The vestibular system

The two components of the vestibular system are: the peripheral part inside the inner ear and the central part in the central nervous system.

Vestibular organ

The vestibular organ is the main part of the peripheral aspect, and add essential information to our equilibrium and our sense of spatial orientation. The function of the vestibular sensory system is to provide the dominant input signal regarding movement and perception of equilibrium.

Inner ear labyrinth

The canals of the vestibular organ, together with the cochlea, that belongs to the auditory system, compose the labyrinth of the inner ear. This organ, situated in the vestibulum, is located in the inner ear. Normally, when entertaining machines or flight inside army jets are not involved, our movements consist of rotations and linear accelerations.

The vestibular system comprises 2 components:

(1) The semicircular canal system, which identifies circulatory movement.

(2) The otoliths, which detects linear accelerations and decelerations.

The vestibular system and our movements

The vestibular system control our movements. It is done via signals that are sent to the neural structures that control the muscles of our eye movements, and to the skeletal muscles that keep us in erect position.

The neural links to the former provide the structural explanation of the vestibulo ocular reflex, which is required for clear and steady vision, and the transmission of signals to the muscles that control our posture are necessary to keep us in erect position.

Identification of circular movements

The semicircular canal system identifies circular movements. The semicircular canals are the main structure that can perform this task. The three semicircular canals include: (1) lateral. (2) Superior. (3) Inferior arches. and may be called also: (I) Horizontal. (II) Anterior. (III) Posterior canals.

One of the most common rotational movements is the rotation of the head around a vertical axis. The result is movement of fluid within the horizontal semicircular canal. The obvious anatomic vertical axis of the head is the neck. The superior and inferior semicircular canals, serves as sensors for round motion of the head in the sagittal plane. It happens when nodding the head.

Movement of head in the frontal plane is also detected by the superior and inferior semicircular canals. The movement of liquid pushes on hair cells.

Cupula: biological transducer

The term for the micro sensor organ is cupula. It works as a biological transducer that modifies the energy the mechanical movements to electrical signals.

The activity of the canals is arranged in bi lateral pairs. When liquid is moving inside one semicircular canal, and activates the cupula, its corresponding canal on the contralateral inner ear is supressed, and vice versa.

Vertical canals go together in a crossed activity. The vestibulo ocular reflex, the push-pull principle and the Halmagyi Curthoys test, are not explained here.

Otolytic organ

Sense changes in velocity

The otolithic organs sense changes in velocity forwards and backwards, that are called in a more scientific terminology: linear accelerations and decelerations (negative accelerations). We have two relevant organs on every side. One is called utricle and the other is saccule.

Crystals

The otoconia crystals, or simply crystals, in the otoconia organization rest on a viscous gel matter, and they are more dense than their environment. They get displaced when linear acceleration or deceleration is applied, and in turn deflects the ciliary bundles of the hair cells. These transduction mechanism generates a sensory electrochemical signal.

Utricular signals, usually have effect on eye movements, while saccular signals, usually go to to muscles that are involved in maintaining our erect posture.

Otolith signals processing

The processing of otolith signals is more complex then analysis of the signals from the semicircular canals. The CNS have to distinguish between linear acceleration of gravity and linear acceleration that is caused by other forces, based on these signals.

Vestibular cortex

By definition, the vestibular cortex is the area of the cerebrum which responds to input from the peripheral vestibular system.

The anatomic location is still controversial, but there are indications that there is a right hemisphere dominance. Lesions of the vestibular nucleus impair the vestibular function of the patient. The current hypothesis is that it is located in the temporo peri sylvian cortex.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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