Download 07.The Ear

Hearing and
Equilibrium
 The ear is the organ of hearing and
equilibrium.
 It consists of three main regions:
1. outer ear
2. middle ear
3. inner ear
Outer Ear
 Consists of auricle (pinna) and the external acoustic
canal.
 Auricle (pinna) – fleshy part attached to head
- acts as a sound collector
 Helix – rim of the auricle
 Earlobe – only part of auricle not supported by cartilage
 External Acoustic (auditory) canal - 2.5 cm long
- carries sound to eardrum
- lined with hairs and sweat glands that produce ear wax
 Tympanic membrane – thin, doublelayered membrane (eardrum)
- 1 cm diameter
- Very sensitive to pain
 Tympanic cavity – air-filled chamber
that contains the auditory ossicles
Middle Ear
Ossicles – 3 tiny bones that carry sound
1. Malleus – hammer
2. Incus – anvil
3. Stapes – stirrup
Auditory Tube – equalizes pressure on
both sides of the eardrum
Inner Ear
Oval window – receives sound waves from stapes
Entire structure of the inner ear is called labyrinth.
Made of 3 areas:
1. Vestibule – chamber that aids in balance
2. Semicircular canals – canals that also aid in
balance
3. Cochlea – shell shaped structure that contains 2
rows of hairs that respond to sound waves.
Auditory Nerve – receives impulses generated by inner
ear and sends them to temporal lobe of brain
Pathway that Sound
Travels through Ear
Sound Waves
pinna
auditory canal
Tympanum ear ossicles cochlea
Auditory nerve
temporal lobe
Sound Waves and Hearing
 Sound waves – travel in all directions and
are characterized by their frequency and
intensity
 Hearing
- Sound waves travel through the external
acoustic canal and produce small vibrations of
the tympanic membrane.
- Vibrations are passed on to the three bones of
the middle ear.
- The ossicles amplify the vibrations and
transmits them to the oval window.
- The hairs inside the cochlea convert the waves
into electrical impulses that are sent to the
brain.
Equilibrium
 Balance involves static equilibrium and
dynamic equilibrium.
 1. Static equilibrium – head position
- Maintained by 2 fluid-filled sacs inside
the vestibule (saccule, utricle)
- Inside these sacs have cilia that move in
the direction of the head.
- This information is sent to the brain.
 Dynamic Equilibrium – body position
- maintained by three semi-circular canals
- can cause motion sickness
- Readings – Pages 445-450