214
0. LOWENSTEIN
numerous mitochondria. Conduction is obviously directed from hair cell
to afferent nerve ending. Besides these postsynaptic nerve endings the
hair cell is innervated by apparently efferent nerve endings. On the hair
cell side of these one finds a flattened space or synaptic sac surrounded
by a membrane located close to the plasma membrane of the cell. The
presynaptic nerve ending, the terminal branch of a relatively thin efferent
nerve, is filled with synaptic vesicles. Conduction is clearly from nerve
ending to hair cell and may serve an inhibitory function.
11. FUNCTION
The labyrinth has four chief functions: It is an organ which is ( 1 )
concerned with the maintenance and regulation of muscle tone, ( 2 ) a
receptor for angular accelerations, ( 3 ) a gravity receptor, and (4) a
sound receptor. This follows from the fact that bilateral total labyrinth
extirpation is followed by temporary or lasting loss in muscle tone, by
severe disturbances of equilibrium, and by deafness.
A. Equilibrium
In the fishes the effector organs showing equilibrium reflexes are the
eyes, the fins, and to a lesser degree, the trunk musculature. The reflexes
are controlled by the receptors of the semicircular canals and of the otolith
organs, and they occur as compensatory rotary and vertical eye movements and postures during active and passive changes of position from
the “normal.” Rotation of the fish in a horizontal plane evokes horizontal
rostro-caudal eye deviations and nystagmus, easily observable when
watching a fish executing right and left turns. These reflex movements
and postures of the eyes facilitate the fixation of a certain visual field
during spatial displacement of the head. When the compensatory eye
deviation has reached its anatomical maximum, the eye is brought back
with a jerk to its normal position in the orbit. Compensatory deviation
and jerklike return together are known as the nystagmus representing its
slow and quick phase, respectively. The slow phase runs counter to and
the quick phase in the same direction as the rotary displacement of the
head. The slow phase is controlled by the labyrinth (and optokinetically
through the eye itself), whereas the quick phase is of central nervous
origin.
Figure 4 shows the reflex response of the fins of the minnow, Phoxinus
phoxinus, to passive sideways tilting toward the right. The posture of the
0. LOWENSTEIN
numerous mitochondria. Conduction is obviously directed from hair cell
to afferent nerve ending. Besides these postsynaptic nerve endings the
hair cell is innervated by apparently efferent nerve endings. On the hair
cell side of these one finds a flattened space or synaptic sac surrounded
by a membrane located close to the plasma membrane of the cell. The
presynaptic nerve ending, the terminal branch of a relatively thin efferent
nerve, is filled with synaptic vesicles. Conduction is clearly from nerve
ending to hair cell and may serve an inhibitory function.
11. FUNCTION
The labyrinth has four chief functions: It is an organ which is ( 1 )
concerned with the maintenance and regulation of muscle tone, ( 2 ) a
receptor for angular accelerations, ( 3 ) a gravity receptor, and (4) a
sound receptor. This follows from the fact that bilateral total labyrinth
extirpation is followed by temporary or lasting loss in muscle tone, by
severe disturbances of equilibrium, and by deafness.
A. Equilibrium
In the fishes the effector organs showing equilibrium reflexes are the
eyes, the fins, and to a lesser degree, the trunk musculature. The reflexes
are controlled by the receptors of the semicircular canals and of the otolith
organs, and they occur as compensatory rotary and vertical eye movements and postures during active and passive changes of position from
the “normal.” Rotation of the fish in a horizontal plane evokes horizontal
rostro-caudal eye deviations and nystagmus, easily observable when
watching a fish executing right and left turns. These reflex movements
and postures of the eyes facilitate the fixation of a certain visual field
during spatial displacement of the head. When the compensatory eye
deviation has reached its anatomical maximum, the eye is brought back
with a jerk to its normal position in the orbit. Compensatory deviation
and jerklike return together are known as the nystagmus representing its
slow and quick phase, respectively. The slow phase runs counter to and
the quick phase in the same direction as the rotary displacement of the
head. The slow phase is controlled by the labyrinth (and optokinetically
through the eye itself), whereas the quick phase is of central nervous
origin.
Figure 4 shows the reflex response of the fins of the minnow, Phoxinus
phoxinus, to passive sideways tilting toward the right. The posture of the