15 Flashcards
Electrical signals in neurons occur?
In all parts of the neuron. Graded potential in the cell body, action potential in the axons, and synaptic potential at the synapse of the neuron.
What potentials result in the changes in membrane potential?
Graded potential, action potential, and synaptic potential
When measuring membrane potential, what do you expect? 2•
•Always reported as charge inside relative to charge outside
•In both animals and plants, the inside of the cell is more negative than the outside.
Does the entire cell have a charge difference?
No, only the surfaces of the membrane.
Equilibrium potential?
Membrane potential where the electrochemical gradient between the two ions balance out.
Once equilibrium potential is reached, what happens to the movement of the ions?
They stop moving.
If the membrane potential gets lower than the equilibrium potential, then what is the movement of the ion that has its channel open?
It goes against its concentration gradient.
What manages the concentration gradient in neurons?
The sodium potassium pump (NA+/K+ - ATPase). This ensures that ions don’t flow in the wrong direction.
3Na+ leaves the cell for every 2K+ that enters the cell.
Can you use equilibrium potential to predict the direction in which an ion will move?
Yes by comparing it to membrane potential.
Sodium is trying to get the cell to?
+62 mV
Potassium is trying to get the cell to?
-90 mV
Why is the membrane resting membrane potential closer to K+ equilibrium potential?
Because K+ is more permeable than Na+.
If you have several ion channels open, what determines membrane potential?
A weighted average based on permeability.
The importance of permeability in setting membrane potential is for mixed in the?
Goldman-Hodgkin-Katz constant field equation (GHK).
GHK = ______ equation if one of three ion channels are open?
Nrest equation.
Why do we only consider Na+, K+, and Cl- in GHK equation?
Because permeability in other ions are so low.
What causes changes in membrane potential?
Changes in membrane permeability.
Gated ion channels?
Those that can open and close
Leak channels?
Those that are always open
What causes gated channels to open and close, and how?
By a signal which switches a protein gate that blocks the channel (pore).
How does the signaling process work in ion gated channels?
Sensory receptor gets a stimulus, and changes the conformation of the receptor. This receptor could be a channel itself, or it signals to a channel.
What type of potential is caused by neurotransmitters binding to a receptor?
A graded potential.
What changes the frequency of signals?
How much of a membrane potential change occurs by opening more ion graded channels.
Steps of graded potential from neurotransmitter?
•Neurotransmitter binds to a ligand-gated Na+ channel
•Na+ enters the cell through the open channel
•Current spreads through the cell
•The strength of the signal decreases with distance.
Why do signals die out eventually when moving through the cell?
Because of Intracellular resistance
How do you get an action potential?
They are triggered by a graded potential by dendrites and cell body. It alter membrane potential in the axon hillock (trigger zone) and results in an action potential in the axon.
Action potentials are triggered when?
Potential exceeds the threshold potential at the “trigger zone” of the neuron.
Spatial summation?
Graded potentials originate at different locations and can influence the net change in Vm. This can allow neuron to reach threshold.
Temporal summation?
The time of graded potentials.
Action potential Phases for membrane potential? 3•
•depolarization phase (less negative rapidly)
•Repolarization Phase (more negative rapidly)
•Hyperpolarization phase (more negative than resting membrane potential, and then back to resting membrane potential)
During hyperpolarization, what ion channels are open and closed?
Potassium channels are open and sodium channels are closed.
Feedback loop of neuron membrane potential?
Sodium channels are initially closed, but then opens and sodium goes to its equilibrium potential. This causes neighbouring sodium channels to open, which causes more depolarization, and a greater change of permeability.
If there is a higher density of voltage gated Na+ channels, then how does action potential threshold change?
Lower threshold required to trigger an action potential since the channels are close enough to be opened from the feedback. Graded potentials can travel in longer distances.
!!!!How to stop membrane potential feedback cycle?
There are two gates in the ion gated channel. The activation gate closes the channel. When there is a graded potential, the activation gate opens and the inactivation gate is also open, which cause rapid flow of Sodium. But over time, the inactivation gate starts to close to slow Na+ diffusion.
Excitatory postsynaptic potential (EPSP)?
Contribute to depolarization.
Inhibitory postsynaptic potential? (IPSP)
Contributes to hyperpolarization
