Ear Anatomy Lecture Notes PDF

Anatomy of the Ear Prof. Dr. Ali Abdulmuttalib Mohammed M.B.Ch.B.F.I.C.M.S.(E.N.T.) Full Professor, Consultant Otolaryngologist Head of ENT Dept, College of Medicine, University of Mosul In charge of Mosul Centre, Iraqi Board of Otolaryngology...

Anatomy of the Ear Prof. Dr. Ali Abdulmuttalib Mohammed M.B.Ch.B.F.I.C.M.S.(E.N.T.) Full Professor, Consultant Otolaryngologist Head of ENT Dept, College of Medicine, University of Mosul In charge of Mosul Centre, Iraqi Board of Otolaryngology University of Mosul College of Medicine Lecture: no.7 Subject ENT/year 2024-2025 Anatomy of the ear Lecturer: Prof. Dr. Ali Abdulmuttalib Mohammed Department: Surgery Date: Dec.3 / 11 / 2024 AIMS OF LECTURE 1. To explain the anatomy of the external, midddle and inner ear in order to understand the diseases of the ear. 2. To explain the anatomy of the facial nerve. Intended Learning Outcomes By the end of this lecture the student will be able to realize anatomy of the ear for further understanding of ENT diseases.  HEADINGS 1. Embryology of the ear. 2. Anatomy of the ear The external ear: Auricle, external auditory meatus. The middle ear: Tympanic membrane, landmarks of ear drum, middle ear cleft, Eustachian tube, contents of mi9ddle ear. The inner ear: Bony labyrinth, membranous labyrinth Sir Morel McKenzie 1869 (Scottish surgeon) The father of ENT Auricle develops from a series of six tubercles which form around the margins of the first visceral cleft about six weeks of.gestation. External Auditory Canal formed from.the ectoderm of the first visceral cleft Tympanic Membrane 1. An outer epithelial layer; from the ectoderm of the first visceral cleft. 2. A middle fibrous layer; from the mesoderm between the first visceral cleft and the tubotympanic recess. 3. An inner mucosal layer; from the endoderm of the tubotympanic recess.  The ear can be divided anatomically and clinically into three parts; the external, the middle and the inner ear. The external and the middle ears are concerned primarily with the transmission of sound. The inner ear functions both as the organ of hearing and as part of the balance system of the body.  It consist of the auricle (pinna) and the external auditory meatus. The auricle consist of a skeleton of yellow elastic cartilage ( except the lobule which is composed of fat) covered with a skin and attached to the side of the head by ligaments and functionless anterior, superior and posterior auricular muscles. The relative safety of piercing the lobule, avoiding cartilage is obvious to clinicians. The Auricle  The external auditory meatus measures 24mm in adults. It is composed of two portions; an outer cartilaginous 1/3 about 8mm long and an inner bony 2/3 (16mm) long. The sebaceous glands, ceruminous glands and hair follicles are present only in the cartilaginous portion. Owing to the closer union of cartilage and skin, any inflammatory lesion such as boil in the cartilaginous meatus is an acutely painful infection.  The epithelium lining the bony meatus is much thinner and is devoid of those structures which characterize the thicker skin of the outer canal. The general direction of the cartilaginous meatus is medially, upwards and backwards, while that of the bony meatus is medially, downwards and forwards. The meatus may be partially straitened in adults by pulling the auricle upwards, outwards and backwards. There are two constrictions in the EAM; one at the junction of the cartilaginous and bony part and the other is in the osseous part..Auriculotemporal nerve (V).1.Facial nerve (VII).2.Auricular branch of the vagus (Arnold).2 Lesser occipital nerve (C2).3 Greater auricular nerve (C2C3).4.Superficial temporal artery.1.Postauricular artery.2.Maxillary artery.3  The tympanic membrane separates the EAM from the middle ear. It is thin, nearly oval disk, forming an angle of about 55 with the floor of the meatus.  The TM has an outer layer of squamous epithelium continuous with that of the meatus, a middle layer of fibrous tissue and an inner layer of mucous membrane continuous with the lining of the middle ear.. The TM is supported around its periphery by a fibrous thickening known as the annulus. The fibrous annulus in turn fits into a slot in the tympanic bone known as the sulcus.  It has a pearly grey colour with a triangular bright area; the cone of light; extending from the centre (umbo) downwards and forwards. The most prominent landmark is the handle of malleus, malleus at its upper end lie a small projection known as the lateral process. The TM is divided into Two parts; the pars tensa and the pars flaccida. flaccida The latter forms the upper most part of the TM where the fibrous layer is absent and frequently referred to as the attic part of the ear drum. Chronic perforations of this area are potentially unsafe. Right tympanic membrane as seen through a speculum  Pseudomonus aeruginosa, Staph. Aureus and Haemolytic streptococci. The Nerve Supply of the outer surface of the TM is similar to that of the EAM. The inner surface is supplied by the tympanic branch of the IX nerve (Jacobson nerve). The Blood supply is by the postauricular and maxillary arteries. The middle ear cleft includes the Eustachian tube, the middle ear and the aditus which leads posteriorly to the mastoid antrum and air cells.  The ET connects the tympanic cavity with the nasopharynx and in the adults is about 36mm in length. In infants the tube is shorter, wider and its course is more horizontal than adults hence acute SOM is common in this age. The tube is closed at rest but is opened on yawning or swallowing by contraction of the tensor palati muscle and thus equality of air pressure is maintained on both sides of the TM.  Auditory tube, laid open by a cut in its long axis The cavity may be described as six-sided box frequently linked in shape to a match box.  