Static equilibrium Vestibule contains two fluid filled sacs (utricle and saccule) U & S are sensory organs responsible for detecting and transmitting information regarding balance, position in space, acceleration, and deceleration. Suspended in the fluid are calcium carbonate particles called OTOLITHS. As the head moves from one position to the other, these ear stones will move too. The otoliths brush against sensory nerve hairs that line the utricle and saccule, which depolarize and send a message to the brain.

Dynamic equilibrium: semi-circular canals also contain fluid and are responsible for detecting changes in motion. There are three semicircular canals (all at different angles), each responsible for detecting motion on a different plane. Within the canals are nerve hairs which sense changes in the movement of the perilymph fluid and depolarize, thus sending a message to the brain.

Filled with perilymph; continuous with cerebral spinal fluid A. BONY LABYRINTH Filled with perilymph; continuous with cerebral spinal fluid Has 3 parts 1. The Vestibule--entryway Central portion Continuous with semicircular canals and cochlea Oval window located on tympanic wall 2. Semicircular canals 3; lie in perpendicular planes to each other Each has dilation where canal meets vestibule called ampulla Located in each ampulla are hair-like cells, called crista ampullaris. These detect angular movements Structures called maculae (hair-like cells) are located in the utricle (opens to semicircular canals) and saccula (opens to cochlea) that provide information about linear acceleration and gravity via otoliths. When the head moves, that movement moves the fluid in the semicircular canal bending the hair cells. When the hair cells bend, they send a signal to the brain through the vestibulocochlear nerve (C VIII). linear acceleration and gravity

Hearing Summary The events that take place to hear a sound are: Sound waves are collected by the pinna, travel down the auditory canal and cause the tympanic membrane to vibrate. The tympanic membrane causes the malleus to vibrate, which transfers this energy to the incus and then to the stapes, amplifying the sound each time as the bones get smaller each time. The stapes rests on the oval window. The oval window vibrates and sets the perilymph of the inner ear in motion. The pressure waves travel through the canals of the cochlea and cause the basilar membrane to move. The hair cells resting on the basilar membrane vibrate against the overlying tectorial membrane, causing them to fire (the organ of Corti). This message is relayed to the auditory nerve that carries it to the brain for processing. The energy of the pressure wave in the cochlea is released when the wave hits the round window, which stretches out and absorbs the energy.