358 Chapter 10 Sensory Physiology

e The sound waveenergy is transferredto the three bonesof the middle ear,which vibrate.

e The stapes is attached tothe membrane of the ovalwindow. Vibrations of theoval window create fluidwaves within the cochlea.

Sound waves strikethe tympanicmembrane andbecome vibrations.

Incus

Ear canal Malleus StapesOval

window

-+-+--\+-- Vestibularduct(perilymph)

o-f---f---- Cochlearduct(endolymph)

----:f--rrr---- Tympanicduct(perilymph)

Tympanicmembrane

Roundwindow

e Neurotransmitter releaseonto sensory neuronscreates action potentialsthat travel through thecochlear nerve tothe brain.

G Energy from the wavestransfers across thecochlear duct into thetympanic duct and isdissipated back intothe middle ear at theround window .

The fluid waves push on theflexible membranes of thecochlear duct. Hair cells bendand ion channels open,creating an electrical signal thatalters neurotransmitter release.

FIGURE 10-20 Sound transmission through the ear

Vestibular duct ----+-l!-,"-f'!'--+--~

Cochlear duct --+H+.F..,.

Tectorial membrane -+"+-----';"-'H---,,?.,..

Organ of Corti --+i~~/

Uncoiled\\\\\\r

,---,4~~ \\\

Vestibularduct

Cochlearduct

Organ ofCorti

Helicotrema

Roundwindow

Tympanicduct

Basilarmembrane

Bony cochlear wall

Basilarmembrane

Tympanicduct

---"'il'tm,firI'-'--" Cochlear nervetransmits actionpotentials fromthe hair cells tothe aud itorycortex.

Tectorial ---.,.L.membrane ""'~---------

Rod (monochromatic vision)

Optic nerve

-=--,-1----- Sclera

111~~~;gj~:-I--/,t---~-The choroid layercontains bloodvessels.

Pigment epitheliumof retina absorbsexcess light.

Rod

Bipolar neuron

Cone

i~~~~~~i'~-~Ganglion cell(c) Light strikes the photoreceptors in the fovea directly

because overlying neurons are pushed aside.

To opticnerve

ilI

I

Bipolarcell

RodPigment

epithelium

receptorsare organized into layers. (e) Convergence in the retina

FIGURE QUESTION

How many rods converge onthe ganglion cell in (e)?

Drawing of photoreceptors in the fovea adapted from E. R.

Principlesof Neural Science, 3rd edition (McGraw Hill: New York, 2000).