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PHGY 209 > Nerve & Synapse > Flashcards

Nerve & Synapse Flashcards

1
Q

What makes up the CNS

A

The brain and spine

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2
Q

What is the peripheral nervous system?

A

Sensory neurons, motor neurons

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3
Q

What is the autonomic nervous system?

A

The autonomic nervous system is a component of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal

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4
Q

What is the enteric nervous system?

.

A

The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract

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5
Q

of neutrons in nervous system

A

100 billion

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6
Q

Neurons are _________ cells

A

Electrical

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7
Q

Communications between neurons take place at sites known as

A

At specialized sites called synapses

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8
Q

of synapses

A

Hundreds of trillions

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9
Q

Do neurons have a specific morphology?

A

No, neurons come in an enormous range of shapes and sizes

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10
Q

What are the characteristic structures of the neurons?

A

Cell body (soma), dendrites, a single axon, presynaptic terminal

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11
Q

What are the things sticking off of the soma called and what is their use?

A

Generic term is processes, aka dendrites, they act like antennas for the neuron

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12
Q

What is the soma’s role

A

Keeps neurons alive
Nucleus
DNA
Protein synthesis

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13
Q

What is the Axons role?

A

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

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14
Q

Information moves along the ___ and is received by neurons at the ____ through the ____

A

Axon, dendrites, synapses

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15
Q

Describe the flow of information

A

Dendrites, cell body (soma), axon, next neuron (dendrites)

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16
Q

Resting Membrane Potential

A

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

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17
Q

At rest, the neuronal membrane is highly permeable to __ and less permeable to ____

A

K+, the other physiological ions

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18
Q

Why is the resting membrane potential important for cells in general?

A

It is a form of potential energy, starting point for the electrical properties of neurons

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19
Q

Where do K+ ions leak to?

A

Out of cell

Down the concentration gradient

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20
Q

The concentration of ____ inside the cell is high and ___ outside the cell

A

k+, low

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21
Q

What creates the electrical gradient?

A

Accumulation of unpaired negative ions after sodium leaks

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22
Q

What creates the electrical gradient?

A

Accumulation of unpaired negative ions after sodium leaks

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23
Q

What does electrical gradient result in?

A

Pull K+ ions back into the cell

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24
Q

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

A

At equilibrium

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25
Q

Membrane potential at equilibrium is described by the

A

Nernst equation

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

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26
Q

Why is the membrane permeable to K but not other physiological ions?

A

Because of Potassium leak channels (proteins that form pores in membrane for K+)

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27
Q

____ makes the inside of the cell less negative, and ____ makes the inside of the cell more negative

A

depolarization and hyper-polarization

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28
Q

Ek (equilibrium potential for K+)

A

-90 mV

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29
Q

Why does the membrane potential never quite get to Equilibrium K?

A

Because Na leaks in, adding positive charges, keeping it above -90 mV

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30
Q

Leak channels are ___

A

Proteins that form K+ selective pores through the membrane

Open at the resting membrane potential

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31
Q

What is membrane potential determined by?

A

Concentration gradients and relative permeability of membrane to different physiological ions

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32
Q

What maintains the sodium and potassium gradient and what is its source of Energy?

A

Sodium Potassium Pump, uses energy produced by ATP hydrolysis to pump sodium out and potassium in against their concentration gradients

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33
Q

Action potentials are ___ ____ that carry information through the Axons

A

Electrical impulses

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34
Q

Describe the general pattern of action potentials?

A

Action potentials usually start at the initial segment of the axon and then propagate down the length of the axon to the presynaptic terminals (like a wave)

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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

What is an action potential?

A

is a transient depolarizing spike that moves down the axon

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37
Q

What determines the threshold level of an action potential?

A

The threshold 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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38
Q

The AP is initiated when the ____ ___ depolarizes to a ___ level

A

membrane potential, threshold

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39
Q

The depolarizing phase of the action potential is caused by

A

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

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40
Q

What are the 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 inactives, stopping the flow of Na+ ions

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41
Q

Where are voltage-gated sodium channels found, and what are the three states they can be found in?

A

closed, open, inactivated

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42
Q

___ channels are found everywhere on the neuron

A

K+ leak channels

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43
Q

What causes the sodium channels to reset?

A

The membrane potential has to reset to -70 mV

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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

What can be said of the amount of Na channels and Leak K channels on a particular segment of axon?

A

There are much more Na+ channels, so at peak action potential, the Na+ permeability swamps the resting permeability of K+ (which is why voltage shoots up)

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46
Q

At the peak of the actional potential the ___+ permeability ____ the resting permeability for __+

A

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

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47
Q

When do K gates channels open?

A

During the decline of the action potential, making it come down much faster as K moves out by leak channels and gated channels

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48
Q

What are the two factors that contribute to falling phase of AP

A

sodium channel inactivation

delayed activation of voltage-gated potassium channels

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49
Q

How do action potentials propagate down the axon?

