BIOL110 Lecture Notes - Vestibulocochlear Nerve, Cochlear Duct, Sound Intensity

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30 Jan 2013
The Ear
I. External Ear
a. Auricle (Pinna)
i. Function—act as collecting device for sound wave; localize source
ii. Anatomical Features: Helix, antihelix, tragus, antitragus, concha, lobule
b. External Acoustic Meatus (from concha to tympanic membrane)
i. Function—channels waves to TM; protects middle ear; acoustic resonator
ii. Anatomical Features
1. lateral 1/3==cartilaginous
2. medial 2/3==bony
c. Innervation
i. Spinal nerves (cervical plexus): greater auricular (C2,3) & lesser
occipital (C2)
ii. Cranial Nerves: CN V3, CN VII, CN X
II. Middle Ear (tympanic cavity)
a. Function
i. Transfer of sound waves from gas to liquid medium (b/c sound waves
don’t have sufficient energy alone)
ii. Protective response to loud sounds (via tensor tympani & stapedius mm)
iii. Maintenance of similar pressures on both sides of TM
b. Bones (ossicles)
i. From lateral to medial: malleus, incus, stapes (from 2nd brachial arch)
ii. Held in place by small ligaments
iii. Since malleus is longer than incus => acts like lever arm => amplifies
pressure waves
iv. Large pressure waves => oscillation & stapes “kicks” oval window
c. Muscles
i. Tensor tympani—associated w/ Malleus, inn by CN V3
ii. Stapedius—associated w/ stapes; inn by CN VII
d. Innervation running through
i. Trigeminal (CN V), Facial (CN VII), Corda Tympani (CN VII),
Tympanic Plexus (mostly CN IX)
e. Other Structures
i. Tympanic Membrane (TM)—eardrum; separates middle ear from EAM
ii. Auditory tube—thin cartilaginous tube running from middle ear to nasal
cavity; normally closed but opens when yawning, etc
iii. Promontory—covered by tympanic nerve (CN IX)
iv. Oval windowfenestra vestibule; where stapes touches inner ear; opens
to scala vestibuli
v. Round windowfenestra cochleae; opens to scala tympani
III. Inner Ear (labyrinth)
a. Bony (osseous) labyrinth
i. Semicircular canals (3)—superior, lateral, posterior; used for balance
(vestibular system)
ii. Vestibule—connection between vestibular system and cochlea
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