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Cellular Neurobiology > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

What is a chemical synapse?

A

Presynaptic terminals release neurotransmitter molecules and these molecules activate receptors in the post-synaptic membrane

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2
Q

What is synaptic release?

A

A series of electrical and biochemical events that occur in the:
1- Presynaptic neuron
2- the synaptic cleft
3- the postsynaptic neuron

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3
Q

Who was one of the first scientists to investigate the Presynaptic event that triggers the release of neurotransmitters?

A

Bernard Katz

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4
Q

What cell did Katz use to study Presynaptic release?

A

The giant axon of the squid

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5
Q

What are the two different types of recordings that Katz made to study Presynaptic release?

A

1) electrodes were used to record the membrane potential in the pre- and post- synaptic neurons

2) another electrode was used to inject current in the Presynaptic neuron.

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6
Q

In Katz experiments, what happened when Enough current was injected into his system?

A

1) the Presynaptic & postsynaptic neuron responded with an action potential.

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7
Q

What happened when Katz added the toxin tetrodotoxin (TTX)?

A

This toxin blocks sodium voltage gated channels, so after a few seconds the pre- and post- synaptic action potentials decreased in amplitude.

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8
Q

What happened to the pre and post synaptic neurons after a few minutes in the presence of TTX?

A

1) the Presynaptic neuro is able to produce a Supra threshold potential

2) the post synaptic neuron responded with an EPSP (excitatory postsynaptic potential.

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9
Q

What happened after about 15 minutes in Katz’ synaptic release experiment?

A

1) the Presynaptic neuron can only produce a potential a Supra threshold potential that correlates with the current injected.

2) the post synaptic neuron was unable to produce a detectable EPSP.

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10
Q

What is synaptic transmission?

A

The process whereby a neuron communicates with another cell (can be a neuron or muscle cell)

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11
Q

What is a synapse?

A

A specialized structure at which one neuron communicates with another cell.

It is the point of contact.

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12
Q

Who coined the term synapse?

A

Charles Sherrington

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13
Q

How many neurons does the human brain have?

A

86 billion

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14
Q

Approximately how many synapses are there in the human brain?

A

8.6 x 10^13

(More than there are starts in our galaxy (10^11))

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15
Q

When a neuron communicates with another cell, which way does the information travel?

A

From the pre-synaptic cell to the post synaptic cell.

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16
Q

Based on the zone of apposition, synapses can be categorized into two types. What are the?

A
  1. Chemical
  2. Electrical.
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17
Q

How are electrical synapses used?

A

They are used mostly to generate rapid and stereotyped depolarizing signals.

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18
Q

How are chemical synapses used?

A

They are capable of variable signaling:

1) they can mediate either excitatory or inhibitory signals

2) they can mediate changes in the electrical properties of the post synaptic cell.

These changes can last from milliseconds to minutes.

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19
Q

Communication in the brain mostly relies on what type of synapses?

A

Chemical synapses.

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20
Q

Where does most of our knowledge of the chemical synapse come from?

A

The neuromuscular junction

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21
Q

What is the neuromuscular junction?

A

The synapse between a neuron and a skeletal muscle cell

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22
Q

Who Introduced the notions of ligands and its receptor?

A

Paul Ehlrich

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23
Q

Who discovered Acetylcholine?

A

Otto Löwie- he discovered that it conveys signals from the Vegus nerve to the heart.

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24
Q

what were the two schools of thought regarding synaptic transmission and who lead each of them?

A
  1. Physiologists - led by John Eccles
  2. Pharmacologists - led by Harry Dale
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25
Q

What did the physiologists believe regarding synaptic transmission?

A

They thought it was electrical. That the action potential in the Presynaptic neuron generates a current that flows passively into the post-synaptic cell.

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26
Q

What did the pharmacologists believe regarding synaptic transmission?

A

That it was chemical. The action potential in the Presynaptic cell Leads to the release of a chemical substance that initiates a current in the post synaptic cell.

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27
Q

Compare and contrast electrical and chemical synapses in the following ways:

1- Pre and post synaptic cell distance

2- cytoplasmic continuity between pre and post synaptic cells.

