Biophysics of the Peripheral End Organs

Abstract

The structural and functional division of the labyrinthine inertia-sensing organs into semicircular canals and otolith organs should be considered in conjunction with the fundamental fact that in three-dimensional space there are two sets of independent degrees of freedom of movement, namely three in rotation (angular movement) and three in translation (linear movement and gravitational acceleration). The physical layout of the semicircular canals is appropriate for transducing the three angular degrees of freedom of movement, independently both of end-organ location in the skull and of coincidental translational motion. This, together with their anatomical structure, leaves the otolith organs as prime contenders for inertial transduction of linear motion and gravity. However, confusion often arises here because, depending explicitly on their fixed location on the moving platform, a set of linear accelerometers can, in some circumstances, yield useful information about angular motion (Benson and Barnes, 1973). In due course we shall also see that there are interactions in the CNS between canal and otolith signals (Chapter 5). Before proceeding, therefore, it may be helpful to attempt clarification of some basic attributes of the two component parts of the peripheral mechanism.