Auditory Modality

Divisions Of The Ear

• Outer ear - pinna and canal
• Middle ear - tympanic membrane (ear drum), three bones (stapes, incus, malleus), and eustachian tube
• Inner ear - oval window, semicircular canals and cochlea
• Outer and Middle ear use resonance to increase the intensity of a sound
• Our ears can hear sounds from 20 - 20,000 Hz
• Our ears resonate best with sounds between 2000 and 5000 Hz

• Responsible for protecting middle and inner ear
• Responsible for moving sound from the external environment to the middle ear.

Middle Ear

• Sound is amplified
• Bones convert air pressure changes (sound waves) to physical movement so it can move through the fluid in the cochlea

Inner Ear

• The cochlea
• The oval window and the round window are the two holes that lead into the cochlea from the middle ear.

The Cochlea

• It begins with the connection of the oval window and the last of the bones (stapes).
• Made of three different chambers all filled with fluid
• Vestibular Duct
• Cochlear Duct
• Tympanic Duct

• Shaped like a wedge
• The base (closes to the middle ear) is thin and stiff --> high frequencies
• The apex is wide and floppy --> low frequencies

• Sits on the basilar membrane
• Contains hair cells that respond to vibrations of the basilar membrane
• Basilar membrane vibrates --> the stereocilia drag against the tectorial membrane (just above the hair cells).
• The hair cells have mechanoreceptors --> stretch causes the hair cells to depolarize (mechanotransduction)
• Ion channels in the stereocilia activate afferent neurons
• The hair cells are connected to nerves that come together to form the cochlear nerve

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From Outer Ear To Auditory Nerve

1. Sound is trapped by the pinna and moves through the ear canal
2. The frequencies cause the ear bones to physically move.
3. The last bone is connected to the oval window and transmits sound into the cochlea
4. The sound is converted from waves to neural signals in the cochlea
5. Auditory nerve (vestibulocochlear nerve) carries sound information out of the ear and into the brain

From Auditory Nerve to Auditory Cortex

• Auditory/vestibular nerve --> Medulla (important for integration of sounds from both ears)
• Medulla --> Midbrain
• Midbrain --> Thalamus
• Thalamus --> Primary Auditory Cortex
• Auditory cortices receive both ipsilateral and contralateral information!

Vestibular Organs

• Semicircular Canals --> detect angular acceleration
• Hair cells in the semicircular canal also have stereocilia
• They are connected to the cupula which can move when endolymph moves

• Utricle and Saccule --> detect linear acceleration
• Utricle - horizontal
• Saccule - vertical