Anatomy and Embryology of the Ear PDF

Anatomy and Embryology of the Ear Keely Cassidy, PhD Wittson Hall 2006 [email protected] https://www.sciencedirect.com/science/article/abs/pii/S1010518217304493  62 year old man History of recurrent aseptic meningitis Presented with fever and headache, developed bilater...

Anatomy and Embryology of the Ear Keely Cassidy, PhD Wittson Hall 2006 [email protected] https://www.sciencedirect.com/science/article/abs/pii/S1010518217304493  62 year old man History of recurrent aseptic meningitis Presented with fever and headache, developed bilateral auricular swelling and redness CSF analysis indicated aseptic meningitis Auricular biopsy indicated inflammation from relapsing polychondritis In rare cases, other types of connective tissue (here the meninges) can be affected Corticosteroid treatment improved symptoms Left ear, pre-treatment Left ear, post-treatment Objectives Describe the structure and components of the external ear. Describe the structure and components of the middle ear and its relationship to surrounding structures. Describe the course of the facial nerve through the middle ear cavity including each of its intracranial branches. Describe the structural organization of the inner ear. Explain the steps of auditory transduction. Distinguish between the structures and functions of the vestibular and cochlear system. Apply knowledge of the ear to explain the anatomical basis of a clinical problem or intervention (e.g., cauliflower ear, otitis media, tympanostomy tubes). Assess how an ear infection could affect surrounding structures and function. Describe the embryological origin of each component (external, middle, internal) of the ear. Relate the stages of ear development with general embryogenesis. Predict the embryological basis of common birth defects relating to the ear (e.g., auricular malformations, congenital hearing loss).  Inner ear (oval window to round window) Regions of the Ear Petrous part of temporal bone Vestibular Its receptors respond to apparatus fluid waves for perception of balance… External ear Cochlea Receive mechanical energy and (through tympanic membrane) convert into fluid waves Collect, funnel sound waves Its receptors respond to fluid Protect tympanic membrane waves for perception of sounds… Middle ear (tympanic membrane to oval and round windows) Amplify and convert sound waves into mechanical energy Provide pressure release Pharynx External ear Auricle aka, Pinna Helix Triangular fossa Elastic cartilage covered in skin Location where sounds waves enter ear and begin to be transferred into mechanical energy via vibrations Oriented to best detect sound from front and sides Scaphoid fossa Antihelix Tragus Concha Cymba Cavity Lobule Antitragus External ear lateral views Auricle Auricular muscles are fairly weak innervation via CN VII Arterial supply is robust and mainly via posterior auricular artery Comes superficially from skin and dives deep to supply cartilage Venous drainage is minimal medial view posterior view Qualitative Analysis of Canine Guilt Based Upon Auricular Position: Case Study of Gunner, a Generally Good Boi if a Bit of a Dumdum Level of Guilt This study was neither IRB approved nor peer-reviewed. Participant compensation was provided in the form of noms. Degree of Ear Retraction Perichondrial hematoma (aka, Cauliflower ear) Permanent, acquired deformity to external ear due to Process: blunt trauma (often seen in wrestling and boxing) trauma → auricular hematoma, disruption of skin- Treatment: cartilage connection → cartilage loses blood Prevention via protective headgear supply, venous blood can’t drain due to Drain asap, pack/compress, and hope for the best inflammation → cartilage dies → fibrotic scarring Recurrence is common complication → shriveled, uneven, pale appearance of auricle Draining an auricular hematoma Packing treatment R L External ear External auditory canal aka, External acoustic meatus Lined by skin with hair and glands that produce cerumen ~2.5 cm sigmoid canal angled anteroinferiorly Cerumen (aka, ear wax) is protective but can become Walls of lateral 1/3 are cartilage, medial 2/3 are bone excessive and/or impacted Embryologically develops from 1st pharyngeal cleft Canal with excessive Canal with normal amount cerumen of cerumen External ear – Middle ear Tympanic membrane Known by laymen as “eardrum” Visualized via otoscope examination ~1 cm diameter circular structure Semitransparent, trilaminar membrane External to internal: skin, connective tissue, mucus membrane Otoscopic view of tympanic membrane Sounds waves vibrate the tympanic membrane Oriented to best detect sound from front and sides Embryologically develops from 1st pharyngeal membrane External to internal: surface ectoderm, head mesoderm, endoderm Endoscopic view of middle ear via myringotomy http://sydneyentclinic.com/sean-flanagan/patient-resources/hearing-loss/tympanic-membrane-perforation/ External ear – Middle ear Tympanic membrane Divided into quadrants Pars flaccida ~11:00-1:00 region Pars flaccida Pars tensa everything else – Malleolar stria – marks malleus’s manubrium – Umbo – point of greatest concavity Malleolar stria – Cone of light – artifact of examination; projects anteroinferiorly in healthy ear Is this image from a right or left ear? ____________ Umbo Deviation from these expected findings may indicate retraction, bulging, inflammation, etc Cone of light Pars tensa http://sydneyentclinic.com/sean-flanagan/patient-resources/hearing-loss/tympanic-membrane-perforation/ External ear – Middle ear R ear, anterior view Sensory Innervation (anterior wall removed) Complex innervation due to embryological development All pharyngeal arches are involved