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Neurobio I > Exam 1: Lectures 1-5 > Flashcards

Exam 1: Lectures 1-5 Flashcards

1
Q

Who allowed us to see the structure of the nervous system?

A

Golgi and Ramón y Cajal

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2
Q

Golgi stain

A

staining a neuron black by formation of silver chromate precipitate

  • aka Golgi technique
  • for the first time, allowed visualization of the cells of the brain
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3
Q

for nerve terminals @ the neuromuscular junction …

A

acetylcholine activates the axon

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4
Q

Reticular Theory

A

posited by Golgi, argues for one individual cell in the nervous system (everything is connected)

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5
Q

Neuron Doctrine

A

large network of cells

  • proved right by discovery of synaptic cleft
  • Golgi technique wasn’t enough to prove this
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6
Q

chemical signals

A

one cell to the other (using neurotransmitters), dominate neuro-activation

  • slight decay in time from one cell to another
  • involve presynaptic vesicles in presynaptic cell
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7
Q

Modern vindication of Golgi

A

“brainbow” technique: genetic labeling of neurons w/ dif. colors (up to 90 colors)

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8
Q

BQ: why do the neurons of the ctenophore not follow the neuron doctrine? (they instead show a continuous plasma membrane forming a syncytium)

A

could depend on where in the evolutionary tree you fall, ctenophores are not as evolutionary advanced as mammals or humans (their closest evolutionary relatives are jellyfish, which are newer and more neurologically advanced than them)

  • as you increase in complexity, you need more than just an interconnected network in order to process all the info and perform computations
  • could also be differences in synaptic strengths, even in a neural network that is entirely connected
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9
Q

cytoskeleton

A

gives neurons their overall shape

  • dense packing of microtubules (MT), actin, and neurofilaments, which are important for shape and movement
  • organelles and motor proteins are transported on MTs in each direction
  • organelles and motor proteins are transported on MTs in each direction
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10
Q

Classification of neurons

A

functional and morphological classification

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11
Q

Functional classification

A
  • Sensory neurons
  • Motor neurons
  • Interneurons
    – Relay (projection) neurons - typically excitatory
    – Local neurons (stay in vicinity) - typically inhibitory
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12
Q

Morphological classification

A
  • Unipolar neurons
  • Bipolar neurons
  • Multipolar
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13
Q

Glia

A

constitute roughly half of the cells of the central nervous system (CNS)

  • long-considered to be static bystanders to its formation and function
  • influence nervous system development from neuronal birth, axon specification, and growth (through circuit assembly and synaptogenesis)
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14
Q

Types of glial cells

A

microglia and macroglia

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15
Q

microglia

A
  • Primary immune cells in CNS (similar to peripheral macrophages in PNS)
  • Activated after injury or infection
  • Scavenging, phagocytosis, repair
  • Interact w/ multiple cell types of CNS and regulate multiple developmental and functional processes (Synaptic pruning, clearing apoptotic neurons, etc.)
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16
Q

Macroglia

A
  • Schwann cells
  • Oligodendrocytes
  • Astrocytes
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17
Q

Schwann cells

A

form myelin sheath (protective layer around axon) in PNS

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18
Q

Oligodendrocytes

A

individua neurons that form myelin sheaths in the CNS (which speed up nerve impulse conduction)

  • provide metabolic support to axons
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19
Q

Astrocytes

A

most abundant in CNS and have various functions

  • Star-shaped
  • Most numerous in glia
  • Provide nourishment to neurons, regulate ionic and neurotransmitter concentrations
  • Intimately connected to neuronal synapses (bi-directional crosstalk w/ neurons)
  • Can uptake key neurotransmitters at the synapse (intimately connected to neuronal synapses)
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20
Q

Functions of glial cells

A
  • Structural support
  • Form myelin sheath
  • Scavenge debris after cell death
  • Help neuronal signaling (e.g. uptake of neurotransmitters)
  • Buffer potassium concentrations at equilibrium
  • Guide neuron migration and axon outgrowth
  • Form blood-brain barrier
  • Release growth factors to nourish nerve cells
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21
Q

Defects in myelination can …

A

… lead to disease (seen in mice and humans)

  • Patients can have impaired gait and limb deformities
  • Most common inherited peripheral neuropathy (protein localities to Schwann cells)
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22
Q

ions

A

charged molecules that have passive affinities to reach an equilibrium

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23
Q

membrane potential, Vm

A

made up by charge separation across the neuronal membrane

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24
Q

diffusion

A

ions move from high concentration to low concentrations (PASSIVE)

