Hearing and Movement

What is sound?

A perceptual experience created by the brain when it processes pressure waves.

What physically happens when a tree falls in a forest?

It produces pressure waves that travel through the air.

Does sound exist without an auditory system to perceive it?

Physical pressure waves exist, but the experience of sound requires an auditory system.

What is hearing?

The process of detecting sound waves and converting them into neural signals interpreted by the brain.

What type of energy does the auditory system detect?

Mechanical energy from pressure waves.

What are the two primary measurements of sound?

Amplitude (intensity) and frequency.

What is amplitude?

The magnitude or intensity of a sound wave.

How is sound amplitude measured?

In decibels (dB).

How do humans perceive amplitude?

As loudness.

What is frequency?

The number of cycles or vibrations in a sound wave per second.

How is frequency measured?

In hertz (Hz).

How do humans perceive frequency?

As pitch.

What does a high-amplitude sound typically sound like?

Loud.

What does a low-amplitude sound typically sound like?

Quiet.

What does a high-frequency sound sound like?

High-pitched.

What does a low-frequency sound sound like?

Low-pitched.

Approximately how loud is a whisper?

30 decibels (dB).

Approximately how loud is normal conversation?

60 decibels (dB).

Around what sound intensity can hearing damage begin?

Approximately 85 decibels (dB), especially with prolonged exposure.

What is the difference between amplitude and frequency?

Amplitude determines perceived loudness; frequency determines perceived pitch.

A sound becomes louder without changing its pitch. What changes?

Amplitude increases while frequency remains the same.

A sound becomes higher-pitched without becoming louder. What changes?

Frequency increases while amplitude remains the same.

What happens when sound waves enter the outer ear?

The outer ear collects and directs them into the ear canal.

What is the pinna?

The visible external part of the ear that collects sound waves.

What is the function of the pinna?

It captures sound waves and helps filter them based on their direction.

What is the ear canal?

The passage that carries sound waves from the pinna to the eardrum.

How does the outer ear help determine sound location?

Its folds filter frequencies differently depending on sound direction.

How can the brain determine whether a sound comes from above or below?

It analyzes frequency patterns created by the folds of the outer ear.

What is sensory transduction in hearing?

The conversion of mechanical sound vibrations into electrical neural activity.

What is the overall function of the external ear?

To collect, focus, and filter incoming sound waves.

What is the middle ear?

The air-filled chamber containing three small bones that transmit vibrations to the inner ear.

What are the three ossicles?

Malleus, incus, and stapes.

What is the malleus?

The first middle-ear ossicle, attached to the tympanic membrane.

What is the incus?

The middle ossicle that connects the malleus to the stapes.

What is the stapes?

The final ossicle, which transfers vibrations to the oval window.

What is the tympanic membrane?

The eardrum, which vibrates in response to incoming sound waves.

What is the oval window?

A membrane-covered opening where the stapes transfers vibrations into the inner ear.

What is the function of the ossicles?

They transmit and concentrate sound vibrations from the eardrum to the oval window.

What is the correct order of the ossicles?

Malleus → incus → stapes.

What are the two muscles in the middle ear?

Tensor tympani and stapedius.

What is the function of the tensor tympani?

It contracts to stiffen the middle-ear structures and reduce sound transmission.

What is the function of the stapedius?

It contracts to dampen vibrations transmitted through the ossicles.

What happens when the stapedius contracts?

It reduces the movement of the stapes and decreases sound energy reaching the inner ear.

What is the purpose of the middle-ear muscles?

They help protect the inner ear by reducing the transmission of intense sounds.

What is the correct answer when asked which ear mechanism engages when bracing for a loud sound?

The stapedius contracts to dampen vibrations reaching the inner ear.

What is the cochlea?

A spiral-shaped structure in the inner ear that converts mechanical vibrations into neural signals.

What is the primary function of the cochlea?

Transducing sound vibrations into electrical signals that activate the auditory nerve.

How many parallel fluid-filled canals are found within the cochlea?

Three.

What are the three cochlear canals?

Scala vestibuli, scala media, and scala tympani.

What is the scala vestibuli?

The upper fluid-filled canal of the cochlea.

What is the scala media?

The middle cochlear canal containing the organ of Corti.

What is the scala tympani?

The lower fluid-filled canal of the cochlea.

What is the round window?

A flexible membrane that allows pressure changes in cochlear fluid to be accommodated.

Why is the round window important?

It provides an outlet for pressure displacement so cochlear fluid can move.

What happens when vibrations enter the cochlea?

