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DEN 7101S Human Structure and Function II > 1/5 Britton Synaptic Transmission > Flashcards

1/5 Britton Synaptic Transmission Flashcards

1
Q

Neuronal action potentials (APs) are the ___ signals

A

Electrical

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2
Q

APs propagate along:

A

the membrane of the nerve axon

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3
Q

How do APs propagate from 1 cell to another?

A

They communicate at synapses

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4
Q

____ is a site of cellular communication

A

Synapse

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5
Q

The _____ is the site where electrical information (action potential) is transmitted from one cell to another

A

Synapse

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6
Q

In an _____ synapse, electrical information is transmitted as an electrical signal

A

Electrical

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7
Q

In a ____ synapse, the electrical information is transmitted as a chemical signal

A

Chemical

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8
Q

_____ allow electrical current to flow from one excitable cell to the next

A

Electrical synapses

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9
Q

Current flows via channels between the cells called ______

A

Gap junctions

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10
Q

What are gap junctions?

A

Intercellular channels that directly connect the cytoplasm of adjacent cells and allow the movement of ions

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11
Q

Gap junctions allow cells to be:

A

Electrically coupled

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12
Q

Where are gap junctions commonly found?

A
  • cardiac muscle
  • some types of smooth muscle (bladder, uterus)
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13
Q

Why are gap junctions unique?

A

They span 2 plasma membranes

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14
Q

Each cell contributes to ____ of the gap junction channel

A

Half

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15
Q

Each half of the gap junction channel is known as a:

A

connexon or hemichannel

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16
Q

Connexons are ____ and each unit is called a _____

A

hexameric; connexin

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17
Q

A chemical synapse transmits APs from one cell to another via release of:

A

Chemical neurotransmitters

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18
Q

Chemical synapses occur where?

A

Throughout the CNS and PNS

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19
Q

Chemical synapses occur between:

A
  • neuron to neuron
  • neuron to target effector cell (muscle, gland)
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20
Q

What are some common features of chemical synapses?

A
  • pre-synaptic cell
  • post-synaptic cell
  • synaptic cleft
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21
Q

Pre-synaptic cell contains:

A
  • axon terminal (terminal portion of the axon)
  • vesicles which contain neurotransmitter
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22
Q

Post-synaptic cell contains:

A
  • receptors on cell membrane
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23
Q

A post-synaptic cell can be:

A
  • nerve cell
  • muscle cell
  • gland
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24
Q

What is the synaptic cleft?

A

gap between pre-synaptic and post-synaptic cell membranes

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25
Q

Width of synaptic cleft

A

less than 40 nm wide

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26
Q

At a chemical synapse, what occurs?

A
  • 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
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27
Q

What happens when NT binds to receptor on post-synaptic cell membrane?

A

NT may initiate an electrical response (may either excite or inhibit)

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28
Q

Overall, at a chemical synapse, the electrical signal is converted into:

A

A chemical signal, then back to an electrical signal

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29
Q

What is synaptic delay?

A

Time required for the multiple steps in chemical neurotransmission to occur

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30
Q

At chemical synapses, neurotransmission is ____ from pre-synaptic to post-synaptic cell

A

uni-directional

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31
Q

Sequence of events at chemical synapses (7)

A
  • 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
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32
Q

What are neurotransmitters?

A

Chemical agents released by neurons which stimulate neurons, muscle, glands

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33
Q

Examples of neurotransmitters

A
  • norepinephrine
  • epinephrine
  • dopamine
  • Ach
  • Serotonin
  • histamine
  • substance P
  • glutamate
  • GABA
  • glycine
  • opioids
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34
Q

Chemical synapses are often classified according to the ___ released

A

Neurotransmitter (glutamatergic, GABAergic, cholinergic, adrenergic)

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35
Q

True or false: each neurotransmitter binds to various cell surface receptors

A

False - specific receptors

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36
Q

Primary chemical signals in the ANS

A

Ach, NE

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37
Q

True or false: there is a wide variety of neurotransmitters that function in the CNS

A

True

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38
Q

Neurotransmitters that are peptides are synthesized via:

A

transcription and translation in ER of the nerve cell body

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39
Q

Once peptide neurotransmitters are synthesized, they are packaged into _____ and then transported to the nerve terminal by _____

A

secretory granules; fast axonal transport

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40
Q

Neurotransmitters that are amino-acid derived are synthesized and packaged into _____ in ____ nerve terminals

A

synaptic vesicles; pre-synaptic

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41
Q

Where does acetylcholine synthesis occur?

