PLASMA MEMBRANE & TRANSPORT OF IONS

There are three ways in which molecules pass through the cell membrane, and they are passive transport, facilitated diffusion, and active transport. The first transport does not require ATP, so molecules move across the cell without the need for energy. Facilitated diffusion is when ions move through the membrane via the aid of a membrane protein. During this diffusion, ions can move in different directions--uniport, symport, and antiport. Active transport requires ATP to move ions through the cell against the electrochemical gradient. 

An example of symport transport is the Na+/glucose symporter. An example of the antiporter is the Na+/K+-ATPase pump. Ths is the process of moving sodium (Na+) and potassium (K+) ions across the plasma membrane. 

http://humanbiologylab.pbworks.com/w/page/45302491/Resting%20Cellular%20Membrane%20Potential

There is a higher concentration of Na+ in the extracellular side of the cell and a higher concentration of K+ inside the cell. So, three sodium comes into the cell and two potassium goes out of the cell. Homeostasis of the membrane potential is associated with the cell's electrical charge and ion concentration. So, a membrane potential of a cell at rest is called the resting potential, a value of -70mV. When an impulse is fired in a neuron down the axon, it's referred to as an action potential (AP). AP are generated by voltage-gated channels embedded in a membranre. A stimulus first causes sodium channels to open, so the neuron becomes more positive becoming depolarized. It takes quite a bit for the K+ channels to open up, but when they do, it rushes out of the cell, sort of reversing the depolarization. At that time, the Na+ channels start to close. The AP then goes below -70mV (hyperpolarization) since the K+ channels stay open for a longer time. Gradually, the ion concentrations go back to the resting level, returning to -70mv. 

 

https://www.moleculardevices.com/what-action-potential