How does the ear work out the following?

1. Loudness2. Pitch3. direction

Loudness

Determined by frequency of action potentials reaching the brain

Loud sounds – greater vibrations in hair cells and a greater rate of action potentials going to the brain

Some hair cells only respond to loud sounds

Pitch

Brain works this out by determining which neurones are conducting impulses.

Hair cells close to the oval window – high pitch

Hair cells furthest away – low pitch

Direction

Determined by differences in impulses coming from left and right ears

Brain compares loudness and timings of impulses

Ear closest to sound sends impulses slightly quicker than the other ear

Objectives

Name parts of the ear involved in control of balance

Describe the function of parts of the ear involved in balance

Consolidate knowledge of the ear

Which parts of the ear are linked with balance? Semicircular

canals Utriculus sacculus

Write an explanation of how the following words fit together Synapse Utriculus Macula Calcium carbonate Sacculus Otoliths Vestibular nerve Stereocilia Hair cells Gelatinous layer

The macula is a patch of cells in both the utriculus and sacculus.

The macula contains many tiny crystals of calcium carbonate called otoliths.

Each macula has many hair cells which have stereocilia

The ends of the stereocilia are embedded in a gelatinous layer.

They form synapses with the vestibular nerve.

Macula in utriculus and sacculus

Hairs cells move with the head as they are heavy

As they move sodium channels open in some of the hair cells

This results in action potentials travelling down the vestibular nerve.

Utriculus – horizontal plane – upright Sacculus – vertical plane – lying

down

Semicircular canals Filled with fluid Ampulla at one

end which has hair cells embedded in a gel structure called an capula

As the head moves the fluid collects in the ampulla and presses on the capula.

This bends the capula to one side This pulls on the cilia and results in

impulses travelling down the vestibular nerve

3 different ampullae in 3 different directions

Task

Produce revision cards on the ear: Structure Role in hearing Loudness, pitch and direction Role in balance Role of eustachian tube