A

In pre-synaptic nerve terminal

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42
Q

Ach is synthesized from ____ and ____ in a reaction catalyzed by _____

A

acetyl coenzyme A (acetyl CoA); choline; choline acetyltransferase

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43
Q

Ach degraded by:

A

Acetylcholinesterase (AchE)

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44
Q

Catecholamines

A
  • norepinephrine
  • epinephrine
  • dopamine

Mnemonic: A CAT named NED

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45
Q

Synthesis of catecholamines: share a common precursor ____ and a common ______

A

tyrosine; biosynthetic pathway

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46
Q

Where does synthesis of serotonin occur?

A

In the presynaptic nerve terminal

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47
Q

Precursor amino acid for serotonin

A

tryptophan

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48
Q

Neurotransmitters are stored in ____ within the synaptic nerve terminal until a ____ arrives, causing their release

A

Vesicles; AP

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49
Q

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 ____

A

voltage gated Ca2+ channels; Ca2+; synaptic vesicles; exocytosis

50
Q

True or false: the strength of the synapse signal is modifiable

A

True - depends on strength of signal (increase in AP frequency)

51
Q

An increase in the intensity of a stimulus in pre-synaptic neurons is represented by ___

A

An increase in AP frequency

52
Q

How does the strength of the synapse signal become modified?

A
  • 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
Q

Once the post-synaptic membrane has responded to the NT in the synaptic cleft, it is either:

A

Inactivated or removed

Switching off chemical transmission at synapses

54
Q

Methods of switching off chemical transmission at synapses

A
  • Diffusion of NT
  • Reuptake of neurotransmitter into the pre-synaptic neuron by transported proteins
  • Enzyme breakdown of neurotransmitter
  • desensitization/internalization
55
Q

During reuptake of NT to switch off chemical transmission at synapses, there are ____ for different NTs.

A

Specific transporters

56
Q

Common mechanism for serotonin and dopamine uptake

A

Reuptake into pre-synaptic neuron by transporter proteins

57
Q

MAO

A
  • monoamine oxidase
  • Enzyme for breakdown of neurotransmitter
58
Q

MAO is used for what NTs?

A
  • dopamine
  • norepinephrine
  • epinephrine

Catecholamines

59
Q

Desensitization/internalization

A

Post-synaptic receptor may become less sensitive to the neurotransmitter or may change its location in the membrane (internalize)

60
Q

Ligand-gated ion channels are also called:

A

Ionotropic receptors

61
Q

GPCRs are also called:

A

metabotropic receptors

62
Q

Ligand-gated ion channel receptor contains _____ which opens after ligand binds, which allows ____

A

ion channel; ion movement across membrane

63
Q

Ligand gated ion channels: speed and length of response

A

Speed: rapid
Length: short-acting

64
Q

In a GPCR, the receptor acts through ____ upon NT binding, which then results in _____

A

2nd messengers; ion channels opening

65
Q

GPCR: speed and length of response

A

Speed: slow
Length of response: prolonged

66
Q

Ligands for ligand-gated ion channels are often:

A

Neurotransmitters

67
Q

When a NT binds to ligand-gated ion channels. what happens?

A

Ion channel pore opens and allows ions to flow across the membrane; ion channel stays open until NT dissociated

68
Q

Examples of ligand-gated ion channels

A
  • nicotinic receptor (Ach)
  • NMDA
  • GABA receptors
69
Q

Nicotinic receptor (nAchR) is composed of what subunits?

A
  • 2 alpha
  • 1 each of beta, gamma, delta
70
Q

Nicotinic receptor subunits assemble to form:

A

Pore

71
Q

___ Ach molecules bind to the 2 alpha subunits of the nAchR, ___ opens, allows diffusion of ____

A

2; ion channel pore; Na+ and K+

72
Q

Movement of ___ into the cell causes a ____ event which leads to _____

A

Na+; depolarization; excitation

73
Q

Location of nicotinic receptors

A
  • neuromuscular junction of somatic nerves
  • autonomic nerve ganglia
  • adrenal medulla gland
  • CNS
74
Q

Other names for GPCR

A
  • metabotropic receptors
  • G protein linked receptors
  • trimeric GPCR
75
Q

G-protein complex is a ____ GTP binding protein

A

Heterotrimeric (a, B, y subunits)

76
Q

NT binding to GPCR changes _____ of the receptor. The G protein alpha subunit exchanges ___ for ____. Then the a subunits ______ which activates _____

A

conformation; GTP for GDP; dissociate from B and y subunits; intracellular 2nd messenger signaling

77
Q

Examples of GPCRs

A
  • muscarinic receptors
  • adrenergic receptors
  • dopamine receptors
  • opioid receptors
78
Q

