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PHGY 209 > Nerve/Synapse > Flashcards

Nerve/Synapse Flashcards

1
Q

of neurons in nervous system

A

100 billion

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2
Q

Neurons are _________ cells

A

Electrical

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3
Q

Communications between neurons take place at sites known as

A

At specialized sites called synapses

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4
Q

Neural networks are (simple/complex)

A

Complex

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5
Q

of synapses

A

Hundreds of trillions

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6
Q

Neurons come in an small/enormous range of shapes and sizes

A

Enormous

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7
Q

Dendrites

A

Antenna
Receives input
Synapses occur

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8
Q

Cell Body (soma)

A

Keeps neurons alive
Nucleus
DNA
Protein synthesis

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9
Q

Axons

A

Extend from neurons to brain
Propagate signals
Few millimeters to more than a meter

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10
Q

Information moves along the ___

A

Axon

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11
Q

Resting Membrane Potential

A

Difference in charge between the inside and outside of the cell
Created by concentration gradient

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12
Q

At rest, the neuronal membrane is highly permeable to __

A

K+

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13
Q

At rest, the neuronal membrane is less permeable to

A

The other physiological ions

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14
Q

Where do K+ ions leak to?

A

Out of cell

Down the concentration gradient

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15
Q

Inside/outside: large concentration of k+

A

Inside

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16
Q

Inside/outside: low concentration of k+

A

Outside

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17
Q

What creates the electrical gradient?

A

Accumulation of unpaired negative ions after sodium leaks

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18
Q

What does electrical gradient result in?

A

Pull K+ ions back into the cell

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19
Q

When chemical and electrical gradients are equal, the system is _________

A

At equilibrium

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20
Q

Membrane potential at equilibrium is described by the _____ equation which is ….

A

Nernst equation

Eion= (2.3RT/zF)(log(ion/ion)

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21
Q

Ek (equilibrium potential for K+)

A

-90 mV

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22
Q

The resting permeability to K+ is caused by

A

Leak channels

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23
Q

Leak channels

A

Proteins that form K+ selective pores through the membrane

Open at the resting membrane potential

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24
Q

Why is the resting membrane potential more positive than Ek

A

Due to the small inward leak of Na+, which pushes the membrane slightly toward E Na

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25
Q

Membrane potential is determined by

A

concentration gradients and relative permeabilities of the membrane to different physiological ions

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26
Q

Concentration gradients do/do not change much

A

do not

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27
Q

Pemeabliities can/cannot change rapidly and dramatically

A

can

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28
Q

What is the dominant permeability at rest

A

potassium - Ek

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29
Q

What makes the greatest contribution to the membrane potential

A

dominant permeability

potassium at rest

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30
Q

Sodium-potassium pump

A

Pumps sodium out and potassium in against their concentration gradient

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31
Q

Sodium-Potassium uses energy produced

A

by ATP hydrolysis

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32
Q

How are sodium and potassium gradients maintained

A

by the sodium-potassium pump

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33
Q

Axons

A

propagate information from one region of the nervous system to another

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34
Q

Axons transport information by

A

electrical impulses called action potentials

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35
Q

Action potentials start at ________ propagate down _________ to ________

A

Action potentials start at the initial segment of the axon propagate down the length of the axon to the presynaptic terminals

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36
Q

Transient depolarizing spike that moves down the axon

A

Actional Potential

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37
Q

At the action potential peak, the membrane potential approaches the potential of

A

E of NA

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38
Q

Occurs when the membrane potential depolarizes to a threshold level

A

initiation of action potential

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39
Q

Threshold

A 
is determined by the properties of ion channels in the axon membrane
especially a class of channels called voltage-gated sodium channels
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40
Q

sodium ions flowing into the cell through voltage-gated sodium channels causes

A

The depolarizing phase of the action potential

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41
Q

Three critical properties of voltage-gated sodium channels

A

1) They are closed at the resting membrane potential, but open when the membrane depolarizes
2) They are selective for Na+
3) The open channel rapidly inactivates, stopping the flow of Na+ ions