They create pressure waves that move cochlear fluid and vibrate the basilar membrane.

What is the organ of Corti?

The sensory structure within the cochlea responsible for converting sound vibrations into neural activity.

Where is the organ of Corti located?

On the basilar membrane within the scala media.

What are the three main components of the organ of Corti?

Sensory hair cells, supporting cells, and auditory nerve fiber endings.

What forms the floor of the organ of Corti?

The basilar membrane.

What is the function of supporting cells in the organ of Corti?

They provide structural support for the sensory hair cells.

What is the basilar membrane?

A flexible membrane inside the cochlea that vibrates in response to sound.

What is the primary function of the basilar membrane?

It separates sound frequencies by vibrating most strongly at different locations.

What is tonotopic organization?

The orderly spatial representation of sound frequencies from low to high.

How does the basilar membrane encode sound frequency?

Different locations vibrate most strongly in response to different frequencies.

Where do high-frequency sounds produce their greatest vibration on the basilar membrane?

At the base of the cochlea.

Why do high frequencies peak at the cochlear base?

The base is narrow and stiff.

Where do low-frequency sounds produce their greatest vibration on the basilar membrane?

At the apex of the cochlea.

Why do low frequencies peak at the cochlear apex?

The apex is wider and more flexible.

What is the difference between the base and apex of the basilar membrane?

The base is narrow and stiff for high frequencies; the apex is wide and flexible for low frequencies.

What is the relationship between frequency and location along the basilar membrane?

High frequencies activate the base; low frequencies activate the apex.

What is a frequency map in the cochlea?

The organization of different sound frequencies along different locations of the basilar membrane.

What does the basilar membrane allow the brain to distinguish?

Different sound frequencies and pitches.

What is the main type of sound that receives especially extensive representation in the human auditory system compared with other mammals?

Speech sounds, which carry language, as well as important vocalizations such as babies crying.

Why is speech particularly important to the human auditory system?

Humans rely heavily on auditory processing for communication and language.

What are cochlear hair cells?

Specialized sensory cells that convert mechanical movement into electrical signals.

What are the two types of hair cells in the cochlea?

Inner hair cells (IHCs) and outer hair cells (OHCs).

How many rows of inner hair cells are in the cochlea?

One row.

Approximately how many inner hair cells are in the cochlea?

3,500.

How many rows of outer hair cells are in the cochlea?

Three rows.

Approximately how many outer hair cells are in the cochlea?

12,000.

What is the primary function of inner hair cells?

They transduce sound vibrations into neural signals that contribute to sound perception.

What is the primary function of outer hair cells?

They amplify and sharpen cochlear vibrations by changing the mechanical properties of the basilar membrane.

Which hair cells are primarily responsible for sending auditory information to the brain?

Inner hair cells.

Which hair cells help amplify and fine-tune sound?

Outer hair cells.

What is the vestibulocochlear nerve?

Cranial nerve VIII, which carries auditory and vestibular information.

What cranial nerve connects to the base of cochlear hair cells?

The vestibulocochlear nerve (cranial nerve VIII).

What are stereocilia?

Hair-like projections extending from the top of sensory hair cells.

What is the function of stereocilia?

They detect mechanical movement and help convert it into electrical signals.

What are tip links?

Protein connections between adjacent stereocilia that help open mechanically gated ion channels.

What happens when stereocilia bend toward their tallest neighbors?

Tip links pull open ion channels, allowing positively charged ions to enter.

What happens when hair-cell ion channels open?

The hair cell depolarizes.

What happens after a hair cell depolarizes?

It releases neurotransmitter onto auditory nerve fibers.

What is the sequence of auditory hair-cell transduction?

Sound vibration → basilar membrane movement → stereocilia bending → tip links open ion channels → depolarization → neurotransmitter release.

What happens when stereocilia bend in the opposite direction?

Tip-link tension decreases, channels close, and the hair cell becomes less depolarized.

What causes hair cells to release neurotransmitter?

Depolarization of the hair cell.

What is the difference between inner and outer hair cells?

Inner hair cells transmit auditory information; outer hair cells modify and amplify cochlear vibrations.

What are IHC afferents?

Auditory nerve fibers carrying signals from inner hair cells toward the brain.

What do IHC afferents transmit?

Action potentials that contribute to sound perception.

What are IHC efferents?

Neural connections carrying signals from the brain toward inner hair cell pathways.

What is the function of IHC efferents?

They allow the brain to regulate the responsiveness of inner hair cell pathways.