Balance and equilibrium, I: The vestibule and semicircular canals (original) (raw)
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Unilateral Labyrinthectomy Modifies the Membrane Properties of Contralesional Vestibular Neurons
Journal of Neurophysiology, 2004
Vestibular compensation after a unilateral labyrinthectomy leads to nearly complete disappearance of the static symptoms triggered by the lesion. However, the dynamic vestibular reflexes associated with head movements remain impaired. Because the contralesional labyrinth plays a prominent role in the generation of these dynamic responses, intracellular recordings of contralesional medial vestibular nucleus neurons (MVNn) were done after 1 mo of compensation. Their firing properties and cell type were characterized at rest, and their response dynamics investigated using step, ramp, and sinusoidal current stimulations. The sensitivity of the contralesional MVNn firing rates to applied current was increased, which, along with increased phase leads, suggests that significant changes in active conductances occurred. We found an increased proportion of the phasic type B neurons relative to the tonic type A neurons in the contralesional MVN. In addition, the remaining contralesional type A...
Journal of Anatomy, 2004
The vestibular, cochlear and facial nerves have a common course in the internal auditory canal (IAC). In this study we investigated the average number of nerve fibres, the average cross-sectional areas of the nerves and nerve fibres, and the apparent connections between the facial, cochlear and vestibular nerve bundles within the IAC, using light and scanning electron microscopy. The anatomical localization of the nerves within the IAC was not straightforward. The general course showed that the nerves rotated anticlockwise in the right ear from the inner ear end towards the brainstem end and vice versa for the left ear. The average number of fibres forming vestibular, cochlear, and facial nerves was not constant during their courses within the IAC. The superior and the inferior vestibular nerves showed an increase in the number of nerve fibres from the inner ear end towards the brainstem end of the IAC, whereas the facial and the cochlear nerves showed a reduction in the number of fibres. This suggests that some of the superior and inferior vestibular nerve bundles may receive fibres from the facial and/or cochlear nerves. Scanning electron microscopic evaluations showed superior vestibular-facial and inferior vestibular-cochlear connections within the IAC, but no facial-cochlear connections were observed. Connections between the nerves of the IAC can explain the unexpected vestibular disturbances in facial paralysis or persistence of tinnitus after cochlear neurectomy in intractable tinnitus cases. The present study offers morphometric and scanning electron microscopic data on the fibre connections of the nerves of the IAC.
Vestibular Disease in Dogs and Cats
Veterinary Clinics of North America: Small Animal Practice, 2010
The vestibular system is the major sensory (special proprioceptive) system that, along with the general proprioceptive and visual systems, maintains balance. 1-4 An individual's sense of balance is best summarized as a normal orientation with respect to the influence of gravitational forces. The vestibular system also functions to coordinate body posture and ocular position in relation to the position or motion of the head. Considering its physiologic roles, the clinical hallmarks of vestibular dysfunction are abnormalities of the gait, head and body posture, and ocular movement. 1,2 VESTIBULAR NEUROANATOMY For clinical purposes, the anatomic constituents of the vestibular system are functionally divided into peripheral and central components. The peripheral portions of the vestibular system are located in the inner ear (Fig. 1A) and consist of the receptors, ganglion, and peripheral axons of the vestibular division of cranial nerve VIII. The central components (Fig. 1B) are the vestibular nuclei in the medulla and the vestibular projections to the cerebellum, spinal cord, and rostral brainstem. 1,2 Peripheral Vestibular System The receptors for the vestibular system are colocalized with those for the auditory system in the bony and membranous labyrinths of the petrous temporal bone (inner ear). The bony labyrinth is divided into 3 major contiguous regions: the semicircular canals, the vestibule, and the cochlea. The lumens of each of these structures are filled with perilymph. Within the bony labyrinth is the membranous labyrinth, which contains 4, endolymph-filled, communicating structures called the (1) semicircular ducts, (2) utricle, (3) saccule, and (4) cochlear duct (see Fig. 1A). The semicircular ducts are contained within the semicircular canals, the utricle and saccule within the vestibule, and the cochlear duct within the bony cochlea. Each of the semicircular ducts is oriented at right angles to the others, thus occupying 3 planes. 2 In one end of each of the membranous semicircular ducts is a terminal dilation called the ampulla, and on
Cochlear anatomy and central auditory pathways
This chapter provides a brief review of the anatomy of the cochlea and its central auditory pathways. Since there is great similarity between the basic features of the human cochlea and those in a variety of animals, we have chosen the chinchilla as a representative animal model.
Cochlear and vestibular functions of the rat after obliteration of the endolymphatic sac
Hearing Research, 1988
A combined morphological and physiological study on the effect of saccus obliteration on the cochlea and the veatihular lahyrinth of the rat is presented. Endolymphatic hydrops was successfully induced in 49% of the animals. It was frequently associated with fistulae of the membranous wall and degenerative changes tn the organ of Corti and sptral ganglion. In hydropic ears electrocochleography revealed a CAP threshold increase only in those cases where hydrops was associated with loss of hair cells and ganglion cells. In two of these animals also an increased negative SP was present. Static otolith reflexes were found to he normal in all hydropic ears despite severe lesions of the saccule in some of these. Abnormal canal reflexes measured by electronystagmography and cupulometrv were established in animals with hydrops of the semicircular canals and in one anrmal with a fistula of the sacculc.