300px The<unk>  is driven by signals arising from the<unk> r system of the inner ear. The semicircular canals detect head rotation and provide the rotational component, whereas the otoliths detect head translation and drive the translational component. The signal for the horizontal rotational component travels via the<unk> r nerve through the<unk> r ganglion and end in the<unk> r nuclei in the brainstem. From these nuclei, fibers cross to the abducens nucleus of the opposite side of the brain. Here, fibres synapse with 2 additional pathways. One pathway projects directly to the lateral rectus muscle of the eye via the abducens nerve. Another nerve tract projects from the abducens nucleus by the medial longitudinal fasciculus to the oculomotor nucleus of the opposite side, which contains motor neurons that drive eye muscle activity, specifically activating the medial rectus muscle of the eye through the oculomotor nerve. Another pathway (not in picture) directly projects from the<unk> r nucleus through the ascending tract of Deiter's to the medial rectus muscle motor neuron of the same side. In addition there are inhibitory<unk> r pathways to the ipsilateral abducens nucleus. However no direct<unk> r neuron to medial rectus motoneuron pathway exists. Similar pathways exist for the vertical and torsional components of the VOR. In addition to these direct pathways, which drive the velocity of eye rotation, there is an indirect pathway that builds up the position signal needed to prevent the eye from rolling back to center when the head stops moving. This pathway is particularly important when the head is moving slowly because here position signals dominate over velocity signals. David A. Robinson discovered that the eye muscles require this dual velocity-position drive, and also proposed that it must arise in the brain by mathematically integrating the velocity signal and then sending the resulting position signal to the motoneurons. Robinson was correct: the 'neural integrator' for horizontal eye position was found in the nucleus prepositus hypoglossi in the medulla, and the neural integrator for vertical and torsional eye positions was found in the interstitial nucleus of Cajal in the midbrain. The same neural integrators also generate eye position for other conjugate eye movements such as saccades and smooth pursuit. Example For instance, if the head is turned clockwise as seen from above, then excitatory impulses are sent from the semicircular canal on the right side via the<unk> r nerve through Scarpa's ganglion and end in the right<unk> r nuclei in the brainstem. From this nuclei excitatory fibres cross to the left abducens nucleus. There they project and stimulate the lateral rectus of the left eye via the abducens nerve. In addition, by the medial longitudinal fasciculus and oculomotor nuclei, they activate the medial rectus muscles on the right eye. As a result, both eyes will turn counter-clockwise. Furthermore, some neurons from the right<unk> r nucleus directly stimulate the right medial rectus motor neurons, and inhibits the right abducens nucleus. Speed The<unk>  needs to be fast: for clear vision, head movement must be compensated almost immediately; otherwise, vision corresponds to a photograph taken with a shaky hand. Signals are sent from the semicircular canals using only three neurons, called the three neuron arc. This results in eye movements that lag head movement by less than 10 ms. The<unk>  is one of the fastest reflexes in the human body. VOR suppression During head-free pursuit of moving targets, the VOR is counterproductive to the goal of reducing retinal offset. Research indicates that there exists mechanisms to suppress VOR using active visual feedback. In the absence of visual feedback, such as during occlusions, humans use anticipatory (extra-retinal) signals to supplement pursuit movements by VOR suppression. Gain The "gain" of the VOR is defined as the change in the eye angle divided by the change in the head angle during the head turn. Ideally the gain of the rotational VOR is 1.0. The gain of the horizontal and vertical VOR is usually close to 1.0, but the gain of the torsional VOR (rotation around the line of sight) is generally low. The gain of the translational VOR has to be adjusted for distance, because of the geometry of motion parallax. When the head translates, the angular direction of near targets changes faster than the angular direction of far targets. If the gain of the VOR is wrong (different from 1)—for example, if eye muscles are weak, or if a person puts on a new pair of eyeglasses—then head movement results in image motion on the retina, resulting in blurred vision. Under such conditions, motor learning adjusts the gain of the VOR to produce more accurate eye motion. This is what is referred to as VOR adaptation. Ethanol consumption can disrupt the VOR, reducing dynamic visual acuity.
Vestibulo–ocular reflex
Oculocardiac reflex
Acoustic reflex
Axon reflex
Moro reflex
Corneal reflex
Pupillary light reflex
Tonic labyrinthine reflex