An Inferno of Neurons

What am I looking at?

This is a sample of tissue from the hippocampus in the brain of a mouse. Shown in green are the excitatory pyramidal neurons (1), and in red are inhibitory interneurons (2).

Biology in the background

The cells in the brain communicate with each other to carry out learning and memory storage. To do this, neuronal cell bodies send out two projections: axons and dendrites. Axons establish contacts with dendrites (and sometimes with other axons) at points called synapses, where neurons can send signals to one another.

A single pyramidal neuron can form tens of thousands of synapses with other neurons all over the brain. One of the characteristic features of a pyramidal neuron – besides the triangular-shaped soma, or cell body, from which its name is derived – is the presence of separate downward- and upward-pointing dendritic trees. Pyramidal neurons integrate information in these dendrites, in the form of excitatory signals from synapses, before a decision is made to communicate excitatory signals to downstream neurons via signals in the axon.

Inhibitory interneurons, on the other hand, form synapses with neurons that dampen excitation. These inhibitory signals help shape how the pyramidal neurons signal to their downstream targets and provide a way to decrease pyramidal cell excitation. Most of the synapses formed by inhibitory interneurons are contained within a small circuit.

A pyramidal neuron in a mouse brain is about 20 micrometers long, or roughly three times smaller than the width of a human hair, and an interneuron is somewhat smaller – about 14 micrometers long, or roughly five times smaller than the width of a human hair.

Technique

This image was created using array tomography from images spread across more than a thousand image layers.