Lecture 7 The Ear 2024 PDF

ANAT3004/3904 The Ear and Vestibulocochlear Nerve (CNVIII) Presented by Dr Jennifer Menzies School of Medical Sciences The University of Sydney The University of Sydney Anatomie Artistique du corps humain. Page 1 Cuyer, Edouard. Paris, 1891. ...

ANAT3004/3904 The Ear and Vestibulocochlear Nerve (CNVIII) Presented by Dr Jennifer Menzies School of Medical Sciences The University of Sydney The University of Sydney Anatomie Artistique du corps humain. Page 1 Cuyer, Edouard. Paris, 1891.  COMMONWEALTH OF AUSTRALIA Copyright Regulation WARNING This material has been reproduced & communicated to you by or on behalf of the University of Sydney pursuant to part VB of the Copyright Act 1968 (the Act) The material in this communication may be subject to Copyright under the Act. Further reproduction or communication of this material by you may be the subject of Copyright protection under the Act. The University of Sydney Page 2 Lecture Objectives 1. Identify the cartilaginous and bony components of the external acoustic meatus. 3. Identify the position of the middle ear and the parts of the inner ear and middle ear beneath the floor of middle cranial fossa. Recognise the features of the middle ear, the tympanic cavity and membrane, the ossicles, the epitympanic recess, the aditus, the antrum, mastoid air cells and auditory tube. Identify the promontory and round and oval windows on the medial wall. Identify the tensor tympani and stapedius muscles and learn their innervations. 4. Identify the bony and membranous labyrinths of the inner ear. Recognise the cochlea, vestibule, semicircular canals and ducts, the utricle and saccule, the cochlear duct and the scalae. 6. Learn the course and features of the Vestibulocochlear nerve (CN VIII). 7. Revise the course and features of the facial nerve including the location of the geniculate ganglion, the chorda tympani and the relationship of the facial nerve to the internal carotid arteries and ear structures. The University of Sydney Page 3 Lecture Outline Middle Ear Overview of the Ear Blood Supply Nerves Overview of the Components Middle Ear – Auditory Tube of the External, Middle and Inner Ear Inner Ear The External Ear Labyrinthine Structure The Middle Ear Perilymph and Endolymph Walls and Relationships The Bony Labyrinth Features of the Middle Ear Cochlea Tympanic Membrane Semicircular Canals Tympanic Cavity The Membranous Labyrinth Epitympanic Cavity Cochlear Duct Vestibule Middle Ear – Ossicles Semicircular Ducts Middle Ear Muscles Utricle Tensor Tympani Saccule Stapedius Vestibulocochlear Nerve CNVIII The University of Sydney Transmission of Sound Page 4 Functions and Components of the Ear The two main functions of the ear are Hearing and Balance. The ear is primarily situated in the temporal bone, aside from the cartilaginous part of the auditory tube which is in a groove alongside the petrosphenoidal suture. The components of the ear and their specific functions are: External ear – the collection of mechanical sound vibrations Eardrum (Tympanic membrane) – transmission, amplification Middle ear (Tympanic cavity) – transmission, amplification Inner ear – Cochlea, vestibule, semicircular canals - sensation The University of Sydney Page 5 Overview of the Ear The University of Sydney Page 6 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Overview of the Ear Internal carotid Auditory tube External ear Cochlea Tegmen tympani – roof of middle Facial nerve ear Vestibulocochlear nerve Semicircular canals 7 Overview of Components - External, Middle and Inner Ear External Ear Middle Ear Inner (Internal) Ear Auricle (pinna) Tympanic membrane and Cochlea cavity External acoustic meatus Epitympanic recess Semicircular canals Tympanic membrane Auditory (aka Eustachian Vestibulocochlear - between outer and middle ear or pharyngotympanic) tube nerve Ceruminous glands/hair Tensor tympani muscle Stapedius muscle Malleus Incus Stapes The University of Sydney Chorda tympani Page 8  External (Outer) Ear The external acoustic meatus is approximately 24mm long Lateral one third is cartilaginous and medial two thirds is bony Lateral one third contains specialized sweat glands called ceruminous glands that produce secretions that mix with sebum and dead epidermal cells to form cerumen (ear wax) Medial two thirds – thin skin The meatus has a slight anterior overlying osseous portion slant Lateral one third – cartilaginous with hair follicles, sebaceous and ceruminous glands The University of Sydney Page 9 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences.  