Otoliths and Uprightness

Abstract

Publisher Summary Positional reflexes from the labyrinth upon the limbs are shown to be asymmetric in their effects. The combination of labyrinth reflexes with neck reflexes serves to provide stabilization of the trunk. The pattern of labyrinth reflexes is altered by acute cerebellectomy and by destroying one labyrinth. The otolith apparatus responds to the stresses imposed by contact forces rather than to gravitational force directly. In place of the traditional view that the otolith apparatus reports orientation with respect to gravity, it is suggested that the role of the labyrinth is to indicate changes in skull momentum, this information being relevant to the use of the skull as an inertia paddle in locomotion and other activities. The requirements for stable balance demand that disturbances from the standard “upright” posture should be met by some system of necessarily asymmetric restoring forces. A set of reflexes that produce symmetrical effects in the limbs when the head is tilted could play no part in stabilization. A study of the profiles of animals in various attitudes of the head and neck establishes that asymmetric attitudes of the limbs are not attributable solely to deformations of the neck, as Magnus maintained, but can be seen to be associated with tilting of the head even when the neck is straight.