NAS Basic Processes

The lipid bilayer is a [blank_start]hydrophobic[blank_end] environment. This means that it is [blank_start]impermeable[blank_end] to most molecules including [blank_start]ions[blank_end] (they are usually [blank_start]hydrophilic[blank_end]). This means that intracellular and extracellular compartments are established with very different [blank_start]ionic[blank_end] compositions. Ion [blank_start]pumps[blank_end] are used to [blank_start]maintain[blank_end] the gradient.

The inside of a cell contains a slight excess of [blank_start]anions[blank_end] which sets up a [blank_start]negative[blank_end] voltage inside the cell. This voltage is known as the [blank_start]membrane potential[blank_end] (Em). In neurons this is usually about [blank_start]-65[blank_end]mV. Em is determined by the [blank_start]balance[blank_end] of charges.

Ion movement across the membrane is [blank_start]passive[blank_end]. Ion channels are therefore required. There are a few [blank_start]permeant[blank_end] ions (ions that can pass through the channels): Na+, K+, [blank_start]Ca2+[blank_end], Cl-. There are three different types of ion channels that are available: Non-gated ([blank_start]leak[blank_end]): these set the [blank_start]Em[blank_end] of the resting membrane [blank_start]Voltage[blank_end]: generate the action potential [blank_start]Ligand[blank_end] (chemical): generate the Em changes at the [blank_start]synapse[blank_end]

The [blank_start]resting membrane potential[blank_end] of the cell is about -65mV. There are several factors that cause this: 1) the [blank_start]chemical[blank_end] gradient - this is set up due to the [blank_start]potassium[blank_end] [blank_start]efflux[blank_end]. 2) the electrical force - the [blank_start]potassium[blank_end] [blank_start]efflux[blank_end] results in the inside being more [blank_start]negative[blank_end] than the outside. This causes [blank_start]potassium[blank_end] influx. At [blank_start]resting membrane potential[blank_end] there is no net movement of [blank_start]potassium[blank_end]. 3) the [blank_start]permeability[blank_end] of the membrane to each ion - how easy it is for ions to move across the membrane through ion [blank_start]channels[blank_end]. The following assumptions are made: - the membrane is only permeable to [blank_start]potassium[blank_end] - the Em is initially [blank_start]0[blank_end]

Which of the following is true about the Nernst and Goldman equation?