Otolaryngology Ear Embryology, Anatomy & Physiology PDF

OTOLARYNGOLOGY EAR EMBRYOLOGY, ANATOMY AND PHYSIOLOGY Dr. Joy C. Alvarez | August 6, 2024 OUTLINE I. Embryology A. Embryological Anomalies B. Derivatives of Pharyngeal Arches C. Summary of the Development of Exte...

OTOLARYNGOLOGY EAR EMBRYOLOGY, ANATOMY AND PHYSIOLOGY Dr. Joy C. Alvarez | August 6, 2024 OUTLINE I. Embryology A. Embryological Anomalies B. Derivatives of Pharyngeal Arches C. Summary of the Development of External Ear II. Anatomy and Physiology A. External Ear B. Middle Ear C. Inner Ear III. References IV. Appendix I. EMBRYOLOGY The development of the head and neck begins in the 4th-5th week of life. → There is a growth of mesenchymal tissue in the cranial region of the embryo that results in the formation of the Figure 2. Cross-section of embryo showing that each branchial arch has its own branchial arches (pharyngeal arches) with branchial nerve, artery and cartilage clefts (pharyngeal clefts). Branchial Arches → Divided by branchial pouches and branchial clefts In the endodermal side (inner surface): → Pharyngeal pouches/branchial pouches In the ectodermal side (outer surface): → Pharyngeal clefts/branchial clefts Figure 3. Section of embryo showing that each branchial arch has its own nerve, artery and cartilage A. EMBRYOLOGICAL ANOMALIES Normally, signaling from the ectoderm results in invasion of mesenchyme and gradual obliteration of the clefts and pouches. Branchial Cleft Cyst Type 1 Failure of the normal obliteration process of branchial clefts and pouches. Figure 1. Branchial arches and grooves Branchial Cleft Cyst Type 2 In the jaw region Branchial Cleft Cyst Type 3 & 4 Not common Trans # 1 Group 7: Reyes, Sacla, Salmon, Samson TC: Guillermo, Martinez 1 of 8  Exam-sensitive – familiarize and memorize the structures Note: According to doc, mahilig siya magpadraw. The structures she mentioned were external ear, tympanic membrane, and the membranes and scala in cochlea (baka label lang tong last, not sure) E. MIDDLE AND INNER EAR Middle Ear Figure 4. Branchial Cleft Cyst Type 1 B. DERIVATIVES OF PHARYNGEAL ARCHES (see Appendix 1. Derivatives of Pharyngeal Arches) C. SUMMARY OF THE DEVELOPMENT OF THE EXTERNAL EAR (see Appendix 2. Summary of the Development of the External Ear) Dr. Alvarez Failure of fusion of the Hillocks → Development of Pre-auricular sinus → Cleft ear Final Size of Auricle Figure 7. Development of middle ear → 5-6 years old 4th week → Proximal part of the pharyngeal pouch becomes constricted D. AURICLE forming the primordial eustachian tube → While distal end is expanding forming the primordial tympanic activity 8th week → Primordial ossicles are almost fully formed → The facial nerve runs over the stapes → Fusion of endoderm, mesoderm, and ectoderm (germ layers that contribute to the tympanic membrane) 20th week → Tympanic membrane and external auditory canal are already formed → Ossicles (malleus, incus, stapes) are well formed and in correct position Formation of Ossicles Figure 5. Development of the auricle Table 1. Development of the auricle 1st BRANCHIAL ARCH 2nd BRANCHIAL ARCH Hillocks 1-3 Hillocks 4-6 1. Tragus 4. Antihelix 2. Helical root 5. Antitragus 3. Helical crus 6. Lobule Figure 8. Formation of ossicles Figure 6. Structure of the auricle/pinna Trans # 1 Group 7: Reyes, Sacla, Salmon, Samson TC: Guillermo, Martinez 2 of 8 Table 2. Formation of ossicles → The aperture of the otic pit narrows into the mesoderm by the 1st PHARYNGEAL ARCH 2nd PHARYNGEAL ARCH meeting of its walls, creating an otic vesicle (Meckel’s) (Reichert’s) → Fusion of otic pit to form otic vesicle Epitympanum ossicles Mesotympanum ossicles → Head of malleus → Long process malleus → Body and short process → Long process incus of incus → Stapes suprastructure ▪ (B) Stapes footplate can also be derived from the otic capsule Inner Ear Figure 10. Development of Inner Ear Dr. Alvarez Crus commune nonampullare → Crus between superior