Rotation-compensating reflexes independent of the labyrinth and the eye

Summary

• 1. The ability of pigeons to compensate reflexly for imposed rotations of the body, via a sensory system not involving the eyes or labyrinths, was investigated quantitatively.

• 2. Muscle-fibre action potentials were measured with the birds in an apparatus producing sinusoidal rotation of the animals in all orientations. Results for labyrinthectomized and normal birds are nearly indistinguishable. Specific deficits following spinal sections at various levels clarify Singer's (1884) and Trendelenburg's (1906) early reports and show that input from at least some of the nerve roots with splanchnic components (those anterior to Nerve 24) are necessary for the tail response to occur at all, a normal response requiring input even from those anterior to Nerve 19.

• 3. The sinusoidal rotational response measured versus the mean angle with respect to gravity is nonlinear, complicated and highly sensitive both to mode of rotation (roll, pitch, or yaw) and to the muscle studied (wing or tail). A generalized set of rules is found, however, for which all such plots superimpose. Hence a receptor organization common to all is suggested.

• 4. Although the role of dynamic inertial factors is unrestricted by the sinusoidal experiment, the persistence of the responses under constant-velocity rotation over many full turns shows that the variables “angle” and “rate of change of angle” suffice to describe the requisite sensory inputs.

• 5. We show that suitable phasic-tonic sensory response to stretch, in an appropriate mesenteric support system of the gut, can in principle account for several of the measured properties of the reflex.