The median acceleration thresholds for the perception of direction of linear movement for anterior-posterior movement was 8. According to the literature, acceleration thresholds depend on the stimulus profile whereas velocity thresholds do not. The median velocity thresholds for the perception of direction of linear movement for anterior-posterior movement was The median velocity thresholds for the perception of direction of linear movement for anterior-posterior movement increased linearly with age, whereas the median velocity threshold for lateral movement was not correlated with age.
The thresholds found in this study are lower than reported in the literature before which may be due to the repetative predictive sinusoidal stimulus which makes it relatively easy to lower the threshold by learning already within one test prophile. The variablity is large in line with the previous literature, but our experiments indicate that variability decreases after a training session. We interprete the literature and our current results that linear velocity thresholds after some training might reflect the sensitivity of the otolith system per se.
Peer Review reports. The vestibular system is the sensory mechanism of the inner ear labyrinth that helps the body maintain its postural equilibrium. There are two distinct sets of end organs in the labyrinth: the utricle and saccule within the vestibule, which respond to linear accelerations and changes in the position of the head with respect to gravity; and the semicircular canals, which respond to rotational movements angular acceleration.
The information that these organs deliver is proprioceptive in nature. The left and right utricular sensory epithelia maculae are in the same, approximately horizontal plane and because of this position they appear to be the dominant partner and are more useful than the saccular maculae in providing information about the position of the head and its side-to-side tilts when a person is in an upright position.
The maculae are stimulated by shearing forces between the otolithic membrane and the cilia of the hair cells beneath it.
However, the measurement or quantification of this 'otolith function' in patients is very difficult. Many methods have been proposed to try and evaluate otolith function: ocular counter-rolling OCR induced by lateroflexion, whole body roll, eccentric rotation and translational acceleration have all been explored and promoted as indicators of vestibular otolith function [ 1 ].
However, these methods showed poor sensitivity and specificity, thereby preventing a sound clinical application [ 1 ]. Lateroflexion or body roll is a simple physiological test that changes the orientation of the head and the otolith system in space and measures the responses, such as eye movements in response to a counter roll.
The subject tilts their head to one side and, as a consequence the eyes counter roll to a certain extent. Unfortunately, this simple test is associated with very low sensitivity and specificity and there is a large overlap between patients and healthy subjects.
For example, an extensive study in healthy subjects can reveal a wide range of ocular counter rolling, from 3 to 11 degrees, induced by this simple lateroflexion test [ 2 ]. It is also possible to measure responses to a linear acceleration translation , which is also one of the specific stimuli for the otolith system. A linear sled device can change a subject's position in space, is motor driven and can move very fast up to 1. However, if the sled is moving very fast and thus causing substantial motion, it is important to reduce the movements of the head using a mask specifically designed for each subject.
In addition, the sled involves complex and advanced technology, and so is very expensive, and again there is limited sensitivity and a large overlap between patients and healthy subjects. Ocular counter rolling can be measured in this way, at constant rotation velocities with the amplitude of the response depending on the centrifugal force acting upon both labyrinths. When combining a centrifuge with a motor driven linear sled, it is also possible to test each of the labyrinths separately by rotation around one labyrinth in order to centrifuge the other labyrinth alone.
Although this centrifuge technology has been used for many years, it is also associated with many problems and low sensitivities.
The equipment is expensive, the eye movement responses are very small and correct position of the labyrinths difficult and responsible for false positive outcomes. The aim of this study was therefore to investigate whether the thresholds for the perception of linear acceleration might allow for a better measure for the clinical evaluation of the otolith function than measurement of eye movements.
When auditory and visual cues are excluded and body movement is minimised, the detection of dynamic motion stimuli of small intensity appears to be primarily dependent on the otolith and the somatosensory systems response to pressure changes on the body surface [ 4 ]. Previous studies have shown that when oscillatory stimuli of 0. However, the literature shows that the acceleration thresholds vary with the stimulus profile used to determine the thresholds sinus, parabolic, linear, steps , but that thresholds expressed in terms of velocity are more constant and less variable with the stimulus profile [ 6 — 9 ].
For example, Gianna et al observed mean normal thresholds of 4. A practical problem of these stimulus profiles is that they require a long sled and that after each stimulus a deceleration period and adaptation period is required, which makes the test procedure long lasting. We therefore investigated the threshold for perception of the direction of linear horizontal motion using a raised cosine bell profile.
Whole body motion stimulus was generated by a motor driven linear sled running on a horizontal track of 4. The seat could be changed into one of two positions in which the AP or the traverse axis of the head was parallel to the direction of motion.
