1. Ears, Hearing

2. The External Ear
Hearing
Figure 8.12

3. Outer Ear Functions
Amplification / Filtering
Protection
Localization

4. The Outer Ear Consists of:
The Pinna - cartilaginous, highly variable in appearance, some landmarks.
External Auditory Canal (or external auditory meatus) cm tube.

5. External Auditory Canal
lateral portion-cartilage
medial portion-osseous (bone)
hairs in lateral part
cerumen (ear wax) secreted in lateral part.
WHY DO WE HAVE EAR WAX?

6. Does Ear Wax Have a Purpose?
2 important functions
1.Keeps skin in ear canal
soft
2. Keeps bugs out 
(they don’t like the taste)

7. Middle Ear Functions
Impedance Matching
Filtering
Acoustic Reflex

8. The Middle Ear: A cleft within the temporal bone
Eustachian tube connects it to nasopharynx
drain cells/tissues
Equalize air pressure

9. Middle Ear Structures 1- Malleus 2- Incus --Ossicles 3- Stapes
4- Tympanic Membrane (Eardrum)
5- Round Window
6- Eustachian Tube

10. Malleus, Incus, and Stapes (How hearing occurs)
When the eardrum moves, the hammer (malleus) moves with it and transfers the vibration to the anvil (incus)
Incus passes it on to the stirrup (stapes, which presses on the oval window
Movement at the oval window sets the fluids of the inner ear into motion
Excites the hearing receptors

11. Middle Ear Muscles
1. The Stapedius Attaches to Stapes,Contracts in Response to Loud sounds, chewing, speaking; Facial (VIIth cranial) nerve
2. The Tensor Tympani Helps open Eustachian tube

13. Otitis Media Most common ailment for children- Why???
Germs travel up eustachian tube-lodge in middle ear
Normal Infected
Ear infection video

14. INNER EAR Inner ear is for hearing and balance Two Halves:
Vestibular--transduces motion and pull of gravity
Cochlear--transduces sound energy
(Both use Hair Cells)

15. Cochlear Functions Semi-circular Canals Auditory (8th cranial) nerve
Transduction- Converting acoustical-mechanical energy into electro-chemical energy.
Frequency Analysis-Breaking sound up into its component frequencies

16. Organs of Equilibrium Vestibule: static equilibrium (not moving)
Semicircular canals: dynamic equilibrium (moving at a constant rate)
Figure 8.14a–b

17. Static Equilibrium
Figure 8.13a–b

18. Dynamic Equilibrium
The semicircular ducts in the semicircular canals each have a swelling called an “ampulla” at their base
Each ampulla contains a “crista ampullaris” that is a receptor made up of a cluster of hair cells with hairs projecting into a cap called the “cupula”
When the head position changes in the angular direction, inertia causes the endolymph in the semicirucular duct to lag behind, and as the cupula moves it drags across the endolymph bending the hair cells in the opposite direction
The bending results in increased impulse transmission in the sensory neurons

19. Inner Ear or Bony Labyrinth
Auditory nerve (VIII)- carries electrical impulses from cilia (in cochlea and semicircular canals) to the brain for interpretation
Figure 8.12

20. Mechanism of Hearing
“Organ of Corti” within the cochlear duct contain hearing receptors (hair cells)
Sound waves that reach the cochlea through vibrations of the eardrum, ossicles, and oval window set the cochlear fluids into motion
Waves from eardrum to the oval window = increase in amplitude
Receptor cells on the basilar membrane are bent by the movement of the tectorial membrane

21. Mechanism of Hearing
Length of fibers over basilar membrane tune specific regions to vibrate at specific frequencies
High pitch sounds = shorter fibers of basilar membrane and stimulate receptor cells close to the oval window
Low pitch = longer fibers and activate hair cells further along the cochlea
Hair cells transmit impulses along the VIII cranial nerve---auditory cortex in temporal lone---interpretation of sound/hearing occurs

22. Mechanisms of Hearing
Figure 8.16a–b

23. Review--Pathway of Sound
Sound waves enter pinna travel through auditory canal
Sound waves strike tympanic membrane causing vibrations (mechanical energy)
Vibrating TM causes ossicles to vibrate
Vibrating stapes bone at oval window generates movement of cochlear fluid (Hydralics)
Fluid movement stimulates cilia- lined cochlea
Cilia sends electrical impulses along auditory nerve to brain for interpretation