How to Construct and Move a Cat's Neck

Extensive information has been accumulated over the past several years about the head-neck sensory-motor system, in particular that relating to cats. Using still x-ray and cineradiographic analysis, the skeletal geometry of head–neck posture in three dimensions—when an animal is resting, actively orienting, or locomoting—is described. From these descriptions, cervical, vertebral, and craniocervical joint biomechanics for all three rotational dimensions are quantified. These behavioral data on muscle and skeletal movements have been incorporated in a biomechanical, functional anatomical model of the head-neck movement system. Individual as well as groups of neck muscles have been measured in detail and their kinematics determined. The role of a number of these muscles will be described for several reflex and voluntary behavioral contexts, including muscle co-contractions. Having established how each movement is accomplished, the neuronal sensory-motor reflex basis of head–neck system stabilization in space is addressed. The vestibular system is largely responsible for acquisition and maintenance of upright posture. The bilateral semicircular canals (horizontal, anterior, posterior) and otoliths (sacculus, utriculus) feed information differentially to specific neck muscles: these connections are reviewed with regard to the origin of the reflex arc from each receptor to its destination of specific muscles. Behavioral data from normal animals, and from animals whose vestibular receptor systems are selectively lesioned, will be reviewed to complement the functional interpretation of the sensory–motor transformations. Finally, the requirements for space–time coordinated cat head-neck movements will be synthesized, based on biomechanics, muscle kinematics, canal/otolith connectivity, and selective lesion experiments.