A

It is caused by the spread of electrotonic currents from the site of the action potential, which excites adjacent regions of axon (+30 mV of AP excites -70 of rest of neuron)

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50
Q

Action potential propagation is self-regulating/terminating

A

Action potential propagation is self-regulating

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51
Q

Why doesn’t the AP move backwards on the axon?

A

Because of the inactivated Na+ Channels

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52
Q

What is the absolute refractory period?

A

The Na channels are inactivated and the membrane is completely unexcitable. While the K channels are open, the membrane potential overshoots its resting level.

53
Q

After an AP ___ ___ are inactivated and the membrane is ____

A

Sodium channels, unexcitable

54
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 (-70 mV)

55
Q

Neurons send information by means of the

A

frequency and pattern of action potentials

56
Q

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

A

T

57
Q

Molecular targets for naturally occurring neurotoxins

A

Sodium channels (AP cannot reach)

58
Q

Sodium channels can be modulated by

A

tetrodotoxin, batrachotoxin, pyrethroid insecticides as well as scorpion and anemone toxins

59
Q

What is slow pain conducted by (like after burning your hand on stove top)?

A

They are called c-fibers (0.5-2.0 meters/sec)

60
Q

propagation rate of the action potential is proportional to

A

Axon diameter (The larger the diameter the faster the AP can move)

61
Q

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

A

making giant axons, 1000 times fatter than our axons

62
Q

How do vertebrate neurons solve the problem of small axons with high conduction velocity?

A

The axon are wrapped by an insulator called myelin (formed by Schwann cells and oligodendrocytes)

63
Q

What is the main responsibility of the Myelin?

A

Myelin acts as an electrical insulator, enabling charge to travel farther and faster down the axon

64
Q

Where is myelin made in the CNS and PNS respectively?

A

In CNS -> oligodendrocytes

In PNS -> Schwann cells

65
Q

What happens to signals in unmyelinated axons?

A

The signal leaks out and fades away over short distances

66
Q

nodes of Ranvier

A

periodic gaps in myelin

67
Q

What is usually found at nodes of Ranvier and why is it important?

A

Nodes of Ranvier has high concentration of voltage gated sodium channels, allowing the signal to REGENERATE at periodic intervals

68
Q

Multiple sclerosis is caused by

A

loss of myelin

Demyelinated region

69
Q

What myelin forming cells are affected by MS?

A

Oligodendrocytes (impacts CNS)

70
Q

What is white matter?

A

Regions of the brain and spinal cord that contain mostly myelinated axons.

71
Q

Gray matter

A

comprises cell bodies, dendrites and synapses

72
Q

Three main types of synapses

A

Axondendritic

Axosomatic

Axoaxonic

73
Q

A single neuron may make synapses with many other neurons through

A

its BRANCHING axon

74
Q

What happens when an AP reaches a branch (fork) on an axon?

A

A full AP goes down each branch

75
Q

Two axodendritic synapses

A

spine and shaft synapse

76
Q

What are the components of the synapse?

A

The presynaptic terminal, the synaptic cleft, and the postsynaptic spine

77
Q

What occurs on the presynaptic Terminal

A

Activation of voltage-gated calcium triggers neurotransmitter release

78
Q

What occurs on the postsynaptic spine

A

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

79
Q

What are the specialized regions that appear darker on the electron micrograph of the postsynaptic spine?

A

Postsynaptic density

80
Q

Fundamental steps of chemical synaptic transmission

A
  1. The action potential invades the presynaptic terminal. Calcium channels open, resulting in Ca2+ influx into the terminal
  2. Synaptic vesicles fuse with the presynaptic membrane, releasing the transmitter into the synaptic cleft.
  3. Transmitter diffuses across the cleft and activates receptors in the postsynaptic membrane.
81
Q

How do the vesicles release the neurotransmitter into the synaptic cleft?

A

The vesicle (which is made from phospholipid), fuse to the membrane and releases contents

82
Q

Transmitter diffuses across the ______ and activates _____ in the _________ _____

A

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

83
Q

What occurs at the active zone

A

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

84
Q

The postsynaptic response to neurotransmitter is either an ______ or _______

A

excitatory postsynaptic potential (EPSP)

inhibitory postsynaptic potential (IPSP)

85
Q

What occurs at the active zone

A

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

86
Q

excitatory postsynaptic potential

A

which depolarizes the postsynaptic membrane

87
Q

inhibitory postsynaptic potential

A

hyperpolarizes the postsynaptic membrane

88
Q

What does Botox do?

A

Botox chews up the proteins that are part of vesicles fusion process, therefore muscles cannot get activated (no neurotransmitters)

89
Q

What is the main excitatory neurotransmitter in the brain?

