BME 603 - Ch. 11

medicineman's version from 2016-03-02 06:02


Question Answer
Basic auditory pathwaySound waves move the tympanic membrane > tympanic membrane moves the ossicles > ossicles move the membrane at the oval window > movement of the oval window moves fluid in the cochlea > movement of fluid in the cochlea causes a response in sensory neurons
The three ossicles Malleus, incus, and stapes. Two muscles connect them. Footplate of the stapes moves like a piston at the oval window. Ossicles are needed to amplify air pressure to move the fluid in the cochlea
Eustachian tubeAir in the middle ear is continuous with air in the nasal cavity via the Eustachian tube. A valve usually keeps this closed
Attenuation reflexOnset of a loud sound triggers a neural response to contract the tensor tympani muscle and the stapedius muscle which causes the ossicles to become more rigid
Three chambers of the cochlea (oval window) scala vestibuli (Reissner's membrane) scala media (basilar membrane) scala tympani (round window). Organ of Corti lies on the basilar membrane and is covered by the tectorial membrane
Perilymph Fluid in the scala vestibuli and scala tympani. Has an ionic content similar to CSF (low K+ and high Na+)
Endolymph Fluid in the scala media. Ionic concentrations similar to ICF (high K+ and low Na+). Potential about 80 mV higher than the perilymph
Helicotrema Hole in the membrane of the cochlea that makes the scala vestibuli continuous with the scala tympani
TonotopySystematic organization of sound frequency within an auditory structure. High frequency sound waves stay near the base of the Basilar membrane and low frequency sound waves travel farther towards the apex. The Basilar membrane is think and stiff at the base and wide and floppy at the apex. Used more for high frequency sounds
Hair cellsNot neurons but specialized epithelial cells. Audio receptors
Stereocilia Extend from the top of hair cells. Bending of stereocilia is important in the transduction of sound into a neural signal
Structure of the organ of Corti Basilar membrane is at the base. Tectorial membrane forms a roof over the structure. Reticular lamina is in the middle, holding on to the hair cells. Rod of Corti span the basilar membrane and the reticular lamina to provide structural support. Stereocilia extend into the endolymph and their tips end either in the tectorial membrane or just below it
Bending of stereociliaTips of stereocilia have ion channels that open and close via bending. When the ion channels open, K+ flows inward and depolarizes the cell and in turn opens calcium channels to release glutamate. K+ depolarizes the cell because of the high K+ concentration in endolymph
Characteristic frequency The neuron is more responsive to sound at one frequency and less responsive to other frequencies
Stimulus intensityCoded by frequency of action potentials and the number of active neurons
Phase lockingThe consistent firing of a cell at the same phase of a sound wave. Used for low frequency sounds
Sound localization Interaural time delay for low frequency sounds (wavelength > distance between ears/200-2k Hz). Interaural intensity difference for high frequency sounds (wavelength < distance between ears/2k-20k Hz)
Duplex theory of sounds localization Interaural time delay and interaural intensity difference
Vestibular labyrinth Includes the cochlea, otolith organs, and the semicircular canals
Otolith organsDetect the force of gravity and the tilt of the head. Paired organs, utricle and saccule. Each contains a sensory epithelium called a macula. The macula contains hair cells which lie on support cells with their cilia projecting into a gelatinous cap. Otoconia encrust the gelatinous cap
Semicircular canalsSensitive to rotation. Cilia project into the gelatinous cupula which spans the ampulla (a bulge in the canal). Filled with endolymph