Anatomy & Physiology

Anatomy & Physiology Study Guide • The external ear includes the auricle, or pinna, which surrounds the entrance to the external acoustic meatus, which ends at the tympanic membrane (eardrum). • The middle ear communicates with the nasopharynx via the auditory (pharyngotympanic) tube. The middle ear encloses and protects the auditory ossicles. • The membranous labyrinth (the chambers and tubes) of the inner ear contains the fluid endolymph. The bony labyrinth surrounds and protects the membranous labyrinth and can be subdivided into the vestibule, the semicircular canals, and the cochlea. • The vestibule of the inner ear encloses the saccule and utricle. The semicircular canals contain the semicircular ducts. The cochlea contains the cochlear duct, an elongated portion of the membranous labyrinth. • The round window separates the perilymph from the air spaces of the middle ear. The oval window is connected to the base of the stapes. • The basic receptors of the inner ear are hair cells, which provide information about the direction and strength of mechanical stimuli. • The anterior, posterior, and lateral semicircular ducts are continuous with the utricle. Each duct contains an ampulla with a gelatinous cupula and associated sensory receptors. • The saccule and utricle are connected by a passageway that is continuous with the endolymphatic duct, which terminates in the endolymphatic sac. In the saccule and utricle, hair cells cluster within maculae, where their cilia contact the otolith (densely packed mineral crystals, called statoconia, in a matrix). • The vestibular receptors activate sensory neurons of the vestibular ganglia. The axons form the vestibular branch of the vestibulocochlear nerve (N VIII), synapsing within the vestibular nuclei. • The cochlear duct lies between the vestibular duct and the tympanic duct. The hair cells of the cochlear duct lie within the organ of Corti.

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