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25
Q

Electrostatic force

A

ions are charged and will move in an electric field (voltage different) towards opposite polarity (PASSIVE)

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26
Q

The membrane is a powerful …

A

… insulator

  • Lipid bilayer has electrical capacitance (works as an electrical insulator to separate electrical charges on either side of it)
  • lipid bilayer is important to ionic flow across it
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27
Q

Resting membrane potential results from …

A

… the separation of charge across the cell’s membrane

  • Extracellular has excess of +
  • Intracellular has excess of -
  • Charge separation maintained by lipid bilayer (a barrier to ion diffusion)
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28
Q

Why is there a membrane potential at rest?

A

Don’t want to be constant in one state, i.e. can’t have the neuron constantly firing

  • dif. in neuron potential = problems w/ communication
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29
Q

Voltage clamp technique (1940s)

A

Wires inside of glass micropipettes connected to voltage amplifier and oscilloscope, oscilloscope records steady membrane potential of -65 mV for most neurons

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30
Q

Depolarization

A

Vm ↑

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31
Q

Hyperpolarization

A

Vm ↓

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32
Q

Repolarization

A

Vm ↓ after depolarization

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33
Q

An ideal model system to study neuronal membrane voltage is …

A

… the squid giant axon

  • Almost no one uses the model anymore, but was very helpful in the 1950s to lay the foundation for neuroscience
  • Very long axon, 1 mm in diameter
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34
Q

Extracellular and intracellular ionic concentrations

A
  • Potassium high on inside of neuron, low on outside
  • Sodium low on inside, high on outside
  • Potassium has high chemical drive to leave cell, sodium wants to get in (wants equilibrium)
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35
Q

Ions strive for _____ AND _____ across the lipid bilayer

A

chemical, electrical equilibrium

  • there is a tug of war between chemical and electrical drives, and when the forces are equal and opposite (no net flow of that ion), that’s the ion’s equilibrium potential
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36
Q

Nernst Equation

A

Ex = (RT)/(zF) * ln([X]o/[X]i)

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37
Q

Is there ever a time when the membrane potential moves towards the Na equilibrium potential?

A

During an action potential (when sodium flows into the cell)

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38
Q

Resting potential determined by the …

A

… proportions of dif. types of ion channels that are open, together w/ the value of their equilibrium potentials

  • resting membrane potential arises when things are not moving (everything is equal)
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39
Q

when only K+ channels are open

A

strong drive for sodium to get into neuron, this is quickly counterbalanced by potassium, which as sodium comes in, potassium goes out of neuron

-creates new membrane potential that is very close to the potential of potassium, b/c there are more potassium channels in the membrane than sodium channels which are also more likely to open (membrane is more permeable to potassium)

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40
Q

for permeability to multiple ions, there is a battle for control of the membrane

A

Ion gradients give rise to currents b/c they each want to be at their Nernst potential, and the one w/ the bigger conductance always win

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41
Q

Why is the resting membrane potential negative?

A
  • Leak channels (voltage independent channels, some for potassium, some for sodium), allows ions to slowly leak
  • Leakage through these K+ channels stabilizes the negative resting membrane potential
  • Anions that balance K+ inside cell cannot exit w/ K+, which leaves behind an excess of negative charge (anions used to be balanced w/ K+)
  • K2P (two-pore domain potassium) leak channels are outward rectifying (outward current flows more easily)
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42
Q

How to balance the K+ leak efflux?

A

Na+ leak channels, which allow sodium to leak inside neuron

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43
Q

Ionic concentration also initiated and maintained by …

A

… active transport

  • ~50% of neuron’s energy used to pump Na+ out and K+ in against their concentration gradients
  • Very slow process; pumps operate at speeds more than 10,000x slower than channels (ions typically flow through channels at a rate of 107 or 108 per second)
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44
Q

energy from ATP hydrolysis pumps …

A

… 3 Na+ ions OUT and 2 K+ ions IN against their electrochemical gradient

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45
Q

What effect does STR have on the resting membrane potential and why?

A

Makes resting membrane potential more positive, makes it closer to threshold which makes it easier to have APs

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46
Q

What effect does STR have on the relationship between current injection and depolarizing events (APs)? Why?