Middle Ear – Walls and Relationships Six boundaries: Lateral, Anterior, Roof, Posterior, Floor, Medial Lateral wall Tympanic membrane Anterior (carotid) wall Auditory tube. Tensor tympani muscle runs in a canal above auditory tube and bends to run along part of medial wall Left ear 10 The University of Sydney Page 10 https://otosurgeryatlas.stanford.edu/otologic-surgery-atlas/surgical-anatomy-of-the-ear/middle-ear-mastoid/ Middle Ear – Walls and Relationships Roof Tegmen tympani – thin bone separating the middle ear from the middle cranial fossa Tegmen tympani is anterolateral to arcuate eminence on the floor of the middle cranial fossa Posterior wall Back of epitympanic recess leading into the aditus, then mastoid antrum and mastoid air cells The chorda tympani nerve, from facial nerve branches, is initially behind the posterior wall The facial nerve turns inferiorly at the level of the aditus The tendon of stapedius muscle emerges at the pyramid in the posterior wall The University of Sydney Left ear Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Page 11 Gray's anatomy for students E-book. Elsevier Health Sciences. Middle Ear – Walls and Relationships Floor (jugular wall) The floor consists of thin bone separating it from the jugular vein* *For this reason, middle ear infection can be transmitted to the internal jugular vein and cause clotting Medial wall Adjacent to the inner ear. Bony except for the oval window (fenestra vestibuli) which is closed by the base of stapes and the round window (fenestra cochlea) which is inferolateral to the oval window and closed by a membrane. Other features of the medial wall include: The promontory overlying the cochlea An elevation overlying the canal for the facial nerve Tensor tympani muscle Tympanic plexus - the tympanic plexus (sensory to the mucosa) is formed on the tympanic promontory by branches of Jacobson's nerve (tympanic branch of the glossopharyngeal nerve) and caroticotympanic nerves originating from the internal carotid artery plexus. The University of Sydney Netter, F. (1995), Interactive Atlas of Anatomy on CD, Ciba-Geigy Corporation, New Jersey. Page 12 Walls of Middle Ear – Diagrammatic representation * Tympanic branch of glossopharyngeal nerve - supplies entire mucosa. Continues as lesser petrosal nerve (parasympathetic fibres to parotid via * auriculotemporal n.) The University of Sydney Page 13 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Middle Ear Tympanic membrane - Features Elliptical shape, the lateral surface is concave Skin externally, mucosa internally Fibrocartilaginous, thickened edge – the tympanic ring – fits into the tympanic groove in the temporal bone The manubrium (handle) of the malleus attaches to the inner surface The region above the manubrium is the pars flaccida and below is the pars tensa The inferior part of the manubrium is at the umbo. This is the point of maximum convexity of the membrane when viewed from the middle ear Tympanic cavity Air filled cavity with connections: - to pharynx via auditory tube - to mastoid air cells via mastoid aditus Variable epithelium - mostly respiratory, otherwise squamous or cuboidal Epitympanic cavity A hollow in the temporal bone where the head of the malleus and part of the body of the incus are contained The University of Sydney Page 14 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. 14 Middle Ear – Tympanic membrane Pars tensa The University of Sydney Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Page 15 Gray's anatomy for students E-book. Elsevier Health Sciences. Clinical Note – Perforation of the Tympanic Membrane Although perforation of the tympanic membrane (eardrum) has many causes, trauma and infection are the most common. Ruptures of the tympanic membrane tend to heal spontaneously, but surgical intervention may be necessary if the rupture is large. Occasionally, it may be necessary to enter the middle ear through the tympanic membrane. Because the chorda tympani runs in the upper one-third of the tympanic membrane, incisions are always below this level. Otitis media (infection of the middle ear) is common and can lead to perforation of the tympanic membrane. The infection can usually be treated with antibiotics. If the infection persists, the chronic inflammatory change may damage the ossicular chain and other structures within the middle ear to produce deafness. The University of Sydney Page 16 A bit more about chorda tympani… Leaves the facial nerve about 5mm above the stylomastoid foramen Arches across posterior wall, across upper part of tympanic membrane then into the bone again and out through the petrotympanic fissure Passes down the medial surface of the spine of the sphenoid and between the deep surface of the lateral pterygoid and inferior alveolar nerve. It then joins the lingual nerve at an acute angle. The University of Sydney Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Page 17 Middle ear - Ossicles The three ossicles of the ear are composed of dense compact bone covered with mucosa The articulations between the incus and the malleus and the stapes are synovial joints and despite their small size each has an articular disc and is surrounded by a joint capsule Ossicles develop via endochondral ossification of the ends of the cartilages (Manubrium) supporting embryonic structures called pharyngeal arches. They are usually entirely compact bone after the first two years of life. Prior to that they have a transitory marrow cavity (spongy bone). The University of Sydney Page 18 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Middle ear - Ossicles As ossicles are compact bone this contains lacunae with osteocytes and vascular channels. There may be small islands of cartilage remnants from the endochondral