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BIOL 2005 (40)

The External Ear

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BIOL 2005
Elizabeth Nisbet

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) 3 ii. Cranial Nerves: CN V , 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 2 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 V 3 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 window—fenestra vestibule; where stapes touches inner ear; opens to scala vestibuli v. Round window—fenestra 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 1. oval window (fenestra vestibule)—closed by footplate of stapes
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