The subjects were seated upright with their feet on a footrest; head fixed against a headrest and the body restrained with safety belts. To eliminate external visual cues subjects were tested with eyes closed and in complete darkness; to eliminate auditory cues, subjects wore headphones; to mask proprioceptive cues, the sled was vibrated continuously by adding a sinusoidal signal to sled motor control profile 70 Hz sinus, 0.
Upon request, all subjects indicated that this continuous vibration prevented them from using the motor vibrations as a cue for detection of sled motion per se. The stimulus was a simple raised cosinus bell cycle of 0.
The impact of wind on movement perception is very difficult to prevent. However, speeds and accelerations were low, and the continuous cosinusoidal movement so smooth, that in a previous pilot study none of the subjects upon request indicated that they could make use of wind as a movement direction cue.
This was considered to be a strong indication that proprioceptive cues played a minor role in perception of the sled movement in the experimental setup results to be published elsewhere. Thresholds for the perception of motion were obtained under two conditions: the seat into a position in which the AP axis of the head was parallel to the direction of motion and with the seat into a position in which the traverse axis of the head was parallel to the direction of motion.
Subjects were required to correctly indicate whether they were moving forward or backward in an AP motion, left or right in lateral motion, or were stationary for all five outward and return cycles. Patient were not pre-informed about the possible sled profile.
The vestibular sensory organs are located in the petrous part of the temporal bone in close proximity to the cochlea, the auditory sensory organ.
Janire Carolino Pundit. What is vestibular balance disorder? Dizziness and vertigo are symptoms of a vestibular balance disorder. Balance disorders can strike at any age, but are most common as you get older. Your ear is a complex system of bone and cartilage. Within it is a network of canals.
Maricel Sabino Pundit. What is linear acceleration? Linear or tangential acceleration refers to changes in the magnitude of velocity but not its direction. We know from Uniform Circular Motion and Gravitation that in circular motion centripetal acceleration , a c , refers to changes in the direction of the velocity but not its magnitude. Emanoil Munyabin Pundit. How many senses do we have? Marlen Azores Pundit. What happens when stereocilia are bent? Deflection away from the utricle causes hyperpolarization and decreases the rate of discharge.
In superior canals these effects are reversed. Borislav Auerbeck Teacher. How do humans sense gravity? Humans ' vestibular sense , for example, detects gravity and balance through special organs in the bony labyrinth of the inner ear.
Receptors in our muscles and joints inform our sense of body position. Xaime Knopper Teacher. What is the cupula? From Wikipedia, the free encyclopedia. The ampullary cupula , or cupula , is a structure in the vestibular system, providing the sense of spatial orientation. The cupula is located within the ampullae of each of the three semicircular canals.
Latrina Horuzhy Teacher. What does the cochlea contain? The cochlea is a portion of the inner ear that looks like a snail shell cochlea is Greek for snail. The cochlea receives sound in the form of vibrations, which cause the stereocilia to move. The stereocilia then convert these vibrations into nerve impulses which are taken up to the brain to be interpreted. Lesme Filipovsky Teacher. What is equilibrium in the body? The vestibular nuclei then pass the information on to a variety of targets, ranging from the muscles of the eye to the cerebral cortex.
The vestibular system is a sensory system that is responsible for providing our brain with information about motion, head position, and spatial orientation; it also is involved with motor functions that allow us to keep our balance, stabilize our head and body during movement, and maintain posture. Thus, the vestibular system is essential for normal movement and equilibrium. Vestibular sensations begin in the inner ear in the vestibular labyrinth, a series of interconnected chambers that are continuous with the cochlea.
The most recognizable components of the vestibular labyrinth are the semicircular canals. These consist of three tubes, positioned approximately at right angles to one another, that are each situated in a plane in which the head can rotate. This design allows each of the canals to detect one of the following head movements: nodding up and down, shaking side to side, or tilting left and right.
These movements of the head around an axis are referred to as rotational acceleration, and can be contrasted with linear acceleration, which involves movement forward or backward. The semicircular canals are filled with a fluid called endolymph, which is similar in composition to the intracellular fluid found within neurons.
When the head is rotated, it causes the movement of endolymph through the canal that corresponds to the plane of the movement. The endolymph in that semicircular canal flows into an expansion of the canal called the ampulla. Within the ampulla is a sensory organ called the crista ampullaris that contains hair cells , the sensory receptors of the vestibular system.
Hair cells get their name because there is a collection of small "hairs" called stereocilia extending from the top of each cell. Hair cell stereocilia have fine fibers, known as tip links, that run between their tips; tip links are also attached to ion channels. When the stereocilia of hair cells are moved, the tip links pull associated ion channels open for a fraction of a millisecond.
0コメント