Hearing

What is sound created by?

Periodic variations in air pressure.

What is the speed of sound in air?

343 m/sec or 767 mi/h.

How is the frequency of sound measured?

In Hertz (Hz), which represents cycles per second.

What is the range of audible frequencies for humans?

20 to 20,000 Hz (or 20 Hz to 20 kHz).

What frequency is categorized as ultrasound?

More than 20 kHz.

What frequency is categorized as infrasound?

Below 20 Hz.

What determines loudness in sound?

Intensity, measured in decibels (dB).

What is the threshold of tolerable sound intensity?

About 120 dB.

What are the three divisions of the ear?

External ear, middle ear, and inner ear.

What is the function of the pinna?

It is a cartilaginous sound-capturing funnel.

What is the anatomical term for the auditory canal?

External acoustic meatus.

What is the diameter of the tympanic membrane?

9 mm.

What are the three ossicles found in the middle ear?

Malleus, incus, and stapes.

What is the role of the tensor tympani and stapedius muscles?

To make the ossicles rigid to dampen very loud sounds.

How much energy would be lost in transition from air to fluid without the middle ear's function?

Only 2%.

How much does the middle ear amplify pressure?

By 22 times.

What are the two membrane-covered holes found at the base of the cochlea?

The oval window and round window.

What are the three fluid-filled chambers of the cochlea?

Scala vestibuli, scala media, and scala tympani.

Which membrane separates the scala vestibuli from the scala media?

Reissner's membrane.

What is contained in the scala media?

Endolymph.

What ion layout is managed by the stria vascularis in scala media?

Secretes potassium while absorbing sodium.

What does the Organ of Corti consist of?

Inner and outer hair cells, rods of Corti, and supporting cells.

What happens when the stereocilia on hair cells bend?

It produces a receptor potential.

What does the calcium entry cause in hair cells?

Release of neurotransmitters such as glutamate.

What structure helps to maintain the tonotopic organization of the cochlea?

The basilar membrane.

What is the role of inner hair cells?

They are sensory receptors for hearing.

Approximately how many inner hair cells are located in the cochlea?

About 3500.

How do outer hair cells contribute to hearing?

By augmenting the movement of inner hair cells.

What forms the cochlear nerve?

The axons of spiral ganglion cells.

Where do cochlear nuclei send their projections?

To the superior olivary nuclei.

What aids in localization of sound along the horizontal axis?

The medial superior olivary nucleus.

What types of cells are in the ventral cochlear nuclei?

Stellate and bushy cells.

What is the function of the dorsal cochlear nucleus?

Sound localization along the vertical axis.

What connects the inferior colliculus to the medial geniculate nucleus?

Inferior brachium.

Where is the primary auditory cortex located?

Near the superior temporal gyrus.

What is the functional difference between conductive and sensorineural hearing loss?

Conductive loss is due to middle ear issues, while sensorineural loss is due to loss of cochlear hair cells.

What is the primary cause of conductive hearing loss?

Insult to the middle ear, such as otitis media.

What is Weber's Test used for?

To determine the type of hearing loss by sound lateralization.

What does Rinne’s Test assess?

To help diagnose conductive hearing loss.

What do hair cells synapse with in the cochlea?

Dendrites of bipolar spiral ganglion cells.

What is a characteristic of the basilar membrane?

It is narrow and stiff at the base and wide and floppy at the apex.

What is the auditory sensory area known as?

The Organ of Corti.

How does the orientation of the cochlea affect frequency perception?

The base codes high frequency sounds, while the apex codes low frequency sounds.

What ions are primarily found in perilymph?

Low potassium and high sodium.

What is the overall fluid composition in the scala media?

High potassium and low sodium.

What happens during depolarization of a hair cell?

Potassium channels open, leading to release of neurotransmitter.

What helps increase the rigidity of ossicles during loud sounds?

Tensor tympani and stapedius muscles.

What happens when sound waves cause tympanic membrane displacement?

It is transmitted to the ossicles.

What occurs with the stapes footplate at the oval window?

Pistoning motion transfers tympanic membrane displacement to the inner ear.

How is sound pressure enhanced in the middle ear?

By reducing the surface area to the oval window and leveraging the ossicles.

What part of the auditory system is responsible for sound localization?

Superior olivary nuclei.

What condition can result from dysfunction in the cochlea?

Sensorineural hearing loss.

What is the process of converting mechanical energy into electrical signals in hair cells called?

Hair cell transduction.

What does the cochlear nuclei consist of?

Two ventral and one dorsal cochlear nuclei.

What happens if the middle ear fails to function effectively?

Energy transfer from external to inner ear drastically decreases.