This news release is available in German.
To write this little piece of text, the brain sends commands to arms and fingers to tap on the keyboard. Neuronal cells with their cable-like extensions, such as axons, transfer this information as electrical pulses that trigger muscles to move. The axonal signal speed can be to up to 100m/s in myelinated axons along the spinal cord.
For a long time, scientists assumed that axonal signal conduction is by and large digital: either there is a signal, "1", or there is no signal, "0".
Strong propagation speed variations
Now, a team of researchers under Douglas Bakkum and Andreas Hierlemann at the Department BSSE of ETH Zurich in Basel presents evidence that there may be more to axons than only digital signal conduction. They could directly measure and demonstrate that the speed of an axonal signal varies considerably within different segments of the very same axon by placing hundreds of electrodes along the axon. Moreover, the velocity pattern changed from day to day or within hours as did the morphology and position of the axon.
The exact meaning of these speed variations and the origin cannot be explained yet, as there is too little information available about axonal conduction. This may, to a large part, be a consequence of the tiny diameter of the axons. The length of an axon can be more than a meter, e.g., in the spinal cord, but the average diameter is in between 80 nm and a few micrometers. This small diameter makes any measurement of axonal potentials difficult, which, of course, also renders establishing the mechanisms that may produce the large speed variations a difficult task.
Up to now, only hypotheses concerning these speed variations exist. The temp
|Contact: Andreas Hierlemann|