Anatomy, Physiology, and Function of Auditory End-Organs in the Frog Inner Ear
Auditory Physiology
Transcript of Auditory Physiology
Prof. Greg Francis
1PSY 310: Sensory and Perceptual Processes
Purdue University
Auditory Physiology
PSY 310
Greg Francis
Lecture 29
A dangerous device.
Purdue University
Hearing
The sound stimulus is changes in pressure
The simplest sounds vary in:
Frequency: Hertz, cycles per second. How fast the pressurechanges
Amplitude: decibels. How big a change there is.
Complex sounds are made up of simple soundssuperimposed on each other
Fourier analysis / synthesis
Obviously, we do not hear all possible sound stimuli
Prof. Greg Francis
2PSY 310: Sensory and Perceptual Processes
Purdue University
Auditory limits
Different species are able to hear different frequencies ofsounds
Purdue University
Audibility curve
Threshold forhearingvaries withfrequency
Perceivedloudnessalso varieswithfrequency
Prof. Greg Francis
3PSY 310: Sensory and Perceptual Processes
Purdue University
Species variability Many animals can hear sounds at frequencies that
we cannot
Purdue University
Speech sounds Speech sounds are an especially important stimulus
They cover particular frequency ranges to which people arevery sensitive
Prof. Greg Francis
4PSY 310: Sensory and Perceptual Processes
Purdue University
Hearing loss As people age, their threshold intensity for hearing tends to go
up
Usually this is because of exposure to loud sounds
Purdue University
iPods Unfortunately, people now listen to quit loud sounds fairly
often
And they turn up the volume in environments with loudsurrounding sounds
Prof. Greg Francis
5PSY 310: Sensory and Perceptual Processes
Purdue University
Hearing loss Worse still,
hearing losstends to coverthe range offrequenciesthat includespeech
No one “getsused” to anoisyenvironment,it means youare goingdeaf.
Purdue University
Auditory system Basic anatomy of ear
Prof. Greg Francis
6PSY 310: Sensory and Perceptual Processes
Purdue University
Sound stimulus Sound waves travel down the ear canal
Hit the tympanic membrane (ear drum)
It vibrates with the sound wave
Purdue University
Ossicles The tympanic membrane
is connected to a smallbone
Malleus
Which connects toanother bone
Incus
Which connects toanother bone
Stapes
The end of the stapes
Pushes against anothermembrane called theoval window, which is onthe cochlea
Prof. Greg Francis
7PSY 310: Sensory and Perceptual Processes
Purdue University
Cochlea Spiral shape
Filled with fluid
Purdue University
Cochlea Several membranes that divide it into separate compartments
The round window pushes into one of these compartments
Prof. Greg Francis
8PSY 310: Sensory and Perceptual Processes
Purdue University
Cochlear chambers A cross-section
view indicatesthe chambersof the cochlea
Purdue University
Cochlear membranes Special cells are located on the middle membrane to respond
to movement of another membrane
These membranes move in response to pressure from thestapes on the oval window
Prof. Greg Francis
9PSY 310: Sensory and Perceptual Processes
Purdue University
Basilar membrane This membrane contains the organ of Corti
Purdue University
Organ of corti Here’s another schematic
The whole organ stretches along the entire membrane
Prof. Greg Francis
10PSY 310: Sensory and Perceptual Processes
Purdue University
Organ of corti Here’s a electron micrograph
Three rows of outer hair cells are visible
Purdue University
Organ of Corti
Three main components
Tectorial membrane Sits on top
Inner hair cells
Outer hair cells
Prof. Greg Francis
11PSY 310: Sensory and Perceptual Processes
Purdue University
Organ of Corti
When sound hits the ear and the pressure istransferred to the oval window, the basilarmembrane moves Show animation
This causes the haircells to bend Show animation
Sound energy istransduced into anelectrical signal at thehair cells
Purdue University
Hair cells Each hair cell has cilia that sticks up on top of the organ of corti
They are arranged in a particular pattern
16,000 to 20,000 along the whole cochlea
Prof. Greg Francis
12PSY 310: Sensory and Perceptual Processes
Purdue University
Inner hair cells This is a electron micrograph of the top of a single inner hair cell
The cilia pivot on their base in response to movement from thetectorial membrane, which is above them
Purdue University
Outer hair cells This is a electron micrograph of the top of a single outer hair cell
The tallest cilia are connected to the tectorial membrane, which isabove them.
The smaller cilia are connected to their larger neighbor
Prof. Greg Francis
13PSY 310: Sensory and Perceptual Processes
Purdue University
Hair cells
Movement of the tectorial membrane opens a“trapdoor” on the top of the cilia
Normally, potassium ions stay outside
Purdue University
Hair cells Movement of the tectorial membrane opens a “trapdoor” on the
top of the cilia
With pressure, the trapdoors open and, potassium ions enter
Animations
Excitation
Inhibition
The potassium leads toneural responses
Prof. Greg Francis
14PSY 310: Sensory and Perceptual Processes
Purdue University
Hearing loss
Here’s another view of a healthy cochlea with normalhair cells
Purdue University
Hearing loss
Exposure to long-term loud noise can damage the haircell cilia
Prof. Greg Francis
15PSY 310: Sensory and Perceptual Processes
Purdue University
Hearing loss Another comparison of a single outer hair cell
Currently, there is no recovering from such damage
It is permanent hearing loss
An iPod (or whatever) played fairly loud can lead to this kind ofdamage
If it’s too loud around you to hear your music, don’t listen
Might be a good idea to keep the earbuds in (to block sound!)
Purdue University
Conclusions Anatomical structure and function of the ear
Outer ear
Middle ear
Inner ear
Cochlea
Basilar membrane
Organ of Corti
Hair cells
Hearing loss
Prof. Greg Francis
16PSY 310: Sensory and Perceptual Processes
Purdue University
Next time
Responses to stimulus properties
Frequency analysis
Place theory