Semicircular Canals Flashcards

Study the semicircular canals, their orientation, membranous ducts, ampullae, sensory receptors, vestibular innervation, and role in balance.

Card 1 of 30Question

What are the semicircular canals?

Three curved bony passages of the inner ear that contain the semicircular ducts involved in detecting rotational head movements.

In This Section

1. What are the semicircular canals?

Three curved bony passages of the inner ear that contain the semicircular ducts involved in detecting rotational head movements.

2. Where are the semicircular canals located?

Within the petrous part of the temporal bone, posterior and superior to the vestibule of the inner ear.

3. What are the three semicircular canals?

The anterior (superior), posterior, and lateral (horizontal) semicircular canals.

4. To which division of the inner ear do the bony semicircular canals belong?

The bony labyrinth.

5. What structures are contained within the bony semicircular canals?

The membranous semicircular ducts.

6. Which fluid fills the semicircular ducts?

Endolymph, a potassium-rich fluid contained within the membranous labyrinth.

7. Which fluid occupies the space between the bony semicircular canals and membranous ducts?

Perilymph.

8. What is the primary sensory function of the semicircular ducts?

To detect angular acceleration of the head during rotational movements.

9. How are the three semicircular canals oriented relative to one another?

They lie in approximately mutually perpendicular planes, allowing detection of head rotation in three dimensions.

10. Which semicircular canal is most closely aligned with the horizontal plane when the head is tilted forward approximately 30 degrees?

The lateral semicircular canal.

11. Which semicircular canals are oriented approximately vertically?

The anterior and posterior semicircular canals.

12. What is the ampulla of a semicircular canal?

An enlarged end of a semicircular canal that contains the ampulla of the corresponding membranous duct and its sensory receptor.

13. How many ampullae are present in each inner ear?

Three, one associated with each semicircular canal.

14. What is the crista ampullaris?

A ridge of sensory epithelium within the membranous ampulla containing vestibular hair cells and supporting cells.

15. What is the cupula?

A gelatinous structure extending from the crista ampullaris across the ampullary lumen, into which hair cell stereocilia project.

16. What are the sensory receptor cells of the semicircular ducts?

Vestibular hair cells located in the cristae ampullares.

17. What structures project from the apical surface of vestibular hair cells?

A bundle of stereocilia and a single kinocilium.

18. How does angular head acceleration stimulate semicircular duct hair cells?

Endolymph inertia produces relative fluid movement that deflects the cupula and bends the hair bundles.

19. What happens when vestibular hair cell stereocilia bend toward the kinocilium?

The hair cell depolarizes, increasing neurotransmitter release and typically increasing vestibular afferent firing.

20. What happens when vestibular hair cell stereocilia bend away from the kinocilium?

The hair cell hyperpolarizes, decreasing neurotransmitter release and vestibular afferent firing.

21. What is the common crus of the semicircular canals?

A shared nonampullary bony channel formed by the union of the anterior and posterior semicircular canals.

22. How many openings do the three bony semicircular canals collectively have into the vestibule?

Five, because the anterior and posterior canals share a common crus.

23. Which membranous vestibular structure receives the openings of the semicircular ducts?

The utricle.

24. Which cranial nerve transmits sensory signals from the semicircular ducts?

The vestibular division of the vestibulocochlear nerve (cranial nerve VIII).

25. Where are the cell bodies of primary sensory neurons from the semicircular ducts located?

In the vestibular ganglion, also called Scarpa's ganglion, within the internal acoustic meatus.

26. Which vestibular nerve division carries sensory fibers from the anterior and lateral semicircular ducts?

The superior vestibular nerve.

27. Which vestibular nerve division carries sensory fibers from the posterior semicircular duct?

The inferior vestibular nerve.

28. Which artery primarily supplies the semicircular ducts?

Branches of the labyrinthine artery, particularly the anterior vestibular and posterior vestibular arterial branches.

29. What is the role of the semicircular ducts in the vestibulo-ocular reflex?

They detect head rotation and initiate compensatory eye movements that help stabilize visual images on the retina.

30. Which semicircular canal is most commonly affected in benign paroxysmal positional vertigo?

The posterior semicircular canal, where displaced otoconia can cause abnormal endolymph movement and positional vertigo.