Vestibular system

Information about Vestibular system

The vestibular system, or balance system, is the sensory system that provides the dominant input about our movement and orientation in space. Together with the cochlea, the auditory organ, it is situated in the vestibulum in the inner ear (Figure 1). As our movements consist of rotations and translations, the vestibular system comprises two components: the semicircular canals, which indicate rotational movements; and the Otoliths, which indicate linear translations. The vestibular system sends signals primarily to the neural structures that control our eye movements, and to the muscles that keep us upright. The projections to the former provide the anatomical basis of the vestibulo-ocular reflex, which is required for clear vision; and the projections to the muscles that control our posture are necessary to keep us upright.

Figure 1 Human Labyrinth, from the left ear. It contains i) the cochlea (yellow), which is the peripheral organ of our auditory system; ii) the semicircular canals (brown), which transduce rotational movements; and iii) the otoliths (in the blue/purple pouches), which transduce linear accelerations. The light blue pouch is the endolymphatic sac, and contains only fluid.

Semicircular canals

Our world has three spatial dimensions. Accordingly, our vestibular system contains three semicircular canals in each labyrinth. They are approximately orthogonal to each other, and are called

Push-pull systems

The canals are cleverly arranged in such a way that each canal on the left side has an almost parallel counterpart on the right side. Each of these three pairs works in a push-pull fashion: when one canal is stimulated, its corresponding partner on the other side is inhibited, and vice versa.

Enlarge picture
Figure 2: Push-pull system of the semicircular canals, for a horizontal head movement to the right.


This push-pull system allows us to sense all directions of rotation: while the right horizontal canal gets stimulated during head rotations to the right (Fig 2), the left horizontal canal gets stimulated (and thus predominantly signals) by head rotations to the left.

Vestibulo-ocular reflex (VOR)

The vestibular system needs to be fast: if we want clear vision, head movements need to be compensated almost immediately. Otherwise our vision corresponds to a photograph taken with a shaky hand. To achieve clear vision, signals from the semicircular canals are sent as directly as possible to the eye muscles. This direct connection involves only three neurons, and is correspondingly called Three-neuron-arc (Fig 3). Using these direct connections, eye movements lag the head movements by less than 10 ms, one of the fastest reflexes in the human body. The automatic generation of eye movements from movements of the head is called vestibulo-ocular reflex, or short VOR.

Figure 3 Three-neuron arc, during a head movement to the right. 8th cranial nerve, from the peripheral vestibular sensors to vn, the vestibular nuclei in the brainstem. VI abducens nucleus. The medial longitudinal fascicle (mlf) projects from the abducens nucleus to III, the oculomotor nucleus. The left lateral rectus muscle lr and the right medial rectus muscle mr get contracted, turning the eyes to the left. The green objects are excited, the orange ones inhibited.


This reflex, combined with the push-pull principle described above, forms the physiological basis of the Rapid head impulse test or Halmagyi-Curthoys-test: when the function of your right balance system is reduced by a disease or by an accident, quick head movements to the right cannot be sensed properly any more. As a consequence, no compensatory eye movements are generated, and the patient cannot fixate a point in space during this rapid head movement. Another way of testing the VOR response is to attempt to induce nystagmus (compensatory eye movements in the absence of head motion) by pouring cold or warm water into the ear.

Mechanics

The mechanics of the semicircular canals can be described by a damped oscillator. If we designate the deflection of the cupula with , and the head velocity with , the cupula deflection is approximately



α is a proportionality factor, and s corresponds to the frequency. For humans, the time constants T1 and T2 are approximately 3 ms and 5 s, respectively. As a result, for typical head movements, which cover the frequency range of 0.1 Hz and 10 Hz, the deflection of the cupula is approximately proportional to the head-velocity (!). This is very useful, since the velocity of the eyes must be opposite to the velocity of the head in order to have clear vision.

Central Processing

Signals from the vestibular system also project to the Cerebellum (where they are used to keep the VOR working, a task usually referred to as Learning or Adaptation) and to different areas in the cortex. The projections to the cortex are spread out over different areas, and their implications are currently not clearly understood.

Otoliths

While the semicircular canals respond to rotations, the otoliths sense linear accelerations. We have two on each side, one called Utricle, the other Saccule. Figure 4C shows a cross section through an otolith: the otoconia crystals in the Otoconia Layer (Fig. 4, top layer) rest on a viscous gel layer, and are heavier than their surroundings. Therefore they get displaced during linear acceleration, which in turn deflects the Hair cells (Fig. 4, bottom layer) and thus produces a sensory signal. Most of the utricular signals elicit eye movements, while the majority of the saccular signals projects to muscles that control our posture. While the interpretation of the rotation signals from the semicircular canals is straightforward, the interpretation of otolith signals is more difficult: since gravity is equivalent to a constant linear acceleration, we somehow have to distinguish otolith signals that are caused by linear movements from such that are caused by gravity. We can do that quite well, but the neural mechanisms underlying this separation are not yet fully understood.

