The Chemical Context of Life

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Slide 26

These vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canal.

Pressure waves in the canal cause the basilar membrane to vibrate, bending its hair cells.

This bending of hair cells depolarizes the membranes of mechanoreceptors and sends action potentials to the brain via the auditory nerve.

Slide 27

Sensory reception by hair cells.

“Hairs” of hair cell

Neuro- trans- mitter at synapse

Sensory neuron

More neuro- trans- mitter

(a) No bending of hairs

(b) Bending of hairs in one direction

(c) Bending of hairs in other direction

Less neuro- trans- mitter

Action potentials

Membrane potential (mV)

0

–70

0 1 2 3 4 5 6 7

Time (sec)

Signal

Signal

–70

–50

Receptor potential

Membrane potential (mV)

0

–70

0 1 2 3 4 5 6 7

Time (sec)

–70

–50

Membrane potential (mV)

0

–70

0 1 2 3 4 5 6 7

Time (sec)

–70

–50

Signal

Slide 28

The ear conveys information about sound waves:

Volume = amplitude of the sound wave

Pitch = frequency of the sound wave

The cochlea can distinguish pitch because the basilar membrane is not uniform along its length.

Each region vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex.

Slide 29

Equilibrium

Several organs of the inner ear detect body position and balance:

The utricle and saccule contain granules called otoliths that allow us to detect gravity and linear movement.

Three semicircular canals contain fluid and allow us to detect angular acceleration such as the turning of the head.

Slide 30

Organs of equilibrium in the inner ear

Vestibular nerve

Semicircular canals

Saccule

Utricle

Body movement

Hairs

Cupula

Flow of fluid

Axons

Hair cells

Vestibule

Slide 31

Hearing and Equilibrium in Other Vertebrates

Unlike mammals, fishes have only a pair of inner ears near the brain.

Most fishes and aquatic amphibians also have a lateral line system along both sides of their body.

The lateral line system contains mechanoreceptors with hair cells that detect and respond to water movement.

Slide 32

The lateral line system in a fish has mechanorecptors that sense water movement