Throughout the CNS and PNS
19
Q
Chemical synapses occur between:
A
- neuron to neuron
- neuron to target effector cell (muscle, gland)
20
Q
What are some common features of chemical synapses?
A
- pre-synaptic cell
- post-synaptic cell
- synaptic cleft
21
Q
Pre-synaptic cell contains:
A
- axon terminal (terminal portion of the axon)
- vesicles which contain neurotransmitter
22
Q
Post-synaptic cell contains:
A
- receptors on cell membrane
23
Q
A post-synaptic cell can be:
A
- nerve cell
- muscle cell
- gland
24
Q
What is the synaptic cleft?
A
gap between pre-synaptic and post-synaptic cell membranes
25
Width of synaptic cleft
less than 40 nm wide
26
At a chemical synapse, what occurs?
- AP in the pre-synaptic neuron converted into release of NT
- NT diffuses across synaptic cleft, binds to receptors located in the membrane of post-synaptic cell
27
What happens when NT binds to receptor on post-synaptic cell membrane?
NT may initiate an electrical response (may either excite or inhibit)
28
Overall, at a chemical synapse, the electrical signal is converted into:
A chemical signal, then back to an electrical signal
29
What is synaptic delay?
Time required for the multiple steps in chemical neurotransmission to occur
30
At chemical synapses, neurotransmission is ____ from pre-synaptic to post-synaptic cell
uni-directional
31
Sequence of events at chemical synapses (7)
- AP arrives at axon terminal
- voltage-gated Ca2+ channels open
- Ca2+ enters the cell
- Ca2+ signals to vesicles
- vesicles move to the membrane
- docked vesicles release neurotransmitter by exocytosis
- NT diffuses across the synaptic cleft and binds to receptors on post-synaptic membrane
32
What are neurotransmitters?
Chemical agents released by neurons which stimulate neurons, muscle, glands
33
Examples of neurotransmitters
- norepinephrine
- epinephrine
- dopamine
- Ach
- Serotonin
- histamine
- substance P
- glutamate
- GABA
- glycine
- opioids
34
Chemical synapses are often classified according to the ___ released
Neurotransmitter (glutamatergic, GABAergic, cholinergic, adrenergic)
35
True or false: each neurotransmitter binds to various cell surface receptors
False - specific receptors
36
Primary chemical signals in the ANS
Ach, NE
37
True or false: there is a wide variety of neurotransmitters that function in the CNS
True
38
Neurotransmitters that are peptides are synthesized via:
transcription and translation in ER of the nerve cell body
39
Once peptide neurotransmitters are synthesized, they are packaged into _____ and then transported to the nerve terminal by _____
secretory granules; fast axonal transport
40
Neurotransmitters that are amino-acid derived are synthesized and packaged into _____ in ____ nerve terminals
synaptic vesicles; pre-synaptic
41
Where does acetylcholine synthesis occur?
In pre-synaptic nerve terminal
42
Ach is synthesized from ____ and ____ in a reaction catalyzed by _____
acetyl coenzyme A (acetyl CoA); choline; choline acetyltransferase
43
Ach degraded by:
Acetylcholinesterase (AchE)
44
Catecholamines
- norepinephrine
- epinephrine
- dopamine
| Mnemonic: A CAT named NED
45
Synthesis of catecholamines: share a common precursor ____ and a common ______
tyrosine; biosynthetic pathway
46
Where does synthesis of serotonin occur?
In the presynaptic nerve terminal
47
Precursor amino acid for serotonin
tryptophan
48
Neurotransmitters are stored in ____ within the synaptic nerve terminal until a ____ arrives, causing their release
Vesicles; AP
49
Neurotransmitter release:
- AP depolarizes the synaptic terminal leading to the opening of ____
- The influx of ____ in the axon terminal allows fusion of the _____ with the cell membrane
- Consequently, the ____ is released into the synaptic cleft by ____
voltage gated Ca2+ channels; Ca2+; synaptic vesicles; exocytosis
50
True or false: the strength of the synapse signal is modifiable
True - depends on strength of signal (increase in AP frequency)
51
An increase in the intensity of a stimulus in pre-synaptic neurons is represented by ___
An increase in AP frequency
52
How does the strength of the synapse signal become modified?
- increased number of vesicles undergoing exocytosis
- increased amount of NT released
- increased NT can bind to post-synaptic receptors
- **more ion channels will open**
53
Once the post-synaptic membrane has responded to the NT in the synaptic cleft, it is either:
Inactivated or removed
| Switching off chemical transmission at synapses
54
Methods of switching off chemical transmission at synapses
- Diffusion of NT
- Reuptake of neurotransmitter into the pre-synaptic neuron by transported proteins
- Enzyme breakdown of neurotransmitter
- desensitization/internalization
55
During reuptake of NT to switch off chemical transmission at synapses, there are ____ for different NTs.
Specific transporters
56
Common mechanism for serotonin and dopamine uptake
Reuptake into pre-synaptic neuron by transporter proteins
57
MAO
- monoamine oxidase
- Enzyme for breakdown of neurotransmitter
58
MAO is used for what NTs?
- dopamine
- norepinephrine
- epinephrine
| Catecholamines
59
Desensitization/internalization
Post-synaptic receptor may become less sensitive to the neurotransmitter or may change its location in the membrane (internalize)
60
Ligand-gated ion channels are also called:
Ionotropic receptors
61
GPCRs are also called:
metabotropic receptors
62
Ligand-gated ion channel receptor contains _____ which opens after ligand binds, which allows ____
ion channel; ion movement across membrane
63
Ligand gated ion channels: speed and length of response
Speed: rapid
Length: short-acting
64
In a GPCR, the receptor acts through ____ upon NT binding, which then results in _____
2nd messengers; ion channels opening
65
GPCR: speed and length of response
Speed: slow
Length of response: prolonged
66
Ligands for ligand-gated ion channels are often:
Neurotransmitters
67
When a NT binds to ligand-gated ion channels. what happens?
