Midterm review

• The external auditory canal has a Cartilaginous portion (1/3 of its length) and Osseous (bone) portion (2/3 of its length)
• The external Auditory canal carries sound waves to the tympanic membrane and protection using ear wax
• The pinna funnels sound
• The tympanic membrane seperates the outer and middle ear
• The tympanic membrane's middle layer contributes the most to vibration
• The cone of light in the tympanic membrane glows when its healthy
• Masseuls pulls at the umbo in the tympanic membrane
• Pars Flaccida: not as much vibrating in the tympanic membrane
• The tympanic cavity is made of 6 walls: lateral, medial, anterior, posterior, roof, floor
• Tympanic cavity Lateral wall is the tympanic membrane
• Tympanic cavity's medial wall is the promontory (nerves protrudes) of the cochlea
• Tympanic cavity's anterior wall is the eustachian tube & sulcus for internal carotid artery
• Tympanic cavity's posterior wall is the mastoid
• Tympanic cavity's roof is the tegmen tympani of the petrous temporal bone
• Tympanic cavity's floor is the sulcus for the internal jugular vein
• impedance matching: When the sound gets transferred from acoustic to mechanical, some sound gets dampened so the ossicular chain helps it.

  The tympanic membrane has a larger surface area with all the pressure but the ossicular chain has a smaller surface area with the same amount of pressure. Not all vibrate to the same extent when it hits the eardrum and requires more pressure and amplifying.
• Tensor tympani: tenses eardrum to reduce vibration
• stapedius: stiffens ossicular chain to reduce vibration
• Cochlea is surrounded by spongy bone called modiolus
• three parts of cochlea: scala vestibuli, scala tympani. scala media
• Scala vestibuli & scala tympani filled with perilymph
• Scala media filled with endolymph
• The chambers of the cochlea need to make electrical impulses and needs to have different electrical charges to be able to do that.
• Oval window flexes in and pushes the “liquid”
• A round window opens/pushes out to release the pressure
• Scala vestibuli and tympani are connected by helicotrema
• Reissner’s membrane – separates scala vestibuli and scala media
• Basilar membrane – separates scala tympani and scala media; holds the organ of corti and tectorial membrane
• Organ of Corti – sensory organ of hearing located on basilar membrane containing hair cells
• Tectorial membrane – thin membrane located on the basilar membrane that overhangs the organ of Corti
• Organ of corti has outer and inner hair cells
• The organ of corti in hearing process: waves moves basilar membrane causing the hair cells to move, causing electrochemical response that is sent to the brain.
• Place theory – perception of sound depends on where component frequencies create vibrations on basilar membrane
• Frequency theory – applies to frequencies below 1000 Hz; make the whole basilar membrane vibrate at different rates, and then cause impulses to be sent at different rates
• The frequency theory: The up and down motion of the basal membrane matches the frequencies of sound; The neural impulses matches the sounds coming in
• The tracts of the auditory nerve comes together at the cochlear nuclei
• From the cochlear nuclei, information is passed (contralaterally and ipsilaterally) to the superior olivary complex
• The auditory nerve tract: superior olivary complex, lateral lemniscus (pons), inferior colliculus (midbrain), Medial geniculate body (thalamus), auditory cortex
• Semi-circular canals are filled with endolymph and help with balance
• semicircular canals has the ampulla (ballooning bits) and crista (in ampulla)