Lecture 6 part two (SECOND MIDTERM) Flashcards
If multiple sodium gates open, the sodium permeability is..
a lot higher
Basic concept:
When a certain channel opens, what changes?
The permeability to that certain ion
In graded potentials, movement of the sodium ions inside of the cytoplasm is called…
local current
Any shift from the resting membrane potential toward a more positive potential is called…
a depolarization
“Getting rid of the polarity (difference) of the cell” - Noriega
Basic concept:
In a voltage gated channel, how can it reach the next “change”?
it MUST reach the next voltage level
In order to depolarize again, what must happen?
It must “repolarize”
What is repolarization?
The process of restoring the normal resting membrane potential after depolarization
The directional, continued depolarization along an axon is known as…
the action potential
There are 2 voltage gated channels. What are they?
- Sodium voltage gated
- Potassium voltage gated
The sodium voltage gated channels have 2 gates to them. What are they?
- Activation (on top)
- Inactivation (on bottom)
At the resting potential, what is the status of the gates?
- Sodium activation gate is closed (inactivation gate is open)
- Potassium activation gate is closed
At threshold, what happens to the gates?
- Sodium activation gate opens (inactivation gate is the same way it was at resting potential)
- Potassium activation gate is closed
Now that the sodium gate is open, what happens to permeability?
The cell is more permeable to sodium; sodium floods inside
When sodium floods in, what happens to the inside?
It becomes more positive; reverses polarity and reaches +30 mV
What happens when the inside reaches +30mV?
- Sodium inactivation gate closes (activation gate doesn’t change)
- Potassium activation gate OPENS
When the sodium gate closes, what happens to the permeability?
It is less permeable to sodium
When only the potassium gate is open, where does the potassium go? What happens? What is it called?
- outside
- the inside becomes more negative
- repolarization
In order to “reset the entire system and go back to the very beginning,” what has to happen? What is it called?
- It has to go past -70mV and go all the way down to -90mV
- Hyperpolarization
Once -90mV is reached, what is the status of the gates?
Sodium inactivation gate opens (activation gate closes)
Potassium gate closes
Since the gates are closed at -90mV but the voltage is still not at -70mV, how does it get back to that resting potential?
the leak channels
What CANNOT happen after depolarization? And what is that period called?
- It CANNOT depolarize again until it re-establishes the resting potential
- The refractory period
When is it when both activation gates are open but the sodium inactivation gate closes?
The refractory phase
The refractory phase has two parts. What are they?
Absolute
Relative
Absolute refractory phase:
The membrane cannot respond to further stimulation from the moment the voltage-gated sodium channels open at threshold until sodium channel inactivation ends, because all the voltage-gated sodium channels are already open or are inactivated.
Relative refractory phase:
Begins when the sodium channels regain their normal resting condition, and continues until the membrane potential stabilizes at resting levels.
How can the speed of the conduction be increased?
Depolarization skips from node to node
Jumping from node to node happens when?
Saltatory proragation
Events of saltatory propagation:
- An action potential occurs at initial segment
- A local current produces a graded depolarization that brings the axolemma at the next node to threshold
- An action potential develops at the next node
- A local current produces a graded depolarization that brings the axolemma at the next node to threshold
To go from one neuron to it’s target cell (or another neuron), chemical signals are needed. They are called:
neurotransmitters
Important functions of myelin:
- insulates axon so it’s easier to maintain differential resting potential
- speeds up conduction
- prevents “cross-talk” between different neurons grouped in a single nerve
Acetylcholine and norepinephrine are what?
neurotransmitters
When that depolarization travels all the way down and the action potential reaches the terminal end (telodendria) of the axon, it’s going to open what kind of channels? Where?
Voltage-gated calcium channels in the cytosol of the axon terminal
Calcium that enters the cell causes what to happen?
It causes vesicles to bond to cell membrane and release its content (neurotransmitters)
What stores the neurotransmitters?
vesicles
The space (gap) where the neurotransmitters are released is what?
synaptic cleft
What happens after the neurotransmitters are released into the synaptic cleft?
They bind to receptors for chemically gated channels on the next neuron
The junction between 2 neurons is called:
the synapse
Presynaptic neuron:
Postsynaptic neuron:
Presynaptic neuron: before synapse
Postsynaptic neuron: after synapse
What can happen to the neurotransmitter when it gets released?
- it can be reabsorbed into the presynaptic neuron
- it can be broken down by enzymes
2 basic ways neurotransmitters can work:
Directly: ionotropic effects (changing ion concentrations across membrane)
Indirectly: metabotrophic effects (changing metabolism of the cell)
Indirect neurotransmitter action:
- metabotrophic effects
- essentially a second messenger system
- effects can last longer that direct action
The effect of a neurotransmitter depends on the __________, NOT the ____________!
receptor, NOT the neurotransmitter!
In indirect actions, what is the “link” between the first messenger and the second messenger?
a G Protein
The indirect action can be ________ or ________; meaning it can make things easier to reach threshold or more difficult to do so.
excitatory (easier), inhibitory (more difficult)
Excitation:
Influx of calcium (Ca2+); decrease passage of chloride (Cl-) and potassium (K+); metabolic changes; change in number of receptors
Inhibition:
Influx of chloride (Cl-); increased passage of potassium (K+); metabolic changes; change in number of receptors
