They found that mitochondria have two distinct membrane systems, the outer membrane and the inner membrane. More modern work has provided details of the macromolecular components of the outer and inner membranes. The inner membrane surrounds the matrix compartment with a barrier impermeable to those hydrophilic molecules and ions which lack specific transport proteins. The inner boundary and the cristal membranes form a membrane system with a much larger surface area than that to of the outer membrane, reflecting its critical function in ATP synthesis. Along with high-resolution, scanning electron microscopy, electron tomography has revealed new information about mitochondrial membrane structure.
Tomography literally means visualization of slices.
We have investigated the use of electron tomography combined with high resolution light microscopy for studies of dendritic spines to determine optimal methods for visualizing and measuring these important structures. Dendritic spines are small protuberances emanating from the dendrites of certain types of neurons that are the major site of excitatory synapses in the central nervous system. Spines are labile structures, changing their size, shape and number during development and in response to environmental stimuli, and are thought to be key structures in mediating synaptic plasticity. They vary in size and morphology, generally ranging in length from 1-4 m with a maximum diameter of 1 m and a minimum of 0.1 m. Their distribution across a neuron is not homogeneous, so one has to examine spines over a sufficiently large portion of the dendrite to get a reasonable estimate of their distribution.