The vestibular system includes a tiny group of organs which sit within the inner ear. It is responsible for providing the brain with information about motion, head position, and spatial orientation. It also plays an important role with motor functions which help to maintain our balance as well as stabilize our head and body during movement. Thus, the vestibular system is integral to normal movement and equilibrium.
It is made up of several parts, including the vestibular labyrinth, which is a series of fluid-filled canals in the inner ear, and the vestibular nerve, which carries information from the labyrinth to the brain. The vestibular system also includes the vestibular nuclei in the brainstem, which help to coordinate the information from the labyrinth with information from other senses.
When we move our head, the fluid in the vestibular labyrinth moves and sends signals to the brain through the vestibular nerve. The brain uses this information to help us maintain our balance and coordinate our movements. 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.
The vestibular system uses two other organs, known as the otolith organs, to detect linear acceleration, gravitational forces, and tilting movements. There are two otolith organs in the vestibular labyrinth: the utricle and the saccule. The utricle is specialized to detect movement in the horizontal plane, while the saccule detects movement in the vertical plane. The otolithic membrane has small crystals of calcium carbonate called otoconia embedded within it. These crystals make the otolithic membrane heavier than the rest of the structure, amplifying any movement of the gel-like substance. The structure of the otolith organs makes them especially sensitive to movements like linear acceleration and head tilts.
The Vestibulo-ocular Reflex
The vestibulo-ocular reflex (VOR) is a reflex that helps to stabilize images on the retina during head movements. It does this by causing the eyes to move in the opposite direction of the head movement, which helps to keep the image of the visual scene stable on the retina. This reflex is important for maintaining clear vision during activities like driving and running.
When the vestibular system is dysfunctional, it causes a disruption in this reflex which causes a mismatch between head and eye movement. This can create feelings of unsteadiness, nausea, and vertigo.
Disorders of the Vestibular System
Benign paroxysmal positional vertigo (BPPV) is a common cause of vertigo and dizziness. It occurs when the small crystals of otoconia become dislodged from the otolith organs and end up in the semicircular canals. This can cause dizziness or vertigo when the head is moved into certain positions.
As the head stops moving, the crystals continue to float through the canals causing the fluid to move – this sends inaccurate information to the brain to compensate for head movement that isn’t there. The result is a nystagmus, or shaking of the eyes which creates a sensation of the room spinning and extreme dizziness.
Physiotherapy can be used to help resolve BPPV, by first assessing which semicircular canal has a crystal dislodged into it and then using a series of head movements which move the crystal out of the canal and back to its normal position. This treatment is very effective and symptoms may resolve in as few as 1-2 sessions!
Other vestibular disorders, such as Vestibular Neuritis, Meniere’s disease and Labyrinthitis, can also be treated with physiotherapy. These conditions are caused by inflammation of the inner ear or vestibular nerve, and can cause dizziness, vertigo, and other symptoms. A physiotherapist can help to develop a treatment plan to reduce symptoms and improve balance and coordination. This may include exercises to help improve the function of the vestibular system, as well as other techniques to help manage symptoms and improve overall function.
If you or anyone you know suffers from dizziness, vertigo, or poor balance book in with one of our physiotherapists to get assessed and start on a treatment plan today!
MPhty, BSc Kin, APAM, AHPRA
Furman, J. M, Cass, S. P (1999). Benign paroxysmal positional vertigo. The New England Journal of Medicine, 341:1590-1596.