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The ear
- 3. THE EAR THE EXTERNAL EAR ⸠ear can be divided into three parts ⸠external ⸠middle ⸠inner ⸠external ear can be divided functionally and structurally into two parts ⸠auricle (or pinna) ⸠external acoustic meatus â ends at the tympanic membrane
- 5. THE EAR THE EXTERNAL EAR: AURICLE ⸠auricle is a paired structure found on either side of the head ⸠functions to capture and direct sound waves towards the external acoustic meatus ⸠mostly cartilaginous structure ⸠lobule - only part not supported by cartilage ⸠cartilaginous part of the auricle ⸠forms an outer curvature - the helix ⸠second innermost curvature runs in parallel with the helix â the antihelix ⸠antihelix divides into two cura ⸠inferoanterior crus ⸠superoposterior crus
- 6. THE EAR THE EXTERNAL EAR: AURICLE ⸠concha - hollow depression in the middle of the auricle ⸠continues into the skull as the external acoustic meatus ⸠acts to direct sound into the external acoustic meatus ⸠tragus - an elevation of cartilaginous tissue immediately anterior to the beginning of the external acoustic meatus ⸠opposite the tragus is the antitragus
- 9. THE EAR THE EXTERNAL EAR: EXTERNAL ACOUSTIC MEATUS ⸠a sigmoid shaped tube that extends from the deep part of the concha to the tympanic membrane ⸠walls ⸠external 1/3 - formed by cartilage ⸠inner 2/3 - formed by temporal bone ⸠does not have a straight path - travels in an S-shaped curve as follows: ⸠initially it travels in a superoanterior direction ⸠then turns slightly to move superoposteriorly ⸠ends by running in an inferoanterior direction
- 10. THE EAR THE EXTERNAL EAR: TYMPANIC MEMBRANE ⸠lies at the distal end of the external acoustic meatus ⸠a connective tissue structure, covered with skin on the outside and a mucous membrane on the inside ⸠membrane is connected to the surrounding temporal bone by a ďŹbrocartilaginous ring ⸠translucency of the tympanic membrane allows structures within the middle ear to be observed during otoscopy
- 11. THE EAR THE EXTERNAL EAR: TYMPANIC MEMBRANE ⸠the handle of malleus attaches to the the inner surface of the tympanic membrane at a point called the umbo ⸠handle of malleus continues superiorly, and at its highest point is a small projection called the lateral process of the malleus ⸠parts of the tympanic membrane moving away from the lateral process are called the anterior and posterior malleolar folds
- 14. THE EAR THE EXTERNAL EAR: VASCULATURE ⸠external ear is supplied by branches of the external carotid artery: ⸠posterior auricular artery ⸠superďŹcial temporal artery ⸠occipital artery ⸠maxillary artery (deep auricular branch) ⸠only supplies the deep aspect of the external acoustic meatus and tympanic membrane ⸠venous drainage is via veins following each of these arteries
- 15. THE EAR THE EXTERNAL EAR: INNERVATION ⸠sensory innervation to the skin of the auricle comes from numerous nerves: ⸠greater auricular nerve (branch of the cervical plexus) ⸠innervates the skin of the auricle ⸠lesser occipital nerve (branch of the cervical plexus) ⸠innervates the skin of the auricle ⸠auriculotemporal nerve (branch of the mandibular nerve) ⸠innervates the skin of the auricle and external auditory meatus ⸠branches of the facial and vagus nerves ⸠innervates the deeper aspect of the auricle and external auditory meatus
- 16. THE EAR THE EXTERNAL EAR ⸠Clinical Note ⸠some individuals can complain of an involuntary cough when cleaning their ears ⸠this is due to stimulation of the auricular branch of the vagus nerve ⸠vagus nerve is part of cough reďŹex ⸠Lymphatics ⸠external ear drains into the superďŹcial parotid, mastoid, upper deep cervical and superďŹcial cervical nodes
- 17. THE MIDDLE EAR
