Semicircular canals
The semicircular canals ( ductus semicirculares ) are three interconnected, thin-walled, annular tubes in each inner ear . They are part of the organ of equilibrium and are used to determine and regulate rotational movements.
The three semicircular canal rings together have the shape of a three-dimensional pretzel, the three rings being arranged in different spatial directions, approximately at right angles to one another. The individual rings have a diameter of about 6 mm in humans. The membranous semicircular tubes are suspended in a duct system ( Canales semicirculares ossei ) of the temporal bone . They are filled with endolymph and surrounded by perilymph . In the swellings of the semicircular canal tubes (semicircular canal ampoules) at their confluence with the utriculus there are sensory hairs over which the endolymph strokes when the head is turned. This induces a sensation of rotation via their nerves .
With longer, uniform rotary movements, friction reduces the flow of lymph in the semicircular canals. This adaptation to the rotation allows orientation in the rotating reference system, which z. B. is important for climbing animals, but also for artistry or waltz dancing.
Illusion effects
When a long rotation ends, the liquid continues to rotate due to its inertia and creates the impression of an opposite rotation. A contradiction to other sensations - especially the eye - can cause dizziness ( vertigo ).
For this reason, pilots train to trust the display of navigation devices more than the impression they make in their heads when flying instruments (without seeing outside) .
When looping (a flight maneuver that represents a 360 ° rollover), the sense of balance only has the impression of flying a high wave. Only a look at the navigation instruments (artificial horizon, etc.) allows the maneuver to be ended at the right moment.
Semicircular canals in animals
All vertebrates have semicircular canals. As with humans, there are usually three pairs. The lampreys with only two pairs of semicircular canals and the hagfish with only one pair are an exception .
In birds, a second organ of equilibrium has recently been discovered in the lateral flaps of the spinal cord . It is comparable to the semicircular canals and is responsible for controlling walking and standing. The sense of balance in the inner ear, on the other hand, controls the movements of birds in flight . In addition, they feel the exact air movements on their feathers and on their beak .
literature
- Joseph Hyrtl : Comparative anatomical studies on the internal auditory organ of humans and mammals. Friedrich Ehrlich, Prague 1845, ( digitized version ).
See also
Web links
- (Archways, disorientation in flight) ( Memento from March 20, 2011 in the Internet Archive ).
Individual evidence
- ↑ Christopher Platt, Arthur N. Popper: Fine structure and function of the ear. In: William N. Tavolga, Arthur N. Popper, Richard R. Fay: Hearing and sound communication in fishes. Springer, New York NY et al. 1981, ISBN 0-387-90590-1 , pp. 3-38, doi : 10.1007 / 978-1-4615-7186-5_1 .
- ↑ Reinhold Necker: Specializations in the lumbosacral vertebral canal and spinal cord of birds: evidence of a function as a sense organ which is involved in the control of walking. In: Journal of Comparative Physiology. A: Neuroethology, Sensory, Neural, and Behavioral Physiology. Vol. 192, No. 5, 2006, pp. 439-448, doi : 10.1007 / s00359-006-0105-x .