Inner mitochondrial membrane

Definition

The inner mitochondrial membrane is the inner membrane of the mitochondrion, an organelle found in most eukaryotic cells. It is an example of a biological membrane. It comprises a lipid bilayer. It is highly folded in order to increase its area, with the folds called cristae. It controls the entry and exit of materials between the intermembrane space on its outside, and the mitochondrial matrix on the inside.

The movement of materials as well as the voltage maintained across the inner mitochondrial membrane are critical to the mitochondrion's role in energy production.

Summary

Item	Value
Type of organisms whose cells contain the inner mitochondrial membrane	Same as the organisms whose cells contain mitochondria: eukaryotic cells only, including plant cells, animal cells, and the cells of protists and fungi
Type of cells within the organisms that contain the inner mitochondrial membrane	Same as the cells that contain mitochondria: all cells except red blood cells in mammals (other vertebrates do have mitochondria in their red blood cells).
Number of inner mitochrondrial membranes per cell	Same as the number of mitochondria: 1 to 1000s, depending on the energy needs of the cell
Size	$~70$ angstrom thickness (very approoximate), similar to the outer mitochondrial membrane, compared with mitochondrial diameter of $0.5-1.0\mu m$ , so the thickness is about 1% of the diameter of the mitochondrion. The area is about five times that of the outer mitochondrial membrane, due to the folds called cristae. High surface area is helpful for its goal of facilitating more energy generation through the transfer of materials (mostly protons) via the membrane.
Nearby stuff	Inside is the mitochondrial matrix. Outside is the intermembrane space, and further out is the outer mitochondrial membrane.
Electrochemical gradient across the membrane	The outside (the intermembrane space) is more positively charged than the inside (the mitochondrial matrix), and has an excess of protons. Moving protons from inside to outside, against the gradient, requires and absorbs energy. Moving protons back inside releases energy that can be captured through either ATP production or heat generation.