The Vestibular System: An Overview of Structure and Function
Kenneth J Ottenbacher, Margaret A Short Degraft in Vestibular Processing Dysfunction in Children, 2013
rise to axons that cross the midline and ascend in the MLF to the contralateral medial rectus subnucleus of the oculomotor nuclear complex. The ascending internuclear fibers in the MLF, therefore, carry a completely assembled motoneuron signal. Oculomotor nucleus motoneurons project to the medial rectus muscle on that side to adduct the eye. In addition to the processing described above, additional signals are coordinated at the motoneuron. Saccades move the eye in the direction opposite to the slow phase movement, so the slow phase signal must be inhibited and a burst of activity added to contract the antagonistic muscle. These other influences are believed to originate in cells located in the pontine or mesencephalic reticular formation 98 ·99 with similar influences affecting vertical eye movements originating from structures located more rostrally.
Discuss the cortical contribution to visual function
Nathaniel Knox Cartwright, Petros Carvounis in Short Answer Questions for the MRCOphth Part 1, 2018
Although the oculomotor nuclei and final common pathways for horizontal and vertical eye movements are subcortical, cortical centres have an important role in the control of eye movements: horizontal saccades originate in the contralateral frontal eye fields of the frontal cortex and are independent of visual stimulipursuit movements originate from the occipitoparietal cortex, where stimulation leads to conjugate eye movement towards the other sidethe temporal cortex, as a centre for relay for motion information, is important in saccadic eye movements to moving objects. It is also involved in the initial detection of objects prior to voluntary fixation.
Cranial Nerve Syndromes
John W. Scadding, Nicholas A. Losseff in Clinical Neurology, 2011
Thus a ‘surgical’ lesion such as an aneurysm (Figure 6.1) or tumour compressing the oculomotor nerve usually result in a large unreactive pupil. There will also be paralysis of the superior and inferior rectus, the medial rectus and inferior oblique muscles. Vascular lesions, which may infarct the nerve, for example as a result of diabetes mellitus or an arteritis, may produce a complete oculomotor palsy with pupillary sparing. Such lesions recover spontaneously over 3–4 months. Because of the anatomical arrangement of the various divisions of the oculomotor nuclei in the midbrain tegmentum, a nuclear lesion will cause bilateral ptosis and loss of upgaze in both eyes, with ipsilateral involvement of the medial and inferior rectus and inferior oblique muscles.
Amplitude of Accommodation in Patients with Multiple Sclerosis
Published in Current Eye Research, 2019
Bekir Küçük, Mehmet Hamamcı, Seray Aslan Bayhan, Hasan Ali Bayhan, Levent Ertuğrul Inan
When the target distance is changed, the lens power must be altered to clearly view it; this is known as ocular accommodation.25 The accommodation reflex starts in the retinal ganglion cells with the light reflex. These impulses are sent through the optic nerve, the optic chiasma, and the optic tract. Most optic tract fibers go to the pretectal area, although some fibers synapse with the second-order neurons in the lateral geniculate nucleus of the thalamus. Then, second-order neurons carry the impulses through the optic radiation to the visual cortex. Impulses pass from the visual cortex to the prefrontal cortex, and fibers pass through the internal capsule to reach the midbrain. Then, the fibers in the midbrain synapse with the oculomotor nucleus and the Edinger-Westphal nucleus.26 The motor fibers are carried by the oculomotor nerve from the oculomotor nucleus to the medial rectus muscle, where both eyes converge. The efferent fibers of the Edinger-Westphal nucleus (which is the parasympathetic autonomic nucleus) accompany the oculomotor nerve and synapse in the ciliary ganglion. Then, the postganglionic fibers of the ciliary ganglion pass the short ciliary nerves to supply the sphincter pupillae muscle and the ciliary muscle, which allows the lens to thicken27 (Figure 1). This mechanism is controlled by the autonomic nervous system.23
Ictal Lid Movements: Blinks and Lid Saccades
Published in Neuro-Ophthalmology, 2021
Nataliya Pyatka, Prasannakumar Gajera, Guadalupe Fernandez-Bacavaca, Samden D. Lhatoo, Aasef G. Shaikh
The physiology of blinks is also remarkably different from that of lid saccades. Stimulation of the supra-orbital branch of the trigeminal nerve, either by mechanically stimulating the corneal surface or by electrical stimulation, triggers the blink reflex. Peri-ocular and corneal sensory projections, the afferent limb of the blink reflex, reach the principal trigeminal nucleus.3,4,21 The trigeminal neurons then project to the ipsilateral facial nucleus innervating the OO.21 The blink-associated trigeminal neurons also inhibit the motoneurons in the caudal most aspect of the oculomotor nucleus that innervates LP. The laterality of this inhibition varies amongst subjects; it could be ipsilateral, contralateral, or bilateral.5,22 Hypothetically, this projection is supposed to facilitate the inhibition of LP when OO is excited.5,15,16 The cerebral cortex is unlikely to play a direct role in eliciting the blink reflex.
Disorders of vision in multiple sclerosis
Published in Clinical and Experimental Optometry, 2022
Roshan Dhanapalaratnam, Maria Markoulli, Arun V Krishnan
Hering’s law dictates that conjugate movements of the eyes require yoked coordination of the extraocular muscles, via the supranuclear communication of ipsilateral and contralateral signalling pathways.81 For example on looking to the left, the left lateral rectus muscle works in tandem with the right medial rectus muscle, and this communication all occurs via pathways involving the brainstem nuclei. The midbrain comprises vertical gaze centres, the rostral interstitial nucleus of the medial longitudinal fasiculus (MLF), trochlear and oculomotor nucleus. Lesions in these areas can result in vertical gaze palsy, superior oblique palsy, third nerve palsy and convergence-retraction nystagmus. The pons contains the abducens nucleus, paramedian pontine reticular formation and the MLF, and lesions can result in an internuclear opthalmoplegia, horizontal gaze palsies, sixth nerve palsies and skew deviation.
Related Knowledge Centers
- Cerebral Aqueduct
- Midbrain
- Oculomotor Nerve
- Red Nucleus
- Third Ventricle
- Tegmentum
- Substantia Nigra
- Cerebral Peduncle
- Edinger–Westphal Nucleus
- Vestibulo–Ocular Reflex