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The Ears: Hearing and Balance

The Ears: Hearing and Balance. External ear- Pinna (auricle) and acoustic meatus (ear canal) funnel sound to the tympanic membrane (eardrum). Cerumen. (earwax) protects from drying, bacteria, fungi. (Auricle). (External Auditory Meatus ). Middle ear:

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The Ears: Hearing and Balance

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  1. The Ears: Hearing and Balance

  2. External ear- • Pinna (auricle) and acoustic meatus (ear canal) funnel sound to the tympanic membrane (eardrum) • Cerumen (earwax) protects from drying, bacteria, fungi

  3. (Auricle) (External Auditory Meatus)

  4. Middle ear: • 3 ossiclesconduct sound vibrations: • hammer (malleus) • anvil (incus) • stirrup (stapes) • Eustachian tube connects to throat and regulates air pressure for proper hearing

  5. Inner ear: (the labyrinth) • Cochlea- Snail shaped hearing organ. Vibrations enter through the oval window. Hair cells on the Organ of Corti vibrate to different pitches.

  6. Inner ear: (the labyrinth) • Vestibule- Central fluid filled, 2 chambered cavity. Senses position relative to gravity. • Semicircular canals- 3 canals. One for each plane of 3 dimensional space. It senses movement in each direction.

  7. The cochlear nerve and vestibular nerves combine to form the auditory nerve which carries info to the brain.

  8. Mechanoreceptors- -Both hearing and equilibrium (balance) rely on mechanoreceptors. -Mechanoreceptors respond to physical movement. -In the ear they are “hair cells”.

  9. Hearing: • Organ of corti (in the cochlea): row of hair cells along a membrane. • The membrane is thin at the beginning and thicker towards the end. -High pitch= vibrates thin membrane low pitch = vibrate thick membrane

  10. Animation of basilar membrane in the cochlea:

  11. Hearing: • When hair cells in cochlea move, ion channels open and an action potential is created • The brain interprets pitch depending on which hair cells are excited. (usually a mix of several) • Loud sound= more cells excited

  12. Too loud/ too long = hair cells or nerve cells destroyed

  13. Equilibrium: 1. Static equilibrium= not moving= relationship to gravity -Sensed in the 2 chambers of the vestibule -A gelatin containing otoliths (“ear stones”) sits atop hair cells -gravity moves the gelatin, stimulating hair cells= send signal to brain. (may cause righting reflex)

  14. 2. Dynamic equilibrium= movement/rotation of head -Sensed in the 3 semicircular canals (3 dimensions) -relies on the motion of fluid in the canals -fluid pushes on a jelly like “float” sitting atop hair cells -these sit at the base of each canal

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