Posterior ampullary crest

Posterior ampullary crest is a raised ridge-like layer of cells situated within the membranous wall of the ampulla of posterior semicircular duct. A gelatinous substance, called the cupula, sits on top of the apex of posterior ampullary crest. Numerous sensory hair cells can be found, interspersed between the crest cells. These hair cells possess cilia which protrude into the cupula, while at their bases they connect with axonal processes of the vestibular ganglionic cells.

The whole apparatus causes obstruction to the flow of endolymph through the ampulla of posterior semicircular duct and is thereby designed to detect angular acceleration during rotational movements of the head in a coronal plane. For instance, when one tilts the head to bring the ear close to the shoulder). This causes the endolymph to deflect the cupula and the cilia contained within it, which stimulates the sensory hair cells leading to changes in the neuronal firing rate of axonal processes of vestibular ganglionic cells.

Please note that–in addition to posterior ampullary crest–the membranous labyrinth also contains anterior and lateral ampullary crests. These are situated within the membranous ampullas of the anterior and lateral semicircular ducts, respectively. They resemble in structure to the posterior ampullary crest and help detect angular acceleration when head rotates in sagittal and horizontal planes.