Unit 2: Nervous System
Hearing Notes
(1) Ear Design
• Ear is like a well designed funnel.
• Sound waves spiral down into auditory
canal.
• Sound Waves smack against ear drum
(tympanic membrane).
(2) Vibrations
• Sound Waves  Tympanic Membrane
– Eardrum literally like the leather on a drum
• T-Membrane  Hammer  Anvil  Stirrup
– Hammer, Anvil and Stirrup are very small bones
in inner ear
• Stirrup  Oval Window  Inner Ear Fluid
(3) Cochlea
• Cochlea = Snail like structure in inner Ear.
• Contains Organ of Corti:
– Contains hearing receptors / hair cells
– Hair cells stimulated by movement of Inner Ear Fluid
• Basilar Membrane
– Type of membrane on specific receptors
– Responds to changes in pitch
• Fluid  Receptors  Cochlear Nerve  Brain
(4) Equilibrium & Balance
• Your ears keep track of your body’s
position.
• Equilibrium receptors lie within the inner ear
of your ears (Vestibular Apparati).
• 2 Types of Equilibrium:
– Static
– Dynamic
(5) Static Equilibrium
• Head Balance
• Static Receptors = Maculae:
– On top of maculae lies the otolithic membrane
(gel-like)
– Head Moves  Otoliths Moves!
– Movement of Otolithic  Receptor  Impulse to
Vestibular Nerve & Brain
• Tells your brain when your head is not
upright.
(6) Dynamic Equilibrium
• Rotation & Angles of Head
• Semicircular Canals of Cochlea:
– Contain receptors = Crista Ampullari
– Crista Ampullari contain receptor hairs,
endolymph fluid and a capula cap
– Body Movement  endolymph movement 
Push on Capula Cap  Receptor Hairs 
Vestibular Nerve & Brain
http://www.youtube.com/watch?v=vTiGskc1o48
(7) Motion Sickness
• Inefficient dynamic equilibrium…
– Semicircular Canals either too sensitive or too
slow at sending messages
• Too many visual messages
• Too many inner ear messages
• Visual conflicts with Inner Ear
• Unique to each individual
(8) Deafness
• Deaf = Any hearing loss
• Types:
– Conduction
– Sensorineural
(9) Conduction Deafness
• Something Blocks Tympanic Membrane
• Sound Waves cannot reach Ear Drum +
Inner Ear
• Causes:
– Ear Wax
– Ruptured Ear Drum
– Injured Hammer, Anvil and/or Stirrup
• Usually Temporary, Solved by Surgery
(10) Sensorineural Deafness
• Damage to actual parts of ears:
– Receptor Cells
– Cochlea
– Vestibular Nerve
• Can be hereditary, damage from
disease/virus, damage from loud noises
• Often permanent