Sound Waves

Sound is created when objects vibrate.

This vibration causes molecules in the surrounding medium to vibrate as well.

This, in turn, causes pressure changes in the medium.

Pressure Fluctuations

Pattern stays the same

Pressure decreases

Quantifying Sound

Amplitude

Intensity

Frequency

Hertz (Hz)

Most Sound is a Mix of Waves

Time (msec)

Spectral Analysis

Differences in Animal Hearing

Differences in Mammalian Hearing

The Range of Human Hearing

Loudness Variations

Outer Ear Variations

Human Ear Divisions

Human Ear Anatomy

Middle Ear Bones

Malleus

Incus

Stapes

Inner Ear - Cochlea

CochleaCross Section

Cochlear Partition

Organ ofCorti

Hair Cells

Hair Cell Neurochemistry

Inner Hair Cells:•afferent: Glu•efferent: ACh

Outer Hair Cells:•afferent: ACh•efferent: GABA

Sound, Vibration,

and Transduction

Stereocilia

Electronmicrographof stereocilia tip links

(Hudspeth, 1992)

Tip Link Neurochemistry

Tip Link Movement:

•Opens non-selective ion channels

•K+ and Ca++ enter cell causing depolarization

•Causing voltage-gated Ca++ channels to open at cells base

•Ca++ triggers the release of neurotransmitter that stimulates afferent fiber

Cochlea

Specific movementof the basilar membranestimulates specific cells

Auditory Pathway

Auditory Cortex

Medial Geniculate Nucleus (MGN)

Inferior Colliculus

Superior Olivary Nucleus

Cochlear Nucleus

Auditory Nerve