3- ultra structural components

4- agent of transmission

5- synaptic delay

6- direction of signal transmission

A

1- Pre and post synaptic cell distance:
Electrical = very short. ~4 nm
Chemical- much larger. Usually 20-40 nm

2- cytoplasmic continuity between pre and post synaptic cells.
Electrical= yes
Chemical = No

3- ultra structural components
Electrical = continuous through gap junctions
Chemical = Presynaptic vesicles, active zones, postsynaptic receptors.

4- agent of transmission:
Electrical = ion current
Chemical = Chemical transmitter

5- synaptic delay:
Electrical = virtually absent
Chemical = Significant. At least 0.3 ms but usually 1-5 ms or longer.

6- direction of signal transmission:
Electrical = usually bidirectional
Chemical = Unidirectional

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28
Q

True/false: when the outward current of a Presynaptic neuron is strong enough, some of that current can flow through the gap junction channels to the post synaptic cell.

A

True

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29
Q

True/false: if the Presynaptic current is sufficient to depolarize the postsynaptic neuron above threshold, then voltage gated ion channels will generate a action potential in the postsynaptic cell.

A

True

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30
Q

I. Order for the Presynaptic neuron in an electrical synapse to generate a current large enough to depolarize both the pre and post synaptic neurons, what two morphological criteria must be met?

A

1) the Presynaptic terminal must be large enough to house a large number of ion channels

2) the postsynaptic neuron must be small enough such that it can be depolarized by the current coming through the gap junction channels.

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31
Q

In order to study the electric synapse, Furshpan and potter used the _________system from crayfish

A

Giant motor synapse

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32
Q

In the giant motor synapse in crayfish, the [Presynaptic/postsynaptic] _______ is the lateral giant fiber and the [Presynaptic/postsynaptic] ________ is a smaller motor fiber.

A
  1. Presynaptic
  2. Postsynaptic
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33
Q

To study the electrical synapse, Furshpan and potterused a pair of electrodes: one was used to _______ and the other was used to record___________.

A

1) inject a current

2) the membrane potential

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34
Q

Furshpan and Potter observed that the time between the Presynaptic spike and the postsynaptic potential is very short. The time between the two spikes is called———-

A

Synaptic delay

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35
Q

True/false: gap junctions are always open

A

False. They can open or close

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36
Q

What are gap junction channels?

A

Specialized membrane proteins that conduct ionic currents.

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37
Q

Gap junctions consist of a pair of__________channels ( one on each cell) to create a _________between the Presynaptic and postsynaptic neurons

A

Hemi-

Pore

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38
Q

How many connexin subunits form a hemi-channel?

A

Six

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39
Q

Six _________subunits form each _________

A

1) connexin

2) hemi-channel

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40
Q

What do gap ion channels allow for?

A

Synchrony between circuits

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41
Q

Cells that are coupled generally have [higher/lower] thresholds.

A

Higher

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42
Q

Once the threshold is reached, electrically coupled cells fire ____________because__________

A

1) synchronously

2) the currents generated in one cell are rapidly conducted to another

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43
Q

What are brain waves?

A

Rhythmic activity patterns that a probably driven by electrical synapses

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44
Q

What is the function of brain waves?

A

Their function, if any, is unknown

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45
Q

What are the five types of brain waves?

A
  1. Alpha
  2. Beta
  3. Gamma
  4. Delta
  5. Theta
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46
Q

When are alpha brain waves detected?

A

They are detected during relaxed states. (Relaxation, reflection)

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47
Q

When are beta waves detected?

A

During alert working states (concentration, learning)

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48
Q

When ate delta waves detected?

A

During deep dreamless sleep (deep healing sleep)

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49
Q

When are theta waves detected?

A

During light sleep and deep meditative states (dreaming, flow states)

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50
Q

When are gamma waves detected?

A

Believed to underlie heightened perception. (Insight, expanded consciousness)

They have been recorded in Tibetan Buddhist monks during transcendental mental states.

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51
Q

In a chemical synapse, how many vesicles can a Presynaptic terminal contain?

A

100-200 synaptic vesicles

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52
Q

True/false: synaptic vesicles cluster at the active zone.

A

True

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53
Q

What is the active zone in a chemical synapse?

A

A specialized structure in the Presynaptic terminal.

