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PHPY 301 > Lec 12 > Flashcards

Lec 12 Flashcards

1
Q

Chemical transmission Steps: What is the first step of chemical transmission?

A

neurotransmitter molecules are packages into the synaptic vesicles. Specific transport proteins in the vesicle membrane use the energy of H+ gradient to energize uptake of the neurotransmitter in the vesicle

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2
Q

Chemical transmission Steps: What happens following the release of quanta of neurotransmitter molecules into the synaptic cleft?

A

the neurotransmitter molecules diffuse across the synaptic cleft and bind to the specific receptors on the membrane of the post synaptic cell.

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2
Q

What type of synapse can be reciprocal ?

A

electrical synapse (connexon)

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3
Q

Where, in a neuron, is the Action potential threshold the lowest?

A

axon hillock - so that an AP can take place

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3
Q

An instantaneous transmission time with no delay occurs with what type of protein?

A

connexon

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4
Q

The length constant is useful in measuring what?

A

how far a passive signal can travel

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5
Q

the decay of a passive response is due to what term?

A

cable properties

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5
Q

consequences of demyelination Total blockade is described as…

A

no action potentials or spikes are propagated as a result of demyelination.

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5
Q

Most ion channels consist of what range of subunits?

A

4-6 in rosette

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5
Q

Linked chemically or electrically? cardiac cells

A

electrically

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6
Q

What type of neuron has a slowly accumulating K+ current ?

A

small pyramidal neuron

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7
Q

“saltatory” transmission is permitted by…

A

intermittent myelination or nodes of ranvier between myelin sheath

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7
Q

the high density of current in the nodes of ranvier results in…

A

generation of an action potential.

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8
Q

Linked chemically or electrically? glia

A

electrically

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9
Q

Cells can be linked through what two types of synapses ?

A

chemical and electrical

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10
Q

Ca2+ activated K+ currents underlying the sAHP is an example of what type of neuron?

A

small pyramidal neuron

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10
Q

in a dendrogram, the various subtypes of connexins are named according to their….

A

molecular mass. Cx32 = ~32 kDa

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11
Q

an active zone is defined as…

A

the currents flow at one instant in time, as a result of an action potential.

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11
Q

The termination of a chemical transmission can occur by what 3 processes?

A
  1. enzymatic destruction of neurotransmitter 2. uptake of transmitter into the presynaptic nerve terminal or into other cells by Na-dependent transport systems 3. diffusion of the transmitter molecules away from the synapse
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13
Q

What type of neuron displays spike frequency adaptation?

A

small pyramidal neuron

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14
Q

What are the 2 types of potentials associated with a graded response?

A

receptor potential, synaptic potential

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15
Q

If a membrane is less leaky, what will happen to the length constant?

A

increase in length constant

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15
Q

Active zones or nodes between myelinated areas of an axon jump from node to node. This is known as a _______ manner.

A

“saltatory”

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15
Q

What happens to the current density of the membrane of an axon when partial myelination or demyelination occurs?

A

current density is greatly reduced

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15
Q

A chemical metabotropic synapse contains what type of membrane protein?

A

receptor/Gprotein

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15
Q

In a dendrogram, what two connexin gene subunits are similar in rats and humans?

A

cx32 and cx43

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16
Q

Which type of synapse has second messengers?

A

metabotropic (gprotein) chemical synapse

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17
Q

Chemical transmission Steps: What happens following the influx of Ca into the presynaptic terminal?

A

Increase in Ca concentration triggers the fusion of synaptic vesicles with the presynaptic membrane. As a result , quanta of transmitter molecules are released into the synaptic cleft

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18
Q

consequences of demyelination Ectopic impulse generation is described as..

A

even though there is no input in the proximal portion of the axon, action potentials arise spontaneously beyond the lesion. Causing unwanted AP

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19
Q

Where are Na channels most concentrated in a neuron?

A

axon hillock and nodes of ranvier

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20
Q

consequences of demyelination: decreased velocity is due to…

A

decreased velocity is due to progressively longer delays in train action potential spikes as a result of demyelination

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21
Q

If an excitatory cell is hyperpolarized by a large amount , the result is…

A

a corresponding negative current that decays with time.

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22
Q

Chemical synapses should be considered a ________ pathway for signal propagation that can be modulated by ______________ chemical communication between two interacting cells.

A

unidirectional, bidirectional

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23
Q

How many connexin in a full function gap junction?

A

12 connexin = 2 connexon= 1 gap junction

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24
Q

There is no delay in propagation of action potentials when what is present in the neuron?

A

Myelin sheath

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25
Q

Nicotinic ACh receptor channels are oligomeric and are known as a ….

A

hetero-oligomer Pentamer (5 subunits)

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26
Q

inactive zones are …

A

neighbours to active zones, and can be depolarized by outward currents

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28
Q

time constant is equal to what?

A

Membrane Resistance * membrane capacitance

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29
Q

electrical synapse contain what membrane protein?

