All cells have a __, a voltage (difference in electrical charge) across their plasma membrane. In neurons,inputs from other neurons or specific stimuli cause changes in this membrane potential that act as signals, trasmitting and processing info. rapid changes in __ enable us to climb trees, read, etc.
membrane potential x2
The membrane potential of a resting neuron- one that isn't sending signals- is its __ and is typically -60 and -80 mV. The minus sign indicates the inside is negative relative to the outside.
K+ and Na+ play critical roles in the formation of __. For each, there is a concentration gradient across the plasma membrane of a neuron.
- concentration of K+ is __ millimolar inside; __ outside
- concentration of Na+ is __ mM inside; __ outside.
These two gradients are maintained by __ in the membrane.
The concentratrion gradients of K and Na across the plasma membrane represent a chemical form of potential energy. Converting this chemical potential to an electrical potential involves __, pores formed by clusters of specialized proteins that span the membrane. __ allow ions to diffuse back adn forthe across the membrane.As they diffuse through channels, they carry with them units of electrical charge. Any resulting net movement of positive and negative charge will generate a __, or potential, across the membrane.
ion channels x2
The ion channels that establish the membrane potential have __, meaning that they allow only certain ions to pass.
The diffusion of K through open potassiuum channels is criticalf or formation of the __. In the resting mammalian neuron, these channels allow K+ to pass in either direction across the membrane. Because the concetration of K+ is much higher inside the cell, the chem concentration gradient favors a net outflow of K+. However, since potassium channels allow only K+ to pass, Cl- and other anions inside the cell cannot accompany the K+ across the membrane. As a result, the outflow of K+ leads to an excess of - charge inside the cell. This buildup of - charge within the neuron is the source of the membrane potential.
What prevents the buildup of negative charge from increasing indefinitely?
- The answer les int eh electrical potential itself. The excess - charges inside the cell exert an attractive force that opposes the flow of additional positvely charged K+ out of the cell. The separation of charge (__) thus results in an electrical gradient that counterbalances the chem concentration gradient of K+.
Page 1051: Example of resting potential!
- When our model neuron reaches equilibrium, the electrical gradient will exactly balance the chem gradient, such hthat no further net diffusion of K+ occurs across the membrane. The magntitude of the membrane voltage at equilibrium for a part ion is called that ion's __.
- For a membrane permeable to asingle type of ion, __ can be calculated using a formula called the __ equation.
equiibrium potential (Eion) x2Nernst
Although the equilibrium potential for K+ is -90 mV, the __ of a mammal neuron is somewhat less -. THe difference reflects the small but steady movement of Na+ across the few open sodium channels in a resting neuron.
True or False:
BEcause hte concentration gradient of Na+ has a direction opposite to thatof K+, Na+ diffuses into the cell and thus make hte inside of the cell less -.
Because neither Na+ or K+ is at equilibrium in a resting neuron, each ion has a net flow (a __) across the membrane. The __ remains steady, which mean sthat the K+ and Na+ currents are equal and opposite.
True or False:
Ion concentrations on either side of the membrane also remain steady because hte charge separation needed to generate hte resting potential is extremely small (about 10-12 mole/cm2 of membrane.) This represnents the movement of far fewer ions than would be required to alter the chem concentration gradeint.
Under conditions that allow Na+ to cross the membrane more readily, the __ will move toward __ and away from __.