Semicircular Canals of the Ear

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 equilibrium. Both the cochlea (part of your hearing sensation) and the vestibular system are housed in the bony labyrinth, a structure with bony passages to secure the structures of the inner ear. Within the vestibular system, there are 3 semicircular canals and 2 otoliths (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 a 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 allows you to walk and move your head while maintaining your gaze on one object. It is this feature that allows us to move all the time without feeling the effects of vertigo... that is while it is all working as designed. 

Development 

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 

When testing the function of the semicircular canals, your ENT, audiologist, or other physicians 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 determine vestibular dysfunction include:

• Electronystagmography or Videonystagmography (ENG/VNG)
• Rotation testing
• Video Head Impulse Testing (VHIT)
• Vestibular Evoked Myogenic Potential
• Computerized Dynamic Posturography (CDP)

Disorders Related to the Semicircular Canals

• Benign Paroxysmal Positional Vertigo (BPPV)
• Labyrinthitis and Vestibular Neuritis
• Meniere's Disease
• Motion Sickness
• Superior Semicircular Canal Dehiscence Syndrome