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A Clinical Approach to Abnormal Eye Movements
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Torsional nystagmus is commonly observed in patients with a lateral medullary infarction (Wallenberg syndrome). The upper poles generally beat away from the side of the infarction, along with a contralateral hypertropia and ipsilateral saccadic lateropulsion. In midbrain lesions, torsional nystagmus beats toward the side of the lesion, unlike lesions lower in the brainstem, which beat away from the damaged vestibular nuclei. Lesions of the caudal vestibular nuclei or vestibular root entry zone cause torsional nystagmus with a large horizontal component.18 Discrete lesions of the rostral part of the lateral vestibular nucleus or superior vestibular nucleus can produce torsional or mixed torsional-vertical nystagmus.
Brain Motor Centers and Pathways
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
There are four vestibular nuclei on each side, located in the rostral medulla and caudal pons (Figure 12.17): superior, lateral, medial, and inferior. The lateral vestibular nucleus is also known as Deiters’ nucleus. Cerebellar afferents to the vestibular nuclei project ipsilaterally from the vermis of the anterior lobe to the lateral vestibular nucleus, from the flocculonodular lobe to the other three vestibular nuclei, and bilaterally from the fastigial nucleus to the lateral and inferior vestibular nuclei. The vestibular nuclei integrate a broad range of visual and somatosensory inputs, including inputs from the spinal cord, particularly neck proprioceptive information, inputs from subcortical visual centers, and inputs from the cerebral cortex, including premotor head movement commands.
Motor Function and ControlDescending Tracts
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The descending motor pathways have been classified into the pyramidal tracts, which originate from the cerebral cortex, and the extrapyramidal tracts, which arise from brainstem nuclei (Table 9.1). The pyramidal tract is the most important motor pathway for motor control and consists of axons of pyramidal cells in layers III and V of the premotor, precentral and postcentral gyrus of the cortex (Figure 9.3). The corticospinal tract descends through the posterior part of the internal capsule on the lateral side of the thalamus and passes through the midbrain, pons and medulla. In the ventral medulla, the axons (90%) cross to the contralateral side and proceed to the spinal cord. Approximately 10%–15% of the axons do not cross to the contralateral side and supply the thoracic respiratory muscles. The corticospinal tract controls the muscles responsible for precise movements (fingers and hands) and the laryngeal muscles. The corticobulbar tract fibres terminate on the lower motor neurons in the brainstem and control facial muscle movements.The extrapyramidal tract is formed by the rubrospinal, vestibulospinal, tectospinal and reticulospinal tracts. These tracts maintain postural tone and direct voluntary movement. The rubrospinal tract arises from cells in the red nucleus, crosses contralaterally in the brainstem, receives input from the cerebral cortex and runs down the spinal cord. The lateral vestibulospinal tract arises from the lateral vestibular nucleus and does not cross to the contralateral side. The reticulospinal tract originates from the reticular system in the pons and medulla. The extrapyramidal system receives inputs from the cerebral cortex and cerebellum (Figure 9.4).
Vestibular function in children with generalized epilepsy and treated with valproate
Published in Expert Review of Clinical Pharmacology, 2022
Sherifa Ahmed Hamed, Amira Mohamed Osiely
The vestibular system is divided into peripheral and central components. The peripheral component is composed of the semicircular canals, otolith (saccule and utricle) organs and the superior and inferior vestibular nerves. The central component begins from the point of entrance of vestibular nerves to the brainstem, the medial and lateral vestibular nuclei and the central inter-relations and connections to the thalamus and cerebral cortex. The semicircular canals sense horizontal angular head accelerations. Their afferents project to the medial vestibular nuclei via the vestibulo-ocular reflex (VOR). They provide reflexive ocular motor responses for maintenance of gaze stability. The otolith organs sense linear acceleration and static tilt in relation to gravity. Their afferents project to the lateral vestibular nucleus via the vestibulo-spinal reflex (VSR) for postural control and via connections to the cerebellar neurons, thalamus, and higher-cortical areas for balance, self-motion, and gravity direction [14].
Effect of vestibular stimulation using a rotatory chair in human rest/activity rhythm
Published in Chronobiology International, 2020
Florane Pasquier, Nicolas Bessot, Tristan Martin, Antoine Gauthier, Jan Bulla, Pierre Denise, Gaëlle Quarck
Although the true nature of the mechanism remains unknown, anatomical evidence, which could explain links between the vestibular system and the circadian timing system, has been demonstrated in rodents. Cavdar et al. (2001) reported vestibular projections from medial and lateral vestibular nuclei to the posterior hypothalamic nucleus. Reciprocal projections between the medial vestibular nucleus and the orexin neurons involved in the sleep/wake cycle were demonstrated in rodents (Horowitz et al. 2005). The paradigms using a hypergravity environment reinforce anatomical observations. In one study, chronic 2 G centrifugation caused a robust c-Fos expression in the SCN of the hypothalamus in wildtype mice compared to het mice (otoconia deficient) (Fuller et al. 2004). This study confirmed the role of the otolithic organs in the mammalian circadian system.