Biomedical Engineering Reference
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Fig. 3 Sherington's model of binocular balance (University Laboratory of Physiology, Oxford
University, Oxford, UK)
movement, divergence is lateral movement). Multiple muscles in both eyes are used
for directional eye movement. Every muscle has its antagonist in the same eye
and synergist and antagonist in the opposite eye. Antagonist muscles work in the
opposite direction, synergists in the same direction. The coordination and fluency
of pair movements is driven in accordance with Hering's [ 8 ] and Sherrington's law
[ 9 ]. According to Hering's law the innervation impulse for eye movement from
the motor centre of the brain cortex is equally divided between the synergists of
both eyes. In this case the synergist acts like a single organ. The same is true of
antagonists in the reverse sense. Sherrinton's law describes reciprocal innervation
of the muscles. Contraction of synergists has to be supplied by relaxing their
antagonists. Movement Sherington's balance was practically modelled (Fig. 3 ).
Ocular muscles are driven by three cranial nerves: n. III (n. oculomotorius), n. IV
(n. trochlearis) and n. IV (n. abducens). Their motor kernels are situated in the rear
of the brainstem and are connected with each other. Eye movements are driven by
three brain centres. The first is occipital brain centre that governs eye-conditioned
reflex movements (optomotorical) - accommodation, convergence, fusion, fixation
and the blink reflex. The second centre is in the frontal brain lobe that drives
volitional movements. The third centre is represented by statokinetical reflexes
that are driven by the motor centre on the vestibular apparatus. Head and body
position changes are aligned by this centre. These reflexes are congenital and are
preserved even with blindness. Sensor fusion is essential for coordinating correct
eye movements.
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