- 18. THE EAR THE MIDDLE EAR ⸠lies within the temporal bone ⸠extends from the tympanic membrane to the lateral wall of the inner ear ⸠main function of the middle ear ⸠transmit vibrations from tympanic membrane to the inner ear via the auditory ossicles
- 20. THE EAR THE MIDDLE EAR: PARTS OF THE MIDDLE EAR ⸠can be divided into two parts: ⸠tympanic cavity ⸠located medially to the tympanic membrane ⸠contains three small bones known as the auditory ossicles: ⸠the malleus, incus and stapes ⸠transmit sound vibrations through the middle ear ⸠epitympanic recess ⸠a space superior to the tympanic cavity, which lies next to the mastoid air cells ⸠malleus and incus partially extend upwards into the epitympanic recess
- 22. THE EAR THE MIDDLE EAR: BORDERS ⸠middle ear can be visualized as a rectangular box ⸠Roof ⸠formed by a thin bone from the petrous part of the temporal bone ⸠separates the middle ear from the middle cranial fossa ⸠Floor ⸠known as the jugular wall ⸠consists of a thin layer of bone ⸠separates the middle ear from the internal jugular vein ⸠Lateral wall ⸠made up of the tympanic membrane and the lateral wall of the epitympanic recess
- 23. THE EAR THE MIDDLE EAR: BORDERS ⸠Medial wall ⸠formed by the lateral wall of the internal ear ⸠contains a prominent bulge, produced by the facial nerve as it travels nearby ⸠Anterior wall ⸠a thin bony plate with two openings: for auditory tube and tensor tympani muscle ⸠separates the middle ear from the internal carotid artery ⸠Posterior wall (mastoid wall) ⸠consists of a bony partition between the tympanic cavity and the mastoid air cells ⸠there is a hole in this partition superiorly allowing the two areas to communicate ⸠hole is known as the aditus to the mastoid antrum
- 24. THE EAR THE MIDDLE EAR: BONES ⸠auditory ossicles ⸠malleus, incus and stapes ⸠connected in a chain-like manner ⸠link the tympanic membrane to the oval window of the internal ear ⸠sound vibrations in the air -> ⸠produce movement of the tympanic membrane -> ⸠transmit movement to the auditory ossicles (oscillation) -> ⸠deliver movement to oval window of the internal ear
- 25. THE EAR THE MIDDLE EAR: BONES ⸠malleus ⸠largest and most lateral of the ear bones ⸠attaches to the tympanic membrane (via the handle of malleus) ⸠head of the malleus lies in the epitympanic recess, where it articulates with the incus ⸠incus ⸠consists of a body and two limbs ⸠body articulates with the malleus ⸠short limb attaches to the posterior wall ⸠long limb joins the stapes
- 26. THE EAR THE MIDDLE EAR: BONES ⸠stapes ⸠smallest bone in the human body ⸠joins the incus to the oval window of the inner ear ⸠stirrup-shaped (head, two limbs, and a base) ⸠head articulates with the incus ⸠base joins the oval window
- 28. THE EAR THE MIDDLE EAR: MASTOID AIR CELLS ⸠mastoid air cells are located posterior to epitympanic recess ⸠a collection of air-ďŹlled spaces in the mastoid process of the temporal bone ⸠air cells are contained within cavity called the mastoid antrum ⸠mastoid antrum communicates with the middle ear via the aditus to mastoid antrum ⸠mastoid air cells act as a âbuffer systemâ for air ⸠release air into the tympanic cavity when the pressure is too low
- 30. THE EAR THE MIDDLE EAR: MUSCLES ⸠two muscles: tensor tympani and stapedius ⸠function to protect the middle ear ⸠contract in response to loud noise ⸠inhibit the vibrations of the malleus, incus and stapes ⸠reduce the transmission of sound to the inner ear ⸠action known as the acoustic reďŹex
- 31. THE EAR THE MIDDLE EAR: MUSCLES ⸠tensor tympani ⸠origin - auditory tube ⸠attachment - handle of malleus ⸠innervated by the tensor tympani nerve (branch of the mandibular) ⸠stapedius muscle ⸠origin - posterior wall of tympanic cavity ⸠attachment - neck of the stapes ⸠innervated by nerve to stapedius (branch of facial nerve)
