Gross anatomy of the ‘ear’

1. GROSS ANATOMY OF THE ‘EAR’

2. EAR Parts: It has 3 parts; 1 st part ……………external ear 2 nd part….................middle ear 3 rd part……………..inner ear The external and middle ear are mainly concerned with the transference of sound to the internal ear internal ear is for hearing and balancing ( equilibrum ) External ear has 2 parts; The Auricle ( pinna ) which projects from the lateral side of the head the External acoustic meatus (ear canal) which is a canal leading inwards

3. AURICLE

4. Auricle ( pinna ) is on the side of the head and assists in capturing sound It consists of cartilage covered with skin and arranged in a pattern of various elevations and depressions The large outside rim of the auricle is the helix It ends inferiorly at the fleshy lobule (ear lobe) The lobule is the only part of the auricle not supported by cartilage It is consists of fibrous tissue, fat, and blood vessels It is easily pierced for taking small blood samples and inserting earrings The hollow center of the auricle is the concha of auricle at the depth of the concha is the opening of the external acoustic meatus Just anterior to the opening of the external acoustic meatus , in front of the concha , is an elevation called the tragus

5. Opposite the tragus, and above the fleshy lobule , is another elevation (the antitragus ) A smaller curved rim, parallel and anterior to the helix is the antihelix The antihelix divides above into 2 legs or crura In between these crura is a depression called the triangular fossa A curved depression lies between the helix and antihelix and it is called the scapha / scaphoid fossa Muscles Include; Intrinsic muscles Extrinsic muscle intrinsic muscles pass between the cartilaginous parts of the auricle and may change the shape of the auricle

6. They include: Helicis major Helicis minor Tragicus Antitragicus Transverse muscle Oblique muscle extrinsic muscles pass from the scalp or skull to the auricle and may also play a role in positioning of the auricle anterior auricular muscle Superior auricular muscle posterior auricular muscle Both groups of muscles are innervated by the facial nerve [VII ] Arterial supply posterior auricular artery superficial temporal artery Venous drainage through vessels following the arteries

7. Innervation superficial surfaces supplied by; great auricular nerve auriculotemporal branch of the mandibular nerve [V 3 ] (anterior superior portion) lesser occipital nerve (posterior superior portion) deeper parts are supplied by; facial nerve [VII] vagus nerve [X] (the auricular branch) Lymphatic drainage : drain anteriorly into parotid nodes posteriorly into mastoid nodes possibly into the upper deep cervical nodes

8. External acoustic meatus extends from the deepest part of the concha to the tympanic membrane (eardrum ) a distance of approximately 1 inch (2.5 cm) Its walls consist of cartilage and bone The lateral 1/3 is formed from cartilaginous extensions from some of the auricular cartilages the medial 2/3 is a bony tunnel in the temporal bone Throughout its length the external acoustic meatus is covered with skin some of this skin contains hairs and modified sweat glands p roducing cerumen (earwax ) cerumen protects the skin of the ear canal, assists in cleaning and lubrication, and also provides some protection from bacteria, fungi, insects and water

9. Clinical anatomy Excess production of cerumen can press against the eardrum and/or occlude (block) the external auditory canal or hearing aids, potentially hindering  hearing Tympanic membrane (ear drum) is a membrane that separates the external acoustic meatus from the middle ear is a thin, oval semi-transparent membrane approximately 1 cm in diameter it is covered with thin skin externally and with mucous membrane of the middle ear internally When viewed through an otoscope , the tympanic membrane appears concave toward the external acoustic meatus with a shallow, cone-like central depression the peak of this cone like depression is called the umbo of the tympanic membrane

10. The l ower end of the handle of malleus is attached to the umbo of tympanic membrane Superior to the handle of the malleus is a small elevation called the lateral process of the malleus the part of the tympanic membrane superior to the lateral process of the malleus is thin and is called the flaccid part /pars flaccida the remaining part of the membrane is thick and is called the tense part / pars tensa The pars flaccida lacks the radial and circular fibers present in the remaining part of the membrane in the anterior-inferior quadrant of the membrane is a bright triangular reflection of light called the cone of light This region is usually visible when examining the tympanic membrane with an otoscope

11. innervation external surface of the tympanic membrane is supplied; the auriculotemporal nerve (a branch of CN V 3 ) {main contribution} a small auricular branch of the vagus (CN X) The internal surface of the tympanic membrane is supplied by the glossopharyngeal nerve (CN IX) Clinical anatomy External Ear Injury Bleeding within the auricle resulting from trauma may produce an auricular hematoma Acute Otitis Externa Otitis externa is an inflammation of the external acoustic meatus The infection often develops in swimmers who do not dry their meatus after swimming and/or use ear drops it may also be the result of a bacterial infection of the skin lining the meatus

12. Middle Ear is the narrow air-filled chamber in the petrous part of the temporal bone It has a cavity called tympanic cavity parts The cavity has 2 parts: tympanic cavity proper epitympanic recess T ympanic cavity proper is the space directly internal to the tympanic membrane while the space superior to the membrane is called the epitympanic recess The middle ear communicates with the mastoid area/ mastoid antrum posteriorly It communicates anteriorly with the nasopharynx via the pharyngotympanic tube

13. contents of the middle ear : Auditory ossicles ( malleus , incus , and stapes ) Stapedius and tensor tympani muscles Chorda tympani nerve, a branch of CN VII Tympanic plexus of nerves Walls of the Tympanic Cavity The middle ear is shaped like a narrow box with concave sides It has 6 walls, which include; Tegmental wall (roof) Jugular wall (floor) membranous wall (lateral wall ) labyrinthine wall (medial wall ) carotid wall (anterior wall) Mastoid wall (posterior wall)

14. Tegmental wall (roof) : is formed by a thin plate of bone called the tegmen tympani This bone separates the tympanic cavity from the middle cranial fossa jugular wall (floor ) is formed by a layer of bone that separates the tympanic cavity from the internal jugular vein Near the medial border of the floor is a small aperture , through which the tympanic branch from the glossopharyngeal nerve [IX] enters the middle ear Membranous wall (lateral   wall) is formed mostly by the tympanic membrane and superiorly by the bony wall of the epitympanic recess labyrinthine wall (medial wall ) separates the tympanic cavity from the internal ear also the lateral wall of the internal ear

15. features on this wall include; promontory of the labyrinthine wall : a round bulge produced by the basal coil of the cochlea Oval window Round window carotid wall (anterior wall): separates the tympanic cavity from the carotid canal superiorly, it has the opening of the ; pharyngotympanic tube canal for the tensor tympani mastoid (posterior) wall   has an opening called the aditus to the mastoid antrum The aditus to the mastoid antrum connects the tympanic cavity ( epitympanic recess) to the mastoid air cells (sinus ) Note: The mastoid antrum is a cavity continuous with collections of air-filled spaces (the mastoid cells ), throughout the mastoid part of the temporal bone

16. Other features on the mastoid wall are : the pyramidal eminence, a small elevation through which the tendon of the stapedius muscle enters the middle ear the opening through which the chorda tympani nerve , a branch of the facial nerve [VII], enters the middle ear Clinical anatomy Mastoiditis : Infection within the mastoid antrum and mastoid cells