A

connexon

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31
Q

What type of neuron exploits the interplay between depolarizing and hyperpolarizing currents?

A

large pyramidal neuron

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31
Q

What happens after the binding of receptors in the postsynaptic cell?

A

The process is terminated by neurotransmitter breaks down and its subunits are taken up by the presynaptic terminal or by other cells OR diffuse away from the synapse.

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32
Q

Electrical synapse proteins contain how many subunits?

A

Connexon –> Hexamer (6 connexin or subunits)

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33
Q

A decrease in internal resistance of an axon, would cause the length constant to …

A

increase in length constant

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34
Q

What type of response decays with distance and time?

A

passive or graded response

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34
Q

A full functioning gap junction consists of how many connexon?

A

2 connexon = 1 gap junction

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36
Q

If there was a sequence of recording sites, and an action potential was initiated in the first site, what would the final action potential look like? (the axon is not myelinated)

A

it would be identical in amplitude and duration, however there would be an increasing delay. the passive portion of the action potential will still decay over time.

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36
Q

By nature, what type of synapses are inherently rectifying or polarized?

A

chemical synapses

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37
Q

A connexon is an oligomer, and is known as..

A

homo-oligomer Hexamer (6 connexin or subunits)

38
Q

When two cells are clamped and connected by a gap junction, what will be the comparison between the current in each cell?

A

the sum of the current through the gap junction and the membrane in cell 1 will be the mirror image of the current through the gap junction and the membrane in cell 2. (ohmic)

39
Q

Which type of neuron has only fast Na+ currents and delayed rectifier K+ curents?

A

inhibitory interneuron

40
Q

Connexon’s transmission speed is…

A

instantaneous

41
Q

What type of response does not decay with distance and time?

A

active response

42
Q

Chemical transmission Steps: What occurs after the vesicles have been filled with neurotransmitters?

A

An AP arrives at the presynaptic nerve terminal (due to Na and K voltage gated)

43
Q

How will our length constant be affected if we have an increase in the resistance of the internal conductor?

A

smaller length constant and greater loss of signal

44
Q

If the demyelination affects two adjacent axons, what can occur?

A

action potentials in one can cause action potentials to propagate in both directions in the adjacent axon. (crosstalk)

45
Q

Because of myelination, the current flowing down the axon is __________. (conserved or dissipating.)

A

conserved

46
Q

if an axon were to increase in its radius, what would happen to the corresponding length constant?

A

decrease length constant

47
Q

The agonist for Chemical synapse is ..

A

Acetylcholine (ACh)

49
Q

What disease is the result of impaired conduction of action potentials in nerve axons?

A

MS - Multiple sclerosis

50
Q

What is crosstalk?

A

When demyelination affects two adjacent axons, action potentials in one can cause actions potentials to propagate in both directions in the adjacent axon.

51
Q

What type of neuron can exhibit “rhythmetic bursting behaviour”?

A

large pyramidal neuron

52
Q

How will our length constant be affected if there is a greater membrane resistance or cable radius?

A

a greater length constant and less loss of signal

53
Q

Of the three types of neurons, which has the fastest firing rate?

A

inhibitory interneuron

54
Q

The two types of chemical synapse are:

A

ionotropic and metabotropic

54
Q

An instantaneous transmission time occurs in what type of synapse?

A

electrical

55
Q

Electrical synapse transmission speed is ..

A

instantaneous

55
Q

What kind of channel is formed by pores in each membrane that are 2.5 nm apart?

A

gap junction

56
Q

Individual Connexon hemichannels could be involved in what..

A

allowing the secretion of substances such as ATP and glutamate from glia to act on neighbouring neurons.

57
Q

What causes a gap junction to close?

A

increase in intracellular Ca

59
Q

What type of response dissipates over long distances?

A

graded response

60
Q

Voltage gated Na, K, Ca, and Ca release channels are oligomeric and are known as a …

A

pseudo-oligomer Tetramer (4 subunits)

62
Q

membrane capacitance is defined as ..

A

“distance between charges”

63
Q

an increase in membrane capacitance will cause the length constant to…

A

decrease in length constant

65
Q

What happens to the capacitance of the membrane of an axon when partial myelination or demyelination occurs?

A

capacitance increases

67
Q

Myelination of Neurons in the CNS is completed by what type of cells ?

A

oligodendrocytes

68
Q

Electrotonic current can exists in the presence of what type of membrane protein?

A

Connexon channels, create gap junctions for the easy passage of small ions and molecules

70
Q

In a myelinated axon, current only flows where?

A

the nodes of ranvier

71
Q

if an excitatory cell is depolarized by a large amount the result is..

A

if the threshold is reach or surpassed, an all or nothing action potential will initiate and there will be no decay with time.

72
Q

In a receptor activated by ACh and contains Gprotein receptors, what is the transmission time?

A

seconds to minutes

74
Q

Where is the most likely trigger point in a neuron?

A

Highest concentration of Na channel - axon hillock or initial segment.

76
Q

What happens to the resistance of the membrane of an axon when partial myelination or demyelination occurs?