semicircular and posterior semicircular canal II. ANATOMY AND PHYSIOLOGY A. EXTERNAL EAR Figure 9. Development of the inner ear Early in the 4th week → Thickening of the surface ectoderm on each side of the hindbrain (rhombencephalon) forms the otic placode ▪ From this thickening will proceed the development of the primordial inner ear Dr. Alvarez Otic placode invaginates → becomes otic pit → fuses to form otic vesicle or otic cyst Trans # 1 Group 7: Reyes, Sacla, Salmon, Samson TC: Guillermo, Martinez 3 of 8  Figure 11. External Ear Pinna/Auricle to the External Auditory Canal Borders → Superior: Temporalis muscle → Ant and Inf: Parotid Gland → Posterior: Mastoids → Superomedial: Epitympanum Function → "collector of sound" ▪ Sound localization − Interaural time difference o Difference in the arrival of sound in each ear depending on which ear is nearer to the source − Interaural amplitude difference o Signal to noise ratio o Signal is higher in ear nearer to source o Noise is higher in ear farther to the source → "acoustic antenna" → Amplifies sounds in 2-4kHz by 10 to 15dB Blood supply and drainage → Anterior/Posterior/Superior Auricular Arteries and Veins Innervation Figure 12. Tympanic membrane → Greater auricular nerve Tympanic Membrane → Auriculotemporal nerve Fusion of ectoderm, mesoderm, and endoderm giving rise to 3 → Auricular branch of vagus layers B. MIDDLE EAR Layers Function → Outer Cutaneous → Conduction → Inner Mucosal ▪ Conduct sound from the outer ear to the inner ear → Lamina Propria → Protection ▪ Radiate layer ▪ Creates a barrier that protects the middle and inner areas ▪ Circular layer from foreign objects Pars tensa - thinner inferior area ▪ Middle ear muscles may provide protection from loud → 80% of the tympanic membrane is composed of the pars sounds through the Acoustic Reflex tensa → Transducer → Has all 3 layers ▪ Converts acoustic energy to mechanical energy Pars flaccida / shrapnell membrane - thicker superior part of − Sound waves moves ossicles the tympanic membrane ▪ Converts mechanical energy to hydraulic energy → Lacks fibrous layer = flaccid − Sound moves from the air-filled middle ear to the Dr. Alvarez fluid-filled inner ear Right or left eardrum based on the cone of light of the ▪ Acoustic E → Mechanical E → Hydraulic E tympanic membrane → Amplifier → Right ear: cone of light in the 5 o’clock position ▪ Transformer action of the middle ear only about 1/1000 of Umbo the acoustic energy in air would be transmitted to the → Tip of the malleus is attached to the depression known as inner-ear fluids (about 30 dB hearing loss) the umbo Small part of the tympanic membrane located superior to that of the anterior and posterior malleolar folds lacks a fibrous layer and is attached superiorly to the bony ring of the notch of rivinus !Take note of the TM drawing and label! Tympanic Cavity Epitympanum Mesotympanum Trans # 1 Group 7: Reyes, Sacla, Salmon, Samson TC: Guillermo, Martinez 4 of 8  Hypotympanum Borders → Anterior: Internal Carotid Artery. → Posterior: Mastoid part of facial nerve → Superior: dura of middle cranial fossa → Inferior: bulb of jugular vein → Medial: Cochlea → Lateral: TM and bony ear canal Blood supply: Branches of External carotid artery → Middle meningeal → Ascending pharyngeal → maxillary → stylomastoid arteries Figure 15. Middle Ear Eardrum/Ossicular Chain: Impedance Matching Two mechanism → Eardrum: footplate ratio 20:1 (26 dB advantage) ▪ Surface area of the tympanic membrane to the stapes footplate → Ossicular chain lever ratio 1.3:1 (2.3 dB advantage) ▪ Difference of the length of manubrium of malleus (long arm) to long process of incus (short arm) Theoretical gain of eardrum/ossicular chain: 28 dB Actual gain or eardrum/ossicular chain: 20 dB Figure 13. Middle Ear Eustachian Tube Auditory Ossicles Malleus Incus Stapes Figure 14. Auditory Ossicles Intra Aural Muscles Tensor tympani → Innervated by CN V Stapedius → Innervated by CN VII Figure 16. Eustachian