What Are the Semicircular Canals of the Ear?

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Semicircular Canals

The semicircular canals are organs that are part of the vestibular system in the inner ear. The vestibular system is responsible for your sense of balance and equilibirum. Both the cochlea (part of your hearing sensation) and the vestibular system are housed in the bony labryinth, a structure with bony passages to secure the structures of the inner ear. Within the vestibular system, there are 3 semicircular canals and 2 otolith (ear stone) organs known as the utricle and saccule.

The three semicircular canals are known by their orientation: anterior, posterior (the longest), and lateral semicircular canals.

The semicircular canals consist of three ducts arranged on three perpendicular planes, with each duct looping back at different angles. The ducts are situated at right angles from each other; similar to the way that three sides of a box come together at a corner.

The semicircular canals are filled with fluid called endolymph. When we move our bodies, the fluid inside the semicircular canals moves as well. Each of the canals has an ampulla (enlargement of the canal) which connects to the utricle. The fluid's movement is detected by hair-like projections called cilia, which starts an electrical signal that is sent to the auditory nerve, where it is processed by the brain.

The semicircular canals are responsible for our sensation of rotational movement. Aeronautic terms can be used to best describe these movements:

  • Pitch describes the up and down movement when you nod your head "yes"
  • Roll describes the tilting of your head to the left or the right
  • Yaw describes the moving of your head to the left or the right when you shake your head "no"

A roller coaster ride will give you the complete sensation and movements associated with your vestibular systems semicircular canals and otolith organs.

The semicircular canals are interconnected with the otolith organs, however they function separately. The combination of information from both parts of the vestibular system allow you to walk and move your head while maintaining your gaze on one object. It is this feature that allows us to moving all the time without feeling the effects of vertigo... that is while it is all working as designed. 

Development of the Semicircular Canals

The development of our balance and equilibrium takes time. The average child does not have a fully developed vestibular system until they are about 6 years old. Disruptions to this development may make it harder to sit upright unsupported or other activities requiring balance like standing or walking. This is why you may notice that children with developmental delays may have problems with these activities. Delays in the vestibular system can also cause a dysfunction of a reflex involving the vestibular system and the eyes known as the vestibulo-ocular reflex (VOR) which includes the following problems:

  • lack of clear vision during rapid head movement
  • reading
  • writing
  • fine motor control
  • gross motor control

Testing  for the Semicircular Canals

When testing the function of the semicircular canals, your ENT, audiologist, or other physician will also test the rest of the vestibular system and your hearing. MRI and CT scans may be performed to look for structural causes including cancer. Other tests that can be used to determind vestibular dysfunction includes:

Disorders Related to the Semicircular Canals

Source:

American Speech-Language-Hearing Association. (n.d.). How Our Balance System Works. Accessed on 2/27/2016 from http://www.asha.org/public/hearing/How-Our-Balance-System-Works/

Lee, S.C., Abdel Razek, O.A., Dorfman, B.E., Talavera, F., Roland, P.S. & Meyere, A.D. (2013). Vestibular System Anatomy. Accessed on 2/27/2016 from http://emedicine.medscape.com/article/883956-overview

Mosby. (2012). Mosby's dictionary of Medicine, Nursing & Health professions. Accessed on 2/27/2016 from http://www.credoreference.com (Subscription Required)

National Aeronautics and Space Administration. (2004). Human Vestibular System in Space. Accessed on 2/27/2016 from http://www.nasa.gov/audience/forstudents/9-12/features/F_Human_Vestibular_System_in_Space.html

The Inner Ear. Accessed: October 26, 2009 from http://hyperphysics.phy-astr.gsu.edu/hbasees/Sound/eari.html

Vestibular Disorders Association. (n.d.). How are vestibular disorders diagnosed? Accessed on 2/27/2016 from http://vestibular.org/understanding-vestibular-disorder/diagnosis

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