A

Glutamate

90
Q

What glutamate receptors are activated when glutamate is released into the synaptic cleft?

A

AMPA and NMDA receptors

91
Q

What is meant by ionotropic receptors?

A

This means that they are ion channels, that open in in response to binding of small molecules (ie neurotransmitters) to receptor sites on their external surfaces

92
Q

Which receptors are responsible for the fast EPSP?

A

AMPA

93
Q

What occurs in AMPA receptors

A

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

94
Q

What does EPSP stand for and what is it?

A

Excitatory PostSynaptic Potential is a small, transient depolarization of the postsynaptic spine

95
Q

How long are EPSPs?

A

20 msec (have to have enough EPSPs to depolarize within this window)

96
Q

The depolarization caused by a single EPSP is ____ millivolts

A

> a few millivolts

97
Q

What happens after the depolarization caused by a single EPSP?

A

Nothing, it is too small to depolarization the axon initial segment

98
Q

How do EPSPs get around this to depolarize the initial segment?

A

From 50 to 100 EPSPs must sum at the initial segment to initiate an AP (they can come from multiple synapses acting in synchrony and/or from individual synapses (activated at high frequencies)

99
Q

The simultaneous EPSPs can come from either

A

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

100
Q

What are key properties of NMDA receptors?

A

At resting membrane potential, the pore is blocked by Mg2+ (depolarizing expels Mg2+, which allows pore to conduct)

The open pore is highly permeable to Ca2+ as well as MONOVALENT cations

101
Q

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

A

AMPA receptors

102
Q

What happens when excitatory synapses are highly active?

A

They become stronger (ie the EPSPs become larger).

103
Q

synaptic plasticity

A

Highly active excitatory synapses become stronger (i.e. the EPSPs become larger) and involve NMDA receptors

104
Q

Long-term potentiation (LTP)

A

is a model of synaptic plasticity

105
Q

High-frequency activity depolarizes the postsynaptic spine, resulting in the

A

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

106
Q

What is the high concentration of glutamate being toxic to neurons called?

A

Excitotoxicity

107
Q

Why is high concentration of glutamate toxic?

A

Too much calcium goes into Neuron -> neuron apoptosis

108
Q

What do neurons release when they die?

A

Release tons of glutamate, which in cases like strokes, kills surrounding neurons, even if they were not affected by the stroke

109
Q

The main inhibitory neurotransmitter in the brain

A

is y-aminobutyric acid (GABA)

110
Q

Where are inhibitory synapses found on the neighbouring neuron?

A

Shaft of dendrite

111
Q

Do neurons change roles during lifetime (ie excitatory to inhibitory)?

A

No

112
Q

What is the name of the postsynaptic receptor called for the IPSP?

A

GABA(a) receptor

113
Q

The GABA receptor is an _______ receptor

A

ionotropic receptor

114
Q

Activation of the GABA(A) receptor causes an influx of ___ which ….

A

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

115
Q

A typical cortical neuron receives

A

thousands of synaptic inputs, some excitatory, others inhibitory

116
Q

inhibitory inputs are often clustered on or near

A

the cell soma, where their inhibitory effect is maximal

117
Q

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

A

the relative balance of EPSPs and IPSPs

118
Q

What are metabotropic receptors (function + names)?

A

Activated by neurotransmitters, but do NOT form ION CHANNELS

G-protein coupled receptors, GPCRs

119
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)

120
Q

Activation of mGluR’s by glutamate relays a

A
  • chemical signal to the inside of the postsynaptic neuron

- generates a chemical signal (changes conformation), called a second messenger, inside the postsynaptic spine.

121
Q

What are some things secondary messengers can do?

A 
Active ion channels
Activate proteins (like protein kinase)
Activate transcription factors
122
Q

What are some examples of neurotransmitters that mainly, or entirely interact with metabotropic receptors?

A

Dopamine, Serotonin, norepinephrine, endorphins (neuromodulators, because they change global neural states, influencing alertness, attention and mood)

123
Q

neuromodulators

A

dopamine, serotonin and norepinephrine

neuropeptides such as endorphins

124
Q

What kind of effects do neuromodulators have?

A

Global, broad effects

125
Q

Where are neuromodulator neurons usually found, and how does their effect reach the entire brain?

A

Usually found in brain stem (or midbrain nuclei), and their axons (that branch A TON), go throughout the whole brain

126
Q

Neurons that release neuromodulators, axons project

A

diffusely throughout the brain

127
Q

Neuromodulator systems are important targets for a

such as

A

wide range drugs

antidepressants

128
Q

antidepressants such as Prozac affect

A

serotonergic transmission

129
Q

antidepressants such as amphetamines, cocaine and other stimulants typically affect

A

dopamine and norepinephrine transmission

PHGY 209 (3 decks)

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