The action potential Flashcards
1
Q
What is Golgi’s reticular theory?
A
The brain is a single connective unit
2
Q
How was the structure of the neuron discovered?
A
By using the Golgi stain (crystallizes in cells, thus darkening the colour of about 2% of brain cells, which allows you to analyze the structure of cells because you see them)
3
Q
Which structure of the neuron is responsible for sensing the external environment?
A
dendrites
4
Q
Which structure of the neuron is responsible for releasing neurotransmitters into the extracellular space?
A
Axon terminal
5
Q
What is the name of the ramifications of axons?
A
Axon collateral
6
Q
Which structure of the neuron is responsible for rapidly transmitting messages?
A
Axon
7
Q
Where does the axon lead the action potential?
A
In the terminal buttons
8
Q
What is the name of the small space between the axon terminal of one cell and the dendrites of the next?
A
Synapse
9
Q
Identify each structure
A
10
Q
What differentiates cells?
A
The diffenrent proteins they express (which depends on which sections of the DNA they read)
11
Q
What is voltage?
A
The difference in electric charges between two points. It represents the quantity of electricity that can pass from one place to another.
12
Q
What is the device used to measure voltage?
A
Voltmeter
13
Q
When is there the possibility for electricity to flow between one site and the other?
A
When there is a voltage difference.
14
Q
What is the resting potential of the membrane?
A
-40 to -90 mV
15
Q
Why can salts not cross the cell membrane?
A
The cell membrane is made of lipids, which do not let charged particles pass.
16
Q
Where is the membrane potential the strongest? Why?
A
- On the outskirts of the membrane
- the charged particles hug the cell membrane, as this is the closest they can be to the outside particles that have the opposite charge to theirs
17
Q
What is involved in transcription?
A
DNA and mRNA
18
Q
What is involved in translation?
A
- mRNA
- ribosomes (read the mRNA)
- protein (formed by the ribosomes by using tRNA)
19
Q
What are the two methods of communication between neurons?
A
- Electrical
- Chemical
20
Q
What is the electrostatic pressure?
A
attractive force between molecules of opposite charges OR repulsive force between molecules that are similarly charged
21
Q
What are ion channels?
A
- protein molecule
- sits in the cell membrane
- pore that only allows specific ions to pass in order to leave or enter the cell
22
Q
What is a leak channel?
A
- Ion channel protein
- is in the membrane
- the pore is always open
23
Q
What is the role of the Sodium Pottasium pump?
A
Sets the concentration gradient
24
Q
What are the ions that are more abundant outside of the neuron?
A
Na+, Ca+, Mg2+, Cl-
25
What ions are more abundant inside of the soma than outside of it?
K+
26
What are the proteins responsible for setting the resting membrane potential?
- Sodium-Potassium Pump
- Leak potassium channel
27
What is the relative concentration gradient of K+?
30x more concentrated INSIDE the soma
28
What is the concentration gradient of sodium?
15x more concentrated outside than inside
29
What is the function of the Sodium-Potassium pump?
- Releases sodium from the cell
- lets potassium in the cell
30
What is the combined effect of the Sodium-potassium pump and the potassium leak channel?
Creates a negative potential INSIDE the cell, because potassium is always entering the cell (via the sodium potassium pump) and immediately leaving it through the leak channel as the concentration of potassium is so much higher inside the cell than outside (principle of diffusion)
31
What are the factors that determine where the ions go?
- Diffusion
- Electrostatic force
32
What are the steps in the action of the sodium-potassium pump?
1) Binding of three sodium ions and a molecule of ATP to the pump
2) The shape of the channel changes by using the energy of ATP
3) Na+ is pushed out to the outshide of the membrane, and K+ binds to the channel
4) The phosphate is released, allowing the channel to regain its original form and to release the potassium into the inside of the membrane.
33
What is the resting potential of the membrane? What does resting potential mean?
- the resting potential is the state where the neuron is not actively either receiving or sending messages
34
Why is K+ trying to attain -90mV?
- represents the electrochemical equilibrium potential, where the electrostatic energy of K+ and its diffusional force are the same
- (if there is only K+ in the cell, the amount of ions going out and coming in will be the same)
35
What is the resting membrane potential mostly dependent on?
The number of leak potassium channels present
36
How does the number of leak potential channel influence the resting membrane potential?
The more there are, the closer the membrane potential will be to the electrochemical potential (-90mV)
37
Why is the resting membrane potential often higher than -90mV?
- other ions than potassium can move throught the membrane via other types of leak channels
38
What are the receptors?
- Proteins that act as sensors
- present in the cell membrane
- sensitive to specific features of the extracellular environment
39
Why do neurons use receptors? Where are receptors situated in the neurons?
- Use of receptors to sense the external world
- on the dendrites
40
What are ion channels?
- type of receptor
- on the dendrites of neurons
- allow the circulation of ions
41
What is depolarization?
