Neurobiology 2 Flashcards
Define membrane potential
The difference in electrical charge between the outside and inside of the cell measured in millivolts (mV)
Where do electrical charges that influence membrane potential come from
Ions
At rest, what are the concentrations of ions inside the neuron
Potassium - High.
Sodium & Chlorine - Low.
What can be said about organic anions (A-) and their concentrations with respect to neurons
High inside concentration and does not leave the cell.
When does the membrane potential change
When an ion is selectively allowed to move down its concentration gradient
Ion flux across a membrane depends on:
- Concentration gradient
2. Electrical difference (membrane potential)
Greatest electrochemical difference is greatest in which type of cells
Neurons
How does a neuron generate a resting membrane potential
By the movement of potassium (K+) down its concentration gradient out of the cell
What type of K+ channels are open at rest in the neuron
Non-gate K+ channels
What direction is the net flux of potassium in the neuron
Out of the cell
What channels determine the net flux of potassium in the neuron
- Non-gated (leaky) potassium channels
2. Na+/K+ ATPase
How is the resting membrane potential generated
Movement of K+ down its concentration gradient
How is the resting membrane potential maintained
Na+/K+ ATPase
How do you calculate the equilibrium potential (E-ion) for a particular ion
Nernst Equation
How do you calculate the membrane potential based on the concentrations, valences, and relative permeabilities of a series of ions
Goldman Equation
The membrane at rest is slightly leaky to what ions
Na+ and K+
Why is the neuron’s resting potential -70mV when potassium’s equilibrium potential is -90mV
Because of leaky Na+ channels making it more positive
If you selectively open a particular type of ion channel, what will the neuron try to do
Cause the membrane potential to approach the equilibrium potential for that ion
How can a neuron rapidly change its membrane potential
By changing its permeability to specific ions
What are gated ion channels
An ion channel where something causes them to open and close
What are three types of gated ion channels
- Ligand-gated channels
- Voltage-gated channels
- Mechanically-gated channels
How do ligand-gated channels work
A signal (ligand) binds to the channel and regulate the opening/closing of the gate
What is an example of a ligand-gated channel
Acetycholine regulatin the entry of Na+ into muscle cells
How do voltage-gated channels work
Regulated by the electrical state of the cell
How do mechanically-gated channels work
Regulated by a physical change (pressure, stretch, etc.)
What are graded potentials
Changes in the membrane potential that cause an electric signal
Graded potentials vary in __ and depend on __
Vary in magnitude and depend on the strength of the stimulus
Graded potentials an lead to what
Depolarizations or hyperpolarizations of the membrane potential depending on stimulatory or inhibitory stimuli, respectively
What do ligand-gated ion channels cause
Graded potential changes in the membrane potential within the dendrites and cell body
What is conduction with decrement
Graded potentials decrease in strength as they get farther away from the opened ion channel
When will an action potential fire
When the membrane depolarization caused by graded potentials is large enough at the axon hillock
What is spatial summation
When signals arrive at the same time at different locations on the cell membrane and are intergated
What part of the neuron integrates/summates graded potentials in space and time
Dendrites and the cell body
What is temporal summation
Integration of signals arriving at different times at the same location on the cell membrane
What are two neurotransmitters that cause excitatory depolarizations
Glutamine & Acetylcholine
What is a neurotransmitter that causes inhibitory hyperpolarizations
Gamma amino butyric acid - GABA
What is the action potential
A small stimulus that generates a small depolarizations that is restored quickly
How is the action potential generated
A large enough stimulus that can bring the membrane potential to the threshold potential
What is the threshold potential
The potential at -55mV at which an action potential will then fire
How high does the action potential reach
+40mV
List the phases of the action potential
- Depolarizing graded potential
- Depolarization phase of action potential
- Absolute refractory period
- Relative refractory period
- Repolarization phase of action potential
- After-hyperpolarization (the dip phase)
What does depolarization of the membrane to threshold potential activate
Voltage-sensitive Na+ channels. Voltage-sensitive K+ channels also open, but with slower kinetics than the Na+ channels
How is the action potential triggered
By the gated opening of voltage-gated Na+ channels
When do the voltage-gated Na+ channels become unstable and close
At the peak of the action potential. They have an intrinsic capacity for inactivation at +30mV
What happens in the action potential’s first step - “Resting State”
Voltage-gated channels are closed
What happens in the action potential’s second step - “Threshold”
In response to a stimulus, voltage-gated Na+ channels open rapidly leading to depolarization->threshold potential is reached->Action potential
What happens in the action potential’s third step- “Depolarization”
Depolarization of the action potential
What happens in the action potential’s fourth step - “Repolarization Phase”
Na+ channels become unstable and the inactivation gates close rapidly. Voltage-gated K+ channels open and K+ moves out of the cell. Closing of Na+ channels and opening of K+ leads to a repolarization
What happens in the action potential’s fifth stop - “Undershot”
After depolarization, the membrane potential goes all the way down to -90mV because both the Na+ channels activation and inactivation gates are closed. K+ channels are still open, but slowly
What is the refractory period
During the undershoot phase of the action potential, the neuron cannot depolarize in response to another stimulus
