Nervous system pt. III (RA) Flashcards
Explain why there is a potential difference across the cell membrane.
There is an unequal distribution of anions and cations between the cytoplasmic side and extracellular side of cell membrane.
State the resting membrane potential.
-60 to -80mV
State the 3 factors contributing to the resting membrane potential.
There are large negatively charged proteins (A-) that are too large to diffuse out of neuron into the extracellular fluid.
The neuronal membrane has a different permeability towards Na+ and K+.
There is a sodium-potassium pump.
Explain how the sodium-potassium pump contributes to the cell’s resting membrane potential.
The sodium-potassium pump actively transports Na+ and K+ using energy from ATP hydrolysis to ADP.
For every molecule of ATP, 3 Na+ are moved out and 2 K+ are moved into the axoplasm (cytoplasm). Rate of Na+ loss versus K+ entry is 3:2.
This established concentration gradients for Na+ and K+ as it ensures:
[Na+] inside < [Na+] outside
[K+] inside > [K+] outside.
Outline how the sodium-potassium pump move the ions in and out of the cell.
The pump binds to 3 sodium ions and 1 molecule of ATP. The splitting of ATP provides energy to change the shape of the channel. The sodium ions are driven through the channel. The sodium ions are released to outside of the membrane, and new shape of the channel allows two potassium ions to bind. Release of the phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane.
Explain how differential permeability of axon membrane towards Na+ and K+ contributes to resting membrane potential.
K+ ions diffuse down the concentration gradient (in to out) via potassium leak channels or non-gated K+ ion channels. Na+ ions diffuse down the concentration gradient (out to in) via sodium leak channels or non-gated Na+ ion channels.
Axon membrane is 20-25x more permeable to K+ than Na+ as there are very few Na+ leak channels compared to K+ leak channels.
Efflux of K+ exceeds influx of Na+ into axon, and the net loss of positive charges from the axoplasm results in a negative resting membrane potential.
Define depolarization and hyperpolarization.
Depolarization is when the membrane potential becomes more positive than the resting potential. Hyperpolarisation is when the membrane potential becomes more negative than the resting potential.
Describe how a stimulus results in changes in membrane potential.
A stimulus results in changes in changes in membrane permeability, causing ion movement, changing the membrane potential.
Describe how depolarization and hyperpolarization are brought about by.
Hyperpolarization is brought about by opening up more potassium channels, resulting more K+ diffusing out of the neuron.
Depolarization is brought about by opening up more sodium channels, resulting in more Na+ diffuse into neuron.
The gates Na+ or K+ channels are opened to increase permeability to these ions, not the leak ion channels.
State the difference between a gated ion channel and a leak/non-gated ion channel.
Leak ion channels are always open, while gated ion channels are only open in response to a stimulus. Non-gated ion channels maintain resting potential while opening and closing of gated ion channels cause changes to this potential.