- the membrane potential of a cell becomes less negative
- caused by a massive influx of Na+ ions
42
What ocurs when Na+ enters massively a neuron through an ion channel?
- K+ immediately leaves through leak channels
43
What are the five proteins involved in the action potential?
- Sodium-Potassium transporter
- Leak potassium channel
- Voltage-gated sodium channel
- Voltage-gated potassium channel
- Voltage-gated calcium channel
44
What is the main function of voltage-gated sodium channels?
initiation and propagation of the action potential
45
What is the main function of voltage-gated potassium channels?
restore the resting membrane potential
46
What is the main function of voltage-gated calcium channels?
Triggers the release of neurotransmitters
47
What is the particularity of voltage-gated channels?
- Normally closed
- open solely based upon the inside voltage of the cell
48
When do the voltage-gated sodium channels open?
- membrane potential becomes less negative than -40mV
49
What are the steps of the action of voltage-gated sodium channels?
1) At the resting potential: channel is closed
2) When the voltage inside the soma becomes less negative than -40mV, then gates open
3) Na+ enters the cell
4) The ball-and-chain block the channel, so the action potential can not go that way anymore
5) When the membrane potential gets back to -70mV, the ball-and-chain stops blocking the channel
50
How do the voltage-gated sodium channels know when to open?
they include receptor proteins that sense the charge of the outside world
51
What is the avalanche effect?
When one Na+ ion channel opens, the membrane depolarizes a step more, which causes the opening of more voltage-gated sodium channels, which causes massive depolarization of the cell, bringing it up to +40mV
52
What is the maximal potential of the cell?
+40mV
53
What is the name of the calue of the membrane potential that must be reached to produce an action potential?
Threshold of excitation
54
What marks the beginning of an action potential?
Entering of Na+ in the neuron, via ion channels **that are not voltage gated **
55
What structure is responsible fo the restoring of the membrane potential?
Potassium leak channels, and voltage-gates potassium channels
56
When do voltage-gated potassium channels open?
Membrane potential >0mV
57
What is the refractory period?
Before the voltage-gated K+ channels completely close, the membrane potential will become more negative that its actual resting potential. Therefore, the cell is hyperpolarized, which makes it very hard to trigger another action potential.
58
During which phase of the action potential is there an increase in permeability to Na+?
Depolarization
59
During which phase of the action potential is there an increase in permeability to K+?
Repolarization and Hyperpolarization
60
During which phase of the AP is there an increase in the permeability to K+?
Repolarization
61
What are the stages of the action potential?
| (7)
1. Baseline
2. Stimulus
3. Upswing
4. Peak
5. Downswing
6. Hyperpolarization
7. Return to baseline
62
What is the voltage of the cell during the baseline stage?
-70mV
63
What is the voltage of the cell during the stimulus? What voltage must be reached for the stimulus to occu?
-55mV
64
What is the volatge during the upswing?
Increasing toward peak
65
What is the voltage at the peak?
40mV
66
What is the voltage at the downswing?
Decreasing toward hyperpolarization
67
What is the voltage during hyperpolarization?
-80 mV
68
What is the voltage during the return to baseline?
Aims to reach -70mV
69
What channels are in action during the stimulus?
A few Na+ channels
70
What channels are in action during the upswing?
A lot of voltage-gated Na+ channels and some voltage-gated potassium channels
71
What channels are in action during the peak?
Voltage-gated potassium channels are opening, but Na+ channels are blocke by the ball and chain
72
What channels are in action during the hyperpolarization?
Some VG K+ are still open
72
What happens to ion channels during the return to baseline?
VG K+ channels close, back to baseline channels
73
Which way does an action potential travel?
From the soma to the axon terminal
74
What is the voltmeter used to measure the electrical change across the membrane?
the oscilloscope
75
What is the relative concentration gradient of Ca2+ ions?
1000x more concentrated outside than inside
76
When do voltage-gated calcium channels open?
When the Action Potential reaches the axon terminal and the axon termianl is depolarized
77
Where are situated the votage-gated calcium channels?
on the axon terminal
78
What is the function of voltage-gates calcium channels?
Activate vesicle release machinery to allow chemical interneuron communication
79
What triggers the release of neurotransmitters?
The influx of calcium ions in the neuron
80
What type of communication occurs between two different neurons?
chemical communication
80
What causes the opening of the voltage-activated calcium channels?
The arrival of the AP at the synapse
81
What type of communicaiton occurs INSIDE a neuron?
Electrostatic communication
82
What is the movement of the action potential through the axon?
Conduction of the action potential
83
What type of movement is that of the action potential? Why?
- unidirectional
- the ball-and-chain blocks the voltage-gated sodium channels, thus forbidding it from passing
84
What is the all-or-none law?
The size of the action potential stays the same. Either it is produced or not. And if it is produced, it will always have the same intensity and propagate toward the end of the axon whilst keeping the same intensity.
85
What is the rate law?
The strength of the stimulus is represented by the rate of the firing axon.