Pathologies

Diseases of the vestibular system can take different forms, and usually induce vertigo and instability, often accompanied by nausea. The most common ones are Vestibular neuritis, a related condition called Labyrinthitis, and BPPV. In addition, the function of the vestibular system can be affected by tumors on the cochleo-vestibular nerve, an infarct in the brain stem or in cortical regions related to the processing of vestibular signals, and cerebellar atrophy. Less severe, but often also with large consequences, is vertigo caused by the intake of large amounts of alcohol.

BPPV

Main article: Benign paroxysmal positional vertigo
BPPV, which is short for Benign Paroxysmal Positional Vertigo, is probably caused by pieces that have broken off from the Otoliths, and have slipped into one of the semicircular canals. In most cases it is the posterior canal that is affected. In certain head positions, these particles push on the cupula of the canal affected, which leads to dizziness, vertigo and nystagmus.

External links

References

  • S. M. Highstein, R. R. Fay, A. N. Popper, editors (2004). The vestibular system. Berlin: Springer. ISBN 0-387-98314-7.  (Comment: A book for experts, summarizing the state of the art in our understanding of the balance system)
  • Thomas Brandt (2003). Vertigo : Its Multisensory Syndromes. Berlin: Springer. ISBN 0-387-40500-3.  (Comment: For clinicians, and other professionals working with dizzy patients.)
  • Driver Drowsiness: Is something missing? J. Christopher Brill, Peter A. Hancock, Richard D. Gilson. University of Central Florida (2003) link (Comment: Research on driver or motion-induced sleepiness aka 'sopite syndrome' links it to the vestibular labrynths.)
 •  • [ e]
Nervous system: Sensory systems/sense
Special sensesVisual system/Visual perception • Auditory system/Hearing • Chemoreception (Olfactory system/Olfaction • Gustatory system/Taste)
Somatosensory systemNociception • Thermoreception • Vestibular system • Mechanoreception (Pressure, Vibration, Proprioception)
OtherSensory receptor
 •  • [ e]
Sensory system: Auditory and Vestibular systems
Outer earPinna (Helix, Antihelix, Tragus, Antitragus, Earlobe) • Ear canal
Middle earEardrum • Ossicles (Malleus, Incus & Stapes) • Stapedius • Tensor tympani • Eustachian tube (Torus tubarius)
Inner ear/LabyrinthBony labyrinth (Vestibule) • Membranous labyrinth
Oval window • Helicotrema • Round window
Cochlea: Spiral ganglion • Modiolus • Cochlear duct/scala media (Endolymph, Stria vascularis, Spiral ligament, Organ of Corti) • Scala vestibuli and Scala tympani (Perilymph)
Reissner's/vestibular membrane • Basilar membrane • Tectorial membrane
Organ of Corti: Hair cells • Stereocilia • Sulcus spiralis (externus, internus) • Limbus spiralis
Vestibular systemStatic/translations: Utricle (Macula) - Saccule (Macula, Endolymphatic sac, Endolymphatic duct) - Kinocilium - Otolith
Kinetic/rotations: Semicircular canals (Superior, Posterior, Horizontal) • Cupula • Ampullae (Crista ampullaris)
Brain (auditory)Cochlear nerve VIII → Cochlear nuclei → Superior olivary nuclei → Lateral lemniscus → Inferior colliculi → Medial geniculate nuclei → Primary auditory cortex
The cochlea is the auditory portion of the inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along the partition separating fluid chambers in the coiled tapered tube of the cochlea.
..... Click the link for more information.
vestibule is the central part of the osseous labyrinth, and is situated medial to the tympanic cavity, behind the cochlea, and in front of the semicircular canals.

It is somewhat ovoid in shape, but flattened transversely; it measures about 5 mm.
..... Click the link for more information.
The inner ear is the bony labyrinth, a system of passages comprising two main functional parts:
  • the organ of hearing, or cochlea
  • and the vestibular apparatus, the organ of balance that consists of three semicircular canals and the vestibule.