Muscarinic receptors ligand

A

Ach

79
Q

Adrenergic receptor ligand

A

NE

80
Q

Dopamine receptor ligand

A

Dopamine

81
Q

Opioid receptor ligand

A

Endorphins

82
Q

Postsynaptic potentials

A
  • Membrane potential in post-synaptic membrane
  • can be excitatory or inhibitory
83
Q

If postsynaptic membrane depolarizes, this potential is called:

A

EPSP (Excitatory post synaptic potential)

84
Q

If the postsynaptic membrane hyperpolarizes, this potential is called:

A

IPSP (Inhibitory post synaptic potential)

85
Q

Whether EPSP or IPSP occurs depends on the:

A
  • NT released from the pre-synaptic nerve terminal
  • receptor and attached ion channel the NT binds to
86
Q

Excitatory NTs cause _____ of the post-synaptic cell

A

Depolarization

87
Q

Inhibitory NTs cause ____ of the post-synaptic cell

A

Hyperpolarization

88
Q

Glutamate: excitatory or inhibitory?

A

Excitatory

89
Q

GABA: excitatory or inhibitory?

A

Inhibitory

90
Q

Glycine: excitatory or inhibitory?

A

Inhibitory

91
Q

Acetylcholine: excitatory or inhibitory?

A

Both

92
Q

Dopamine: excitatory or inhibitory?

A

Both

93
Q

Norepinephrine/epinephrine: excitatory or inhibitory?

A

Excitatory

94
Q

Serotonin: excitatory or inhibitory?

A

Inhibitory

95
Q

Histamine: excitatory or inhibitory?

A

Excitatory

96
Q

Ach can bind to both ____ and ___ receptors

A

Nicotinic and muscarinic

97
Q

____ is the major inhibitory NT in the CNS

A

GABA

98
Q

Activation of GABA ligand-gated receptors is inhibitory due to:

A

Cl- influx through this channel, results in hyperpolarization (inside is more negative)

99
Q

Benzodiazepine modulates the action of ____ and increases ___

A

GABA receptors; frequency of Cl- channel openings

100
Q

___ is the major excitatory NT in the CNS

A

Glutamate

101
Q

Glutamate activates 2 types of glutamate receptors:

A
  • ionotropic receptors (ligand gated)
  • metabotropic receptors (GPCR)
102
Q

If Glutamate binds to ionotropic receptor, generates ____

A

EPSP

103
Q

GPCRs activate _____

A

second messenger cascades (ex: GluR1-GluR8 receptors)

104
Q

Summation

A

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
Q

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

A

True - many pre-synaptic APs are needed in a process called summation

106
Q

Synaptic transmission between neurons within the CNS are organized to form:

A

Pathways ranging from relatively simple to extremely complex

107
Q

Converging pathway in nervous system

A

2 or more neurons synapse with (converge on) same neuron

108
Q

Converging pathways allows for:

A

Information to be transmitted in more than one neuronal pathway to converge into a single pathway

109
Q

Diverging pathway in the nervous system

A

Axon from 1 neuron divides (diverges) and synapses with more than one other neuron

110
Q

Diverging pathway allows for:

A

Information transmitted in one neuronal pathway to diverge onto two or more pathways

111
Q

During summation, PSPs produced by each active synapse can sum together in ____ and ____ to determine the behavior of the post synaptic neuron

A

Space and time (location and rate of firing)

112
Q

Spatial summation

A

occurs when impulses originate from different locations (converging pathways)

113
Q

temporal summation

A

How quickly APs are being fired in the same neuron (greater the frequency, greater the release of NTs, greater electrical transmission)

114
Q

In summation, each neuron connects with _____

A

Numerous other neurons - receives numerous APs from them

115
Q

The sum of EPSP’s and IPSP’s determine whether:

A

Postsynaptic neuron will fire an AP

116
Q

What is the neuromuscular junction synapse?

A

Chemical synapse between motor neuron of somatic nervous system and skeletal muscle fiber

117
Q

NMJ neurotransmitter

A

Always ACh

118
Q

ACh binding to the nAChR on the skeletal muscle cell causes:

A

Depolarization of the motor end plate and results in muscle contraction

119
Q

EPSPs produced on the postsynaptic membrane of a skeletal muscle of a NMJ junction are termed:

A

End-plate potentials

120
Q

Biosynthetic pathway of the catecholamines

A

Tyrosine –> DOPA –> dopamine –> norepinephrine –> epinephrine

DEN 7101S Human Structure and Function II (21 decks)

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