Oculomotor System


The oculomotor system is composed of six extraocular muscles attached to the orbit and to the eyeball, extraocular motor neurons located in three different brainstem motor nuclei, and premotor centres and circuits involved in the generation and control of the different types of eye movement. Its precise functional design and robust biomechanics have allowed this motor system to survive, almost unchanged, across different trends in vertebrate evolution.

Keywords: extraocular muscles; extraocular motor neurons; eye blinks; eye movements; optokinetic reflex; vestibulo‐ocular reflex

Figure 1.

Different types of eye movement: (a) vestibulo‐ocular reflex; (b) optokinetic reflex; (c) saccade and eye fixation; (d) smooth pursuit; (e) vergence; (f) air‐puff evoked reflex blink. RH, LH, horizontal position of the right and left eyes; RV, vertical position of the right eye; LP, lid position. HP, FP, TP, head, global visual field and visual target position; AP, air‐puff presentation. Calibration in (e) applies also to (a)–(d).

Figure 2.

Typical discharge rate of an abducens motor neuron (ABD Mn) during different types of eye movement: (a) diagram illustrating the location of the abducens nucleus in the brainstem and of the innervated lateral rectus muscle; (b) firing rate of abducens motor neurons during saccades in the on and off direction, and during spontaneous eye movements, and vestibulo‐ocular and optokinetic reflexes.

Figure 3.

Neuronal organization of the premotor system for horizontal eye movements: (a) diagram illustrating the location of the different neuronal groups projecting monosynaptically on abducens nucleus (ABDn); (b) typical discharge rate recorded in neuronal elements of each premotor centre during saccades in the on and off direction and the subsequent eye fixation. EBN, excitatory burst neurons; IBN, inhibitory burst neurons; MVn, medial vestibular neurons; PHn, prepositus hypoglossi neurons; LH, horizontal position of the left eye; i, c, ipsi‐ and contralateral.

Figure 4.

Basic circuit underlying conjugate eye movements in the horizontal plane: (a) diagram illustrating the location of abducens motor neurons (ABD Mns) and internuclear neurons (ABD Ints), and medial rectus motor neurons (MR Mns); (b) expected discharge rate of neuronal elements depicted in (a) during a leftward conjugated saccade followed by a new eye fixation. Note the different firing rates of Mns and Ints. i, c, ipsi‐ and contralateral.



Robinson DA (1970) Oculomotor unit behavior in the monkey. Journal of Neurophysiology 33: 393–404.

Further Reading

Baker R (1998) From genes to behavior in the vestibular system. Otolaryngology – Head and Neck Surgery 119: 263–275.

Büttner‐Ennever JA and Horn AKE (1997) Anatomical substrates of oculomotor control. Current Opinion in Neurobiology 7: 872–879.

Delgado‐García JM (2000) Why move the eyes if we already move the head?. Brain Research Bulletin 52: 475–482.

Delgado‐García JM and Gruart A (2002) The role of interpositus nucleus in eyelid conditioned responses. The Cerebellum 1: 289–308.

Fritzsch B (1998) Evolution of the vestibulo‐ocular system. Otolaryngology – Head and Neck Surgery 119: 182–192.

Fukushima K, Kaneko CRS and Fuchs AF (1992) The neuronal substrate of integration in the oculomotor system. Progress in Neurobiology 39: 609–639.

Gruart A, Schreurs BG, Domínguez del Toro E and Delgado‐García JM (2000) Kinetic and frequency‐domain properties of reflex and conditioned eyelid responses in the rabbit. Journal of Neurophysiology 83: 836–852.

Ilg UJ (1997) Slow eye movements. Progress in Neurobiology 53: 293–329.

Moschovakis AK, Scudder CA and Highstein SM (1996) The microscopic anatomy and physiology of the mammalian saccadic system. Progress in Neurobiology 50: 133–254.

Porter JD, Baker RS, Ragusa RJ and Brueckner JK (1995) Extraocular muscles: basic and clinical aspects of structure and function. Survey of Ophthalmology 39: 451–484.

Robinson DA (1981) The use of control system analysis in the neurophysiology of eye movements. Annual Review of Neuroscience 4: 463–503.

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How to Cite close
Delgado‐García, José M(Sep 2005) Oculomotor System. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0004090]