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42
Q

Three sodium channel states

A

closed, open, inactivated

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43
Q

T/F: The rising phase of the action potential is a regenerative process

A

T

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44
Q

Depolarization of the membrane to threshold activates

A

a small fraction of sodium channels, which further depolarizes the membrane, resulting in activation of more sodium channels and so forth

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45
Q

The positive feedback mechanism results very (slowly/rapidly) in …

A

rapidly

  • maximal activation of sodium channels,
  • a large sodium influx
  • depolarization of the membrane from the resting level to a new level, near Ena
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46
Q

Inactivation of the mechanism results in

A

termination of the sodium influx, causing the membrane to relax back to the original resting level

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47
Q

Which density is greater: voltage-gated sodium channels or leak potassium channels

A

voltage-gated sodium channels

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48
Q

T/F: At the peak of the actional potential, the K+ permeability swamps the resting permeability for Na+

A

F: At the peak of the actional potential, the Na+ permeability swamps the resting permeability for K+

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49
Q

2 factors contributing to the falling phase of the action potential

A

sodium channel inactivation

delayed activation of voltage-gated potassium channels

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50
Q

What happens when the neuron is firing a lot of action potentials?

  • sodium and potassium gradients
  • pumps
A
  • sodium and potassium gradients run down faster

- the pumps have to keep up with neuronal activity

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51
Q

Action potential propagation is caused by

A

spread of electrotonic currents from the site of the action potential, which excited adjacent regions of axion

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52
Q

Action potential propagation is self-regulating/terminating

A

Action potential propagation is self-regulating

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53
Q

Why does the action potential not move back?

A

The sodium will not re-excited
Not able to be activated for a small amount of time then returns to the closed state
inactivation of sodium channel

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54
Q

What happens to sodium channels after an action potential

A

for a few milliseconds, sodium channels are inactivated and the membrane is completely unexcitable

55
Q

Absolute refractory period

A

The sodium channels are inactivated and the membrane is completely unexcitable

56
Q

Relative refractory period

A

Longer period where the voltage gated potassium channels are open and the membrane potential overshoots its resting level
axons are less excitable and is unlikely to fire an action potential

57
Q

Neurons send information by means of the ______ and ______ of ______ ________

A

frequency and pattern of action potentials

ex. Transduction of pressure on skin surface into neuronal activity

58
Q

T/F: Each action potential is an all-or-none event.

A

T

59
Q

Molecular targets for naturally occurring neurotoxins

A

Sodium channels

60
Q

Tetrodotoxin

A

extremely potent inhibitor of sodium

blocks flowing of sodium

61
Q

Batrachotoxin

A

a powerful sodium channel hibitor,

appears to bind to an open form of the sodium channel, preventing the closing of the channel

62
Q

Tetrodotoxin, batrachotoxin, pyrethroid insecticides as well as scorpion and anemone toxins can modulate

A

Sodium channels

63
Q

Sodium channels are blocked by therapeutically important drugs for example:

A

local anaesthetics and some antiepileptic agents.

Local anesthetics
Lidocaine 
Benzocaine
Tetracaine 
Cocaine

Antiepileptics
Phenytoin (Dilantin) Carbamazepine (Tegretol) Lamotrigine

64
Q

required for survival, especially in situations that require rapid, reflexive responses

A

rapid propagation of action potentials

65
Q

propagation rate of the action potential is proportional to

A

axon diameter

66
Q

How squids solved the problem of how to send fast-moving signals

A

making giant axons, 1000 times fatter than our axons

67
Q

Myelin is formed by

MATCH:

  • Schwann cells
  • Oligodendrocytes
  • PNS
  • CNS
A

Schwann cells (in the PNS) or oligodendrocytes (in the CNS).