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54
Q

Synaptic vesicles are filled with_________

A

Several thousand neurotransmitter molecules

55
Q

In a chemical synapse, what causes voltage gated Ca++channels to open?

A

The Presynaptic action potential

56
Q

What happens when the Ca++ channels open?

A

Ca++ flows inside the Presynaptic zone

57
Q

In a chemical synapse, what happens when intracellular Ca++ rises?

A

It triggers a biochemical reaction that causes the vesicles to fuse with the Presynaptic membrane.

58
Q

In a chemical synapse, what happens when synaptic vesicles fuse to the Presynaptic membrane ?

A

Neurotransmitters are released into the synaptic cleft.

59
Q

In a chemical synapse, what happens when neurotransmitter molecules diffuse across the synaptic cleft?

A

They bind and activate their cognate receptors.

60
Q

In a chemical synapse, what happens when a receptor on the post synaptic cell is activated?

A

It leads to an opening or closing of ion channels which affect membrane conductance and potential of the postsynaptic neuron.

61
Q

In a chemical synapse what accounts for its longer synaptic delay?

A

Influx of ca++ to cause vesicles to fuse with the membrane

Release of and diffusion of the neurotransmitter across the synaptic cleft

Neurotransmitter binding and activating their receptor.

62
Q

If the neurotransmitter receptor is a Na+ ion channel, will the postsynaptic neuro depolarize or hyperpolarize in response to neurotransmitter release?

A

Depolarize

63
Q

If the neurotransmitter receptor is a Cl- ion channel, will the postsynaptic neuron depolarize or hyperpolarize in response to neurotransmitter release?

A

Hyperpolarize

64
Q

A neurotransmitter can be ________ or _________ depending on the nature of its post synaptic receptor.

A

Excitatory or inhibitory

65
Q

What two biochemical features to all neurotransmitter receptors have in common?

A

1) they are membrane proteins: these receptors have an extra cellular domain that binds to the neurotransmitter.

2) they have an effector function.

66
Q

Ionotropic neurotransmitter receptors do what?

A

Have a direct function, for e.g. opening or closing an ion channel

67
Q

Metabotropic receptors do what?

A

Have an indirect function, e.g. the production of secondary messenger molecule.

68
Q

The Acetylcholine receptor is an example of what kind of receptor (ionotropic or metabotropic)?

A

Ionotropic

69
Q

Ionotropic receptors (gate ion channels directly are composed of how many subunits?

A

4 to 5

70
Q

For Ionotropic proteins which domain forms the ion conducting pore

A

The trans membrane domain

71
Q

For Ionotropic receptors, the binding site is located on wheat domain?

A

The extra cellular domain

72
Q

What happens to an Ionotropic receptor when it’s neurotransmitter binds?

A

The receptor undergoes conformational changes that lead to the opening of the gate.

73
Q

How many subunits do metabotropic receptors (receptors that gate ion channels indirectly, e.g. G protein coupled) have?

A

One or two subunits

They are distinct from the ion channel they regulate

74
Q

How do metabotropic receptors act?

A

By altering intracellular metabolic reactions and stimulating the production of secondary messengers.

75
Q

What are second messager molecules?

A

Small freely diffused molecules such as cAMP or diaglycerol.

76
Q

True /false: many secondary messengers activate protein kinases which in turn phosphorylate phosphorylation gated channels

A

True

77
Q

True/false: some neurons release neuromodulator molecules

A

True.

78
Q

Neuromodulators act through what kind of receptor (Ionotropic or metabotropic)

A

Metabotropic

79
Q

What is a major advantage of a chemical synapse over an electrical synapse?

A

Amplification

80
Q

What is the property of amplification?

A

The release of just one synaptic vesicle is sufficient to release several thousand molecules of neurotransmitter, which can open thousands of ion channels.

Thus, a small Presynaptic nerve terminal- which can only generate a weak electric current, can depolarize a large synaptic cell.

81
Q

True/false: the neuromuscular junction is the most studied synapse.

A

True

82
Q

Where does the motor neuron innervate a muscle fiber?

A

At the end plate

83
Q

Does a motor neuron have a Mylin sheath at the end plate?

A

No

84
Q

True/false: a motor neuron splits into fine branches at the end plate.

