The ear structure is in charge of the sense of balance and position of the head in space. The middle and outer ear structures are involved in hearing sensation. These structures are called semicircular ducts or semicircular canals.
The fluid that fills the three semicircular canals—the lateral (horizontal), anterior, and posterior—remains in place while the head moves. As a result, each one delivers specific information about balance and body position, assisting in maintaining steady vision even in motion and synchronising total activity.
Table of Contents
- Semicircular Canals Location
- Structure
- Functions of Semicircular Canals
- Frequently Asked Questions (FAQs)
Semicircular Canals Location
The interconnected semicircular canals are situated in distinct semicircular ducts in the labyrinth bone of the inner ear. They are found in the petrous region of the temporal bone, a pair of bones near the skull base and its sides.
They essentially hang over the cochlea and the vestibule, the organ attached to it resembling a snail shell. A group of nerves, the vestibular ganglion, is connected to the canals by nerves that eventually travel to nuclei (receptor areas) in the upper spinal column.
Structure
Each semicircular canal begins and ends in the vestibule. Although slightly varied in length, each one creates a loop with a 1-millimetre diameter.
Lateral or Horizontal Semicircular Canal: Because of its angle of around 30° to the horizontal plane, the lateral semicircular canal is called the “horizontal” canal. This is the shortest of all three canals.
Anterior or Superior Semicircular Canal: The anterior semicircular canal is positioned vertically to separate the left and right sides of the body. It is perpendicular to the petrous portion of the temporal bone.
Posterior or Inferior Semicircular Canal: This canal is positioned at the frontal plane, vertically dividing the body’s front and back sides.
Functions of Semicircular Canals
The semicircular ducts, or canals, play a crucial role in detecting the head’s rotational position. Inertia causes the endolymph to move slower than the head, encouraging the cells of hair to produce signals essential for stabilising and regulating body posture.
As a result of the complementary aspect of the canal activity, head movements boost signalling on one side while inhibiting communication from the opposite side.
As a result, the eyes can perform a better oculomotor activity, i.e. smooth eye movement, maintaining stable vision even when the head is turned or twisted. This is the reason we feel the head moving or bending.
The semicircular canals and the otolithic organs (saccule and utricle of the vestibule) are essential for proprioception (also known as kinaesthesia, the awareness of one’s own body in space and when moving) and balance.
Hence, the vestibular nuclei of the brain stem receive this information and transmit it to other brain regions involved in coordination and movement.
Because of this crucial role, diseases of semicircular canals can have serious consequences. These include a prolonged feeling of dizziness, motion sickness, various forms of vertigo, and nystagmus (fast, abnormal eye movements).
The caloric reflex test can assess the functionality of semicircular canals and the vestibular system overall.
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