Exam 2 Flashcards
Sound
an energy wave of molecules (or pressure wave) that creates a vibration
-vibrations sets particles in the surrounding medium (typical air) in vibrational motion, thus transporting energy through the medium
-cycles per second
Frequency vs intensity and their units
Frequency is the rate of pressure fluctuations in the sound wave
-measured in Hertz (Hz)
-how often
vs.
Intensity is the magnitude of the pressure change in a sound wave (amplitude)
-measured in decibels (dB)
-how strong
Pure tone vs. Complex sounds
Pure tones are a single waveform for which variation as a function of time is a sine function (Sine wave)
vs.
Complex sounds are a combination of pure tones; different frequencies combined at different intensities
What is Fourier analysis?
a method to divide a complex sound into its pure tone components
Basic Structures of the auditory system listed in order
Outer Ear
-Pinna
-Ear canal
Tympanic membrane
Middle Ear
-Ossicles
Oval Window
Inner Ear
-Cochlea
-Organ of Corti
Basic Structures of the auditory System and their functions: Pinna
=the outer part of the ear that sticks out; the curly structure on the side of the head that we typically call an ear
-The ridges in the ear help detect and localize sounds
Basic Structures of the auditory System and their functions: Ear Canal
=the canal that conducts sound vibrations from the pinna to the tympanic membrane
-enhances sound frequencies
-conducts sound vibrations from the pinna to the tympanic membrane and prevents damage to the tympanic membrane
Basic Structures of the auditory System and their functions: Tympanic Membrane
= a thin sheet of skin that moves in and out in response to the pressure changes of sound waves
-eardrum; the border between the outer and middle ears
Basic Structures of the auditory System and their functions: Ossicles
= 3 tiny bones in the middle of the ear (MIS)
-amplify sound waves and transmit the vibrations from the tympanic membrane to the oval window
Basic Structures of the auditory System and their functions: Oval Window
the border between the middle and inner ear
-its movement causes movement of fluid within the cochlea (inner ear)
Basic Structures of the auditory System and their functions: Cochlea
=the change in pressure causes the vestibular canal to bulge in a location related to the frequency of the sound
-Interacts with the middle ear to relieve pressure
-These bulges in the vestibular canal cause the middle canal to move up and down shearing the Organ of Corti
Function of the inner hair cells
-focus on loudness and pitch
-Each stereocilia is connected to its neighbor by tip link (=a tiny filament)
-So they bend together when deflected by the shearing force
-When a stereocilium ( inner hair cell) deflects, the tip link pulls on the taller stereocilia in a way that opens an ion pore allowing potassium (K+) to flow into the cell => rapid depolarization
-The harder you pull, the more potassium is going to come in
-This depolarization leads to a rapid influx of calcium ions and initiates the release of neurotransmitters- stimulating the dendrites of the auditory nerve
Function of the outer hair cells
-Function: makes parts of the tectorial membrane stiffer through an electromotile response; works to make inner cells more sensitive and sharply tuned
-The sharpness of afferent nerve fibers connected to inner hair cells is dependent upon the outer hair cell
-Electromotor response, actually change shape/grow when stimulated
Need more force to stay sturdy
-Adds structures while inner hair cells move
How does the cochlea encode intensity?
-If the amplitude of the sound wave is increased, the tympanic membrane and oval window move farther in & out with each pressure fluctuation
=>making the bulge in the vestibular canal bigger, causing the cochlear partition to move farther up & down, causing the tectorial membrane to shear across the organ of Corti more forcefully, which causes the hair cells to pivot farther back & forth, which causes more neurotransmitters to be released, which causes auditory nerve fibers to initiate action potentials more quickly
-The location of the cochlea is frequency and how much it bends is intensity
How does the cochlea encode frequency?
-Cochlear place code= different portions of the cochlea are tuned to different frequencies
-different spots that move up and down more
-closer to oval window is high pitch/frequency, closer to the other window is low pitch/frequency
-The location of the cochlea is frequency and how much it bends is intensity
How the nerve fibers are organized to carry frequency information
What does tonotopic mean?
the organized tuning of different frequencies
The function and importance of the outer hair cell
Function: makes parts of the tectorial membrane stiffer through an electromotile response
-works to make inner cells more sensitive and sharply tuned
Rate saturation
= as the sound gets louder, auditory nerve fibers become more broadly tuned
-To circumvent rate saturation, the auditory system uses auditory nerve fibers with different spontaneous rates
-High spontaneous rate fibers respond at low levels of sound
-Low spontaneous rate fibers respond at a broader range of intensities but not at low intensities
Cochlear Place Code
different portions of the cochlea are tuned to different frequencies
Phase locking
=many fibers will fire action potentials at one particular point of the sound wave; a neuron fires with the specific phase of the stimulus/response
Volley principle
= multiple neurons encode frequency as a group
