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semicircular duct
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Diagram showing the physiology of balance with two main parts: at left, a cross-section of the crista in the horizontal canal with labeled hair bundles, hair cells, and cupula above a stationary person; at right, the same structures during head rotation above a spinning person, illustrating how the cupula shifts to detect movement.
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semicircular duct

anatomy
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Quick Summary

Diagram showing the physiology of balance with two main parts: at left, a cross-section of the crista in the horizontal canal with labeled hair bundles, hair cells, and cupula above a stationary person; at right, the same structures during head rotation above a spinning person, illustrating how the cupula shifts to detect movement.
sensory organs of balance; human ear The cristae of the semicircular ducts, which form one of the two sensory organs of balance (the second being the maculae of the utricle and saccule), respond to rotational movements and are involved in dynamic equilibrium.

The semicircular ducts are loop-shaped organs within the inner ear that are crucial for maintaining balance and stability. They are part of the vestibular system, which also includes the vestibule (containing the utricle and saccule) and the cochlea.

Anatomy and Function

There are three semicircular canals: the lateral, anterior (superior), and posterior. They are positioned at roughly right angles to each other, allowing them to detect rotational and angular movements of the head in three-dimensional space. Each canal contains a fluid called endolymph and a sensory structure called the crista. The crista is lined with hair cells that have hairlike projections called stereocilia, including a longer one called the kinocilium.

When the head moves, the endolymph shifts, causing a jelly-like mass called the cupula to bend. This bending displaces the stereocilia, altering the electrical potential of the hair cells. These changes trigger nerve impulses that are sent via the vestibular nerve to the brainstem, signaling changes in the head's position and enabling coordinated body movement and visual stability.1234

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5 Britannica Sources
  1. vestibular system
  2. human ear - Detection of linear acceleration: static equilibrium
  3. semicircular canal
  4. human ear - Semicircular canals
  5. inner ear

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