CHAPTER XLII 



Central control of eye movements 



D. W H I T T E R I D G E | Department oj Physiology, Edinburgh University, Edinburgh, Scotland 



CHAPTER CONTENTS 



Anatomical Considerations 



Muscle Fibers 



Motor End Plates 



Muscle Spindles and Other Receptors 



Motor Units in Eye Muscles 



Nerve Fiber Size 

 Time Relations in Eye Muscles 

 Afferent Discharges from Eye Muscles 



Afferent Paths From Eye Muscles 

 Effects of Stretch 

 Vestibular ReHexes 



Reactions to Rotation in Horizontal Plane 



Reactions to Vertical Movement 

 Neck Reflexes 

 Nystagmus 



Adversive Movements of Eyes 

 Superior CoUiculus 



Anatomy 



Electrophysiological Studies 



Effects of Stimulation and of Lesions 



Proprioceptors 

 Eye Movements and Visual Cortex 

 Subsidiary Centers of Gaze 

 Eye Movement in Man 



Fixation Movements 



Saccadic and Pursuit Movements 



Integration of Eye Movements 



Proprioceptors and Sensation 



Peiiiaps the most strikinu; feature of eye movements is 

 the extent to which they are under the control of 

 tlie higliesl centers of tire nervous system. Corre- 

 spondingly we find little or no local reflex activity; 

 however, close relations exist with the balancing 

 mechanisms of the head and with the very complex 

 mechanisms by which retinal stimuli in particular, 

 and many other stimuli to some extent, can give rise 

 to precise and appropriate eye movement. 



Much of the physiology of the mammalian limb 

 muscles has been worked out on the cat, but to con- 

 fine the work on eye muscles to the study of a limited 

 series of the more usual laboratory animals has in 

 the past sometimes proved not only unhelpful, but 

 misleading. A much wider comparati\e studv of 

 these cranial muscles reveals species diflTerences that 

 are often of great value in iielping to elucidate the 

 main problems. The four recti and two obliques are 

 found in all vertebrates from fish to man, but the 

 degree of eye movement they are called on to bring 

 about varies enormously. For work on the eye 

 muscles sheep and goats have recently proved to be 

 valuable (36) for these animals possess many typical 

 sensory endings, i.e. muscle spindles, in their eye 

 muscles (31) and they also have discrete sensory 

 nerve trunks leasing these luuscles (146, 150, 151). 



THE MOVEMENT OF THE EYES is brought about by the 

 extraocular muscles. These movements are extremely 

 rapid and the eye muscles are much the most rapidly 

 acting in the body. Correspondingly we find a series 

 of anatomical and physiological specializations by 

 which this speed of movement is attained. Their 

 movements are not only very quick but also very 

 precise. Again we find anatomical and physiological 

 mechanisms adapted for precision of movement. 



AN.^TOMICAL CONSIDERATIONS 



The anatomy of human eye muscles has been ade- 

 quately described elsewhere (60, 145). Their actions 

 are given in detail in most textbooks of ophthal- 

 mology, while textbooks of physiological optics deal 

 with the nature of the movements in secondary and 

 tertiary positions. Their comparative anatomy has 

 been described by Duke-Elder (60) and by WolfT 



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