Roof; is formed by a thin pate of bone (tegmen tympani). This plate separates the tympanic cavity and mastoid antrum from the middle cranial fossa. Injury to this plate by a trauma or tumour leads to CSF otorrhea. Floor; a thin plate of bone separates the cavity from the bulb of the internal jugular vein. Posterior wall; contains an opening high up which is known as the aditus connecting the tympanic cavity with the mastoid antrum which communicates with mastoid air cells. Just below the aditus is a small projection of bone, the pyramid, which contains the stapedius muscle. The tendon of this muscle passes forwards to its insertion in the neck of the stapes.  Anterior wall; a thin plate of bone separates the cavity from the internal carotid artery. The anterior wall has two openings; one being the Eustachian tube which connects the middle ear with the nasopharynx. Above it is the canal for tensor tympani muscle which is inserted into the neck of malleus. Lateral wall; is the TM. Medial wall: The promontory which is the bony covering of the basal turn of the cochlea. The facial nerve runs horizontally superior to it enclosed in a thin bony canal (canal of Fallopius) which is sometimes deficient. Posteroinferior to the promontory is the round window whereas posterosuperior to the promontory is a somewhat similar opening; the oval window; which is occupied by the footplate of the stapes.  Cochlea diagram Ear anatomy  Horizontal section through left ear 1. Air. 2. Ossicles: Malleus, incus and stapes. 3. Muscles: Tensor tympani and stapedius. The former tenses the TM, while the latter comes into action reflexly in response to loud noise and this serves to stiffen up the conducting mechanism and possibly to protect the inner ear against damage. 4. Nerves a. Chorda tympani: Arises from the facial nerve in the Fallopian canal. b. Tympanic plexus: Lies on the promontory. It's formed by the tympanic branch of the 9th nerve (Jacobson) and branches from the sympathetic plexus. This plexus supplies the lining mucosa of the ET, tympanic cavity and mastoid  The inner ear lies within the petrous part of the temporal bone. It is called the labyrinth (from it's complexity) and it consist of a membranous labyrinth enclosed in a bony labyrinth (otic capsule).  The membranous labyrinth contains fluid known as endolymph which is similar to the intracellular fluid. The space within the bony labyrinth between it's wall and the membranous labyrinth contains another fluid known as perilymph. The composition of the perilymph is very similar to the extracellular fluid. The Bony Labyrinth Anteriorly; lies a snail like cochlea. In the middle; lies the vestibule. The fenestra ovale (oval window) is situated on it's lateral wall and is closed by the footplate of the stapes. Posteriorly; lie three semicircular canals. The Membranous Labyrinth 1. The membranous cochlear duct; is situated in the bony cochlea. The neuroepithelium of the cochlea is arranged along the entire length of the cohlear duct and is known as the organ of Corti. Nerve fibres from the organ of Corti pass centrally as the cochlear nerve. 2. Saccule and utricle; lie in the bony vestibule. Saccule and utricle are stimulated by linear acceleration. 3. The membranous semicircular canals; occupy the corresponding bony canal and are set at right angles to each other, each represent a plane in space. The stimulus which excite the ampulla is angular acceleration.  The SCC, utricular and saccular nerves unite to form the vestibular nerve. The vestibular and cochlear nerves together constitute the 8th cranial nerve. Blood Supply The main supply comes from the labyrinthine artery (internal acoustic artery) which arises from the basilar or anterior inferior cerebellar artery.  Inner ear The Inner Ear Cochlear chambers Pathophysiology  The nerve emerges from the pons and after crossing the cerebellopontine angle it enters the temporal bone at the internal auditory meatus. It passes over the labyrinth until it reaches the medial wall of the tympanic cavity. Here it bends backwards at right angle where the geniculate ganglion is situated and passes almost horizontally, enclosed in the Fallopian canal, above the oval window. When it reaches the aditus it turns downwards behind the pyramid and continues almost vertically till it emerges from the stylomastoid foramen. Facial nerve The nerve to the stapedius is given off close to the pyramid. The chorda tympani nerve leaves the descending part of the facial nerve and enters the tympanic caity.  The right membrane tympani with the hammer and the chorda tympani, viewed from within, from behind, and from above SUMMARY Familiarity with ear anatomy and surgical landmarks is fundemental to otological practice.  LET’S CHECK OUR KNOWLDEGE The anterior wall of the middle ear: A/ It separates the cavity from the common carotid artery. B/ It has only one opening. C/ It has two openings, the lower one being the auditory (Eustacian) tube and above it lies the canal for the tensor tympani muscle. D/ It separates the cavity from the IJV E. It is separated from the external canal by tympanic memrane. Regarding posterior wall of the middle ear: A/ Aditus is an opening leading from the middle ear to the middle cranial fossa. B/ Pyramid is a conical bony projection lying below the aditus. C/ Stapedius tendon comes out of the pyramid and is inserted to the incus. D/ It contains the opening of Eustachian tube E/ All the above are true. References Lecture notes on Diseases of the Ear Nose and Throat. Hall and Coman,s Diseases of the Ear Nose and Throat. Logan Turner,s Diseases of the Ear Nose and Throat. PL Dhingra Diseases of the Ear Nose and Throat. Scott-Brown,s Otolaryngology Head and Neck Surgery Questions?