Motor control of extraocular muscle

Abstract

Six pairs of extraocular muscles (EOMs) are innervated by three pairs of cranial nerves whose cell bodies lie in three cranial nerve nuclei on each side of the brain, namely the oculomotor, trochlear, and abducens nuclei. Early studies of the oculomotor system examined neuronal responses of extraocular motoneurons within these motor nuclei and developed a framework for understanding the motor control of EOM (Fuchs and Luschei 1970; Keller and Robinson 1971). Perhaps one of the most significant and elegant outcomes of some of these studies was the proposal for a final common pathway for eye movements (Robinson 1968, 1981). Thus, according to the oculomotor final common pathway theory, motoneuron innervation of EOM was independent of the type of eye movement that was being executed. While this framework still has validity in understanding the neural control of eye movements, there have been new developments in the last couple of decades that has brought about renewed interest in the oculomotor periphery and cast doubt on the so-called final common pathway. The goals of this chapter are to review ocular biomechanics and motor control of EOM while highlighting new developments and identifying issues that are yet unresolved. We have confined our discussion to the motor neurons and their effector organ, the eye. Central control of eye movements is outside the scope of this chapter.