New England College of Optometry - Scope Yearbook (Boston, MA)

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THE SCOPE - FUNCTIONAL DIFFERENCES In the course of investigation the following results were obtained: a. a lesser stimulation of the frontal center was required to effect a cer- tain conjugate movement than if the corresponding occipital or temporal cen- ters were stimulated. b. a similar intensity of stimulus resulted in quicker eye movements when the frontal area was stimulated, than if either of the other two was sti- mulated. c. destruction of the frontal centers resulted in an abolition of the voli- tional pathways for conjugate eye movements, but Hxation of gaze was possible due to the mediation of the efferent impulses originating in the occipital lobe. d. fixation depends upon the occipital lobe, while direction depends upon the frontal lobe. e. destruction of both calcarine areas, abolished convergence. CORTICO-NUCLEAR PATHWAYS l,Suprasegmental Pathwaysb lUpper Motor Neuronj The nuclei of the eye muscles are connected with the frontal cortex not by the regular pyramidal system, but by two systems of fibers of what Dejerinc terms the aberrant pyramidal system. known as the subthalamic and peduncular components of the aberrant pyramidal tracts. The axones of the cortical cells pass downward through the corona ra- diata in the pyramidal system, pass through the genu of the internal capsule into the mesencephalon or mid-brain. Here the fibers destined for the oculomotor and trochlear nuclei detach themselves from the remainder of the aberrant pyramidal system and pass to the nuclei of the opposite side, while the fibers destined for the abducens nucleus pass down further in the stem to the upper pontine region and pass to the opposite abducens nucleus. The subthalamic group is principally concerned with vertical movements and is associated with the muscles of the upper eyelid and the frontalis. It leaves the aberrant pyramidal system in the subthalamus, and passes backward to reach the superior colliculus. Here the fibers are redistributed and sent to the nuclei in- nervating the muscles concerned in vertical movements. The peduncular group is concerned with lateral movements of the eyes, and leaves the aberrant pyramidal system in the cerebral peduncle as two sets of fibers, known as the pes lemnisci profundus, and the pes lemniscis superficialis. The pes lemnisci profundus is situated in the basis mesencephali dorso- medial to the occipito-parieto-temporo-ponto-cerebellar tract, and is the deep layer of the aberrant pyramidal system which blends with the median lemniscus or Hllet. The pes lemnisci superficialis is situated in the basis of the mid-brain dor- sal to the fronto-ponto-cerebellar tract. These two bundles descend for a short distance in the medial fillet and proceed dordally to the tegmentum to the center for lateral movements which is believed to be the nuclus of Fuse. which is part of the triangular nucleus. From here fibers are relayed to the nuclei concerned with lateral movements. Convergence movements have been produced by stimulating an area in the frontal lobe, and also by exciting a part of the lateral convexity of the oc- cipital lobe. The aberrant pyramidal system also sends branches to the spinal accessorv nerve as well as to the upper segments of the spinal cord for the associated move- ments of the head and eyes. l4l

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