A

True

85
Q

The motor neuron fine branches form multiple ___________

A

Synaptic boutons

86
Q

In motor neurons acetylcholine is released from these structures_____

A

Synaptic boutons

87
Q

True/false: synaptic boutons contain vesicles filled with acetylcholine, the calcium channels and the regulators of synaptic vesicle release.

A

True

88
Q

What is the junctional fold?

A

It is a specialized region of the muscle membrane which contains the nicotinic acetylcholine receptor

89
Q

In the neuromuscular junction synaptic cleft , acetylcholinesterase is an enzyme that does what?

A

Hydrolysis acetylcholine

90
Q

In the neuromuscular junction, the motor neuron action potential which triggers the release of acetylcholine, which then binds to the receptor on the muscle cell generates an _________current that depolarizes the muscle cell.

A

Inward

91
Q

What is an EPSP?

A

An excitatory postsynaptic potential

92
Q

In the neuro muscular junction, EPSPs are large, being about ________mV

A

70 mV.

This is much larger than EPSPs normally generated by the neurons in the brain

93
Q

In the neuromuscular junction, EPSPs rapidly activate ________ inducing an_________ which then propagates along the muscle fiber inducing_____.

A

Voltage gated na+ channels

Action potential

Contractions

94
Q

In what ways are muscle fiber action potentials similar to and different than action potentials seen in neurons?

A

Similarities:
The muscle fiber AP has a rising phase from the opening of the voltage gated sodium channels and a falling phase from the opening of K+ channels.

Differences:
The riding phase is steep, but The shape of the falling phase is prolonged in muscle fibers,

  It has no hyperpolarization phase

  It lasts a long time:  from 2-4 ms

   The resting potential of the muscle fiber is typically-90 mV which is more negative than the resting potential of most neurons
95
Q

Katz and fatts studied the end plate potential by isolating it from the action potential by using ______ which is a weak inhibitor of the acetylcholine receptor.

A

Curare

96
Q

In investigating the end plate potential, Katz and fatts found that_______

A

The opening of all acetylcholine receptor channels is required to generate action potential in the muscle.

97
Q

According to Katz and fatts experiment, a reverse potential of 0 mV means___\

A

The acetylcholine receptor is not selective and is permeable to both na and k. The fluxed cancel reach other

98
Q

The acetylcholine receptor differs from voltage gated channels as it has a much larger pore that can accommodate ______

A

Cations such as Na, K end Ca

99
Q

Katz and fatts postulated that the rapid rise of the endplate potential might be from———-

A

The sudden release of acetylcholine into the cleft .

100
Q

Katz and fatts postulated that the slow decay of the endplate potential might be from———-

A

The removal of acetylcholine from the cleft following hydrolysis by the enzyme acetylcholinesterase

101
Q

How do acetylcholine receptors differ from voltage gated channels? (3 Of them)

A
  1. The acetylcholine receptor is ligand gated (not voltage gated) . The number of acetylcholine channels open depends on the number of acetylcholine molecules available not on membrane potential
  2. The acetylcholine receptor is not selective for particular cation species. Instead it is permeable to na, k and ca ions . Voltage gated channels are selective
  3. The acetylcholine receptors and voltage gated channels belong to different gene families.
102
Q

How many subunits make up the acetylcholine receptor?

A

5

103
Q

How many binding sites does the acetylcholine receptor have?

A

2

104
Q

True/false: both sites of the acetylcholine channel need to be occupied for the channel to open.

A

True

105
Q

True/false: one miter neuron can innervate different muscles.

A

True.

106
Q

True/false: in mammals muscle fibers are innervated by a single neuron

A

True

107
Q

What is a connectome?

A

A comprehensive map of the neutral connections in a brain

108
Q

What is the goal of connectomics?

A

To map all the synapses making a brain

109
Q

Why is the neuromuscular junction a helpful system to study synaptic integration?

A

Most muscle fibers are connected to a single motor neuron. (Interneurons can receive from a few up to 200,000 inputs)

Muscle fibers receive only excitatory input (most interneurons receive both excitatory and inhibitory inputs)

End plate potentials are mediated by a single neuro transmitter- acetylcholine- to one receptor - the acetylcholine gated channel. (In the brand there are many neuro transmitters.

