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Dr. Richard Bräucker


Glossar English: (the terms marked by a green link in some pages will be explained here)

ciliates: unicellular organisms (size about 0.04 - 2 mm) which propel themselves by means of numerous cilia. 

experiments under increased gravity are done using a special centrifuge for ciliates (CECILIA) which has been designed by our study group, and has been built by the workshops of the faculty of Biology. CECILIA provides accelerations up to 16g.

experiments under weightlessness were done in the drop tower of ZARM at the university of Bremen and in the Japanese Microgravity Centre (JAMIC).

gravitaxis: reaction of an organism related to gravity. Gravitaxis induces an oriented locomotion of the organism either towards the source of the stimulus (i.e. parallel to the gravity vector) (= positive gravitaxis) or away from the source of the stimulus (i.e. anti parallel to the gravity vector) (= negative gravitaxis). In older publications the term of geotaxis is used (reaction to the direction of earth's gravity vector).

gravikinesis: modulation of locomotion rate of an organism depending on its graviorientation. Ciliates investigated regulate their swimming rate as to partly neutralize their sedimentation rate (negative gravikinesis). This is achieved by an active increase of swimming rate in the upward direction and an active decrease of swimming rate in upward direction. 

heart-rate conditioning: approach of classical conditioning (after Pawlow) using the change in heart rate of the subject as indicator.

experiments were done with Paramecium caudatum, Paramecium tetraurelia, Loxodes striatus, Didinium nasutum, Tetrahymena pyriformis Stylonychia mytilus and Bursaria truncatella. In all these species we have evidence of both, gravitaxis and gravikinesis. 

phototaxis: reaction of an organism related to light. 

non parametric statistics: statistical methods that do not depend on Gaussian distribution. (In most of our experiments Gaussian distribution could not be assured.) Values of data are transformed into rank values which are then analyzed. Examples: median with confidence ranges, Mann-Withney U-test, Spearman's rank correlation test.

sedimentation rate: velocity of settlement of immobilized cells (the cell density is larger than the density of the experimental solution). The sedimentation rate is measured with cells which are immobilized by the effect of Ni2+ or Mn2+.

mechano receptor channels: ion channels integrated in the cell membrane. They change their conductance for defined ions due to mechanical stimuli (pressure, pull...).

hyperpolarization: change of then (negative) membrane potential in negative direction: The absolute value of the membrane potential is increased. Hyperpolarizations are generally caused by an increase of the K-conductance of the cell membrane.

depolarization: change of then (negative) membrane potential in positive direction: The absolute value of the membrane potential is decreased. Depolarizations are generally caused by an increase of the Ca-conductance of the cell membrane.

electromotor coupling: correlation between membrane potential and locomotion behaviour of ciliates caused by changes in ciliary beat direction and ciliary beat frequency. A hyperpolarized cell swims faster forward on a narrow helical track. With increasing depolarization the forward speed of the cell is decreased until the cell movement stops. With even more increased depolarization then cell starts swimming backwards. 

extension of the statocyst hypothesis (Lyon 1905) by Machemer (1988)

the figure shows an upward swimming cell




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Last update: 28.12.2003