The Ear: Fri, Oct. 13

Front 1

Auricle:

Back 1

**funnels sound waves down toward external auditroy meatus

Parts:
1. helix: outer portion of elastic cartilage
2. lobule: most commonly pierced
3. tragus: "goat"
4. antihelix: located on internal aspect of helix
5. Darwin's tubercle: @ tip of some people's ears
6. concha

Functions of Ear:
1. appreciates actual hearing
2. internal ear appreciates vestibular functions and balance

Front 2

Innervation of Pinna:

Back 2

1. ACT nerve: anterior
2. lesser occipital: posterior
3. greater auricular: inferior
4. minor innervation from branches of CNs VII (concha region), IX, X (both tend to be on external ear)

**CC: Ramsay Hunt Syndrome: involves herpetic infection of geniculate ganglion of CNVII (affects vessicle of concha)

Front 3

Innervation of EAM:

Back 3

1. ACT: anterior 1/2 (as well as most of skin on anterior pinna
2. CNX: posterior portion (some help from CNIX, VII)

Reflexes due to innervation of EAM:
1. CNX has several branches that go to heart as well as cutaneous innervation to EAM; use of otoscope in some pts inadvertently stimuate other vagus branches-may result in decreases heart rate and subsequent fainting
2. CNX responsible for some cough reflexes
3. other people may experience emesis (vomiting) from cough reflexes
4. CNV3 (ACT) innervation: tooth pain can be referred to ear, and vice versa

Front 4

EAM:

Back 4

1. 1cm in kids, 2-3cm in adults
2. medial 2/3 bony, lateral 1/3 some elastic cartilage that forms pinna
3. skin lined with specific gland that secretes cerumen, waxy substance; ability to trap things
4. lymphatic drainage of EAM and auricle together with some tympanic memebrane is from 2 regions: a) superficial parotid, b) retroauricular-behind ear (commonly enlarged as result of otitis media

Front 5

Tympanic Membrane:

Back 5

**very thin area attached by limbus
**inferior aspect of manubrium or handle of malleus attaches and pulls: deepest part of TM--umbo

Innervation:
1. ACT, CNX (some CNVII,IX?): anterior aspect
2. tympanic plexus + chorda tympani: internal aspect

Front 6

Middle Ear:

Back 6

Muscles:
1. stapedius
2. tensor tympani: attaches to manubrium of malleus

Ear ossicles:
* smallest bones in body
* do not grow
* covered by mucous membrane instead of periosteum

1. malleus: "hammer", has superior head, neck, and handle or manubrium
2. incus: "anvil", both short and long processes
3. stapes: "stirrup", smallest, has neck, 2 crura, and footplate
**stapedial artery, an embryological vessel, courses through 2 crura to cause defect (shape) of footplate

Nerves:
1. chorda tympani
2. tympanic plexus

Recess:
1. epitympanic: houses malleus and most of incus

Front 7

Middle Ear as a Box:

Back 7

1. superiorly: middle cranial fossa separated from middle ear by thing plate of bone called tegmen tympani
2. epitympanic recess located just below middle cranial fossa
3. lateral wall, TM
4. medial wall, bulge from first part of turn of cochlea protruding from inner ear (promontory)with tympanic plexus laying over it; facial nerve
5. posterior wall: aditus leading into antrum, where mastoid air cells are covered with mucosa
6. anterior wall: opening of Eustachian tube; small canal that houses tensor tympani; ICA
7. floor: superior bulb of IJV

Front 8

Tympanic Plexus:

Back 8

**formed primarily by tympanic branch of CNIX
**arises near exit of CNIX from skull base via jugular foramen
**ascends up between opening for ICA adn jugular foramen in small canal called tympanic caniliculus
**enters middle ear, fans out on promontory, and mixes fibers with branches of facial and sympathetic fibers of caroticotympanic branch of IC sympathetic plexus
**parasympathetics from tympanic nerve, after mingling with 2 other branches, leave plexus and coalesce to form lesser pretrosal nerve
**lesser petrosal nerve perforates into middle cranial cavity, leaves through foramen ovale, adn synapses on otic ganglion-fibers travel to parotid gland for salivating

Front 9

Muscles:

Back 9

1. stapedius
a) smallest skeletal muscle
b) arises from pyramidal eminence
c) inserts into neck of stapes
d) function: pull on stapes away from inner ear: dampens loud sounds
e) innervated by CNVII: injury results in hyeracusis (often seen Bell's palsy pts)

2. tensor tympani:
a)runs in groove just above Eustachian tube
b) some attachment to tube
c) some attachments to greater wing of sphenoid and petrous part of temporal bone
e) attaches to malleus
f) helps stapedius in dampening sounds
g) involved in swallowing, may be somewhat continuous with tensor veli palatine (both innervated by CNV3)
h) takes a turn around processus cochlearformis

Front 10

Chorda Tympanic:

Back 10

**comes off facial ~5mm superior to where facial exits through stylomastoid foramen
**enters and leaves in convoluted fashion
**enters middle ear via posterior ider, travels around junction of neck and handle of malleus just superior to where tensor tympani attaches into malleus
**leaves via anterior ider, which takes it to petrotympanic fissure-foudn in lateral aspect of mandibular fossa on inferior
**anterior tympanic artery travels with chorda tympani in fissure
**chorda tympani runs over malleus which is attached to TM (runs near upper part)

**CC: injury does not result in loss of salivation but some complain of food tasting metallic; submandibular gland may decrease metallic taste

**lower portion of TM has less blood supply (draining out middle ear)

Front 11

Eustachian tube:

Back 11

**mostly cartilaginous
**posterolateral 1/3 is bony
**just anterolateral of opening of carotid canal
**opening into nasopharynx is widest portion
**@ junction of cartilaginous and bony parts is narrowest part called isthmus
**usually mostly collasped, opens when need to equalize pressure between middle ear and nasopharynx

Innervation:
1. tympanic plexus
2. nervous spinosus innervates some of cartilaginous portion

**tensor veli palatini is main opener of tube by pulling

Front 12

Inner Ear:

Back 12

**footplate of stapes is secured by annular ligament into oval window
**as air strikes TM, pushes it, makes head of malleus fold laterally, TM pulls incus and its long process pushes like a piston, this pushes stapes into oval window

Front 13

Inner ear parts:

Back 13

1. bony labyrinth: has vestibule within which round and oval windows are found; perilymph within, and it coats inner endolymph and cochlear duct (like CSF); has internal membranous labyrinth, basically soft tissue lining of bony portion

**mechanical push of stapes sets in motion wave of fluid around endolymph-lined cochlear duct for hearing

2. cochlea: more anterior than canals; cochlear ducts filled with endolymph

3. semicircular canals (3): lateral canal parallels horizontal part of facial nerve prior to turning to exit stylomastoid foramen; have semicirucular ducts within

4. arcuate eminence: found on petrous ridge, serves as landmark for anterior semicircular canal

5. helicotrema: two scala communicate with each other @ tip of cochlea

6. utricle and saccule: 2 small communicating sacs in vestibule of bony labyrinth

8. ampullar

9. modiolus: central core of bone around cochlear nerve

10. scala vestibuli (oval window) and scale tympani (round window): work to mechanically push stapes; filled with perilymph

11. vestibulocochlear nerve (CNVIII): some fibers travel to vestibular apparatus, semicircular canals