Hearing and Balance

Hearing and Balance

Importance of Hearing Across Species

  • Survival and Communication:

    • Hearing is vital for survival and communication purposes among species.

    • It signifies various states such as emotions, danger, and attraction.

  • Auditory System:

    • The auditory system is responsible for sensing sounds and is integral for interaction with the environment.

    • It detects changes in the physical vibrations of air molecules.

  • Characteristics of Sound:

    • Intensity: Measured in decibels (dB), perceived as loudness.

    • Frequency: Measured in hertz (Hz), perceived as pitch.

    • Human hearing ranges from 20 Hz to 20,000 Hz.

Mechanics of Sound

  • Waveform and Sound Anatomy:

    • Sound is produced by the compression and expansion of air molecules due to vibrations from a source, like a loudspeaker.

    • Wavelength: Represents one cycle of sound.

    • Amplitude: Indicates the pressure waves of sound; greater amplitude yields louder sounds.

Auditory System Function

  • Mechanical Process of Hearing:

    • The auditory system captures, focuses, and transduces air molecule vibrations into action potentials.

    • The ear is divided into three sections responsible for processing sound:

    1. External Ear

    2. Middle Ear

    3. Inner Ear

External Ear

  • Components and Functions:

    • Pinnae:

    • The visible part of the ear, assists in filtering sounds and funneling them into the ear canal.

    • Ear Canal:

    • Plays a role in focusing sound and is commonly where Q-tips are used.

Middle Ear

  • Functionality:

    • Converts air vibrations into physical vibrations.

    • Air pressure impacts the tympanic membrane, causing it to vibrate.

    • Contains tiny bones known as ossicles:

    • Malleus (Hammer)

    • Incus (Anvil)

    • Stapes (Stirrup)

    • These bones amplify and concentrate sound before it reaches the cochlea via the Oval Window.

Inner Ear

  • Transduction of Energy:

    • The cochlea is a fluid-filled structure that converts physical energy into action potentials.

    • Different frequencies induce maximal vibrations in the basilar membrane.

Frequency Detection in the Cochlea

  • Role of the Organ of Corti:

    • Breaks down complex sounds into respective frequencies.

    • Base: Detects higher frequencies.

    • Apex: Detects lower frequencies.

    • The Organ of Corti is the site where transduction occurs, involving hair cells and stereocilia which detect the ripples in the basilar membrane.

Hair Cells and Action Potentials

  • Conversion Process:

    • Hair cells translate the ripples in the basilar membrane into action potentials using:

    • Mechanically gated K+ and Ca2+ channels

    • Depolarization Process:

      • When depolarized, Ca2+ channels near neurotransmitter vesicles open, leading to vesicle fusion and release of neurotransmitter substances.

Auditory Pathway

  • Transmission to the Brain:

    • Action potentials generated by hair cells travel via the Vestibulocochlear Nerve into the spinal cord and eventually reach the primary auditory cortex located on the superior surface of the temporal lobe.

Types of Deafness

  • Site of Disruption:

    • Hearing impairment can stem from disruptions across the auditory system:

    • A) Conduction Deafness

    • B) Sensorineural Deafness

    • C) Central Deafness

    • Discussion point: Does the type of deafness affect functionality of the primary auditory cortex?

Balance and the Inner Ear

  • Vestibular Apparatus:

    • Detects head position and aids in balance.

    • Comprising semicircular canals which are fluid-filled and possess mechanically gated channels alongside hair cells for balance detection.

Case Study: A Woman Perpetually Falling

  • Impact of Gentamycin:

    • An antibiotic that can damage hair cells affected in the cochlea and semicircular canals.

    • Example: After treatment, Cheryl experienced perpetual falling.

  • Innovative Adaptation:

    • Paul Bach-y-Rita proposed that the balance system might adjust using alternative sensory feedback.

    • Combination of an Accelerometer and a 144 Electrode Tongue Device allowed the brain to decode tongue sensations providing Cheryl with a method to regain balance.

    • Use of a helmet yielded residual effects suggesting plasticity in the vestibular system.

Goals of Understanding Hearing and Balance

  • Describe the essence of sound as a type of energy and its measurement techniques.

  • Analyze how sound appears visually and understand the variations in pitch and loudness.

  • Identify and describe the structural and functional components of the outer, middle, and inner ear.

  • Elucidate the hearing process including specialized cells involved in sound transduction and their gating mechanisms.

  • Define types of deafness and explore Bach-y-Rita's method used to assist a woman in regaining balance after auditory damage.