10.7 Sense of Hearing

1. 10.7 Sense of Hearing By: Riki Byler, Rebecca Gambrell, &Trent Lackey,1st even

2. What is hearing? • The organ of hearing, the ear, has outer, middle, and inner parts. The ear also functions in the sense of equilibrium.

3. Outer (External) Ear The outer ear consists of three parts: • Auricle= outer funnel-like structure. • External Acoustic Meatus (External Auditory Canal)= S-shaped tube that leads inward through the temporal bone for 2.5 cm. • Eardrum= It has an oval margin and is cone-shaped, with the apex of the cone directed inward.

4. Auricle • The auricle of the ear helps collect sound waves traveling through the air and directs them into the external acoustic meatus. • Acts as a funnel amplifying sound directing it into the ear canal.

5. External Acoustic Meatus • The auricle of the ear helps collect sound waves traveling through the air and directs them into the external acoustic meatus. The meatus terminates with the eardrum.

6. Eardrum • The eardrum is a semitransparent membrane covered by a thin layer of skin on its outer surface and by mucous membrane on the inside. • Sound waves that enter the external acoustic meatus change the pressure on the eardrum, which moves back and forth in response and reproduces the vibrations of sound waves.

7. Middle Ear (Tympanic Cavity) • An air filled space in the temporal bone. • Contains three small bones make up the auditory ossicles: • Malleus • Incus • Stapes

8. Oval Window • Ligaments hold the stapes to an opening in the wall of the tympanic cavity called the oval window, which leads into the inner ear. • Vibration of the stapes at the oval window moves a fluid within the inner ear which stimulates the hearing receptors.

9. Auditory Tube • An auditory tube (eustachian tube) connects each middle ear to the throat. This tube conducts air between the tympanic cavity and the outside of the body by way of the throat and mouth. • The auditory tube helps maintain equal air pressure on both sides of the eardrum.

10. Inner (Internal) Ear • The inner ear is a complex system of communicating chambers and tubes called a labyrinth.

11. Labyrinth • Each ear has two parts of the labyrinth: the osseous, and the membranous. • The ossesous is a bony canal in the temporal bone. • The membranous is a tube that lies within the osseous and has a similar shape. • The Labyrinth contains two fluids: the perilymph and the endolymph.

12. The parts of the labyrinth include three semicircular canals, which provides a sense of equilibrium, and a cochlea which functions in hearing.

13. Cochlea • The cochlea has a bony core and a thin, bony shelf that winds around the core like the threads of a screw. The shelf divides the osseous labyrinth of the cochlea into upper and lower compartments. • The upper compartment, called the scalavestibuli, leads from the oval window to the apex of the spiral. • The lower compartment, the scala tympani, extends from the appex of the cochlea to a membrane covered opening in the wall of the inner ear called the round window. • The spiral organ has hearing receptors. It is located on the upper surface of the basilar membrane and stretches from the apex to the base of the cochlea.

15. Auditory Nerve Pathway • The nerve fibers associated with hearing enter the auditory nerve pathways, which pass into the auditory cortices of the temporal lobes of the cerebrum, where they are interpreted.