Instead of conducting electrical impulses, axons ____ an impulse at each point. The impulse travels along a line without weakening because at each point it generates anew.
In the absence of any outside disturbance, the neurons membrane maintains an ____ ____, also known as ____ - a difference in electrical charge between the inside and the outside of a cell.
electrical gradient : polarisation
The neuron inside the membrane has a slightly negative electrical potential with respect to the outside. The difference in voltage in a resting neuron is called the ____ ____.
The membrane is ____ ____. That is some chemicals pass through it more freely than others do.
____, ____ ____, ____, and ____ pass freely through channels that are always open.
Oxygen, carbon dioxide, urea, and water
A few biologically important ions, such as ____, ____, ____, and ____, cross through membrane channels (or gates) that are sometimes open and sometimes closed.
sodium, potassium, calcium, and chloride
When a membrane is at rest, the sodium channels are ____.
The ____-____ ____, a protein complex, repeatedly transports three sodium ions out of the cell while drawing two potassium ions in.
As a result of the sodium-potassium pump, sodium ions are more than 10 times more ____ outside the membrane than inside, and potassium ions are slightly more ____ inside than outside.
When the neuron is t rest, two forces act on sodium, both tending to ____ it into the cell.
The first force is the ____ ____. Sodium is positively charged and the inside of the cell negatively charged, these opposite electrical gradients attract, so the electrical gradients tend to pull sodium into the cell.
The second force is the ____ ____, the difference in distribution of ions across the membrane. Sodium is more concentrated on the outside than inside, therefore, sodium is more likely to enter the cell than to leave it.
During rest the sodium channels are ____ and almost no sodium flows except for the sodium pushed out of the cell by the sodium-potassium pump.
Potassium is subject to ____ forces.
Potassium is positively charged and the inside of the cell is negatively charged, so the ____ ____ tends to pull potassium in.
Potassium is more concentrated inside the cell than outside, so the ____ ____ tends to drive it out.
The cell has ____ ions too. Negatively charged proteins inside the cell are responsible for the membranes polarisation.
____ ions, being negatively charged, are mainly outside the cell.
The resting potential prepares the neuron to respond ____.
Messages sent by axons are called ____ potentials.