in some way Great auricular nerve (C2, C3) majority of auricle Auriculotemporal nerve (branch of CN V3) tragus and superoanterior region; superior and anterior walls of external acoustic meatus; superoanterior 2/3 of external surface of tympanic membrane Auricular nerve (branch of CN X) concha; posterior and inferior walls of external acoustic meatus; posteroinferior 1/3 of external surface of tympanic membrane CN VII eminence of concha CN IX (not pictured) R tympanic membrane, internal surface of tympanic membrane external surface Middle ear Middle Ear In petrous part of temporal bone Air filled cuboidal chamber lined with mucous membrane Contains many important and delicate structures Embryologically develops from 1st pharyngeal pouch anterior view Important connections: to nasopharynx, via auditory tube aka, pharyngotympanic tube, Eustachian tube Equalizes pressure between middle ear and pharynx Allows drainage (route for URTI movement) Pharyngeal tonsils adjacent to pharyngeal opening (when inflamed → adenoids) to mastoid air cells, via mastoid antrum Protect inner ear from temperature and pressure fluctuations superior view Middle ear Middle Ear Contains significant bones, muscles, nerves Contains minor vessels, mucus membrane Epitympanic recess space superior to plane of tympanic membrane contains mastoid antrum Tympanic cavity (proper) space directly internal to tympanic membrane Understanding anatomical relationships to surrounding structures is clinically relevant because _______________________________. anterior view Middle ear 3 If you are sitting in the tympanic cavity, there are four exits: 1. Push through a membrane and walk into a tunnel… External auditory canal 1 2. Slide down a wet tunnel… Auditory tube 3. Climb out a tiny hole… Mastoid antrum → Mastoid air cells 4. Wiggle out through a round window… 3 Round window → Cochlea 2 4 Endoscopic view of middle ear via myringotomy Middle ear If you are sitting in the tympanic cavity, there are six walls: Direction Wall Related anatomical structures Superior (roof) Tegmental middle cranial fossa (meninges, temporal lobe, pituitary gland) Inferior (floor) Jugular internal jugular vein sigmoid sinus posterior cranial fossa (meninges, cerebellum, some CNs) Lateral Membranous tympanic membrane external acoustic meatus Medial Labyrinthine inner ear CN VII Anterior Carotid auditory tube (not shown in image) internal carotid artery Posterior Mastoid mastoid air cells CN VII anterior view Middle ear Contents of Middle Ear: Auditory Ossicles Three extremely dense bones covered by mucous membrane (not periosteum) and connected via synovial joints Numerous ligamentous and muscular attachments to walls Embryologically develop from 1st (malleus, incus) or 2nd (stapes) pharyngeal arches’ cartilage Malleus hammer Handle/manubrium embedded in tympanic membrane Incus anvil Stapes stirrup Footplate attached to oval window Middle ear Function of Auditory Ossicles 1. Sound waves encounter the tympanic membrane and are converted into mechanical energy (waves) 2. Waves are progressively amplified (10x) through ossicular chain before entering the inner ear at the oval window 3. If waves persist after the inner ear, that pressure is released back into the middle ear via the round window. The auditory ossicles are a very reliable source of ancient DNA because of their strength and location (compared to cochlea). Middle ear Contents of Middle Ear: Muscles Two muscles attach auditory ossicles to middle ear walls, on opposite sides Embryologically develop from 1st (tensor tympani) or 2nd (stapedius) pharyngeal arches’ muscle Tensor tympani Attaches anterior wall to malleus’ manubrium Innervated by CN V3 Stapedius Attaches posterior wall to stapes Innervated by CN VII R ear, superolateral view (very deep) Middle ear Function of Middle Ear Muscles Contract reflexively in response to loud auditory stimuli (acoustic startle response) High-pass filter = higher frequencies are allowed in easier than low frequencies Tensor tympani Action: To tense the tympanic membrane = Decrease waves moving through ossicular chain 16% of humans can voluntarily contract the tensor tympani Stapedius Action: To tense the ossicular chain = Decrease waves moving through ossicular chain Middle ear Contents of Middle Ear: Nerves Chorda tympani nerve Branch of CN VII that crosses between malleus and incus Does not have any protection within tympanic cavity Vulnerable! After tympanic cavity, eventually merges with lingual nerve (branch of CN V3) Actions: Convey taste sensation from anterior 2/3 of tongue Carry preganglionic parasympathetic fibers to the submandibular ganglion Tympanic plexus Branches of CN IX on medial wall of tympanic cavity After tympanic cavity, forms lesser petrosal nerve Action: Carry preganglionic parasympathetic fibers to the otic ganglion Injury to these nerves during otological surgeries have the capacity to affect taste and/or salivatory abilities. https://meetingarchive.ami.org/2020/project/chorda-tympani-pathway/ Otitis media (aka, Middle ear infection) Collection of pus and fluid in middle ear, inflammation of mucous membranes Often secondary to upper respiratory tract infections Potential consequences: Earache Bulging, red tympanic membrane Blockage of auditory tube Ruptured tympanic membrane Time lapse of progression of otitis media Hearing loss due to scarring on auditory ossicles Fracture wall(s) of tympanic cavity and spread of infection Note the changes to the cone of light. Healthy tympanic membrane Inflamed tympanic membranes with mild, moderate, and severe bulging. Tympanostomy tubes (aka, pressure equalization/grommet/myringotomy tubes) Small tubes placed in tympanic membrane to keep Children