- 32. THE EAR THE MIDDLE EAR: AUDITORY TUBE ⸠auditory tube (eustachian tube) ⸠cartilaginous and bony tube ⸠connects the middle ear to the nasopharynx ⸠acts to equalize the pressure of the middle ear to that of the external auditory meatus ⸠extends from the anterior wall of the middle ear, in an anterior, medioinferior direction ⸠opens onto the lateral wall of the nasopharynx ⸠can function as a pathway by which an upper respiratory infection can spread into the middle ear ⸠tube is shorter and straighter in children ⸠middle ear infections tend to be more common in children than adults
- 35. THE INNER EAR
- 36. THE EAR THE INNER EAR ⸠innermost part of the ear ⸠houses the vestibulocochlear organs ⸠two main functions: ⸠to convert mechanical signals from the middle ear into electrical signals, which can transfer information to the auditory pathway in the brain ⸠to maintain balance by detecting position and motion
- 38. THE EAR THE INNER EAR: ANATOMICAL POSITION AND STRUCTURE ⸠located within the petrous part of the temporal bone ⸠lies between the middle ear (laterally) and the internal acoustic meatus (medially) ⸠two main components: bony and membranous labyrinths ⸠bony labyrinth ⸠consists of a series of bony cavities within the petrous part of the temporal bone ⸠composed of the cochlea, vestibule and three semi-circular canals ⸠all these structures are lined internally with periosteum and contain a ďŹuid called perilymph
- 39. THE EAR THE INNER EAR: ANATOMICAL POSITION AND STRUCTURE ⸠membranous labyrinth ⸠lies within the bony labyrinth ⸠consists of the cochlear duct, utricle and the saccule, and semi-circular ducts ⸠membranous labyrinth is ďŹlled with ďŹuid called endolymph ⸠inner ear has two openings into middle ear - both covered by membranes ⸠oval window separates the middle ear and the vestibule ⸠round window separates the middle ear from the scala tympani (part of the cochlear duct)
- 40. THE EAR THE INNER EAR: BONY LABYRINTH - COCHLEA ⸠contains the cochlear duct of the membranous labyrinth â the auditory part of the inner ear ⸠twists upon itself around a central portion of bone called the modiolus, producing a cone shape which points in an anterolateral direction ⸠branches from the cochlear portion of the vestibulocochlear (VIII) nerve are found at the base of the modiolus
- 41. THE EAR THE INNER EAR: BONY LABYRINTH - COCHLEA ⸠spiral lamina ⸠a ledge of bone extending outwards from the modiolus ⸠attaches to the cochlear duct, holding it in position ⸠presence of the cochlear duct creates two perilymph-ďŹlled chambers above and below: ⸠scala vestibuli ⸠located superiorly to the cochlear duct, continuous with the vestibule ⸠scala tympani ⸠located inferiorly to the cochlear duct, terminates at the round window
- 42. THE EAR THE INNER EAR: BONY LABYRINTH - VESTIBULE ⸠vestibule ⸠central part of the bony labyrinth ⸠separated from the middle ear by the oval window ⸠communicates anteriorly with the cochlea and posteriorly with the semi-circular canals ⸠two parts of the membranous labyrinth located within the vestibule ⸠the saccule and utricle
- 43. THE EAR THE INNER EAR: BONY LABYRINTH - SEMI-CIRCULAR CANALS ⸠three semi-circular canals ⸠anterior, lateral and posterior ⸠contain the semi-circular ducts ⸠responsible for balance (along with the utricle and saccule) ⸠canals are situated superoposterior to the vestibule, at right angles to each other ⸠swelling at one end, known as the ampulla