68
Q

Myelin

A

the insulator that is wrapped around the axon to make a small axon with high conduction velocity

69
Q

Myelin wraps around the

A

axon

70
Q

as an electrical insulator, enabling charge

to travel farther and faster down the axon

A

Myelin

71
Q

nodes of Ranvier

A

periodic gaps in myelin

72
Q

Nodes of Ranvier sodium channel concentration… why?`

A

These regions of bare axon contain very high concentrations of voltage-gated sodium channels, enabling the signal to be regenerated at periodic interval

73
Q

Multiple sclerosis is caused by

A

loss of myelin

Demyelinated region

74
Q

White matter

A

corresponds to regions of the brain and spinal cord that contain mostly myelinated axons

75
Q

Gray matter

A

comprises cell bodies, dendrites and synapses

76
Q

Three main types of synapses

A

Axondendritic
Axosomatic
Axoaxonic

77
Q

A single neuron is able to make synapses with many other neurons by

A

its branching axon

78
Q

Two axodendritic synapses

A

spine and shaft synapse

79
Q

What occurs on the presynaptic Terminal

A

Activation of voltage-gated calcium triggers neurotransmitter release

80
Q

What occurs on the postsynaptic spine

A

Ligand-gated ion channels are postsynaptic receptors for transmission at brain synapses

81
Q

Steps of chemical synaptic transmission

  1. The action potential invades
  2. Calcium channels … resulting in ….
  3. Synaptic vesicles fuse with … releasing … into ….
  4. … diffuses across the cleft and activates …. in the …. membrane
A
  1. The action potential invades the presynaptic terminal.
  2. Calcium channels open, resulting in Ca2+ influx into the terminal
  3. Synaptic vesicles fuse with the presynaptic membrane, releasing the transmitter into the synaptic cleft.
  4. Transmitter diffuses across the cleft and activates receptors in the postsynaptic membrane.
82
Q

Synaptic transmission: The action potential invades the

A

presynaptic terminal

83
Q

Synaptic transmission: Calciums channels ______ resulting in Ca2+ influx _____ the terminal

A

Calcium channels open, resulting in Ca2+ influx into the terminal

84
Q

___________ fuse with the presynaptic membrane releasing the ______ into the ________

A

Synaptic vesicles fuse with the presynaptic membrane, releasing the transmitter into the synaptic cleft.

85
Q

_______ diffuses across the cleft and activates receptors in the postsynaptic membrane.

A

Transmitter diffuses across the cleft and activates receptors in the postsynaptic membrane.

86
Q

What occurs at the active zone

A

Calcium-dependent fusion of a synaptic vesicle at an active zone

87
Q

The postsynaptic response to neurotransmitter is either an ______ or _______

A

excitatory postsynaptic potential (EPSP)

inhibitory postsynaptic potential (IPSP)

88
Q

The depolarization of the postsynaptic membrane

A

excitatory postsynaptic potential

89
Q

hyperpolarization of the postsynaptic membrane

A

inhibitory postsynaptic potential

90
Q

The main excitatory neurotransmitter in the brain

A

glutamate

91
Q

Rapid excitatory transmission at synapses is primarily due to the actions of glutamate on two types of ionotropic glutamate receptors:

A

AMPA receptors

NMDA receptors

92
Q

AMPA receptors and NMDA receptors are examples of

A

ionotropic receptors

93
Q

ionotropic receptors

A

are ion channels, that open in response to binding of small molecules (e.g. neurotransmitters) to receptor sites on their external surfaces.

94
Q

_____ receptors are responsible for the “fast” EPSP at excitatory synapses.

A

AMPA receptors are responsible for the “fast” EPSP at excitatory synapses.

95
Q

What occurs in AMPA receptors

A

Glutamate binds to AMPA, allowing Na+ to flow into the postsynaptic spine

96
Q

EPSP Characteristics

A

The EPSP is a small, transient depolarization of the postsynaptic spine

97
Q

The depolarization caused by a single EPSP is ____ millivolts

A

> a few millivolts

98
Q

The depolarization caused by a single EPSP lasts

A

20 msec

99
Q

Can the depolarization from a single EPSP depolarize the axon

A

No, the depolarization caused by a single EPSP too small to depolarize the axon initial segment to threshold

100
Q

How many EPSPs must sum at the initial segment to initiate an action potential

A

50 to 100 EPSPs

101
Q

The simultaneous EPSPs can come from either

A

multiple synapses acting in synchrony and/or from individual synapses, activated at high frequencies

102
Q

NMDA Receptors key properties

A

– At resting membrane potentials, the pore is blocked by Mg2+;
depolarization expels Mg2+, enabling the pore to conduct.
– The open pore is highly permeable to Ca2+ as well as monovalent cations.

