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
