Sound Transmission to Inner Ear

. Sound Transmission to Inner Ear. 1- Ossicular route:.

. labs.

. Scala Vestibuli Cochle Scala Medi Scala Tympani —.

. Modiolus.

. the cochlea has a bony core called the MODIOLUS the modiolus defines the medial direction in the cochlea (the outside wall is lateral) the bony SPIRAL LAMINA is represented by the threads of the screw the cochlea has a base (= screw head) and an apex (=point).

Vestibular membrane. Basilar membrane. Scala vestibuli.

. 11-8.

Inner Ear (Labyrinth). iearbas. Vestibular. Auditory.

. AABKFCNa.

. AABKFCNb[1].

. Image206.

. ckearcoch3.

. tins_a.

. Cochlear fluids: endolymphatic potential Na+ cr Driving Force For Potassium Na+ cr perilymph In mM: 145 Na+ 130 cr I Ca2+ Endolymph In mM: 160 K+ 130 cr 0.02 Ca2+ + 80 mV cre -70.v.

. Resting membrane potential and receptor potential of hair cells.

. ear3a[1]. AFFERENT AND EFFERENT NERVES.

. Arrangement and Function of Basilar Membrane. cochshake.

. Stapes Oval window Round window Cochlear duct (endolymph) Malleus Tympanic mernbtane Tynwanic Vestibular mernbrane Scala vestibuli Scala tympani (perilymph) membrane Receptors (hair alls) high pitch 20,000 cps 1 cps low pitch soo'cps 20 cps.

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. Responses of basilar membrance to sound.

Mechanism of Hearing Sound waves are collected by the auricle, which directs them towards the external auditory meatus. Sound waves cause vibration of the tympanic membrane by the same frequency. Movements of the tympanic membrane are transmitted and amplified by the bony ossicles of the middle ear to the oval window The movements of the foot plate of the stapes (produced by the sound vibrations transmitted through the bony ossicles) are transmitted to the membranous covering of the oval window leading to displacement of the perilymph in the scala vestibluli and scala typani . A displacement of the staps inwards causes a downward movement of the basilar membrane and vice versa. In both conditions, the movement of the basilar membrane produce a shearing force between the 2 rigid structures, the tectorial membrane and the reticular lamina, leading to bending of the hair processes (= the stereocilia) of the hair cells. When the stereocilia of a hair cell move toward the tallest cillium , the hair cell is depolarized; when the stereocilia bend in the opposite direction, the hair cell is hyperpolarized.

8) These changes in the membrane potential of the hair cells resulting from changes in cation conductance in membranes at the apical ends of hair cells. The potential gradients that affect ion movement into the hair cells include both the positive potential of the endolymph. The total gradient across the membrane of the hair cell is about 140 mv. 9) A change in membrane conductance in the apical membranes of the hair cells results in a large current flow, which produces the receptor potential in these cells. This current flow can be recorded extracellularly as the cochlear microphonic potential (= an oscillatory event that has the same frequency as the acoustic stimulus). The cochlear microphonic potential actually represents the sum of the receptor potentials of a number of hair cells. 10) Hair cells release an excitatory neurotransmitter (probably glutamate or aspartate) which depolarizes the auditory nerve making action potential which travel along the nerve. 11) As sound waves consists of 2 phases, compression and rarefaction, movement of tympanic and membrane covering the oval window is also biphasic as inward and outward. 12) As fl uids are incompressible, inward movement of the membrane covering oval window is accompanied by outward movement of the membrane covering the round window..

. Mechanism of stimulation of Auditory Nerve. movie.

. coch_mech[1].

. ear3a[1]. AFFERENT AND EFFERENT NERVES.

. Hair cells. Inner Hair Cell. ihc. Outer Hair Cell.

. Function of inner and outer hair cells. Inner hair cells Outer hair cells arrangement single row on cells inner to rods of corti 3-5 rows outer to rods of corti connection Connected mainly to afferent neurons Connected mainly to efferent neurons function Main receptor of hearing which transduce mechanical sound energy into electrical action potential signals Regulate sensitivity of the coclea toward certain sound, as it amplifies the movement of basilar membrane at specific regions according to the stimulating sound, a function called fine tunnig or filtration of signals or noise cancellation.

. coutcuuus suetno• COLLICULI LA TERA L turf7010 oo•sAt Cc:XHLCAR NUCLEOS contSPONOENCE BETWEEN COCHIfA Acoustic ANA O' stctv0N A TURN C" COCHIEA OROAN OF VENT. At ceil SCALA ORGAN OF CANCLION cogu INN* f ctlt5.

. 11-18.

. Image203.

. 9_21.

. Auditory cortex is concerned with:. 1- Perception of sound and giving the psychic sensation of:.

. Association auditory cortex. Concerned with interpretation the heard sound..

Unilateral lesion of the auditory cortex:. Slight reduction of hearing in the opposite ear.

Auditory Encoding. The ability of the auditory system to determine:.

. Determination of Sound Frequency. bma6k3. bma2k3[1].

anipart[1]. part6[1]. anipartb. ani2parb. 2part1.

. Tonotopic Organisation:. 11-21.

11-29.

. Humans can discern a difference in frequency of just 0.1 percent..

. Determination of Sound Intensity:. 11-20.

. Localization of Sound:.

. 11-28.

. Determination of sound pattern:. Cortical function.

. Hearing Impairments. Tinnitus:. Irritative stimulation of.

. Hearing test: Weber Test. s14d. Conductive Deafness.

Hearing Test: Rinne Test. s14b. s14c.

Audiometry. ear.