103
Q

At -70 mW almost all the synaptic current at an excitatory glutamate synapse is carried through

A

AMPA receptors

104
Q

If the postsynaptic membrane is depolarized, a substantial current flows through

A

NMDA receptors

105
Q

Highly active excitatory synapses become stronger and involve NMDA receptors

A

Synaptic plasticity

106
Q

model of synaptic plasticity

A

Long-term potentiation (LTP)

107
Q

High-frequency activity depolarizes the postsynaptic spine, which affects the NMDA receptors by removing the

A

Mg2+ block of NMDA receptors and enabling them to conduct Ca2+

108
Q

EPSP/IPSP are larger, hours after induction of LTP.

A

EPSP

109
Q

What is toxic to neurons

A

High concentrations of glutamate

110
Q

Excitotoxicity

A

High concentrations of glutamate are toxic to neurons

involves calcium influx through NMDA receptors

111
Q

______ contributes to neuronal degeneration after stroke and in some neurodegenerative diseases

A

Excitotoxicity

112
Q

The main inhibitory neurotransmitter in the brain

A

is y-aminobutyric acid (GABA)

113
Q

The postsynaptic receptor responsible for the IPSP

A

is called the GABAA receptor

114
Q

The GABA receptor is an _______ receptor

A

ionotropic receptor

115
Q

Activation of the GABAA receptor causes an influx of __ ions which __ polarizes the __ synaptic membrane

A

Activation of the GABAA receptor causes influx of Cl-, which hyper-polarizes the postsynaptic membrane.

116
Q

A typical cortical neuron receives ________ of synaptic inputs

A

thousands of synaptic inputs, some excitatory, others inhibitory

117
Q

Excitatory inputs tend to be located on

A

dendritic spines

118
Q

inhibitory inputs are often clustered on or near

A

the cell soma, where their inhibitory effect is maximal

119
Q

Whether or not a neuron fires an action potential at any given moment depends on

A

the relative balance of EPSPs and IPSPs

120
Q

T/F The output of the neuron the all-or-none firing of action potentials down the axon

A

T

121
Q

What type of receptors are G-protein coupled receptors, GPCRs

A

Metabotropic receptors

122
Q

Glutamate synapses have ionotropic receptors (AMPA and NMDA receptors) or metabotropic glutamate receptors (mGluR’s) or both

A

both ionotropic receptors (AMPA and NMDA receptors) and metabotropic glutamate receptors (mGluR’s)

123
Q

What generates a chemical signal (second messenger) inside the postsynaptic spine?

A

Activation of mGluR’s by glutamate

124
Q

2nd messengers activate

A

a range of cellular proteins, including ion channels, protein kinases and transcription factors

125
Q

Glutamate and GABA activate

A

both ionotropic and metabotropic receptors

126
Q

Many types of neurotransmitters interact mainly, or entirely with

A

metabotropic receptors

127
Q

dopamine, serotonin and norepinephrine are examples of

A

neuromodulators

128
Q

They are not directly involved in the fast flow of neural information, but modulate global neural states, influencing alertness, attention and mood.

A

neuromodulators

129
Q

Neurons that release neuromodulators often originate in

A

small brainstem or midbrain nuclei

130
Q

The axons of the neurons that release neuromodulators project ….

A

diffusely throughout the brain

131
Q

Important targets for a wide range of drugs

such as antidepressants

A

Neuromodulator systems

132
Q

The prozac antidepressants affects

A

serotonergic transmission

133
Q

antidepressants such as amphetamines, cocaine and other stimulants typically affect … (which transmitters)

A

dopamine and norepinephrine transmission

PHGY 209 (10 decks)

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