Hearing

Final Exam

Amplitude/Intensity

The magnitude of displacement (increase or decrease) of a sound pressure wave. Perceived as loudness.

Frequency

For sound, the number of times per second that a pattern of pressure change repeats. Perceived as pitch.

Pressure fluctuation of a sound in relation to distance

Sound waves are described by the frequency and amplitude of pressure fluctuations

Hertz (Hz)

A unit of measure for frequency (equals one cycle per second)

Loudness

The psychological aspect of sound related to perceived intensity (amplitude)

Pitch

The psychological aspect of sound related mainly to the fundamental frequency

Decibel (dB)

A unit of measure for the physical intensity of sound. Defines the difference between 2 sounds as the ration between 2 sound pressures (Ex: 10:1 sound pressure = 20dB, and a 100:1 ratio = 40dB) ((ON A LOG SCALE))

Sine wave/Pure tone

The waveform for which variation as a function of time is a sine function

Spectrum

A representation of the relative energy (intensity) present at each frequency.

Fundamental Frequency

The lowest-frequency component of a complex periodic sound (go from Low A 27.5 Hz to High C 4.2 kHz) ((middle C is 261 Hz)

Acoustic Energy

Disturbance in the density of particles which comprise an elastic medium

Phase

Position of a sound wave within its cycle at a specific point in time (measured in degrees)

Transmission

Process by which sound waves are collected, amplified and converted into electrical nerve impulses for the brain to interpret as sound.

Absorption

Process by which sound energy is taken in by a material when sound waves encounter it rather than being reflected back into the environment

Reflection

Occurs when sound waves travel through the air and when these waves encounter a surface they don’t simply stop, they bounce off creating echoes.

Sound Vs. Light

1. In vision amplitude and phase is irrelevant (never changes)

2. Light is significantly faster than sound

Concentric Waves

Circular waves that emanate outward from a certain point

A sine wave is a circular motion extended over time

Every complex sound wave can be analyzed as a combination of sine waves

Harmonic sounds with the same fundamental frequency can sound different

Pinna

The outer, funnel-like part of the ear

Ear Canal

Conducts sound vibrations from the pinna to the tympanic membrane and prevents damage to the tympanic membrane

Tympanic Membrane

The ear drum; a thin sheet of skin at the end of the outer ear canal. Vibrates in response to sound.

Outer Ear

The external sound gathering portion of the ear, consisting of the pinna and the ear canal

Middle Ear

An air-filled chamber containing the middle bones (ossicles). Conveys and amplifies vibration from the tympanic membrane to the oval window

Ossicle

Any of three tiny bones of the middle ear: malleus, incus, and stapes

Malleus

Receives vibration from the tympanic membrane and is attached to the incus

Incus

Middle of the three ossicles, connecting the malleus and the stapes

Stapes

Connected to the incus on one end, it presses against the oval window of the cochlea on the other end.

Oval Window

The flexible opening to the cochlea through which the stapes transmits vibration to the fluid inside

Inner Ear

A hollow cavity in the temporal bone of the skull and the structure within its cavity: the cochlea and the semicircular canals of the vestibular system canals

Tensor Tympani

The muscle attached to the malleus; tensing it decreases vibration

Stapedius

The muscle attached to the stapes; tensing it decreases vibration

Acoustic Reflex

Protects the ear from intense sounds via contraction of the stapedius and tensor tympani muscles

Cochlea

A spiral structure of the inner ear containing the organ of Corti

Tympanic Canal

One of three fluid-filled passages in the cochlea. Extends from the round window at the base of the cochlea to the helicotrema at the apex

Vestibular Canal

One of three fluid-filled passages in the cochlea. Extends from the oval window at the base of the cochlea to the helicotrema at the apex

Middle Canal

One of three fluid-filled passages in the cochlea. Sandwiched between the tympanic and vestibular canals and contains the cochlear partition

Helicotrema

The opening that connects the tympanic and vestibular canals at the apex of the cochlea

Reissner’s Membrane

A thin sheath of tissue separating the vestibular and middle canals in the cochlea

Basilar Membrane

A plate of fibers that form the base of the cochlear partition and separates the middle and tympanic canals in the cochlea

Cochlear Partition

The combined basilar membrane, tectorial membrane and organ of Corti, together responsible for the transduction of sound waves into neural signals.

Round Window

A soft area of tissue at the base of the tympanic canal that releases excess pressure remaining from extremely intense sounds.

Organ of Corti

A structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites of auditory nerve fibers

Hair Cell

Any cell that has stereocilia for transducing mechanical movement in the inner ear into neural activity sent to the brain; some receive inputs from the brain

Auditory Nerve

A collection of neurons that convey information from hair cells in the cochlea to (afferent) and from (efferent) the brain stem

Stereocilium

Any of the hairlike extensions on the tips of hair cells in the cochlea that, when flexed, initiate the release of neurotransmitters

Tectorial Membrane

A gelatinous structure, attached on one end, that extends into the middle canal of the ear, floating above inner hair cells and touching outer hair cells

Tip Link

A tiny filament that stretches from the tip of a stereocilium to the side of its neighbor

Place Code

Tuning of different parts of the cochlea to different frequencies in which information about the particular frequency of an incoming sound wave is coded by the place along the cochlear partition that has the greatest mechanical displacement

Afferent Fiber

A neuron that carries sensory information to the central nervous system

Efferent Fiber

A neuron that carries information from the central nervous system to the periphery.

Threshold Tuning Curve

A graph plotting the thresholds of a neuron on fiber in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response

Characteristic Frequency (CF)

The frequency to which a particular auditory nerve fibers is most sensitive

Eustachian Tube

A narrow passage leading from the pharynx to the cavity of the middle ear, permitting the equalization of pressure on each side of the eardrum.

Vestibular Nerve

A component of the inner ear, plays a fundamental role in maintaining balance and spatial orientation. It relays information about head position and movement to the brain.

Tunnel of Corti

Spiral passage located in the cochlea that plays a crucial role in the transmission of sound waves to the hair cells.