The Inner Ear SPA 4302 Summer 2006

Two Halves: ____________--transduces motion and pull of gravity ____________-transduces sound energy (Both use Hair Cells) INNER EAR Sensory Endorgans encased within very dense bone

Subdivision into spaces containing ___________ (blue), and spaces containing __________ (red)

Cochlea is Divided into 3 “Scala” Scala Vestibuli –__________ Membrane Scala Media –__________ Membrane Scala Tympani ___________ - the opening between 2 outer Scala

Fluids filling the Inner Ear ___________- in S. Vestibuli and S. Tympani –High Sodium / Low Potassium concentrations –Low Voltage (0 to +5 mV) ___________- in S. Media –High Potassium / Low Sodium concentrations –High Positive Voltage (85 mV)

Cross-Section of the Cochlea Third Turn Second Turn First Turn

A Cross Section Shows the 3 Scala

Within S. Media is the Organ of Corti

I = Inner Hair Cells P = Pillar Cells O = Outer Hair Cells D = Deiter’s Cells

The Stereocilia on IHCs and OHCs ________ (at top) V or W shaped ranks ________ (at bottom) straight line ranks

Stereocilia bent toward tallest row ________ flows into cell Voltage shifts to a less __________ value More neurotransmitter is released

Cochlear Afferent (Sensory) Neurons __________ (95%) –synapse w/ IHC –1 IHC to 20 neurons –well myelinated __________ (5%) –Synapse with OHCs –Many OHCs to 1 neuron –unmyelinated

Cochlear Functions __________- Converting acoustical- mechanical energy into electro-chemical energy. ___________- Breaking sound up into its component frequencies

Development of the Inner Ear ________________Beginning in week 3, ________________ develops, _______________Invaginates to form _______________, _________________Which then closes off, leaving an _________________.

Capsule divides into saccular, utricular divisions –________: cochlea (begins forming in week 6) –________: semicirc. canals, endolymphatic sac & duct Organ of Corti forms from week ___ Inner ear fully formed by ___ weeks

Hearing Loss and Disorders of the Inner Ear Vast majority of SNHL results from inner ear disorder. ____________.Cochlear pts often hear, but cannot distinguish what they hear very clearly: ____________. –Arises from frequency and other distortions associated with changes in inner ear function.

Inner Ear Disorders: Prenatal Causes Genetic mutation/inheritance Cytomegalovirus (CMV) __________ Rubella Rh incompatibility __________

Anatomical Anomalies Often seen as Bony malformations Examples: Mondini (incomplete cochlea) Enlarged Duct (shown here)

Age Effects

Noise Damage Temporary Threshold Shift (TTS) Permanent Threshold Shift (PTS) Duration, Timing and Intensity influence Typical “Noise Notch” often seen between ____________ first. Notch widens and deepens over time, with hearing loss spreading to adjacent frequencies, and increasing in degree.

Ototoxicity Substances poisonous to the ear Medicines –___________ antibiotics –___________ drugs for CA –___________ Industrial Chemicals (tolulene, etc) May affect __________ Degree of hearing loss varies Synergy with noise or other ototoxic agents

Meniere’s Disease Really a Syndrome: –_________ Vertigo –Roaring, Low Freq. Tinnitus –Fluctuating ___________ Hearing Loss –Sensation of Aural Fullness ____________________Thought to be produced by ____________________, a condition in which too much endolymph accumulates in the inner ear.