How a tardigrade nerve makes contact to a tardigrade muscle

It is fascinating to go back in history of science and to learn how much the 19th century tardigrade specialists did already know about tardigrade anatomy.

The historical line drawing below is attributed to the famous french tardiologist Louis Doyère (1811 - 1863) and probably was made by Doyère himself around 1850. It depicts in detail the ventral muscles and ventral nerves of   Milnesium tardigradum .

Comments:
a) (four) ganglion nodes, i.e. nervous centres, that are interconnected via
b) nervous fibres to a ladder like structure
c) nerve attachment to the muscle
d) the muscles
n) the nerve endings serving the papillae in the head region
o) eye nerves connecting to the eye pigment spots.

Nervous system and ventral muscles of the water bear  Milnesium tardigradum .
Line drawing attributed to Louis Doyère, presumably made around 1850 (!).

The most appropriate situation for tardigrade anatomic study is the so-called   asphyctic state . When looking at the asphyctic tardigrades we can easily follow Doyère's brilliant studies even today. Though muscles and nerves have only little contrast, a simple bright field microscope reveals everything - we just have to take care that some kind of raking light will assist us in working out the delicate structures.

Nervous system and ventral muscles of the water bear Milnesium tardigradum .
The arrows in red point out the nerves which link the ganglion nodes. The wider bands running parallel to the nerves are muscles.
Photomicrograph, bright field illumination with oblique light.
Image width ca. 250 µm.

As the tardigrades do have no skeleton the muscles have to link to other somewhat rigid structures. For this reason the tardigrade cuticula has local bulb-like reinforcements that can be seen in the image above, on the left side and a little bit right from the image center.

And in case you always wanted to investigate the anatomic link between a nerve and a muscle you can just look through one of those crystal-clear tardigrade bodies - no reason to murder one of those poor frogs:

Link between a nerve and a muscle within the body of the water bear Milnesium tardigradum .
The nervous fiber marked by the red arrow does link the second ganglion node with a muscle that is controlling the movement of a tardigrade leg.

The tiny protrusion which is characteristic for a nerve-muscle joint was detected for the first time by Louis Doyère when he was studying tardigrades. Later on it turned out that this node is present as well in in many other (less crystal-clear) organisms.

More information on nerves and muscles, also on scanning electron microscope (SEM) investigations:

H. Greven: Die Bärtierchen. p. 21 - 29. Wittenberg Lutherstadt 1980.
J. Müller: Zur vergleichenden Myologie der Tardigraden. Zeitschrift für wissenschaftliche Zoologie 147 (1936) p. 171 - 204.

and last but not least our video clip which is showing some real tardigrade  muscle action  .

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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