What are some adaptations of nerve cells

Fully energized - how nerve cells communicate

Enlarge image
Isolated nerve cell (electron microscope image)
Isolated nerve cell (electron microscope image)
© Max Planck Institute for Developmental Biology / Jürgen Berger
© Max Planck Institute for Developmental Biology / Jürgen Berger

Nerve cells, or neurons, make up the most important part of the brain and, in many ways, are the most extraordinary cells that life has produced. Most of the neurons in the brain are tiny, some no larger than a few millionths of a meter in diameter, but they are vast in number. Their main task is to process information and pass it on to other neurons. They thus form the basis for all sensory and behavioral performances.

As far as we know, the nerve cells in all animals - from jellyfish to humans - use the same electrochemical mechanisms to transmit information. It looks as if the primitive mechanism in the jellyfish nerve cell has proven itself so well that it has been given a permanent place in evolution. In order to produce more complicated and more adaptable behavior, only a larger number of such nerve cells had to be put together in a more complex way.

Nerve cells use two very different “languages” to communicate with one another. One of them is the nerve impulse, also called action potential, an electrical signal that propagates along the axon, the long nerve fiber, to the nerve end, the synapse. When it reaches the endings, the action potential disappears, but at the same time triggers a completely different process: the transfer of information via the synapse to the recipient neuron.

"Domino Day" in the nervous system

Synaptic transmission is the neuron's second “language”. This process is based on the release of chemical messengers or neurotransmitters. Small membrane-covered vesicles, so-called vesicles, absorb the messenger substances like message packages and transport them to the synaptic membrane, where they are released into a gap and diffuse to the recipient cell. Hundreds of “transporters” release thousands of messenger molecules - it's like a short, localized rain shower. The molecules bind to so-called receptors - signal receivers in the manner of an “antenna” - in the membrane of the downstream nerve cell, where they cause an electric current through the cell membrane and a change in the membrane potential.

While synaptic transmission is a graduated process, the action potential is an all-or-nothing event: once started, it cannot be stopped and continues to the end of the axon. The action potential represents a change in the electrical voltage across the cell membrane, which results from the influx of sodium ions into the cell and a subsequent outflow of potassium ions out of the cell; the ion movements take place through specialized pores in the cell membrane, so-called ion channels.

Neighboring ion channels register that the voltage across the cell membrane has changed and open their pores. Since the channels are close together along a nerve fiber, the signal propagates rapidly as a chain reaction of changes in tension. A channel is switched more or less indirectly by its predecessor - almost like a row of dominoes falling one after the other. With this chain reaction, the signal manages between one and one hundred meters of cell fiber every second. The amplitude of the action potential of 100 to 120 millivolts remains constant over the full length of the nerve fiber because the all-or-nothing impulse is constantly being rebuilt as it migrates from the cell membrane.