110
Q

What is the function of the brain?

A

Information integration

111
Q

True/false: the neuromuscular junction is an efficient synapse.

A

True

One action potential is is sufficient to generate an action potential in a muscle fiber.

112
Q

True/false: synapses in the brain are not so efficient

A

True:

Several action potentials need to be simultaneously generated in as many as 50 to 100 of the Presynaptic neurons for an action potential to be generated in the post synaptic neuron.

113
Q

Why are synapses in the brain inefficient?

A

Redundancy. So if lose a neuron the impact is minimized.

114
Q

What are the differences between the synapse at the neuromuscular junction and other synapses?

A

Neuromuscular junction synapse:
- the muscle fiber is innervated by a single axon, and therefore only integrates one input.

  • muscle fibers only receive excitatory inputs
  • synaptic action is mediated by one type of neurotransmitter— Acetylcholine
  • a single action potential in one motor neuron is sufficient to generate an action potential

—————_
Other synapses:

  • the post synaptic cell - a neuron- is connected to many axons and therefore integrates several inputs across different types of neurons.
  • most neurons receive excitatory and inhibitory inputs
  • synaptic action is mediated by different types of neurotransmitter binding to different receptors.
  • multiple excitatory neurons must fire together to generate an action potential in the postsynaptic neuron.
115
Q

What is an antagonistic muscle pair?

A

When one muscle contracts, the other relaxes (eg biceps/triceps)

116
Q

Antagonistic muscle pair circuits consist of both ______ and ______ synapses.

A

Excitatory and inhibitory

117
Q

In antagonistic muscle pairs, IPSPs are generated by an ______ interneuron.

A

Inhibitory

118
Q

In antagonistic muscle pairs, the sensory neuron is connected to the extensor _____ neuron innervating the extensor muscle and an _________ interneuron

A

Motor

Inhibitory

119
Q

The activation of a extensor motor neuron requires the simultaneous activation of many ______neurons

A

Sensory

120
Q

Antagonistic action of antagonistic muscle pairs depends on the ability of the motor neuron to ____________ excitatory and inhibitory inputs

A

Integrate

121
Q

True/false: purkinje neurons receive as many as 200,000 inputs- and thus generate action potentials most of the time.

A

True

Neurons located in the cerebellum

122
Q

True/false: without inhibitory input, a neuron fires continuously at a fixed interval

A

True

123
Q

True/false: with inhibitory input, some action potentials are inhibited. This results in a distinct pattern of activity

A

True

124
Q

True/false: information can be encoded by inhibition.

A

True

125
Q

How can information be encoded by inhibition?

A

IPSPs sculpt the pattern of firing in neurons that fire spontaneously at a given interval

126
Q

Besides chemical and electrical synapse, how else can synapse be distinguished?

A

The whether they are excitatory or inhibitory

127
Q

Whether a given neurotransmitter generates an excitatory or inhibitory current depends on_________

A

The type of ligand gated channels found in the postsynaptic terminal.

128
Q

Generally glutamate generates (excitatory or inhibitory) _________ currents.

A

Excitatory

129
Q

Generally glycine and GABA produce (excitatory or inhibitory) currents.

A

Inhibitory

130
Q

True/false: the synaptic terminals of excitatory and inhibitory neurons are morphologically distinguishable.

A

True:

131
Q

Terminals if excitatory and inhibitory neurons are referred to as either _______

A

Gray type 1 or gray type 2 synapses.

132
Q

What are the anatomical creatures of gray type 1 synapses. (4)

A
  1. The synapses have asymmetrical membrane differentiations (there is a dark electron dense region at the active zone of the Presynaptic membrane and an even larger one on the post synaptic membrane
  2. They have round vesicles
  3. They usually contact specialized regions on the dendrite called the spine
  4. They are often glutamatergenic and thus excitatory
133
Q

What are the anatomical creatures of gray type 2 synapses. (4)

A
  1. They have symmetrical membrane differentiations.
  2. The have oval or flattened vessicles
  3. They do not contact spines. Instead they contact the shaft of a dendrite or cell body
  4. They are often GABAergic and therefore inhibitory

Cellular Neurobiology (5 decks)

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