week 2 Flashcards
What is the nature of signaling within a neuron?
Electrical signaling
Neurons can extend over relatively long distances and signals move from one part of a neuron to another.
Why is electrical signaling used instead of chemical diffusion in neurons?
Diffusion of chemicals would be too slow
Therefore, the signal is electrical in nature.
What is an action potential?
A sudden change in membrane voltage of a neuron in response to a stimulus
It depends on the resting membrane potential.
What is the resting membrane potential for a neuron?
-70 mV
This is the difference between the electrical potential inside and outside the cell.
How do neurons send information to other neurons?
By temporarily altering their overall polarity (electrical charge)
This involves changing the membrane potential.
What alters the membrane potential in a neuron?
The movement of ions in and out of the cell
This movement is influenced by diffusion and electrostatic pressure.
What are the two forces that prevent ions from moving freely in and out of the cell?
- Diffusion
- Electrostatic pressure (opposites attract)
These forces regulate ion movement across the cell membrane.
What are cations?
Positively charged ions
Examples include potassium (K+) ions.
What are anions?
Negatively charged ions
Examples include chloride (Cl-) ions.
What is the fluid inside the cell called?
Intercellular fluid
This fluid contains potassium (K+) ions.
What is the fluid outside the cell called?
Extracellular fluid
This fluid contains sodium (Na+) and chloride (Cl-) ions.
What is the primary movement of Na+ ions into the cell?
Diffusion
Na+ ions want to enter the cell due to concentration gradient.
What prevents Na+ ions from entering the cell despite diffusion?
Electrostatic pressure
Electrostatic pressure creates a barrier for Na+ ions.
What drives Na+ ions to want to leave the cell?
Diffusion
Na+ ions have a tendency to move out of the cell due to concentration gradient.
What prevents Na+ ions from leaving the cell?
Electrostatic pressure
The positive outside of the cell creates a force against Na+ leaving.
What is the electrostatic pressure’s effect on K+ ions wanting to enter the cell?
Can go in
Electrostatic pressure allows K+ ions to enter the cell.
What is the charge inside the cell compared to the outside?
Inside of cell = negative, Outside of cell = positive
This charge difference is important for ion movement.
What is the function of sodium-potassium pumps?
Pump Na+ out and K+ in
Sodium-potassium pumps help maintain the electrochemical gradient.
What happens to Na+ ions as the concentration inside the cell increases?
A lot of Na+ ions travel into the cell
This accumulation necessitates the action of sodium-potassium pumps.
Fill in the blank: Sodium-potassium pumps pump all the _______ out of the cell.
Na+
This action is crucial for maintaining the cell’s resting potential.
Fill in the blank: Sodium-potassium pumps pump the escaped _______ back into the cell.
K+
This helps regulate potassium levels inside the cell.
What does the sodium-potassium pump do?
It pumps out Na+ that entered the cell and pumps back in any K+ that managed to escape.
This pump is essential for maintaining the resting membrane potential in neurons.
What analogy is used to describe the sodium-potassium pump?
A sexist bouncer who believes that only boys cause fights.
In this analogy, Na+ represents boys that are kicked out, while K+ represents girls that are persuaded to return.
What is the charge change in a neuron called when sending information?
Action potential.
The action potential is a rapid change in electrical charge necessary for neuronal communication.
Fill in the blank: The sodium-potassium pump kicks out all of the _______.
Na+
Fill in the blank: The sodium-potassium pump manages to persuade the _______ (K+) who left to return.
women
What is an action potential?
A rapid change in the polarization (electrical charge) of the neuron to send a signal down said neuron.
What must a neuron reach to send a signal?
The threshold of excitation.
How can the threshold of excitation be metaphorically described?
As a big red button that must be pushed by reaching a certain action potential.
What type of process is an action potential?
An all-or-nothing process.
What happens during the neuron firing process?
Voltage-dependent ion channels open or close depending on the current membrane potential.
What do voltage-dependent ion channels allow?
Ions to enter or leave the neuron.
What is depolarization?
A decrease from normal resting potential where the overall charge moves closer to zero.
What is hyperpolarization?
An increase in action potential where the overall charge becomes more negative.
Fill in the blank: Depolarization means _______.
less charged.
Fill in the blank: Hyperpolarization means the overall charge becomes _______.
more negative.
What is the first step in the process of a neuron firing?
Start threshold of excitation is reached
This initiates the sequence of events leading to an action potential.
What happens when Na+ channels open during neuron firing?
Na+ enters the cell
This influx of sodium ions causes depolarization of the neuron.
What occurs after Na+ enters the cell?
K+ channels open
This leads to potassium ions leaving the cell.
What effect does K+ leaving the cell have on the neuron?
Cell becomes more positive
This is part of the depolarization process.
At what membrane potential do Na+ channels close?
+40 mV
This marks the peak of the action potential.
What happens to the neuron after Na+ channels close?
+ becomes refractory
The neuron cannot fire again immediately.
What continues to happen after Na+ channels close?
K+ carries on leaving the cell
This contributes to repolarization of the neuron.
What occurs to the membrane potential (MP) after too much K+ leaves the cell?
MP overshoots and drops below resting potential (RP)
This phenomenon is known as hyperpolarization.
What happens after K+ channels close?
Sodium-potassium pump resets the Na+ levels
This restores the original ionic balance in the neuron.
What happens to the escaped K+ from the overshoot?
Diffuses away
This helps to stabilize the ionic environment around the neuron.
Stage 1 in more detail
Na+ channels open
Na+ enters the cell
Membrane depolarisation
Sodium channels open at ~55mV
—> open depending on voltage of the membrane
Stage 2 in more detail
K+channels open
K+ leaves the cell
Potassium channels also open
Sodium cautions flood into the neuron
-membrane potential becomes more positive (depolarisation)
