Outer Ear
What is the mode of operation for the outer ear?
Acoustic
What is the mode of operation for the middle ear?
Mechanical
What is the inner ear? And what does it consist of?
Series of canals and cavities within Petrous portion of temporal bone (aka bony labyrinth)
Cochlea and Vestibular system
What fluid is in the bony labyrinth and the membranous labyrinth? And what is the chemical makeup of the fluid?
-Bony labyrinth - perilymph (Na+ up, K+ down)
-Membranous labyrinth - endolymph (Na+ down, K+ up)
What is the primary function fo the auditory system?
To receive vibrations form the environment and convert them into neural information to be used by the brain.
What are the three main functions of the outer ear?
Protect, amplify, & localize
What are the two main functions of the middle ear?
Protect and transfer of sound
What are the three main characteristics of the oval window?
-separates air-filled ME space from fluid-filled IE
-Connected to the base of the stapes
-Vibrations from ME bones send into motion
What are the four main structures that make up the bony labyrinth?
Modiolus, osseous spiral lamina, scala tympani, and scala vestibuli
How much gain (in dB) does the outer ear (pinna) provide from 1500 - 7000Hz (frequencies important for speech understanding)?
15 - 20dB gain
What three components make up the lateral portions of the external auditory canal? And what purpose do they serve?
Cartilage, cerumen glands, & small hairs
Cerumen glands - secrete sebum and cerumen (antibacterial/fungal and genetic)
Small hairs - upright at enterance to repel objects and flat against canal medically to aid keratin migration
What 6 components make up the middle ear?
Tympanic membrane, epitympanic recess, ossicles, muscles, ligaments, and Eustachian tube
What are the two main characteristics of the round window?
-vibrates in opposite phase of oval window
-allows fluid within cochlea to move
What are the four main structures that make up the membranous labyrinth?
Helicotrema, basilar membrane, reissner’s membrane, and scala media
What is the difference between interaural intensity (level) difference (ILD) and interaural time difference (ITD)?
Interaural intensity (level) difference (ILD) helps localize high frequency sounds and includes head shadow effect.
Interaural time difference (ITD) helps localize low frequency sound.
What is the name of the bony growth that forms in the external auditory canal when it is exposed to cold water?
Exostosis
What is the purpose of the ligaments in the middle ear?
To help keep ossicles connected and in alinement
What are the three layers of the tympanic membrane?
Outer -> skin lining EAC - fibrous tissue layer - mucus tissue -> inner
Base: narrow, stiff = high frequencies
Apex: wide, loose = low frequencies
What are three ways the middle ear amplifies sound? And by how much dB?
1. Area ration advantage ~25dB gain
2. Curved membrane advantage ~6dB gain
3. Lever advantage ~2.2dB gain
IN TOTAL 33dB GAIN!!!
What is the name for the part of the temporal bone that houses the inner ear and sensory organs?
Petrous (it is not visible externally)
What are the two muscles in the middle ear? And what nerve are the connected to?
Stapedius - CN7
Tensor Tympani - CN5
What muscle cause the Eusachian tube to open?
Tensor veli palatini
Describe the summary of the transfer of sound from the hair cells to CN VII.
1. Hair cells are moved by shearing (bending) forces
2. Channels ar open-end and closed on the cilia (stereocilia)
-open trapdoor on stereocilia
-ions (esp. potassium) move in and out of hair cells
-voltage int eh hair cells changes (fluctuates)
3. Neurotransmitters are released at the bottom of hair cells
-neurotransmitters are chemicals that are used by sensory cells or nerve cells to convey information to other cells
4. Cochlear nerve picks up neurotransmitters and produce nerve impulses that transmit to the brain
What kind of waves’ pressure variations cause the basilar membrane to react?
Traveling waves