Ion channel pore opens and allows ions to flow across the membrane; ion channel stays open until NT dissociated
68
Examples of ligand-gated ion channels
- nicotinic receptor (Ach)
- NMDA
- GABA receptors
69
Nicotinic receptor (nAchR) is composed of what subunits?
- 2 alpha
- 1 each of beta, gamma, delta
70
Nicotinic receptor subunits assemble to form:
Pore
71
___ Ach molecules bind to the 2 alpha subunits of the nAchR, ___ opens, allows diffusion of ____
2; ion channel pore; Na+ and K+
72
Movement of ___ into the cell causes a ____ event which leads to _____
Na+; depolarization; excitation
73
Location of nicotinic receptors
- neuromuscular junction of somatic nerves
- autonomic nerve ganglia
- adrenal medulla gland
- CNS
74
Other names for GPCR
- metabotropic receptors
- G protein linked receptors
- trimeric GPCR
75
G-protein complex is a ____ GTP binding protein
Heterotrimeric (a, B, y subunits)
76
NT binding to GPCR changes _____ of the receptor. The G protein alpha subunit exchanges ___ for ____. Then the a subunits ______ which activates _____
conformation; GTP for GDP; dissociate from B and y subunits; intracellular 2nd messenger signaling
77
Examples of GPCRs
- muscarinic receptors
- adrenergic receptors
- dopamine receptors
- opioid receptors
78
Muscarinic receptors ligand
Ach
79
Adrenergic receptor ligand
NE
80
Dopamine receptor ligand
Dopamine
81
Opioid receptor ligand
Endorphins
82
Postsynaptic potentials
- Membrane potential in post-synaptic membrane
- can be excitatory or inhibitory
83
If postsynaptic membrane depolarizes, this potential is called:
EPSP (Excitatory post synaptic potential)
84
If the postsynaptic membrane hyperpolarizes, this potential is called:
IPSP (Inhibitory post synaptic potential)
85
Whether EPSP or IPSP occurs depends on the:
- NT released from the pre-synaptic nerve terminal
- receptor and attached ion channel the NT binds to
86
Excitatory NTs cause _____ of the post-synaptic cell
Depolarization
87
Inhibitory NTs cause ____ of the post-synaptic cell
Hyperpolarization
88
Glutamate: excitatory or inhibitory?
Excitatory
89
GABA: excitatory or inhibitory?
Inhibitory
90
Glycine: excitatory or inhibitory?
Inhibitory
91
Acetylcholine: excitatory or inhibitory?
Both
92
Dopamine: excitatory or inhibitory?
Both
93
Norepinephrine/epinephrine: excitatory or inhibitory?
Excitatory
94
Serotonin: excitatory or inhibitory?
Inhibitory
95
Histamine: excitatory or inhibitory?
Excitatory
96
Ach can bind to both ____ and ___ receptors
Nicotinic and muscarinic
97
____ is the major inhibitory NT in the CNS
GABA
98
Activation of GABA ligand-gated receptors is inhibitory due to:
Cl- influx through this channel, results in hyperpolarization (inside is more negative)
99
Benzodiazepine modulates the action of ____ and increases ___
GABA receptors; frequency of Cl- channel openings
100
___ is the major excitatory NT in the CNS
Glutamate
101
Glutamate activates 2 types of glutamate receptors:
- ionotropic receptors (ligand gated)
- metabotropic receptors (GPCR)
102
If Glutamate binds to ionotropic receptor, generates ____
EPSP
103
GPCRs activate _____
second messenger cascades (ex: GluR1-GluR8 receptors)
104
Summation
addition of multiple signals at the post-synaptic cell which bring the membrane potential of the post-synaptic cell to threshold and trigger an AP
105
True or false: within many synapses of the CNS, a single pre-synaptic AP by itself usually does not cause a large enough potential to reach threshold and produce an AP in the target cell
True - many pre-synaptic APs are needed in a process called summation
106
Synaptic transmission between neurons within the CNS are organized to form:
Pathways ranging from relatively simple to extremely complex
107
Converging pathway in nervous system
2 or more neurons synapse with (converge on) same neuron
108
Converging pathways allows for:
Information to be transmitted in more than one neuronal pathway to converge into a single pathway
109
Diverging pathway in the nervous system
Axon from 1 neuron divides (diverges) and synapses with more than one other neuron
110
Diverging pathway allows for:
Information transmitted in one neuronal pathway to diverge onto two or more pathways
111
During summation, PSPs produced by each active synapse can sum together in ____ and ____ to determine the behavior of the post synaptic neuron
Space and time (location and rate of firing)
112
Spatial summation
occurs when impulses originate from different locations (converging pathways)
113
temporal summation
How quickly APs are being fired in the same neuron (greater the frequency, greater the release of NTs, greater electrical transmission)
114
In summation, each neuron connects with _____
Numerous other neurons - receives numerous APs from them
115
The sum of EPSP's and IPSP's determine whether:
Postsynaptic neuron will fire an AP
116
What is the neuromuscular junction synapse?
Chemical synapse between motor neuron of somatic nervous system and skeletal muscle fiber
117
NMJ neurotransmitter
Always ACh
118
ACh binding to the nAChR on the skeletal muscle cell causes:
Depolarization of the motor end plate and results in muscle contraction
119
EPSPs produced on the postsynaptic membrane of a skeletal muscle of a NMJ junction are termed:
End-plate potentials
120
Biosynthetic pathway of the catecholamines
Tyrosine --> DOPA --> dopamine --> norepinephrine --> epinephrine
