Ocular reflexes compensate for the condition of the cornea and for changes in the visual stimulus. The ocular reflexes are the simplest ocular motor responses. In contrast, voluntary eye movements (i.e., visual tracking of a moving object) involve multiple areas of the cerebral cortex as well as basal ganglion, brain stem and cerebellar structures. The eye blink reflex is the simplest response and does not require the involvement of cortical structures. In this chapter we will start at the level of reflex responses and move onto more complex voluntary responses in the following lecture. The complexity of the circuitry (the chain or network of neurons) controlling a ocular motor response increases with the level of processing involved in initiating, monitoring, and guiding the response. Ocular motor responses include ocular reflexes and voluntary motor responses to visual and other stimuli. Neuromuscular systems control the muscles within the eye (intraocular muscles) the muscles attached to the eye (extraocular muscles) and the muscles in the eyelid. The visual system provides afferent input to ocular motor circuits that use visual stimuli to initiate and guide the motor responses. The ocular motor systems control eye lid closure, the amount of light that enters the eye, the refractive properties of the eye, and eye movements. We use our eyes to monitor our external environment and depend on our ocular motor systems to protect and guide our eyes.
They involve the action of few muscles and of well defined neural circuits. The simplicity of the motor systems involved in controlling eye musculature make them ideal for illustrating the mechanisms and principals you have been studying in the preceding material on motor systems.
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