Synaptic Stars

What am I looking at?

This is a video showing a section of the cerebral cortex from a mouse. The video was taken by moving the focal plane of a microscope from the bottom of a thick section of brain tissue to the top. This way of collecting a 3D dataset, known as a stack, is called Z-stack scanning. The green lines moving across the screen are sections of one excitatory pyramidal neuron. The red dots are both excitatory and inhibitory presynaptic terminals. And the blue dots are excitatory postsynaptic terminals.

Biology in the background

The cells in the brain communicate with each other to carry out their biological responsibilities. To do this, they send out projections called axons and dendrites from their cell body, or soma; the axons send outgoing signals, and the dendrites receive incoming signals. These projections contact each other at points called synapses. There are different types of synapses; some communicate with neurons through chemical signals called neurotransmitters, and others send electrical signals directly to cells they connect with.

Further, some synapses are excitatory, which means they increase the activity of the cells receiving the signal, and some synapses are inhibitory, which means they decrease the activity of the cells receiving the signal. When multiple types of signals are received by a single neuron, it does a bit of math – adding up the excitatory signals, subtracting the inhibitory ones, and ultimately coming up with a value that, if it crosses a certain threshold (called the action potential threshold), causes the neuron to fire.

A neuron sending a signal is called a presynaptic neuron, and the signal is sent from a portion of the neuron called the presynaptic terminal. A neuron receiving a signal is called a postsynaptic neuron, and the signal is received at the postsynaptic terminal.

The gap between neurons at a synapse is between 20 nanometers and 40 nanometers across, or between 4,000 and 2,000 times smaller than the width of a human hair.

Technique

This image was created using a type of fluorescence microscopy called lightsheet microscopy.