ossification but no spongy bone Haversian bone is sometimes present (Haversian canals surround blood vessels and nerve fibres throughout this type of bone and communicate with osteocytes) The University of Sydney Page 19 Middle ear - Ossicles Remodelling, blood and nerve supply Blood and nerve supply (tympanic plexus) is via the mucosa covering the ossicles which is in communication with the mucosa lining the other parts of the tympanic cavity The ossicles are full sized at birth and bone turnover is very low. Repair of small cracks or damage has been reported as “feeble” The ossicles are lightly stressed yet do not show the resorption associated with low stress that is typical of other bones The University of Sydney Page 20  Middle ear - Ossicles *Note continuity of mucosa over tympanic membrane & malleus Tensor tympani tendon Handle of * malleus 21 Tympanic membrane Middle Ear – The Muscles of the Tympanic Cavity Tensor tympani Stapedius The muscles work together in a reflex response to high intensity sounds. The muscle fibres contract and this reduces the vibration of the ossicles which in turn reduces sound intensity before it reaches the inner ear. The reaction time, however, is not fast enough to moderate the effects of sudden noise such as a gun shot so only provides partial protection The University of Sydney Page 22 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences.  Middle Ear – The Muscles of the Tympanic Cavity Tensor tympani Stapedius They are both composed of skeletal muscle but contract involuntarily (pharyngeal constrictors are similar – involuntary skeletal muscle) Only the tendons of the muscles are in the middle ear (covered in mucosa) – the bellies of the muscles are in bony channels The University of Sydney Page 23 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences.  Middle Ear – Tensor Tympani Tensor tympani The tensor tympani muscle is situated within a bony canal above the cartilaginous auditory tube. The tendon makes a 90 degree turn when it emerges and runs across the middle ear to the handle of the malleus. As well as working with stapedius it pulls the tympanic membrane inward also reducing sound transmission including chewing It is innervated by the medial pterygoid branch of V₃ from CNV The University of Sydney Page 24 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences.  Middle Ear – Stapedius Stapedius The muscular part of stapedius lies in a canal in the posterior wall. The tendon emerges from the pyramid and attaches to the neck of stapes It is innervated by a small branch of CNVII, the nerve to stapedius The University of Sydney Page 25 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences.  Blood Supply to the Middle Ear Numerous arteries supply the structures in the middle ear The two largest branches are the tympanic branch of the maxillary artery and the mastoid branch of the occipital or posterior auricular arteries Smaller branches come from the middle meningeal artery, the ascending pharyngeal artery, the artery of the pterygoid canal, and tympanic branches from the internal carotid artery Venous drainage of the middle ear returns to the pterygoid plexus of veins and the superior petrosal sinus. The University of Sydney Page 26  Nerve Supply to Tympanic Cavity - Summary 1. Tensor tympani nerve - from medial pterygoid branch of mandibular division of trigeminal 2. Chorda tympani from the facial nerve – just passing through! 3. Nerve to stapedius 4. Glossopharyngeal nerve - And tympanic branch/plexus (tympanic branch enters middle ear through a tiny opening on underside of the skull between carotid canal and jugular foramen) The University of Sydney Page 27 Middle Ear - Auditory tube (aka Eustachian or pharyngotympanic tube) Lined with respiratory mucosa Bony posterolaterally, cartilaginous anteromedially Bony opening (to cartilaginous part) on skull is just medial to spine of sphenoid (reminder - to locate opening of bony auditory tube on skull - look medial to spine of sphenoid between foramen spinosum and carotid canal) Cartilaginous part runs in a groove between petrous temporal bone and greater wing of sphenoid (petrosphenoidal suture). Opens into lateral wall of nasopharynx The University of Sydney Page 28 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences.  Auditory tube, tensor tympani and ossicles Arcuate eminence Internal carotid artery Stapes Malleus Tympanic cavity Tympanic membrane Auditory tube The University of Sydney Page 29 Photographic Atlas of Anatomy, 9th Ed, J2006, Johannes W. Rohen, Elke Lutjen-Drecoll, Chihiro Yokochi Middle Ear - Auditory tube and related muscles The auditory tube is normally closed but opens during swallowing, coughing and positive pressure. Muscles play a role in opening. Levator palati Medial pterygoid plate and hamulus Kulkarnee,N. 2006 Anatomy for Students Jaypee Publishers The University of Sydney Page 30  Inner Ear - Labyrinthine Structure The inner ear consists of a bony labyrinth within the temporal bone. The labyrinth is lined with hard, compact bone which is continuous with the spongy bone of the petrous temporal region. The bony labyrinth is filled with a fluid – perilymph – which separates the bony labyrinth from the membranous labyrinth. All the chambers of the osseous labyrinth interconnect. The membranous labyrinth is a separate series of hollow, epithelial lined chambers that include sensory tissue. The membranous labyrinth contains a fluid called endolymph. The University of Sydney Page 31 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear – Perilymph and Endolymph Perilymph Perilymph is similar in composition to cerebrospinal fluid. The sites of production and absorption for perilymph are still under debate. Endolymph Endolymph is produced by capillaries underlying the lining of the membranous labyrinth. Absorption is via the endolymph duct and sac (ultimately returning to the blood in small vessels surrounding the endolymph sac). Damage or blockage of the endolymph pathway leads to an accumulation of excess endolymph causing a condition called endolymphatic or cochlear hydrops. The University of Sydney Page 32 Inner Ear – Bony and Membranous Labyrinths in Horizontal Section tympanic membrane & malleus Cochlear duct (membranous labyrinth) chorda tympani Cochlea (bony facial nerve in posterior wall middle ear labyrinth)- compact bone mastoid Spongy bone Vestibulocochlear nerve Vestibule & semicircular canals (bony labyrinth) The University of Sydney Page 33 Inner Ear - The Bony Labyrinth The bony labyrinth consists of the vestibule, three semicircular canals and the cochlea. The bony cavities are lined with periosteum and contain the perilymph. Cochlea The cochlea is anterior to the vestibule. It turns around a central bony modiolus with the apex of the cochlea directed anterolaterally. It turns 2.5 times and the first turn produces the promontory on the medial wall of the middle ear. The vestibule contains the oval and round windows in its lateral wall. The wide base of the modiolus is placed near the internal acoustic meatus, where it is entered by branches of the cochlear part of the vestibulocochlear nerve CNVIII. The University of Sydney Page 34 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear - The Bony Labyrinth Semicircular canals Projecting in a posterosuperior direction from the vestibule are the anterior, posterior and lateral semicircular canals. Each of these canals forms two-thirds of a circle connected at both ends to the vestibule and with one end dilated Anterior to form the ampulla. semicircular canal The canals are oriented in such a way that each canal is at right angles to the other two. The University of Sydney Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Page 35 Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear - The Bony Labyrinth Semicircular canals The lateral canal causes a horizontal bulge on the medial wall of the middle ear above the canal for the facial nerve The anterior/superior canal Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. produces the arcuate eminence in the floor of the middle cranial Arcuate eminence fossa The University of Sydney Photographic Atlas of Anatomy, 9th Ed, J2006, Johannes W. Rohen, Elke Lutjen-Drecoll, Chihiro Yokochi Page 36 Inner Ear - Bony Labyrinth Spongy bone Mastoid antrum Lateral semicircular canal Cochlea Middle ear with Compact bone ossicles The University of Sydney Page 37 Photographic Atlas of Anatomy, 9th Ed, J2006, Johannes W. Rohen, Elke Lutjen-Drecoll, Chihiro Yokochi  Inner Ear- Bony Labyrinth Anterior semicircular canal Cochlea Posterior semicircular canal Lateral semicircular canal The University of Sydney Page 38 Photographic Atlas of Anatomy, 9th Ed, J2006, Johannes W. Rohen, Elke Lutjen-Drecoll, Chihiro Yokochi Inner Ear - Membranous Labyrinth Membranous Labyrinth The membranous labyrinth is smaller than the osseous labyrinth and does not fill it. It is composed of three interconnecting parts. The Cochlear Duct MEMBRANOUS LABYRINTH - within perilymph are epithelial lined chambers The Vestibule collectively called the membranous labyrinth. Certain areas of the epithelia contain sensory regions. (all chambers of the membranous labyrinth Semicircular Ducts interconnect) - membranous labyrinth is also fluid filled – endolymph The University of Sydney Page 39 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear – The Cochlear Duct Cochlear Duct The cochlear duct is in the middle of the cochlea in the bony labyrinth and divides it into two canals (the scala vestibuli and the scala tympani). It is held in this position by attachments to the lamina of the modiolus, a thin lamina of bone extending from the modiolus (the central bony core of the cochlea) and peripherally to the outer wall of the cochlea. The cochlear duct contains endolymph and incorporates the sensory spiral organ (Organ of Corti). The University of Sydney Page 40 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear – The Cochlear Duct The Spiral Organ (Organ of Corti) Receptor organ for hearing The scala vestibuli is continuous with the vestibule. The scala tympani is separated from the middle ear by the secondary tympanic membrane covering the round window. They The University of Sydney contain perilymph. Vibrations in perilymph transmit sound Page 41 