1. SENSORY PHYSIOLOGY: THE EAR

3. Inner ear Vestibular apparatus- Cochlea For equilibrium
Semicircular canals
Vestibule
Utricle
Saccule
Cochlea
For hearing

4. Vestibular apparatus Two senses
Static equilibrium – when you are still; detects non- movement and positions of body and head
Dynamic equilibrium – detects body position in motions, such as rotation; sends signals to the brain to maintain balance

5. Vestibular Apparatus: Mechanism
Bending of hair cells results in the production of action potentials Bending opens up ion channels  K+  in  depolarization
Bent towards kinocilium: depolar- ization bent away from kinocilium: hyperpolarization

6. Vestibular Apparatus: Equilibrium
Two parts: 1) Semicircular canals -- rotational, or angular, acceleration -- oriented in 3 planes -- help us maintain balance when turning our head, spinning, tumbling 2) Otolith organs (utricle and saccule) --provide information about linear acceleration (static) -- utricle: horizontal acceleration --saccule: vertical acceleration

7. Static Equilibrium (the otolith organs) review
Maintained by organs located in the vestibule (in inner ear)
Contains 1) utricle, and 2) saccule
Both involved in detecting static equilibrium
Utricle – horizontal acceleration (car)
Saccule – vertical acceleration (airplane)
AKA “otolith organs”
Send sensory impulses to the brain via the vestibular nerve (CN-VIII)
Contain “macula”… a structure with hair cells that detect movement of fluid (fluid moves because “crystals” move

8. Vestibular Apparatus: The Otolith organ
How do the hair cells bend?
Otoliths (crystals) fall against them.
The hair cells project in an endolymph-filled membrane the membrane contains the CaCO3 crystals horizontal acceleration bends utricle hair cells; vertical acceleration bends saccule hair cells

9. Vestibular Apparatus: Semicircular canals

10. Neural Pathways

11. VESTIBULOOCULAR REFLEX
Click here for a 30 second you tube video.

12. Hearing: The Cochlea
Sound waves enter the auditory canal and vibrate the tympanic membrane Middle ear: malleus, incus, stapes oval window

13. Hearing: The Middle Ear
The stapes is the last bone in the sequence
Stapes vibrates  oval window, vibrates endolymph inside cochlea
ALSO: Eustachian tube (auditory tube) is connected to nasopharynx.
Equalizes pressure of middle ear with changing atmospheric pressure.

14. Hearing: The Cochlea
Sounds of different pitch cause vibrations of basilar membrane in different regions
Low (500 Hz) vibrate membrane towards apex
High (20,000 Hz) vibrate membrane towards base of cochlea

15. Hearing: The Cochlea
Scala vestibuli – outer tube containing perilymph  contiguous with Scala tympani
Perilymph vibrates tectorial membrane

16. Hearing: Cross Section through Cochlea
Tectorial membrane vibrates  Hair cells stuck into membrane  vibrate Basilar membrane vibrates  causes K+ (from endolymph) to enter hair cells Action potential is sent to cranial nerve VIII

17. Neural Pathways for Hearing
Sensory neurons from the vc nerve synapse in the medulla oblongata
neurons extend from medulla to midbrain
neurons extend from midbrain to auditory cortex of temporal lobe

18. Hearing Impairment
Conduction deafness: Sound waves are not conducted from the outer to the inner ear.
due to
a buildup of earwax,
too much fluid in the middle ear,
damage to the eardrum, or
overgrowth of bone in the middle ear
Impairs hearing of all sound frequencies
Can be helped by hearing aids

19. Hearing Impairment, cont.
Sensorineural/perceptive deafness: Nerve impulses are not conducted from cochlea to auditory cortex.
May be due to damaged hair cells (from loud noises)
May only impair hearing of particular sound frequencies and not others
May be helped by cochlear implants
Presbycusis – age-related hearing impairment