Psych 211 (neuro) > Action potential > Flashcards

Action potential Flashcards

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1
Q

What is the Golgi stain?

A
  • a mixture of silver nitrate and potassium chromate that causes 2% of brain cells to darken in colour
  • generates silver chromate, which can crystallize inside of neurons, highlighting every nook and cranny
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2
Q

What is crystallization?

A
  • process of atoms or molecules arranging into a well-defined, rigid crystal lattice in order to minimize their energetic state
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3
Q

What is the basic structure of the neuron?

A
  • cell body/soma
  • dendrites
  • axon
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4
Q

What is the cell body of a neuron?

A
  • where its nucleus is located
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5
Q

What are dendrites?

A
  • branched, treelike extensions from the soma
  • collecting information relevant to the cell
  • sense what’s outside the cell and receive information
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6
Q

What is an axon?

A
  • neuron has one
  • can branch many times; axon collaterals
  • axon terminal is end of axon
  • send information to downstream cells by releasing signalling molecules (neurotransmitters) onto them from the axon terminal
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7
Q

What is a synapse?

A
  • junction between an axon terminal and a downstream cell
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8
Q

What is voltage?

A
  • difference in electric charge between two points – the electrostatic potential between two points
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9
Q

How is voltage measured?

A
  • voltmeter (oscilloscope)
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10
Q

What do voltmeters do?

A
  • let a negligible amount of electricity to pass through them (from one wire to the other)
  • The amount of resistance needed to allow just a little bit of electricity to flow indicates the charge difference (the voltage) between the two wires
  • measured in mV
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11
Q

What happens when there is a voltage?

A
  • makes charged particles want to move to neutralize the charge difference
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12
Q

What is the charge of the extracellular fluid of the brain?

A
  • 0 mV
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13
Q

What is a neuron’s resting membrane potential?

A
  • Membrane potential of a neuron when it is at rest
    -40 mV to -80 mV
    the voltage (the electrostatic pressure) across the membrane makes positively charged ions want to enter the cell and negatively charged ions want to leave the cell
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14
Q

What is an ion?

A
  • an atom or molecule that has a net electrical charge
  • move around freely in water
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15
Q

What are cations?

A
  • positively charged
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16
Q

What are anions?

A
  • negatively charged
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17
Q

What is electrostatic pressure?

A
  • the attractive force between ions that are oppositely charged and the repulsive force between ions that are similarly charged
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18
Q

What are ion channels?

A
  • Proteins that form a pore (a hole) through which ions can pass/flow
  • These proteins are placed in the cell membrane
  • When open, they let specific ions freely flow in and out of the cell
  • Most are bidirectional
  • proteins that are encoded in a cell’s DNA
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19
Q

What is a leak channel?

A
  • An ion channel that permanently stays open
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20
Q

What are the important monovalent cations?

A
  • sodium
  • potassium
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21
Q

What are the important divalent cations?

A
  • calcium
  • magnesium
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22
Q

What are the important monovalent anions?

A
  • chloride
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23
Q

Which ion is more abundant inside of cells?

A
  • potassium
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24
Q

What is the cell membrane?