A

Increases frequency of APs b/c it inhibits the Na-K pump (only leakage is happening), so will slowly and slowly get more depolarized

  • active process is needed to balance the sodium and potassium leakage
  • this causes the neuron to fire more easily (easier to activate neuron), there are situations where you do not want this to happen (e.g. too much neurotransmitter could cause tremors, epilepsy, seizures, etc)
47
Q

GHK equation

A

Vm = (RT)/(F) * ln (permeability of K+ out, Na+ out, Cl- in)/(permeability of K+ in, Na+ in, Cl- out)

  • like Nernst, but takes into consideration permeability too
48
Q

resting membrane potential is generated due to 3 main factors

A
  • Uneven distribution of ions
  • Uneven permeability
  • Existence of ion pumps
49
Q

why neurons need ion channels

A
  • Plasma membrane is an insulator made of hydrophobic fatty acid tails that compose the lipid bilayer
  • There is a pore inside the ion channel that is water-filled, ion stays there
50
Q

Essential properties of ion channels

A
  • Proteins that place an aq. path through the hydrophobic (impermeable) membrane
  • Can support high rates of flow, up to 100 million ions per second (in single file)
  • Can be highly selective ford particular ions, e.g. potassium channels have a PK:PNa of 1000:1
  • Can always be open (leak channels) or gated in multiple ways
51
Q

What changed early views on ion channels?

A

Hill built on Hodgkin and Huxley’s initial diagrams w/ a drawing w/ pores and channels, later found a drosophila gene that encoded a potassium channel (Shaker)

52
Q

Molecular biology and recombinant DNA technology advanced the study of ion channels

A

Amino acid sequences are conserved, high level of conservation tells you that they must be important (when something works, you tend to see them over and over again)

53
Q

there are diverse ion channels for …

A

… diverse functions

  • lots of genes encoding K+ channels, 78 in total (compared to 27 total Na+/Cl- channel genes)
54
Q

opening/closing of ion channels

A

Most channels are gated (not just open), there needs to be a system so ions can flow

  • Conformational change in one region
  • General structural changes
  • Some channels have a blocking particle
  • Ligand gating
  • Phosphorylation gating (post-translational modification)
  • Voltage gating
    Stretch or pressure gating
55
Q

structure of the bacterial KcsA K+ channel

A

Doyle wanted to know how ions moved so quickly and have so much selectivity, so he keyed in on the selectivity factor: K+ stabilized by electrostatically favorable interactions w/ oxygen atoms (in the binding site)

  • water molecules are shed, so oxygen sticks out of the AA in the binding site, so weak interactions can then be formed w/ oxygen atoms, only K+ can fill this space
  • speed also a factor, during K+ efflux, K+ comes in, + charges repel each other, forcing the next ion to move to the next spot, which causes the pushing (the speed) (repulsion pushes K+ through the channel)

a combination of weak electrostatic interactions and repulsions

56
Q

How can you select for potassium, not sodium (if sodium is smaller)?

A

Sodium won’t go through b/c its water molecules won’t be shed to form this interaction

  • K+ sheds its water molecules, then has a slight electrostatic interaction w/ the oxygen atoms (the cavity ion dehydrates as it enters the K+ selectivity factor)
57
Q

Currents through single ion channels can be recorded using the …

A

… patch-clamp technique

  • apply a small amount of suction to the patch pipette to create a very tight seal between the pipette and the membrane, seal has extremely high resistance between the inside and the outside of the pipette
  • allows you to measure conductance through a single ion channel
58
Q

R = V/I

A

Pass a known current through a nerve membrane, measure the change in potential, and then calculate the membrane resistance

59
Q

I = V/R

A

Measure the membrane potential difference produced by an unknown current and know the membrane resistance, can calculate the current (I)

60
Q

V = IR

A

Pass a known current through the membrane and know its resistance, then we can calculate the change in potential (Vm)

61
Q

Calculation of current (I) or membrane conductance (g) from voltage-clamp experiments

A

Current through each class of voltage-gated channel may be calculated from a modified version of Ohm’s law that takes into account both the electrical and chemical driving forces on Na and K

IK = gK(Vm - Ek)
INa = gNa(Vm-ENa)
(Vm - Ek) = electrochemical driving force)

62
Q

Characteristic of the current in a single ion channel

A
  • Channels open all-or-nothing, which allows current to flow through the membrane
  • Changing the Vm proportionally changes the current
  • Lots of voltage-gated channels are rectifying, non-linear relationship between voltage and current (e.g. only allow current at positive voltages), the structure of the channel determines if it is rectifying or not
63
Q

individual voltage-gated channels open in an …

A

… all-or-none fashion

  • discovered through patch technique
64
Q

How to study ion channels?

