Neurons in Central Nervous System

Neurons in Central Nervous System

Communication between neurons, or nerve cells, is the cellular basis for thinking, decision making, and control of muscular movements. Neurons are cells with a particular shape: they possess two types of long ramification, called the axon and the dendrites. The axon of one neuron is in contact with the dendrites of other neurons. These contacts are termed synapses. Each neuron forms thousands of synapses with other neurons. Neurons communicate by sending electric signals along their axons.

When a signal reaches a synapse, it triggers the release of neurotransmitters, which are small molecules that diffuse in the intercellular space and activate receptor on the surface of the other cell forming the synapse. In turn, activated receptors generate electric signals of variable intensity. The signals coming from every synapses of a neuron passively converge to the base of its axon and are summed up. If the resulting signal is intense enough, the axon will actively propagate the signal further; otherwise, the signal will stop there.

Electron microscopy (EM) has been used for more than 50 years for this purpose. However, specimens are usually dehydrated prior EM observation and this generates several distortions. Our goal is to provide a better picture of the synapse that reflects its native, intact structure. We can achieve that by applying cryo-electron microscopy of vitreous sections (CEMOVIS), a recently developed technique where specimens can be observed without dehydration. We have already shown that the space between the two cells, termed the synaptic cleft, contains a high density of regularly arranged molecules. To get further insights, we want to obtain three dimensional images of model synapses by using a method termed cryo-electron tomography. This should notably allow us to decipher the arrangement of the cellular skeleton at the synapse and of the scaffold holding receptors in place. These are highly involved in the regulation of synaptic transmission.

Neurons

The body contains more than 100 billion neurons. Neurons are similar to other cells in the body in that they have a cell membrane, a nucleus containing genes, and organelles that carry out basic cellular functions such as energy production. One important difference is the presence of extensions that receive messages (dendrites) and transmit messages (axons). Although mostly concentrated in the brain, neurons are also important for both communicating sensory information and controlling body functions such as muscle activity.



How Neurons Communicate

Various stimuli such as light, sound, temperature and pain interact with specific sensory receptors which transform the stimulus into a neural code that is carried by a chain of neurons to the brain. Systems of neurons in the brain are then responsible for interpreting this information -- information processing.

Information is carried along axons and dendrites by changes in electrical properties called action potential. An action potential is initiated when a chemical messenger attaches to a specific site called a receptor. This attachment triggers an electrical signal to be generated that travels through the neuron. Once the electrical signal reaches the end of the axon, a neurotransmitter ...