transport mechanisms

diffusion

means random molecular movement of substances molecule by molecule, either through intermolecular spaces in the membrane or in combination with the channel protein

energy of the normal kinetic motion of matter

it is the energy that causes diffusion

active transport

means movement of ions or other substances across the membrane in combination with the carrier protein in such a way that the carrier protein causes a substance to move against an energy gradient, such as from a low concentration tape to a high concentration state

channel proteins

some proteins have watery spaces all the way through the molecule and allow free movement of water, as well as selected ions or molecules

carrier proteins

proteins that bind with molecules or ions that are to be transported, and confirmational changes in the protein molecules then move the substances through the interstices of the protein

lipid solubility of substance

an important factor for determining how rapidly diffuses through the lipid bilayer

aquaporins

protein pores contained by body cell membrane that selectively permit rapid passage of water through the membrane

dating of protein channels

provides a means of controlling ion permeability of the channels

voltage gated channels

ligand gated (chemical) setting

two principal ways of gating channels

voltage gating

in this case, the molecular confirmation of the gate or its chemical bonds response to the electrical potential across the cell membrane

chemical or ligan gating

some protein channels kids are opened by the binding of a chemical substance with the protein, which causes a confirmational or chemical bonding change in the protein molecules that opens or closes the gate

acetylcholine receptor

serves as a ligand gated ion channel

acetylcholine

opens the gate of this channel, providing a negatively charged pore about 0.65 nm in diameter that allows uncharged molecules or positive ions smaller than this diameter to pass through

-70 to -80 mV

resting potential of a neuron

action potential

a brief depolarization or repolarization that propagates from the site of origin

<+20

amount of depolarization that will normally result in recovery without effect

graded potentials

are short lived depolarizations or hyperpolarizations of an area of membrane