A
  • phospholipid bilayer
  • impermeable to atoms and molecules that readily dissolve in water (nucleic acids, amino acids, ions)
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25
What does the intracellular fluid of cells contain?
- lots of negatively charged nucleic acids and amino acids
26
What is the resting membrane potential of cells?
-20 mV
27
What is the resting membrane potential of neurons?
-40 mV to -80 mV
28
Why do neurons create this especially negative resting membrane potential?
- To be able to communicate very quickly from one end of the cell to the other
29
How do neurons create this especially negative resting membrane potential?
Neurons create an electrical potential across their membrane using two proteins: - sodium potassium pump - potassium leak channel
30
What is the action potential?
- The rapid propagation of information down the length of an axon - brief electrical impulse that propagates down the axon - rapid change in membrane potential - involves 2 proteins: voltage gated sodium channel and voltage gated potassium channel - end of the action potential trigger the release of neurotransmitter
31
What is the protein involved in the release of neurotransmitter?
- voltage gated calcium channel
32
What is the sodium potassium pump?
- Neurons fill their cell membrane with the protein - continually pumps sodium ions out of the cell and potassium ions into the cell - uses ATP for energy - makes the concentration of K+ ions 30x higher inside the cell than out - makes the concentration of Na+ ions 15x more concentrated outside the cell than in
33
What are the steps for the sodium potassium pump?
- at rest, pump is open to inside of cell - pump binds 3 sodium ions and a molecule of ATP - splitting of ATP provides energy to change shape of channel; pump switches to outside of cell and sodium ions are driven through and out of cell - potassium ions bind - phosphate (molecule of ATP) releases and pump reverts to original form; open inside - potassium ions released inside cell
34
What are the concentration gradients of a neuron?
- Potassium is concentrated in - Sodium is concentrated out - these concentration gradients generate a force: the force of diffusion
35
What is diffusion?
- if there is a concentration gradient and no forces or barriers in the way, then atoms and molecules will move, on average, from regions of high concentration to regions of low concentration
36
What are potassium leak channels?
- Neurons fill their cell membrane with the protein - permanently open ion channels that freely let K+ ions enter or leave the cell - more likely to leave the cell than enter it - force of diffusion competes with force of electrostatic pressure - K+ ions leave the cell because of diffusion, but they enter the cell because it is negatively charged inside relative to outside - forces become equal and opposite when the membrane potential falls to -90 mV
37
What happens when the membrane potential is less negative than -90mV?
- force of diffusion wins - more K+ ions leave
38
What happens when the membrane potential is more negative than -90mV?
- electrostatic pressure wins - more K+ ions enter
39
Why is the resting membrane potential not -90 mV?
- other ions (primarily Na+) continuously flow into neurons - permeability of the membrane to K+ ions that largely determines the resting membrane potential - When a neuron opens up more K+ channels, the membrane potential falls closer to -90 mV - When a neuron removes some K+ channels from the membrane, the membrane potential becomes less negative
40
What is a membrane potential?
- Electrical charge across a cell membrane - The difference in electrical potential inside and outside the cell
41
Which proteins are responsible for setting up and maintaining the resting membrane potential of neurons?
- sodium potassium pumps - potassium leak channels
42
What are receptors?
- sensitive to some aspect of the extracellular environment - detect and pull in nutrients from the extracellular space - gain a better understanding of the world around them
43
What are ion channel receptors?
- receptors that are ion channels - gated - when activated, change shape and open a pore through which specific ions can flow
44
What is depolarization?
- When the membrane potential of a cell becomes less negative than it normally is at rest
45
What happens when there are changes in the membrane potential?
- changes are transient (short lived) - neurons quick to return to resting state because K+ leak channels are always open
46
Why is a change in membrane potential never long?
- because of the abundance of K+ leak channels
47
Why are changes in membrane potential important?
- because neurons express a variety of voltage-gated ion channels - gate on these channels is electrically charged, so it opens (and closes) in response to changes in the membrane potential
48
What is the voltage gated sodium channel?
- used to initiate and propagate the action potential - protein encoded in the genome - line the entire length of the axon
49
What is the voltage gated potassium channel?
- to quickly restore the resting membrane potential - protein encoded in the genome - line the entire length of the axon
50
What is the voltage gated calcium channel?
- to trigger the release of neurotransmitter - protein encoded in the genome - found at the axon terminal
51
What are the steps in the voltage gated sodium channel?
- At rest, the electrically charged gate is pulled closed by the negatively charged interior of the cell - gate opens when membrane is depolarized to -40 mV (by activated receptor) - open pore allows Na+ to rush in, further depolarizing - open for half millisecond before it is clogged with ball and chain - clog until membrane potential back at rest (half millisecond) - chain reaction that propagates down length of axon
52
What is the axon hillock?
- where axon connects to soma - where the action potential starts
53
When do forces of diffusion and electrostatic pressure balance for sodium?
+60 mV
54
When the membrane is at rest, what do sodium ions want to do?
- enter because of diffusion and electrostatic pressure
55
Why do neurons not reach +60 mV?
- because neurons voltage-gated sodium channels get clogged by the ball and chain - In the 1⁄2 millisecond they are open, the membrane potential reaches +40 mV
56
What are the 2 ways to prevent current flow through a voltage gated sodium channel?
- The pore closes whenever the membrane potential is more negative than -40 mV (at rest) - the pore gets clogged within a 1⁄2 millisecond after opening; receptor is said to be inactivated until membrane potential returns to rest
57
What is the threshold of excitation?
- value the membrane potential must reach to trigger an action potential
58
What is the initial depolarization that starts an action potential?
- driven by a small influx of Na+ ions through an activated receptor on a dendrite
59
How long would it take for resting membrane potential to be restored with potassium leak channels?
- ten milliseconds - too long to support rapid action potential firing
60
What are the steps in the voltage gated potassium channel?
- open on upward swing of action potential - outward flow of K+ ions through both leak channels and voltage-gated potassium channels restores the resting membrane potential within a 1⁄2 millisecond -when at rest, close and reset - extra potassium outside diffuses away
60
What speeds up the restoration of membrane potential?
- the voltage-gated potassium channel
61
What is the refractory period?
- post action potential hyperpolarization - membrane potential fallen below what it normally is at rest
62
How many action potentials can be fired per second?
- some neurons are capable of firing 400 action potentials per second
63
What happens at the end of the action potential?
- when it reaches the axon terminal, it triggers the opening of voltage gated calcium channels
64
What are the steps to the voltage gated calcium channel?
- action potential arrives at axon terminal - voltage gated calcium channels open and calcium enters the axon terminal - calcium triggers the fusion of neurotransmitter filled vesicles with cell membrane - neurotransmitters are released into the synapse; activate receptors on downstream (postsynaptic) neuron
65
Why does calcium enter the cell with the action potential?
- Calcium is 1000x more concentrated outside the cell than in, so it rushes into the cell, when the gate opens
66
What is synaptic transmission?
- primary means of communication between neurons - transmission of chemical messages (neurotransmitters) from one neuron to another via synaptic connections - diffusion of molecules from one neuron to another over synaptic space - Released neurotransmitters activate receptor proteins on downstream neurons (muscles), which can allow Na+ ions to enter those cells; trigger action potential
67
How does the action potential travel?
- unidirectional - start in axon hillock and travel down the axon toward axon terminals
68
What prevents the action potential from reversing direction?
- ball and chain inactivation mechanism of the voltage-gated sodium channel
69
What is the all or none law?
- An action potential can occur or not, but once triggered it propagates down the length of the axon without growing or diminishing in size - no such thing as a strong or weak action potential
70
What is the rate law?
- the strength of the "message” is represented by the rate of firing (the number of action potentials per second, not size or speed)
Psych 211 (neuro)
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