Exam 3 Week 14 ppt 8 outer, middle, inner ear Flashcards
Function of auditory system
Detects and analyzes sounds from the environment
What makes up the outer ear?
- Consists of pinna & external auditory meatus
- Tympanic membrane separates outer and middle ear
What makes up the middle ear?
-Within the temporal bone
-Air-filled cavity Contains:
3 ear ossicles: malleus, incus, and stapes
2 muscles – tensor tympani & stepedius
What happens inside middle ear?
Vibrations of tympanic membrane conducted by ear ossicles to vibrate oval window
Why is there a 25 fold increase in pressure on oval window compared to tympanic membrane?
- Different size of membranes
- Mechanical advantage ear ossicles
What can control conduction of the vibrations in middle ear?
Tensor tympani
Tensor tympani innervated by ______
CN V
What controls controls the movement of the stapes?
Stapedius
Stapedius innervated by _________
CN VII
How do Stapedius and tensor tympani work?
Reflexive contraction to lessen movement & sound conduction (lower the acuity of the sound)
What makes up the inner ear?
Separated from middle ear by oval & round windows
- Cochlea- Spiral bony container, wound around central core – Modulus, bipolar cells of spiral ganglion in modulus
- Fluid filled- Perilymph between bony & membranous labyrinth, Several membranous structures form the cochlear duct, Endolymph in cochlear duct
- 3 chambers- Scala vestibuli (1) & scala tympani (2) – filled with perilymph Scala media (3) (cochear duct), formed by vestibular & basilar membranes, filled with Endolymph
The pathway of vibrations in the inner ear
- Vibrations in perilymph produced by vibration of oval window
- Vibrations carried down the scala vestibuli & around the heliotrema into the scala tympani
- This vibrates the basilar membrane
Basilar Membrane- 3 points to know
- Varies in width and stiffness from base to apex of cochlea
- Thinner & more compliant near oval window – vibrated by higher frequency vibrations of perilymph
- Thicker & stiffer toward cochlear apex – vibrated by lower frequency vibrations of perilymph
Tonotopic map of cochlea
Highest frequencies base
Lowest frequencies apex
Where does auditory transduction occur?
in the hair cells of the organ of Corti
Structures of the organ of Corti
- Outer & inner rows of hair cells rest on basilar membrane
- Tectorial membrane is gelatinous shelf resting on stereocilia of the outer hair cells
- Bipolar cell processes of the spiral ganglion surround base of hair cells
What holds together structures of the organ of Corti?
supporting cells
Where are the hair cells?
Positioned within the endolymph-filled scala media
Numbers and hair cells
3500 flask-shaped inner hair cells
>15,000 cylindrical outer hair cells
Differences between inner and outer hair cells (7)
- Inner on least flexible portion of basilar membrane
- Outer on most flexible portion
- Inner hairs do not touch tectorial membrane – outer do
- Outer hair cells depolarized by pivoting hair cells against tectorial membrane
- Inner hair cells depolarized by movement of endolymph in inner spiral sulcus
- 95% of afferent axons in cochlear nerve receive their input from inner hair cells
- Only 5% receive it from outer hair cells
Role of outer hair cells (3)
- Outer hair cells have motor proteins activated by depolarization of hair cell
- Shortens outer hair cell
- Amplifies movement of basilar membrane up to 100 fold