PSY 324 Chapter 9

How is sound created?

Sound is created when objects vibrate which causes air molecules around objects to vibrate as well. This leads to pressure changed in the medium (air, water, etc)

How fast does sound travel through air and water?

Air: 340 meters/second

Water: 1500 meters/second

• Faster in water because the particles are a lot closer together. So, this causes the particles that are a lot closer together to move.

Describe Frequency

Pitch; Higher = Higher pitch

• Measured in Hertz (Hz) - 1Hz = 1 cycle per second

• How many times the sound wave repeats itself is the frequency

Describe Amplitude

Volume; Higher = Higher Volume (How far the peak is from neutral)

• Measured in Decibels (dB)

• Each 10:1 ratio of pressure is equal to 20b=dB

• Decibels change logarithmically (not a lineal scale)

  • Result: Small changes in dB = large physical changes in pressure

    • 6dB increase is equivalent to double the pressure!

What is Presbycusis?

The general loss of sound

Simple Sounds (Pure tones)

Consists of a single sine wave

Used in hearing research and is very rare in the real world

Complex Sounds

• The lowest (base) frequency is called the fundamental frequency

• Other frequency components are called harmonics

• Timbre: The shape of complex sounds allows us to distinguish between sound sources (the quality of sound)

Parts of the outer ear and their functions

Pinna = Ear flap itself; captures the sound (animals can move theirs)

Ear Canal = Funnels sound down to the end of the ear canal

Tympanic Membrane (aka eardrum) = A drum; a flap of skin that vibrates when sound hits it

Parts of the middle ear and their functions

Ossicles: Three bones

• Malleus = The most exterior of the three ossicles. The malleus receives vibration from the tympanic membrane and is attached to the incus

• Incus = The middle of the three ossicles, connecting the malleus to the stapes

• Stapes = The most interior of the three ossicles. Connected to the incus on one end, the stapes presses against the oval window of the cochlea on the other end

Muscles

• Tensor Tympani = The muscle attached to the malleus. Tensing the tensor tympani decreases vibration

• Stapedius = The muscle attached to the stapes. Tensing the stapedius decreases vibration

Parts of the inner ear and their functions

Oval Window = Membrane between middle ear and inner ear

Cochlea = Snail-shaped structure

• Three parallel canals

• Filled with water-like fluid

Structures that make up the Organ of Corti

Structure in the middle canal of the inner ear

• Consists of basilar membrane with hair cells connected to dendrites auditory nerves

  • Function: Transduce sound waves into nerve signals which are sent to the brain through auditory nerve

What are the two types of hair cells and what are their functions?

Inner (one row): Convey information to the brain

Outer (three rows): Receive information from the brain

How does hearing work?

The tectorial membrane floats above inner hair cells and rests on outer hair cells (not moving just floating - As the tectorial membrane shears against the hair cells it pulls on the tip links that connect the stereocilia of the hair cells which results in the opening on the mechanical-gated ion channels and a depolarization of the cell (Tip links get pulled hard enough and potassium (K+) goes into the cell.

Afferent Nerve Fibers

Take information from hair cells to the brain

• 90% synapse with inner hair cells

Efferent Nerve Fibers

Send information from the brain to the hair cells

• Feedback from the brain causes portions of the basilar membrane to stiffen

  • Result: Only certain portions of the membrane vibrate which makes your hearing more sensitive to certain frequencies

Rate Saturation

Auditory nerves will fire at the highest rate to their characteristic frequencies

• Rate will increase as intensity (amplitude) increases … but only to a point!

How auditory nerve fibers tuned

Each auditory nerve is tuned to a specific frequency

• This requires very little stimulation to trigger that specific nerve at that frequency

Two-Tone Suppression

If an auditory nerve is exposed to two different tones, it will lower the firing rate of the tone it is not tuned to

• Takes place in the inner ear