Question

How do neurons in the oculomotor nuclei signal amplitude versus direction of an eye movement?

Answer 1

• Normally the eye can move 50 degree medially,30 degree upwards,and 50 degree downwards.When the eye ball is placed temporally (abducted positions),the superior rectus causes elevation and the inferior rectus causes depression of the eyeball.
• When the eyeball moves nasally the superior and inferior oblique elevate and depress .
• The amplitude of eye movement is determined by the activity in the lower motor neurons within the three occulomotor nucleii.
• The direction of a movement is determind by which muscles are activated ,as dictated by the activity in the premotor neurons within two seperate gaze centers in the brain stem.
• The rapid movements occurs when the gaze shift from one object to other(saccades).
• Their function is to keep the new object in focus by changing the orientation of the eyeballs.Thus they prevents the adaptation of the neurons in the visual pathway.
• When a gaze is fixed on an object for longer period,the extraocular muscles remain contracted to maintain the position of the eyeball and may lead to fatigue.
• These movements are regulated in the frontal cortex and superior colliculi.