Augiology

• How long is the external auditory meatus (EAM) in adults?

  2.5cm
• The medial 1.5cm of the EAM is supported by the temporal bone.
• The outer ear protects the tympanic membrane from direct injury.
• Steps in the self-cleansing action of the outer ear

  1️⃣ Jaw action

  2️⃣ Hair movement

  3️⃣ Production of wax
• The outer ear resonates to increase sound pressure at the tympanic membrane.
• At what frequency range does the outer ear provide the peak pressure gain?

  2-5kHz
• The outer ear aids in sound localization by reducing high-frequency sounds when the source is behind the ear.
• The fibrous layer of the tympanic membrane extends throughout the pars tensa.
• Match the auditory ossicles with their descriptions:

  Malleus ↔️ Hammer-shaped

  Incus ↔️ Anvil-shaped

  Stapes ↔️ Stirrup-shaped
• Steps in the sound energy transfer process of the middle ear

  1️⃣ Acoustic energy in air vibrates tympanic membrane

  2️⃣ Ossicles transmit vibrations

  3️⃣ Sound pressure increases at oval window
• What is the surface area ratio between the tympanic membrane and the stapes footplate?

  17:1
• Force collected over a large area is focused on a smaller area to increase pressure.
• What is the pressure increase factor due to the lever action of the middle ear bones?

  1.3
• The middle ear improves hearing sensitivity by up to 27dB.
• Sound originates from a vibrating source and is propagated through a medium.
• How long is the cartilaginous portion of the Eustachian tube?

  24mm
• Match the Eustachian tube function with its purpose:

  Aeration of middle ear ↔️ Equalizes pressure

  Drainage of fluids ↔️ Prevents hearing loss
• Developmental changes in the Eustachian tube from birth to adulthood

  1️⃣ Almost horizontal at birth

  2️⃣ Grows in length

  3️⃣ Pharyngeal orifice moves downward
• The inner ear is located within the temporal bone.
• Which ion is high in endolymph?

  Potassium
• The cochlea has 2¾ turns in humans.
• What is the central conical core of the cochlea called?

  Modiolus
• Sound waves travel as alternate regions of high and low pressure.
• Match the cochlear sections with their boundaries:

  Scala vestibuli ↔️ Basilar membrane

  Scala media ↔️ Vestibular membrane

  Scala tympani ↔️ Helicotrema
• What is the auditory receptor organ located on the basilar membrane?

  Organ of Corti
• The stapes pushes against the oval window of the cochlea.
• The cochlea converts acoustic signals into the neural code.
• Sound energy travels along the basilar membrane in the form of a travelling wave.
• The basilar membrane is narrow and stiff at the base, responding to high-frequency sounds.
• What is the sensitive element in the inner ear called?

  Organ of Corti
• The frequency of sound waves determines the sound's pitch.
• Steps in the cochlear process when sound waves move the basilar membrane

  1️⃣ Sound waves move the basilar membrane up and down

  2️⃣ IHC stereocilia are deflected

  3️⃣ Ion channels open, allowing potassium ions to flow

  4️⃣ The cell depolarizes

  5️⃣ A signal is sent to the auditory cortex
• What role do outer hair cells play in the cochlea?

  Amplify basilar membrane motion
• Outer hair cells at the base of the cochlea respond to lower frequencies.

  False
• The human ear can detect frequencies from 20 to 20,000 Hz.
• The efferent input to the cochlea fine-tunes the action of outer hair cells.
• What are otoacoustic emissions produced by?

  Outer hair cell action
• The efferent system helps suppress background noise.
• The cochlear division of the eighth cranial nerve carries both afferent and efferent signals.
• How is sound information transmitted to the brain from the cochlea?

  Trains of action potentials