The inner ear of the human consists of the cochlea and the vestibular organ.
The basis of the cochlea borders at the middle ear with the auditory ossicles. The stapes is attached to the membrane of the oval window (fenestra ovalis) behind which lies the Scala vestibuli that connects at the apex of the cochlea (helicotrema) to the Scala tympani which borders the round window, which may swing to buffer pressures onto the oval window.
The Scala media is divided by Reissner's membrane (vestibular membrane) from the Scala vestibuly and by the basilar membrane from the Scala tympani. The Scala vestibuli and Scala tympani are filled with perilymph that is exchanged through the helicotrema. The Scala media contains endolymph. Both fluids are of very different composition.
Pictured here is the macula of the sacculus of the vestibular organ. The saccule is a bed of sensory cells situated in the inner ear. The saccule translates head movements into neural impulses which the brain can interpret. The saccule is sensitive to linear translations of the head, specifically movements up and down. When the head moves vertically, the sensory cells of the saccule are disturbed and the neurons connected to them begin transmitting impulses to the brain. These impulses travel along the vestibular portion of the eighth cranial nerve to the vestibular nuclei in the brainstem.
