4.2 HY Transmission of Neural Impulses Flashcards
What is the action potential?
It is an all or nothing message, that helps to relay electrical impulses down the axon to the synaptic bouton.
This ultimately results in the release of neurotransmitters in the synaptic cleft.
What is the resting membrane potential?
The net electric potential difference that exists across the cell membrane, created by movement of charged molecules across that membrane.
For neurons, it is -70 mV, the the neuron being negative relative to the outside.
It is the net effect of sodium and potassium’s equilibrium potentials.
Where is potassium more prevalent (in or out of the cells)?
In the cell. In the cell the concentration is about 140 mM, outside it is 4mM
How does potassium move out of the cell cell?
Through potassium leak channels. This causes the cell to lose a small amount of positive charge, leaving the inside of the cell slightly negative and outside the cell slightly positive.
However, as the cell becomes more negative, it can draw the positively charged potassium back in.
What is the equilibrium potential of potassium?
This is where there is an equal amount of potassium going into the cell as going out of the cell. It is about -90mV
For example, initially, there is some potassium leaving the cell given the high concentration of potassium in the cell (concentration gradient).
However, after some potassium has left, the inside of the cell becomes very negatively charged, drawing the potassium back in (electrostatic force).
So when the potassium going in is equal to the potassium going out, it is in equilibrium.
What is the equilibrium potential of sodium?
What are sodium leak channels?
- 60 mV
- Sodium leak channels allow the sodium to go INTO the cell, because there’s a high gradient of sodium OUTSIDE the cell.
What is Na/K ATPase?
This is an enzyme that continually pumps sodium and potassium back to where they started.
This requires ATP, because you are moving them AGAINST the concentration gradient.
More ATP is spent on this process than any other function in the body.
It helps to restore the resting potential after firing.
What is depolarization and hyperpolarization?
Depolarization- this raises the membrane potential, Vm, from its resting potential, and thus makes the neuron more likely to fire an action potential (excitatory)
Hyperpolarization- lowering the membrane potential from its resting potential, and makes the neuron less likely to fire the action potential.
What is summation in regards to depolarization?
Summation- when multiple inputs are received that are additive, they may be either excitatory or inhibitory.
What are the two types of summation?
Temporal Summation- multiple signals that are integrated during a relatively short period of time, which may result in a firing of the action potential.
Spatial Summation- the additive effects are based on the number location of the incoming signals (and where they are at). For example, a neuron may receive inhibitory signals at the soma, which cause more hyperpolarization, and excitatory signals at the dendrites, which cause less excitation.
What happens if the cell is brought to its threshold?
The voltage-gated sodium channels open in the membrane and permit the passage of sodium ions. Because of the electrochemical gradient, it promotes the the migration of sodium into the cell.
As the sodium goes in, the membrane potential becomes more positive, and cell rapidly depolarizes. The depolarization actually inactivates the sodium channels when they reach + 35mV, and will need to be brought back near the resting potential to be reactivated.
What are the three states of the sodium channels?
Closed: before the cell reaches the threshold, and after inactivation has been reversed
Open: from threshold to approximately + 35mV
Inactive: from approximately + 35 mV to the resting potential.
What does the positive potential inside the cell do?
In inactivates the sodium channels.
It triggers the voltage gated potassium to open, which favors the flux of potassium OUT of the cell.
As they are driven out, it causes the cell membrane or inside of the cell to become more negative, called repolarization. The potassium actually overshoots its mark, causing hyperpolarization.
What are the two types of refractory periods?
Absolute refractory period: no amount of stimulation can cause another action potential to occur
Relative Refractory Period: There must be a greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than its resting value.
What is impulse propagation?
Essentially, it the depolarization of the membrane as it moves down the membrane.
Because of the refractory period, the propagation moves only in one direction.
What is the difference between electrical and chemical transmission?
Electrical conditions occurs within the neuron, passing signals down the axon.
Chemical transmission occurs between the neuron , passing signals to subsequent neurons or gland/muscles.
