1. Special Senses Hearing

2. Ear is a very sensitive structure. – The sensory receptors convert vibrations 1,000 times faster than the photoreceptors of the eye can respond to light

3. Structure Three main regions – Outer Ear Collects sounds waves and channels them inward – Middle Ear Conveys the sound vibrations to the oval window – Inner Ear Which houses the receptors for hearing and equillibrium

4. Structure of the Ear

5. Outer Ear Consists of: – Auricle – External Auditory canal – Eardrum

6. Auricle Part of the ear you see Structure: – Skin covered flap of elastic cartilage Function: – Collect sound waves and direct them toward external auditory canl

7. External Auditory Canal Structure: – Two structures help keep out invaders Few Hairs Ceruminous gland – Secret cerumen (earwax) Function: – Curved tube directs sound waves toward the eardrum

8. Eardrum A.k.a. Tympanic membrane Structure: – Thin, semitransparent partition between external auditory canal and the middle ear Function: – Changes sounds waves into vibrations

9. Middle/Inner Ear

10. Middle Ear Small, air-filled cavity between eardrum and inner ear Consists of – Auditory tube – Auditory ossicles

11. Auditory Tube Opening in the anterior wall of the middle ear leads to auditory tube (Eustachian tube) – Connects the middle ear to upper portion of throat – When it is open, air pressure equalizes on both sides of the eardrum When closed – if air pressure builds the eardrum can rupture – Swallowing or yawing opens up the auditory tube

12. Auditory Ossicles 3 tiny bones span across the middle ear by means of ligaments – Malleus – Incus – Stapes Forms a small opening, oval window, where the inner ear begins Function – To pass the vibration from the outer ear to the inner ear

13. Ossicles

14. Inner Ear Divisions – Bony Labyrinth Series of cavities in the temporal bone, including the cochlea, vestibule, and semicircular canals Contains a fluid called perilymph – Inner membranous labyrinth Series of sacs and tubes with the general shape as the bony labyrinth Contains a fluid called endolymph

15. Bony Labyrinth Cochlea – Sense organ for hearing Semicircular canals and vestibule – Sense organs for balance and equilibrium

16. Inner Ear

17. Process of Hearing Auricle directs sound waves to external auditory canal External auditory canals continues to direct sounds waves to the eardrum Eardrum converts sound waves into vibrations Eardrum vibrates the malleus Malleus vibrates the incus then to the stapes Stapes move back and forth and pushing oval window in and out Movement of oval window sets up the fluid pressure waves in the perilymph of the cochlea Fluid pressure waves build and eventually cause the endolymph to transmit waves to the hairs inside the cochlea Hairs are stimulated they release neurotransmitter molecules, change waves into electrical impulses Electrical impulses to the brain through the auditory nerve