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear – The Vestibule The bony vestibule contains membranous parts of the inner ear - consisting of two connected sacs containing endolymph – the utricle and the saccule The University of Sydney Page 42 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear – Semicircular Ducts, Utricle and Saccule The semicircular ducts, utricle, and saccule are the organs of balance. The utricle is the larger of the two sacs. It is oval, elongated and irregular in shape and is in the posterosuperior part of the vestibule of the bony labyrinth. The three semicircular ducts empty into the utricle. Each semicircular duct is similar in shape, including a dilated end forming the ampulla, to its complementary bony semicircular canal, only much smaller. The saccule is a smaller, rounded sac lying in the anteroinferior part of the vestibule of the bony labyrinth. The cochlear duct empties into it. The University of Sydney Page 43 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear – Semicircular Ducts, Utricle, Saccule(cont.) The utricle and saccule each contain a sensory structure called the macula. The semicircular ducts each incorporate a dilated region or ampulla at the vestibular end containing a sensory structure called the crista ampullaris. The utricle responds to linear acceleration in the horizontal plane and sideways head tilts, while the saccule responds to linear acceleration in the vertical plane, such as forward-backward and upward-downward movements. In contrast, the receptors in the three semicircular ducts respond to rotational movement in any direction. The University of Sydney Page 44 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Inner Ear – Innervation The facial and vestibulocochlear nerve emerge at the inferior border of the pons with nervus intermedius between. The vestibulocochlear nerve passes through the canal and the two components separate at the external end of the internal acoustic canal. The University of Sydney Page 45 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Innervation - Summary The vestibulocochlear nerve CNVIII carries special afferent fibres for hearing (the cochlear component) and balance (the vestibular component). The vestibular nerve enlarges to form the vestibular ganglion, before dividing into superior and inferior parts, which distribute to the three semicircular ducts and the utricle and saccule. The cochlear nerve enters the base of the cochlea and passes upward through the modiolus. The ganglion cells of the cochlear nerve are in the spiral ganglion at the base of the lamina of the modiolus as it winds around the modiolus. Branches of the cochlear nerve pass through the lamina of the modiolus to innervate the receptors in the spiral organ. The University of Sydney Page 46 Cochlear Duct The microvilli trigger nerve This is a cross section impulses that travel along through one of the turns the cochlear nerve to the showing the sensory brain, where they are structures - hair cells interpreted as sound These “hairs” are specialised microvilli Stria vascularis Spiral organ (Organ of Corti) The University of Sydney Page 47  Transmission of Sound 1. Sound waves entering the external ear strike the tympanic membrane, causing it to vibrate. 2. Vibrations initiated at the Base plate tympanic membrane are of stapes transmitted through the ossicles of the middle ear and their articulations. 3. The base of the stapes vibrates with increased strength and decreased amplitude in the oval window. 4. Vibrations of the base of the stapes create pressure waves in the perilymph of the scala vestibuli. 5. Pressure waves in the scala vestibuli cause Secondary Phatyngotympanic tympanic tube displacement of the basilar membrane of the cochlear membrane in duct. Short waves (high pitch) cause displacement near round window the oval window. Longer waves (low pitch) cause more distant displacement, nearer to the helicotrema at the 6. Vibrations are transferred across the cochlear duct to the perilymph apex of the cochlea. Movement of the basilar of the scala tympani. membrane bends the hair cells of the spiral organ. 7. Pressure waves in the perilymph are dissipated (dampened) by the Neurotransmitter is released, stimulating action secondary tympanic membrane at the round window into the air of potentials conveyed by the cochlear nerve to the brain. the tympanic cavity. The University of Sydney Page 48 Drake, R., Vogl, A.W. and Mitchell, A.W., 2009. Gray's anatomy for students E-book. Elsevier Health Sciences. Clinical Note: Noise Induced Damage to Spiral Organ Effects (industrial, recreational, military) are more pronounced in spiral organ (Organ of Corti) as this responds to a wider range of higher frequencies (20 - 20,000hz). Maculae and cristae of the vestibule and semicircular canals respond to 0 – 10hz but can be damaged as well. Damage includes temporary or permanent loss of sensory hairs (microvilli) and possible damage to nerves and ganglia. The University of Sydney Page 49 https://en.wikipedia.org/wiki/Howitzer Clinical Note: Damaged vs Undamaged Hair Cells Inner & outer hair cells SEM Image The University of Sydney Page 50