The Human Brain
Portraits of the Mind
While all cells in the body hold the same genome, only a particular set of its genes get turned on in various cells; each type of neuron switches on a gene set that defines its character.
In this picture, a gene called JAM-B had been switched on, which then turned on a fluorescent protein to reveal a small group of brain cells. The resulting image shows that all of the neurons' projections called dendrites are aligned in the same direction; moreover, these retinal neurons are known to detect only objects moving in an upward direction.
Baroque Blood Vessels
View of a Stroke
Artsy Brain Cells
Color My Cerebellum
While Golgi's staining method did wonders for finding structures hidden in a tangle of neurons, it couldn't distinguish individual brain cells that were illuminated in the same color.
Enter a bit of genetic trickery called Brainbow: Robert Tsien and other chemists tinkered with and discovered fluorescent proteins responsible for the different colors emitted by various sea creatures (such as corals and jellyfish). By coaxing different sets of neurons or even different individuals of a species (say a male and female) to express different proteins, scientists could pick out the cells by the color they glowed.
Here, several motor-neuron axons (slender projections on neurons that transmit signals to other neurons) travel side by side as they lead to the muscles whose contractions they regulate.