Chapter 5: The Auditory System, Sound and Ear

Presbycusis

Age-related hearing loss.

Outer Hair Cells

Amplify the signal by causing vibration of the basilar membrane; remember the outer 3 rows do not do signal transduction, only the inner hair cell is responsible for that

Cochlear Microphonic

An alternating current potential produced at the reticular lamina that mimics the vibration pattern of the basilar membrane; as the basilar membrane moves up and down, the cochlear microphonic alternates between positive and negative polarity, mimicking the shape of the input signal.

Tonotopic Map

An ordered map of frequencies created by the responding of neurons within structures in the auditory system. There is a tonotopic map of neurons along the length of the cochlea, with neurons at the apex responding best to low frequencies and neurons at the base responding best to high frequencies.

Incus

Anvil-shaped small bone or ossicle in the middle ear, connects the malleus to the stapes

Stapes

Auditory ossicle attached to oval window.

Usher Syndrome

Born deaf, go blind by age 40.

Bell Jar Experiment

Boyle, sound produced by a bell becomes less audible if enclosed in a jar from which the air is slowly pumped out becoming silent when the jar is free of air, air is required as a medium for the transmission of sound

Organ of Corti

Center part of the cochlea, containing hair cells, canals, and membranes

Clarity

Clearness

Footplate

Flat bottom portion of the stapes that moves in and out like a piston at the oval window and transmits sound vibrations to the fluid in the cochlea

Reissner's Membrane

Forms a boundary between the scala vestibuli and the duct from the scala tympani

Sterocilia

Hairlike process that are actually microvilli containing actin fibers

Cochlear Duct

Hole that the Organ of Corti resides in.

Frequency Theory

In hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch.

Condensation Effect

The sound pressure collected on the entire area of the TM is concentrated of the oval window

Scala Media

This structure houses the sensory apparatus for hearing, and is made up of the Scala Vestibuli and the Scala Tympani.

Arch of Corti

hair cells lean against this structure and it functions in support of the hair cells.

Malleus

hammer; first of the three auditory ossicles of the middle ear

Eustachian Tube

A narrow tube between the middle ear and the throat that serves to equalize pressure on both sides of the eardrum

Basilar Membrane

A structure that runs the length of the cochlea in the inner ear and holds the auditory receptors, called hair cells.

Isofrequency Sheets

single layer of neurons in the inferior colliculus that all display the same characteristic frequency

Ohm's Law of Hearing

that the sound quality of a complex tone depends only on the amplitudes of its harmonics and not on their relative phases

Ossicular Chain

the three interconnected bones in the middle ear that conduct vibration from the tympanic membrane to the cochlea.

Frequency Response Curve

A graphic representation of the effect that a device, such as a microphone or speaker, will have on the tone of an instrument.

Pinna

A high peak or point

Tectorial Membrane

A membrane located above the basilar membrane; serves as a shelf against which the cilia of the auditory hair cells move

Waardenburg Syndrome

4 types, pale blue eye, white forelock

Cochlea

A coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses.

Tuning Curve

A graph of the responses of a single auditory nerve fiber or neuron to sounds that vary in frequency and intensity.

Vestibulocochlear Nerve (Cranial Nerve VIII)

Cranial nerve VIII, which runs from the cochlea to the brainstem auditory nuclei

External Auditory Canal

Curved tube that extends from the auricle and directs sound waves toward the eardrum, contains a few hairs and earwax

Oval Window

Is at the boundary between the middle ear and inner ear., causing vibrations to pass into a coiled, fluid filled tube, known as the Cochlea.

Scala Vestibuli

Large hole located in the Cochlear Duct above the Organ of Corti.

Spiral Ganglion

Location of the cell bodies of the sensory neurons of the organ of Corti

Efferent Fibres

Nerve fibres that carry (motor) information from the brain towards the periphery (e.g. to act on muscles). (Book 2, Chapter 1)

Afferent Fibres

Nerve fibres that carry (sensory) information (for example, regarding touch or painful stimuli) towards the brain from the periphery.

2 Types of Hair Cells:

Outer and Inner Hair cells, only single row of inner cells.

Inner Hair Cells

Single row on BM. Ovoid or flask-shaped. Have more mitochondria than the OHCs. The stereocilia are arranged in 3 rows, are in a U-shape patter on top of the hair cells, and are NOT embedded in the Tectorial membrane. Many to one.

Bony Labyrinth

Rigid outer wall of the inner ear that consists of three parts: the vestibule, semicircular canals, and cochle

Vestibuar System

sensory info about head movement and head position relative to gravit

Tympanic Membrane

The eardrum. A structure that separates the outer ear from the middle ear and vibrates in response to sound waves.

The Place Theory

The fact that the various parts of the basilar membrane are tightly bound together is problematic for which of the following?

Characteristic Frequency

The frequency at which a neuron in the auditory system has its lowest threshold.

Hair Cells

The hairlike sensory receptors for sound, which are embedded in the basilar membrane of the cochlea.

Subcortical Auditory Structures

a collection of neurons that make up a defined anatomical unit residing below the cerebral cortex usually in the brain stem or thalamus.

Heliotrema

a hole at the apex of the cochlea in the inner ear that connects the scala tympani to the scala vestibuli

Fourier Spectrum

a plot that shows the composition of a sound at one moment in time by plotting frequency vs. amplitude for the individual sine wave components

Suppression Response

a type of binaural interaction where a neuron is excited by one ear and inhibited by the other.

Summation Response

inputs from both ears are excitatory and therefore the neuron can be driven by sound stimulation of either ear though there is usually a stronger preference for the ear on the opposite side

Phase-Locked Response

neural firing that has a precise timing relationship to the sound waveform, either linked to each compressive portion of spaced out every few cycles

Olivocochlear Neurons

neurons in the superior olive that belong to the descending system and give rise to efferent fibres that project to the cochlea and innervate the hair cells

Descending System

this system sends messages to the dorsal horn of the spinal cord, where it suppresses the transmission of pain signals to the higher brain centers

Semicircular Canals

three canals within the inner ear that contain specialized receptor cells that generate nerve impulses with body movement

Ossicles

three tiny bones in the middle ear