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Physical Motion
Published in Alfred T. Lee, Vehicle Simulation, 2017
For linear acceleration and gravity sensing, the vestibular systems also contain the otolith organ, which is composed of two membranous sacs: the saccule and the utricle. Hair cells embedded within calcium carbonate inside these sacs are triggered when linear accelerations are applied to the head. As the saccule and utricle are oriented at 90° to one another, they respond to vertical (saccule) and horizontal (utricle) linear accelerations independently. Although the semicircular canals rely on physical movement, the otolith functions as both a dynamic and a static system. The gravity sensing component of the otolith is the principal means by which we sense the earth vertical. The process is occurring even when the head is not moved. When aligned with the earth-vertical axis, gravitational forces apply a shearing action on the otolith and this, in turn, sends signals to the brain that the head is upright. As the head is moved away from the vertical axis, signals are sent to the brain to automatically correct for this deviation, that is, to regain postural stability. Lateral and longitudinal acceleration of the head, as well as vertical accelerations, affect the otolith and these forces play an important role not only in postural stability, but also in how a vehicle operator responds to forces resulting from operator control inputs or from disturbances external to the vehicle.
Spatial Orientation
Published in Pamela S. Tsang, Michael A. Vidulich, Principles and Practice of Aviation Psychology, 2002
The otolith organs indicate the orientation of the head relative to gravity. Like the carpenter’s plumb bob, they usually indicate the direction of the vertical and are crucial in maintaining human balance and equilibrium. However, just as with any other physical accelerometer, they follow Einstein’s equivalence principle and cannot distinguish between gravity and the inertial reaction force to any linear acceleration, so they actually indicate the orientation of the head relative to the gravito-inertial force (GIF). This is the apparent vertical, or the direction in which a plumb bob would hang.
Spatial Orientation and Disorientation
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
Each otolith organ contains a sensory epithelium, the macula, consisting of a carpet of hair cells, the hairs of which project into the base of the overlying statoconial membrane (Figure 4.6). This membrane is rendered more dense than the surrounding endolymphatic fluid by the incorporation within it of crystals of calcium carbonate, giving the membrane a stony appearance, from which the name otolith is derived. The hair cells of the sensory epithelium have a directional sensitivity and will change their rate of firing if there is relative movement in the appropriate direction between the sensory epithelium and the statoconial membrane. Such movement comes about if, as a result of tilt, there is a change in the component of gravity acting on the statoconial membrane in the plane of the macula, or if, as a result of a dynamic acceleration, it is subject to an inertial force. The direction of maximum sensitivity of the hair cells changes progressively across the surface of the macula in such a way that, whatever the direction of acceleration acting in the plane of the macula, there will always be a group of hair cells that are maximally stimulated. Since the macula of the utricle lies approximately in the horizontal plane and that of the saccule in the sagittal plane, the anatomical arrangement of these two structures allows sensation of the direction and intensity of any acceleration acting on the head. The only force in terrestrial life that acts continuously on the inner ear is that associated with gravity. As a result, though sensitive to the transient accelerations associated with locomotion, the predominant function of the otolith organs is to act as sensors of tilt of the head with respect to the direction of gravity.
Vestibulo-ocular reflex characteristics during unidirectional translational whole-body vibration without head restriction
Published in Ergonomics, 2020
Tomoko Sugawara, Hiroyuki Sakai, Yutaka Hirata
The characteristics of the VOR elicited along or around single-axis head movements are well established. When the head rotates, the semicircular canals detect head angular acceleration and induce counter-rotation of the eyes to stabilise retinal images (Gresty, Hess and Leech 1977; Leigh and Brandt 1993; MacDougall and Moore 2005). In the dark, VOR gains (eye velocity amplitude divided by head angular velocity amplitude) in humans are approximately 0.9 in the yaw rotation (Paige 1994; Tabak et al. 1997; Tweed et al. 1994), 0.7 in the pitch rotation (Goumans et al. 2010; Tweed et al. 1994) and 0.6 in the roll rotation (Goumans et al. 2010; Leigh et al. 1989) (see Figure 1 for the definition of axes and directions). When the head moves translationally, the otolith organs in the inner ear detect head linear acceleration and trigger the VOR, which contributes to ocular stability. Specifically, vertical and lateral accelerations elicit vertical and horizontal VORs, respectively (Baloh et al. 1988; Busettini et al. 1994; Merfeld et al. 2005; Paige 1989), while longitudinal acceleration elicits both vertical and horizontal VORs (Angelaki 1998; Baloh et al. 1988; Paige and Tomko 1991b; Ramat and Zee 2005).
Caloric and galvanic vestibular stimulation for the treatment of Parkinson’s disease: rationale and prospects
Published in Expert Review of Medical Devices, 2021
The peripheral vestibular system is cocooned within the dense temporal bone of the inner ear and comprises two organ types: the semi-circular canals and otoliths. The three semi-circular canals are co-located in a perpendicular arrangement and together detect rotational head movement across the three cardinal depth planes. The otoliths comprise the saccule and utricle and together detect linear head movement and gravitational pull, sensitivities that mean that the vestibular nerve never falls quiet. The dimensions of the vestibular organs seem so well optimized that over roughly seven orders of magnitude of mass variation in mammals, the overall size of the vestibular organs varies over one [1].
Smart platform for the analysis of cupula deformation caused by otoconia presence within SCCs
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Radun Vulović, Milica Nikolić, Nenad Filipović
Humans have the ability to detect angular motion due to the specific structures of the inner ear: three semicircular canals (SCCs) with cupulae located within their ampullae. During angular head movements, a fluid (endolymph) inside the SCCs starts to flow thus forcing the afferent hair cells in the SCC’s wall to start their movement. Unfortunately, that flow can be disturbed by the small particles called otoconia, i.e. otoliths, which leads to benign paroxysmal positional vertigo. Such condition is called canalithiasis.