A

decreased resistance

77
Q

The size and shape of a “passive response” due to what 2 things?

A

is due to: 1. Ohm’s law (V= IR or current amplitude * resistance) 2. and the size of cell capacitance.

78
Q

Which is more efficient? Myelinated or unmyelinated axon?

A

Myelinated.

79
Q

A half gap junction channel, or a Connexon is made up of how many connexins?

A

6 connexin = 1 connexon (half channel)

80
Q

A decrease in membrane capacitance will cause the length constant to…

A

increase in length constant

82
Q

If an axon were to get small or have a decrease in radius, what would happen to the corresponding length constant?

A

increase in length constant

83
Q

A synapse that contains connexon can be reciprocal (equally efficient in both directions) or efficient in only a single direction. The second scenario is known as ..

A

rectifying (one direction only)

85
Q

Which type of neuron is star shaped?

A

inhibitory interneuron

86
Q

Chemical transmission Steps: What happens following the arrival of an AP in the presynaptic terminal?

A

depolarization opens the voltage-gated Ca2+ channels which allows Ca to enter the presynaptic terminal.

88
Q

What is the speed of transmission in a chemical ionotropic synapse?

A

~1ms delay

89
Q

In a dendrogram, the degree of difference between two connexins is determined by what?

A

the summed length of the horizontal line segments connecting two connexins.

91
Q

Myelination of Neurons in the PNS is completed by what type of cells?

A

Schwann cells

92
Q

What is the speed of transmission in a chemical metabotropic synapse?

A

seconds to minutes

93
Q

Under what 2 conditions can an inactive zone fire its own action potential after being activated by an adjacent active zone?

A
  1. If the unactivated zone is not in absolute refractory period 2. if the stimulus (current) is great enough to overcome the threshold
94
Q

consequences of demyelination Increased mechanosensitivity-ectopic action potentials are described as..

A

arise by mechanical stimulation, causing unwanted firing of AP.

95
Q

Ion channels that are made up of identical distinct subunits are called..

A

homo-oligomers

96
Q

A neuron with a longer length constant (lambda) will have what degree of voltage-change spread?

A

a longer length constant = farther down the axon a voltage change can spread. (greater)

98
Q

What disease is the result of demyelinated axons ?

A

MS - Multiple sclerosis

99
Q

Why doesn’t current flow through the inter-nodal (myelinated) membrane ?

A

high resistance of myelin

100
Q

What are the 5 consequences of demyelination?

A

1.decreased velocity 2. frequency-related block 3. total blockade 4. ectopic pulse generation 5. increased mechanosensitivity-ectopic action potentials

101
Q

What are three neuron types?

A

inhibitory interneuron small pyramidal large pyramidal

101
Q

Where , in a neuron, is the Action potential threshold the highest? - dendrites - soma -axon hillock

A

dendrites (-35mV)

102
Q

can cells connected by a gap junction propagate an AP?

A

not identically, there is dissipation of current density and amplitude drops.

103
Q

Define “the greater the stimulus, the greater the voltage response”

A

graded response

104
Q

what is the length constant? (lambda )

A

determines how far the electronic spread of a local change in membrane potential is able to influence neighbouring regions of membrane.

105
Q

What type of neuron has its firing rate regulated by A-type K+ currents?

A

inhibitory interneuron

106
Q

Ion channel that are made up of distinct subunits that are homologous but not identical are called..

A

hetero-oligomers

107
Q

How does Myelination affect the speed of a neuron transmission ?

A

by increasing membrane resistance and decreasing the membrane capacitance.

109
Q

Ion channels that are made up of distinct subunits that are repetitive sub-unit like domains within a single polypeptide are called …

A

pseudo-oligomers

110
Q

If a membrane is less leaky, what will happen to the membrane resistance?

A

increase in membrane resistance

111
Q

A chemical ionotropic synapse contains what type of membrane protein?

A

receptor/channel protein

112
Q

What happens to the length constant (lambda) of the membrane of an axon when partial myelination or demyelination occurs?

A

length constant decreases.

113
Q

Electrical synapse cells can function as a network known as :

A

syncytium

114
Q

The generation of unwanted action potentials in demyelination are called? (2 consequences)

A
  1. ectopic pulse generation 2. increased mechanosensitivity-ectopic action potentials
115
Q

Fast Na currents and delayed rectifier K+ currents have their firing rate regulated by what type of current?

A

A-type K+ current

116
Q

Because axon current is conserved by myelinated portions, the current density in nodes is …

A

very high current density in nodes

117
Q

What type of synapse can be reciprocal or rectifying? which is Ohmic? (linear relationship)

A

reciprocal and reciprocal is ohmic

118
Q

consequences of demyelination frequency-related block is described as…

A

does not pass high frequency trains, as a result some of the spikes are missing distally.

119
Q

If an excitatory cell is depolarized by a small amount the result is…

A

a corresponding small positive current that decays with time

PHPY 301 (23 decks)

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