2. SENSORY PHYSIOLOGY: THE EAR

4. MEMBRANOUS LABYRINTH

5. 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 -- utricle: horizontal acceleration --saccule: vertical acceleration

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

7. Vestibular Apparatus: The otolith organ
The hair cells project in an endolymph-filled membrane the membrane contains CaCO3 crystals horizontal acceleration bends utricle hair cells; vertical acceleration bends saccule hair cells

8. Vestibular Apparatus: Semicircular canals

9. Neural Pathways

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

11. Student Activity
Meniere’s disease is thought to be due to pressure changes in the inner ear. Why do patients show up at the doctor complaining of dizziness and exhibiting Nystagmus?

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
This is a close up of the middle ear
The stapes is the last bone in the sequence
It vibrates the oval window, which mechanically vibrates the endolymph inside the cochlea The eustachian tube (auditory tube) is connected to the nasopharynx. It equalizess the pressure of the middle ear with the changing atmospheric pressure.

14. Hearing: The Cochlea

15. Hearing: Cross Section through Cochlea
the membrane that the hair cells are stuck into is called the tectorial membrane Fluid makes the basilar membrane bounce and this bends the hair cells and causes depolarization Action potential is sent to cranial nerve VIII

16. Hearing: PITCH
High pitch wiggles the basilar membrane closer to the oval window medium pitch wiggles the basilar membrane further along the path low frequency wiggles the basilar membrane further away
In the figure to the left, this is shown as 20,000 Hertz (the lowest frequency).

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.
May be 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 the cochlea to the 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