The Inner EarThe Inner Ear

SPA 4302SPA 4302

Summer 2006Summer 2006

Two Halves:• ____________--transduces motion and pull of gravity• ____________-transduces sound energy

(Both use Hair Cells)

INNER EARSensory

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• ________ 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.

OtotoxicitySubstances 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.