- 45. THE EAR THE INNER EAR: MEMBRANOUS LABYRINTH ⸠a continuous system of ducts ďŹlled with endolymph ⸠lies within the bony labyrinth, surrounded by perilymph ⸠composed of: ⸠cochlear duct, saccule and the utricle, and three semi-circular ducts ⸠cochlear duct ⸠situated within the cochlea and is the organ of hearing ⸠semi-circular ducts, saccule and utricle ⸠organs of balance (also known as the vestibular apparatus)
- 46. THE EAR THE INNER EAR: MEMBRANOUS LABYRINTH - COCHLEAR DUCT ⸠located within the bony scaffolding of the cochlea ⸠held in place by the spiral lamina ⸠presence of the duct creates two canals â  the scala vestibuli (above) and scala tympani (below) ⸠cochlear duct can be described as having a triangular shape: ⸠lateral wall â formed by thickened periosteum (the spiral ligament) ⸠roof â formed by a membrane which separates the cochlear duct from the scala vestibuli (the Reissnerâs membrane) ⸠ďŹoor â formed by a membrane which separates the cochlear duct from the scala tympani (the basilar membrane) ⸠basilar membrane houses the epithelial cells of hearing â the Organ of Corti
- 48. THE EAR THE INNER EAR: MEMBRANOUS LABYRINTH - SACCULE AND UTRICLE ⸠two membranous sacs located in the vestibule ⸠organs of balance which detect movement or acceleration of the head in the vertical (saccule) and horizontal (utricle) planes ⸠utricle is the larger of the two - receives the three semi-circular ducts ⸠saccule is globular in shape - receives the cochlear duct ⸠endolymph drains from the saccule and utricle into the endolymphatic duct ⸠duct travels through the vestibular aqueduct to the posterior aspect of the petrous part of the temporal bone ⸠duct expands to a sac where endolymph can be secreted and absorbed
- 49. THE EAR THE INNER EAR: MEMBRANOUS LABYRINTH - SEMI-CIRCULAR DUCTS ⸠semi-circular ducts are located within the semi- circular canals ⸠with movement of the head, the ďŹow of endolymph within the ducts changes speed and/or direction ⸠sensory receptors in the ampullae of the semi- circular canals detect this change, and send signals to the brain, allowing for the sense of balance
- 51. THE EAR THE INNER EAR: VASCULATURE ⸠bony and membranous labyrinths have different arterial supplies ⸠bony labyrinth receives its blood supply from three arteries (also supply the surrounding temporal bone) ⸠anterior tympanic branch (from maxillary artery) ⸠petrosal branch (from middle meningeal artery) ⸠stylomastoid branch (from posterior auricular artery)
- 52. THE EAR THE INNER EAR: VASCULATURE ⸠membranous labyrinth is supplied by the labyrinthine artery ⸠(branch of the inferior cerebellar artery or occasionally the basilar artery) ⸠it divides into three branches: ⸠cochlear branch â supplies the cochlear duct ⸠vestibular branches (x2) â supply the vestibular apparatus ⸠venous drainage ⸠labyrinthine vein ⸠empties into the sigmoid sinus or inferior petrosal sinus
- 54. THE EAR THE INNER EAR: INNERVATION ⸠inner ear is innervated by the vestibulocochlear nerve (CN VIII) ⸠enters the inner ear via the internal acoustic meatus and divides ⸠vestibular nerve ⸠responsible for balance ⸠enlarges to form the vestibular ganglion ⸠splits into superior and inferior parts to supply the utricle, saccule and three semi-circular ducts ⸠cochlear nerve ⸠responsible for hearing ⸠enters at the base of the modiolus ⸠branches pass through the lamina to supply the receptors of the Organ of Corti ⸠facial nerve (CN VII) passes through the inner ear, but does not innervate any of the structures present
- 56. References ⸠These slide reďŹect a summary of the contents of TeachMeAnatomy.info and are to be used for educational purposes only in compliance with the terms of use policy. SpeciďŹc portions referenced in this summary are as follows: ⸠https://teachmeanatomy.info/head/organs/ear/ Additional sources are referenced on the slide containing that speciďŹc content.