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Welcome The Ear The ear functions to provide hearing and equilibrium. It has three regions THE THREE OSSICLES (BONES) ARE LATIN FOR HAMMER THE OUTER EAR ANVIL AND THE INNER STIRRUP DUE COMPOSED OF EAR TO THEIR PINNA COMPOSED OF SHAPES. THE AUDITORY CANAL THEY ARE THE MIDDLE SACCULE CLASSIFIED AS SMALLEST EAR UTRICLE THE VESTIBULE BONES AND COMPOSED OF ARE FULLY TYMPANIC MEMBRANE SEMICIRCULAR CANALS DEVELOPED OSSICLES - MALLEUS INCUS STAPES AT BIRTH COCHLEA EUSTACHIAN TUBE Did you know? • Cats are able to move their pinna (which collect and concentrate sound) toward the source making them able to hear even when facing a different direction. • Humans do not have this ability, yet the three muscles that turn the pinna in the cat are still found surrounding the human pinna. • Evolutionary biologists call it a vestigial structure. So do like Mickey Mouse says, because you really can wiggle your ears This little muscle attached The tympanic to the stapes can pull it membrane away from the oval window vibrates with sound. The ossicles transfer the vibrations to the oval window of the cochlea The stapes hits the oval window with a force 3x greater The Eustachian tube equalizes air than the pressure in the middle ear cavity. eardrum Hey, my ears just popped! vibration The Middle Ear Did you know? Consistent loud blaring sounds cause the stapedius muscle to retract in a reflex that prevents damage to the inner ear. Just don’t expect it to work on a sudden sound as it takes time for this reflex to occur! The Inner Ear The utricle and saccule are involved in static equilibrium. They are shown here in between the cochlea and semicircular canals. They contain otoliths suspended in a endolymph liquid and use these to determine the head orientation Notice the fluid perilymph shown in the picture is red The fluid endolymph is shown in purple Endolymph is found in the cochlear duct Perilymph is found in the vestibular and tympanic canals shown FLUID FACTS • Endolymph or cochlear fluid is involved in equilibrium information and is high in potassium. (Found in the membranous labyrinth) • Perilymph transfers sound information and is similar to cerebrospinal fluid in consistency with high sodium. (Found in the bony labyrinth) Otoliths and static equilibrium The otoliths shown at the left are small calcium carbonate granules that can move fluid based on how they are affected by gravity. When the head changes position with respect to gravity, the gelatinous fluid moves stimulating the hair cells. This registers in your brain and tells you if you are upside down, right side up, or sideways. The Semicircular Canals These fluid filled canals establish dynamic equilibrium These three canals extend in all three dimensions to register movement when fluids shift due to motion like: ROTATION ACCELERATION THE AMPULLA The ampulla at the bottom of each of the semicircular canals contain cilia attached to hair cells. When the endolymph moves, the cilia bend the hair cells transmitting nerve impulses. MOTION SICKNESS? Overstimulation of the hair cells from rapid and continuous fluid movement AMPULLA Like whoa, my ampulla hair cell cilia are being stimulated! The Cochlea Vibration of the stapes at the oval window causes the perilymph in the tympanic canal to move. The cochlea is coiled and the canals, being more narrow and rigid at the top, register the higher frequency sound. Once the perilymph moves past the top of the coil, it enters the vestibular canal and moves to the round window which releases the pressure wave. ORGAN OF CORTI When the perilymph in the tympanic canal moves, the basiliar membrane moves. The hair cells connect this membrane to the stationary tectorial membrane and send a signal through the cochlear nerve Vestibular canal Tympanic canal FUN FACT • When you hear a mosquito in your room the energy is only one quadrillionth of a watt With hearing like that its a wonder I ever get any sleep at all! The end