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Histology Spotlight - Balance

Welcome to the wonderful world of histology. Histology is how we study the body on a cellular level. Last week we got an insight into the histology of hearing so this week we are going to investigate the equilibrium of the vestibular system, also commonly known as balance, as the two are very closely related.

Balance originates in the ear and is controlled by the eighth cranial nerve – the vestibulocochlear nerve. Detecting position and motion depends on receptive hair cells. Those in the utricle and saccule detect the position of the head. Those in the semi-circular canals detect movement. The utricle and saccule are in the vestibule and these fluid-filled spaces are lined by simple cuboidal epithelium. This is present everywhere except for a small patch of sensory epithelium called the macula.

The vestibular system, balance, is all dependent on hair cells, similar to that of the auditory system. Each semi-circular duct contains a swelling called the ampulla which is the sensory organ the crista ampullaris. It has a core of connective tissue bulging into the lumen with a covering of epithelium containing hair cells with stereocilia. The stereocilia are embedded in a dome of gel called the cupola. When the head turns, the movement of the fluid bows the cupola, and this bends the stereocilia. This changes the amount of transmitters released by these cells. They have a resting output so bending one-way increases output and bending the other way decreases output.

The hair cells of the vestibular system have rows of stereocilia at the apical ends that vary in height. They also have cilia called kinocilium.

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