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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THE SCOPE Relatively little is known about the oculogyratory control in the occipital lobe. and practically nothing about the center in the temporal lobe. The cortico- nuclear tracts from the occipital lobe pass through the corona radiata over the occipital radiation to the white substance of the cerebrum, and thence to the ocu- logyric center by way of the posterior longitudinal bundle of the tecto-bulbar tracts, which innervate the abducens nucleus, which in turn innervates the op- posite oculomotor nucleus. Bernheimer in a famous experiment has shown that the iibers of the angular gyrus decussate ventral to the cerebral aqueduct, since total extirpation of the superior colliculi did not interfere with ocular move- ments. These nbers after decussation pass to the opposite abducens nucleus, which in turn by means of the posterior longitudinal bundle and communicating fibers innervates the dpposite oculomotorius. Fibers from the temporal cortex are believed to pass down with the tem- poro-pontine group which pass through the corona radiata, thence to the su- perior colliculus, and onward to the oculogyratory nuclei. Some however, are of the opinion that the fibers from the temporal lobe pass to the pons communi- cating with the abducens nucleus of the opposite side, which sends fibers by way of the posterior longitudinal bundle to the opposite oculomotor nuclei. REFERENCES Tilney and Riley Forms and Functions of the Nervous System Archives of Neurology and Psychiatry, 1930 Archives of Ophthalmology, Nov. and Dec. 1930 Archives of Ophthalmology, 1932 Ranson Anatomy of the Nervous System Zoethout Physiological Optics ff? P57 - ff'2tPEGh5Qzi05!.IS3' -wwrrgimw I 7696 'Eli-EQ' I5I