A
  • Expression of ion channels in heterologous systems (e.g. in frogs, oocytes)
  • use DNA sequencing technology, these systems are very good expression systems (use RNA of the channel you want to study, that will be expressed on the membrane of the cell)
65
Q

What are the potential limitations of studying an ion channel in one of these systems (heterologous or DNA sequencing)?

A

Native environment in our cells may be very dif. from the native environment you choose to study

  • can’t tell the dif. between an endogenous protein and the one you want to study (e.g. the one you are expressing is very similar to the ones already there)
66
Q

If Vm = Ex

A

no net current

67
Q

If Vm > Ex

A

electrical current is OUTWARD

68
Q

If Vm < Ex

A

electrical current is INWARD

69
Q

Currents flow in the direction that would …

A

… take the cell towards that ion’s equilibrium potential

70
Q

take the cell towards that ion’s equilibrium potential

A
  • Based on selectivity (e.g. leak channels)
  • Based on gating mechanisms (e.g. voltage-gated channels)
71
Q

Pharmacological blockade of specific ion channels

A

ion channel inhibitors, drugs bind to a pocket inside the channel that prevents ions from flowing (NOT a conformational change)

72
Q
A
72
Q

Na+ channel inhibitors

A

tetrodotoxin (TTX), saxitoxin (STX), local anesthetics such as lidocaine

73
Q

K+ channel inhibitors

A

tetraethylammonium (TEA)

74
Q

Ca2+ channel inhibitors

A

dihydropyridines, Ca2+

75
Q

Nicotinic ACh receptors

A

α-bungarotoxin

76
Q

Inward rectifier K+ channels

A

opened by intense hyperpolarization

  • “P” is the pore domain, every potassium channel will have this similar domain
77
Q

Voltage-gated K+ channels

A

S4 is the voltage sensor in voltage-gated channels, no S4 = no longer voltage-dependent (right ion can still be selected, but not in voltage dependent matter)

78
Q

How does voltage open and close a K+ channel?

A

there are amino acids in the channel that sense voltage, and after that voltage is sensed, the channel opens

  • charge moves on S4 domain, movement causes bending on S6 domain, which causes the channel to open (S4-S5 linker forms a connection between the voltage sensor and the pore and is critical for channel opening)
79
Q

MtgK channel gated by Ca2+ caused …

A

bending of inner helices (conformational change) opens the gate on the channel

80
Q

inactivation

A

the process by which ion channels terminate ion flux through their pores while the opening stimulus is still present, the third state of ion channels

  • like a refractory period before cell goes back to closed (like closed → open → inactivated → closed → etc.)
  • e.g. the “ball-and-chain” mechanism of inactivation
81
Q

Mutations in ion channels causes …

A

… disease

82
Q

spikes

A

language of the nervous system

83
Q

Four main properties of action potentials (APs) or “spikes”

A
  • APs have a threshold of activation
  • APs are all-or-nothing event
  • Each AP has essentially the same shape
  • AP is self-regenerating (if signal wasn’t propagating, it would just dissipate = no movement, activity should be similar across axon)
  • Each AP is followed by a brief refractory period
84
Q

Hodgkin and Huxley

A

revolutionized neuroscience by recording APs in a nerve fiber and making modifications to voltage-clamp technique to help expand on work (command voltage incorporated, can see how much current is needed to get to new command voltage)

85
Q

Action potential shape and phases

A

Resting potential, depolarization phase, overshoot, repolarization phase, after-hyperpolarization (during undershoot)

86
Q

the all-or-nothing AP is the …

A

… unit of activity in the nervous system

  • w/ increased pressure, amplitude doesn’t increase: FREQUENCY increases
  • amplitude doesn’t increase b/c APs are already all-or-nothing (so size doesn’t change)
87
Q

Membrane depolarization needs to hit a _____ to trigger an action potential

A

threshold

88
Q

threshold is _____ for every channel

A

slightly different (typical is 15-20 mV)

89
Q

What is the ionic basis of the rising phase of the AP?

A

H+H used voltage-clamp technique, used sea water to cause depolarization, theorized that Na+ influx into neuron is what causes AP; when reduced [Na+], not as much depolarization as when extracellular Na+ is also added, looked @ dif. between Na+ and choline

90
Q

With the autism-associated gene in an old mouse (P60) and a young mouse (P4), what is the relationship between current/voltage/APs in P4 vs. P60?