Tube Trans # 1 Group 7: Reyes, Sacla, Salmon, Samson TC: Guillermo, Martinez 5 of 8 Figure 12 ADULTS have longer, narrower and more angulated (45 degrees) eustachian tube CHILDREN have shorter, wider and less angulated eustachian tube → This is why otitis media is common among infants and children The lining of the eustachian tube is pseudostratified columnar epithelium w/ goblet cells Normally, the eustachian tube has the ff 2 openings: → NASOPHARYNGEAL (Proximal 3rd): closed at rest, open when one is talking , chewing or yawning ▪ That’s why when we try to equalize pressure, we do the Valsalva and Toynbee maneuvers to open the eustachian tube → TYMPANIC ORIFICE Functions Figure 18. Inner Ear → Pressure equalization → Mucociliary clearance and drainage → Middle ear protection C. INNER EAR Figure 19. Schematic Cross-sectional View of the Human Cochlea SCALA VESTIBULI → Begins at the oval window at the stapes footplate → Progresses up the spiral cocoon apex and communicates via the helicotrema to the scala tympani Figure 17. Vestibular System → Contains perilymph Bony Labyrinth SCALA TYMPANI 3 mm thick → Takes off from the helicotrema and spirals down the cochlea Lined by endosteum towards the round window Contains perilymph → Contains perilymph PARTS (housed in the bony labyrinth): SCALA MEDIA → Vestibule → 35 mm long, membrane-bound spiral tube along the cochlea → Semicircular canals → Between the scala vestibuli and scala tympani → Cochlea → Walls: Membranous Labyrinth ▪ Basilar membrane: divides scala media and scala Located within the bony labyrinth tympani Contains endolymph ▪ Reissner membrane: divides the scala media and scala Consists of the: vestibuli → Utricle ▪ Stria vascularis: maintains the endocochlear potential, → Saccule provides nutrition for the scala media, maintains → Semicircular ducts endolymph → Cochlear duct / Scala media → Contains endolymph ▪ Very important because it houses the organ of Corti Trans # 1 Group 7: Reyes, Sacla, Salmon, Samson TC: Guillermo, Martinez 6 of 8  Figure 20. Schematic showing Sound Propagation in the Cochlea Figure 20 Vibratory wave or acoustic energy → oval window → scala vestibuli → cochlear partition (helicotrema) → scala tympani → round window Because the pressure is higher in the scala vestibuli than in the scala tympani, a pressure gradient is created that causes Figure 23. Semicircular Canals and Parts of the Vestibulocochlear (VIII) Nerve of the cochlear partition to vibrate as a traveling wave the Right Ear Figure 23 Superior Semicircular Canal → Vertical → Right angle to the long axis of petrous bone Posterior Semicircular Canal → Vertical → Parallel to the long axis of petrous bone Lateral Semicircular Canal → Horizontal to the medial wall of the auditus to the mastoid bone → Above the facial nerve canal III. REFERENCES Alvarez, J. (2024). Powerpoint Presentation. Embryology, Anatomy and Physiology, Common Ear conditions and Diseases Kapil, A. (2023). Physiology or ear. Retrieved from https://www.slideshare.net/slideshow/physiology-of-ear-ugpptx/257796232 Figure 21. Mechanoelectrical Transduction of the auditory signal in the Organ of Corti Figure 21 Mechanoelectrical transduction of auditory signal depends on the recycling of potassium ions in the Organ of Corti → Vibratory wave → deflection of hair cell stereocilia (towards the tallest hair cell) → potassium influx → depolarization (resting potential in endolymph +60-100 mV relative to perilymph) → action potential at first level neurons of spiral ganglion → Potassium recirculated back through supporting cells and back into the perilymph via the stria vascularis Nice to Know: Figure 22. Mechanoelectrical Transduction in Hair Cells Trans # 1 Group 7: Reyes, Sacla, Salmon, Samson TC: Guillermo, Martinez 7 of 8  IV. APPENDIX Appendix 1. Derivatives of Pharyngeal Arches Appendix 2. Summary of the Development of the External Ear Trans # 1 Group 7: Reyes, Sacla, Salmon, Samson TC: Guillermo, Martinez 8 of 8