Vestibular Apparatus
Definition
It is the organ of the vestibular system, or balance system
It is a sensory system
It provides the dominant input about movement and equilibrioception.
Vestibular apparatus + cochlea = Labyrinth of the inner ear
Parts of the Inner Ear
1. Vestibule
Part nearest the middle ear
Contains oval and round windows.
2. Cochlea
Snail shaped
Broad base
Continues with vestibule
Spirals +
At the centre of the spirals there is bone
3. The Semicircular Canals
Three tubes
one in each of the three planes of space
they are continuous with the vestibule
Parts of the Vestibular System
Vestibular apparatus comprises of two components:
1) The semicircular canal system, - rotational movements
2) The otoliths, - linear translations.
Movements consist of rotations and translations
Structure
Three semicircular canals
The horizontal (or lateral)
The anterior (or superior)
The posterior (or inferior)
Movement of fluid within the horizontal semicircular canal corresponds to rotation of the head around a vertical axis
The anterior and posterior semicircular canals detect rotations of the head in the sagittal plane (as when nodding)
The movement of fluid pushes on a structure called cupula, which contains hair cells that transducts the mechanical movement to electrical signals
Push-pull systems
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.
The vestibulo-ocular reflex (VOR)
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 field. For example, when the head moves to the right, the eyes move to the left, and vice versa.
Otolithic organs
The otolithic organs sense linear accelerations.
Utricle
Saccule
Functions
The vestibular signals eye movements, and control the muscles that keep upright posture
Utricular signals elicit eye movements
Saccular signals control muscles that maintain posture.