..... Click the link for more information.
The semicircular canals are three half-circular, interconnected tubes located inside each ear that are the equivalent of three gyroscopes located in three orthogonal planes.
..... Click the link for more information.
An otolith, (oto-, ear + lithos, a stone), also called statoconium[1] or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth.
..... Click the link for more information.
vestibulo-ocular reflex (VOR) or oculovestibular reflex is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual
..... Click the link for more information.
The semicircular canals are three half-circular, interconnected tubes located inside each ear that are the equivalent of three gyroscopes located in three orthogonal planes.
..... Click the link for more information.
For more uses of the word labyrinth, see Labyrinth (disambiguation)


The labyrinth is a system of fluid passages in the inner ear, including both the cochlea which is part of the auditory system, and the vestibular system which provides the
..... Click the link for more information.
In mathematics, orthogonal, as a simple adjective, not part of a longer phrase, is a generalization of perpendicular. It means at right angles, from the Greek ὀρθός orthos
..... Click the link for more information.
The lateral or horizontal canal (external semicircular canal) is the shortest of the three canals.

It measures from 12 to 15 mm., and its arch is directed horizontally backward and lateralward; thus each semicircular canal stands at right angles to the other two.
..... Click the link for more information.
The introduction to this article provides insufficient context for those unfamiliar with the subject matter.
Please help [ improve the introduction] to meet Wikipedia's layout standards.

..... Click the link for more information.
The posterior semicircular canal, vertical like the superior, is directed backward, nearly parallel to the posterior surface of the petrous bone. It is part of the bony labyrinth and is used by the vestibular system to detect rotations of the head in the sagittal plane.
..... Click the link for more information.
vestibulo-ocular reflex (VOR) or oculovestibular reflex is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual
..... Click the link for more information.
Nystagmus
Classifications and external resources

ICD-10 H 55.
ICD-9 379.50 , 794.14

DiseasesDB 23470

MeSH D009759

Nystagmus, is involuntary eye movement that can be part of the vestibulo-ocular reflex (VOR).
..... Click the link for more information.
An otolith, (oto-, ear + lithos, a stone), also called statoconium[1] or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth.
..... Click the link for more information.
Utricle ("pouch") can refer to:
  • Utricle (ear)
  • Prostatic utricle
  • a fruit type, similar to achene, found in beet and dock

..... Click the link for more information.
The introduction to this article provides insufficient context for those unfamiliar with the subject matter.
Please help [ improve the introduction] to meet Wikipedia's layout standards.

..... Click the link for more information.
Vestibular neuronitis
Classification & external resources

ICD-10 H 81.2
ICD-9 386.12

Vestibular Neuronitis, also called Vestibular neuritis
..... Click the link for more information.
Labyrinthitis
Classification & external resources

ICD-10 H 83.0
ICD-9 386.3

DiseasesDB 29290

MeSH C09.218.568.315 Labyrinthitis is a balance disorder.
..... Click the link for more information.
Benign paroxysmal positional vertigo
Classification & external resources

Exterior of labyrinth.
ICD-10 H 81.1
ICD-9 386.11

OMIM 193007
DiseasesDB 1344

eMedicine ent/761   emerg/57 neuro/411
MeSH D014717
..... Click the link for more information.
Nystagmus
Classifications and external resources

ICD-10 H 55.
ICD-9 379.50 , 794.14

DiseasesDB 23470

MeSH D009759

Nystagmus, is involuntary eye movement that can be part of the vestibulo-ocular reflex (VOR).
..... Click the link for more information.
Neurobiology is the study of cells of the nervous system and the organization of these cells into functional circuits that process information and mediate behavior.[1] It is a subdiscipline of both biology and neuroscience.
..... Click the link for more information.
Washington University in St. Louis is a private, coeducational, research university located in St. Louis, Missouri. The University was co-founded in 1853 by William Greenleaf Eliot and Wayman Crow[4] as Eliot Seminary.
..... Click the link for more information.
Sopite syndrome is a poorly understood manifestation of motion sickness that causes drowsiness, mood changes, mental depression, and fatigue.[1] Sophite syndrome may be the cause of motion-induced sleepiness that is experienced in situations such as driving, flying and
..... Click the link for more information.
nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. Prominent parts of a nervous system include neurons and nerves, which are used in coordination.
..... Click the link for more information.
sensory system: in this case, vision, for the visual system. ]]

A sensory system is a part of the nervous system responsible for processing sensory information.
..... Click the link for more information.
Senses are the physiological methods of perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology (or cognitive science), and philosophy of perception.
..... Click the link for more information.
special senses are the first four of these; touch is specifically excluded as a special sense. Instead, the various aspects of touch (pain, heat, pressure) are all categorized as somatic senses.
..... Click the link for more information.
The visual system is the part of the nervous system which allows organisms to see. It interprets the information from visible light to build a representation of the world surrounding the body.
..... Click the link for more information.
In psychology, visual perception is the ability to interpret visible light information reaching the eyes which is then made available for planning and action. The resulting perception is also known as eyesight, sight or vision.
..... Click the link for more information.

This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.