A

This particular voltage-gated channel responsible for activation (in early development, goes away in P60)

  • @P60, b/c there are many versions of voltage-gated sodium channels, there is a dif. expression of channels at dif. points of development (an exchange of what is expressed)
91
Q

Why is there a phenotype at P4 and not P60?

A

This is a particular voltage-gated sodium channel, even in a given neuron, you can express dif. sodium-gated channels, you can see dif. channels throughout development

  • gone at P60 b/c there are other channels that compensate for the loss of P4 (there is plasticity in a system across dif. channels)
92
Q

What is the ionic basis of the rising phase of the action potential?

A

Pharmacological tools

  • e.g. TTX from pufferfish, TEA from garlic
  • TTX binds to channel, improves ability for ion to move through the channel
  • TEA directly binds in K+ channel, prevents K+ from moving through the channel
93
Q

Why does Na+ current decay w/ continued depolarization?

A

Voltage-gated sodium channels undergo an inactivation process that terminates the sodium current within 1-2 milliseconds to support rapid AP firing

94
Q

Kinetic properties of ion permeation are best described by the channel’s _____

A

conductance

95
Q

conductance is …

A

… determined by measuring the current (ion flux) through the open channel is response to an electrochemical driving force

96
Q

Voltage dependent change of Na+ and K+ conductance

A
  • Rapid rise and rapid fall of conductance of sodium during AP
  • Potassium has a slower and not as sharp rise as you get more depolarized, not as sharp as sodium (slower conductance)
97
Q

How an AP starts

A

Sodium wants to influx b/c of change in voltage

98
Q

Leak channels are _____ of voltage-gated channels

A

independent

  • leak channels are in the membrane and they are always open (efflux down concentration gradient)
99
Q

conductance is …

A

… NOT the same as permeability, but they are related

  • conductance is a physical value, how much goes through at a time
100
Q

refractory period

A

Na+ channels remain inactivated for a few milliseconds after a depolarization

101
Q

_____ is the only place where Na+/K+ pump is relevant

A

setting resting membrane potential

  • It does NOT have a direct effect on the spike, only contributes to setting the baseline
102
Q

AP trigger zone/axon hillock/initiation zone

A

AP starts here b/c axon hillock has the highest concentration of voltage-gated sodium channels, easier to get sodium in here to initiate

103
Q

The passive properties of an axon do not support …

A

… long distance propagation

  • neurons are poor conductors of electricity, so currents below AP threshold generate weakly propagating passive flow
  • change in Vm decays exponentially w/ distance from the site of current injection
104
Q

only an _____ propagates down an axon w/o decay in the signal

A

AP

  • why APs are self-regenerating
105
Q

Ion channel properties during the spike dictate …

A

… direction of propagation

106
Q

In theory, an AP could propagate in either direction, but it does not … why?

A

Refractory period and localization of channels

  • Potassium channels tend to be placed right behind the sodium channel, these voltage-gated potassium channels are open, potassium efflux repolarizes neuron
107
Q

myelin

A

made by glial cells, forms electrical insulator around neuron, helps signal propagation

108
Q

What to conclude about the function of Nav1.1

A
  • Knocking out Nav1.1 causes inconsistent static firing, it can initiate a spike, but cannot maintain consistent spiking
  • Loss of Nav1.1 alters receptor potentials (uncoordinated movement and poor limb positioning)
  • It’s probably more important for continuous firing
  • If you block any one of the sodium channels, there is an overall reduction in total sodium channels, but there should still be some activity (there should still be some voltage-gated sodium channels not blocked by each toxin applied, except for TTX which blocks all voltage-gated sodium channels)
109
Q

nodes of Ranvier

A

1 micrometer region of axon w/o myelin, has a high degree of voltage-gated sodium channels (depolarized region)

110
Q

juxtaparanodal region contains …

A

… voltage-gated potassium channels

  • allows for AP to propagate down the axon in one direction
  • proper distribution of voltage-gated channels @ node of Ranvier are critical for normal action potentials
111
Q

saltatory conduction

A

AP hops from node to node

112
Q

how a spike travels down a neuron

A
  • spike starts @ axon hillock, is then propagated down axon through saltatory conduction
  • current passively flows b/c of myelination (no leakage), then recharged @ node (active)
  • follows active, passive, active, passive, etc. pattern
113
Q

diameter of the axon affects …

A

… speed

  • larger axon leads to less resistance against the flow of ions = faster propagation

Neurobio I (4 decks)

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