Exam 1 Week 2: ppt 4 Resting Membrane Potential Flashcards
what are two fundmentally different types of electrical signals?
- Graded
- All or None (nongraded)
Graded Potentials
Varies in size & shape with a Seemingly unlimited variabilty
Locally conducted only short distances along a neuronal membrane
Include the generator potentials & postsynaptic potentials
What are two types of graded potentials?
- generator potentials
- postsynaptic potentials
Graded or All or None (nongraded) Potentials?
generator potentials
postsynaptic potentials
both are graded potentials
Nongraded - All or None potentials
They are Uniform in size & shape
They are All-or-none – that is that they either occur in their entirety or not at all
They are the Propagated electrical signal within the neuron and are the action potential seen in neurons
Is an action potential Graded or All or None?
All or None!
What are channel proteins?
Channel proteins span the neuron’s plasma membrane and form ion pores for (most channels have 4-6 subunits forming the channel). They regulate all of the electrical signals we have been talking about in this presentation.
Some pores remain open – non-gated or leak channels while Some pores open in response to certain circumstances – gated channels
What are two main types of Channel proteins?
- Leak channels (also called non-gated channels)
- Gated channels
What are non-gated (leak) channels?
They are ion channel proteins in the cell membrane that remain open
What are gated channels?
They are ion channel proteins in the cell membrane that only open in response to certain circumstances
What is Ionic Diffusion (with an example explaining it using Na and channel proteins)?
In the leak channels or when gated channels are opened, Ionic diffuse down a concentration gradient through channels specific to that ion. Ions are affected by both their concentration gradient and the charge differences across the membrane. Ions carry a charge with them – in this case Na ion carries a positive charge. So if it is entering a region with a high positive charge it will be reluctant to enter because like charges repel. On the other hand if it is entering a region of negative charge its entry will be accelerated because opposite charges attract
What are two big things that effect ion diffusion through ion channels?
- ion concentration on both side of the cell membrane (will want to flow down the concentration gradient - ions in area of more ions will want to move to area of less ions)
- Electrical charge. Like charges will repell and opposite charges will attract.
Diffusion dependant on these two factors together called diffusing down an electrochemical gradient
What produces the electrical current across cell membrane?
the movement of ions produces Electrical current.
What does the electrical current, produced by the movement of ions, depend on?
- Size of chare difference (voltage or electrical potential)
- Size of the concentration gradient
What are three key ions in producing electrical currents across membranes?
Na+ (cation)
K+ (cation)
Cl- (anion)
What is an equilibrium potential?
Equilibrium Potential is the Electrical potential (voltage) produced across the membrane as a result of the movement of a single ion to electrochemical equilibrium – equal combination of charge & concentration balance across the membrane. The magnitude of the equilibrium potential across the membrane is Predicted by the Nernst Equation. You will notice that it is predicted by a series of constants, the valence of the ion (amount of charge) and the internal vs external ion concentrations across the membrane.
What are the driving forces for potentials in neurons?
describe influence of Na+, K+, Cl- and intracellular proteins
Extracellular concentrations of Na+ and Cl- ions are quite high and K+ is quite low. Inside of membrane is more negative because of negatively charged intracellular proteins.
So if only Na+ is allowed to flow, There is a great influx of Na+ across the membrane when it is allowed to flow so it produces a large positive equilibrium potential because it is going down both its charge and chemical gradient. Cl- ion tends also to enter the cell because it is going down its concentration gradient but is repelled by the negative charge of the proteins. K+ ion tneds to leave the neuron because of its very large concentration gradient but that is modified somewhat by the negative charge inside the neuron (attracting its positive charge)
Why is the inside of a cell more negative?
negatively charged intracellular proteins
What is the equilibrium potentials for spinal motor neurons for Na+ K + and Cl- ?
(numeric value)
Na+ EP = +61 mV
K+ EP = -94 mV
Cl− EP = -64 mV
So as a result of the great influx of Na+ it has a high positive equilibrium potential, due to the efflux of K+ and influx of Cl both have a negative equilibrium potentials – greater efflux of K+ than influx of Cl- so K+ equilibrium potential more negative than CL-
(I don’t understand the narrative here too well)
explain the resting neuron membrane potential
Resting potential of a spinal motor neuron is about -65 mV inside compared to outside and is due to the combination of the leakage currents. By the way, each each type of neuron will have different resting membrane potential based upon the fluxes across the membrane in that neuron.
What is a common value talked about for the resting membrane potential for a neuron?
Dr. Lake’s slide this time said -65mV
I’ve more commonly heard -70mV
(By the way, each each type of neuron will have different resting membrane potential based upon the fluxes across the membrane in that neuron.)
What maintains the resting membrane potential?
the combination of the currents produced by ionic leakage.
Why is it not surprising that the resting membrane potential is closer to the equilibrium optential of K+ than Na+?
The resting membrane potential in a neuron is Dependent on both equilibrium potentials and permeability for all ions but will focus on Na+ & K+ ions. Since there is a much greater permeability for K+ than Na+ at rest (K+ permeability 100X > Na+ permeability) and the Na+ EP = +61 mV & K+ EP = -94 mV – it is not surprising that the resting membrane potential is closer to the equilibrium potential of K+ than Na+
Is the resting memberane potential closer to the equilibrium potential (EP) of K+ or Na+?
K+
What is the RANGE of resting membrane potential in most human neurons?
Resting membrane potential is -65 to -81 in most human neurons
what happens to the charge inside of the cell during depolarization?
it becomes more positive (less negative) than the resting potential
what is it called when the inside of the cell becomes more negative than the resting potential?
hyperpolarization
(the cell becomes hyperpolarized)
What is the Na+K+ ATPase pump?
- –Important role in returning ions to their original location
- –Operates continuously (moving 3 Na+ out and 2 K+ in to the cell with each pump)
- –Requires energy derived from hydrolysis of ATP via enzyme ATPase
Now as these ions leak through their leak channels too much Na+ would leak in and too much K+ would leak out and the balance would be disrupted. At rest this balance is maintained because of active pumping of ions. Na+-K+ ATPase pump
Important role in returning ions to their original location – Na+ to the outside and K+ to the inside in a 3 to 2 ratio respectively. This pump Operates continuously and so requires a huge amount of energy derived from hydrolysis of ATP via enzyme ATPase.
do neurons use energy when no electrical impulse is flowing through them?
yes
The NaK ATPase pump uses energy to maintain the membrane potential
Not surprising then that the brain which constitutes only 3% of the body mass uses 20-25% of all of the bodies energy use at rest – 20-25% of the basal metabolic rate is the brain alone. This high rate of energy use is an important negative in the evolution of the large brain.
The brain is only ____% of body mass, yet it uses _____% of all body energy at rest.
The brain is only 3% of body mass, yet it uses 20-25% of all body energy at rest.
