Ear
Surgical anatomy
developmente of the ear
Auricle : developed from a series of six tubercles which form around the margins of the 1st visceral cleft .
Extarnal auditory canal : developed from the 1st visceral cleft .
Tempanic membarane : has 3 layers
Auter epithleal layer deve . from ectoderm of the cleft .
Middle fibrous layer deve . from mesoderm btween 1st visceral cleft and the tubotympanic recess
Inner layer deve . from entoderm which it is a parte of the tubotympanic recess .
Eustachian tube and Tympanic cavity : deve . from 1st and 2nd pharengeal pouches during 6-7 months of pregnency .
Inner ear deve . from neural crest at 16 weeks of pregnency .
Anatomy of the Ear :
External ear consist of two parts
1-auricle : has a framework of cartilage except in the lobule , the skin closely adherent to prerichondrium at the anterior surfec of the auricle .
2-Ext . aud . canal : extened for 2.5 cm in length , the outer 1/3 of the canal is cartilagenious part , the inner 2/3 of the canal is bony part .
Nerve supply of the ext . ear :
1- 5th , 7th ,9th 10th cranial nerve
2- lesser occipetal nerve C 1
3- greater auricular nerve C 2,3
Lymphatices : pre and post auricular L.N
Upper superfecial cervical L. N
Middle Ear claft : consist of
Eustachian tube : pass from anterior wall of tym panic cavity to the nasopharynex for 3.7 cm in length .
Tympanic cavity : this biconcave disc –shaped cavity
Anterio-posterior diameter is 1.3 cm , inferio-superior diameter is 1.5 cm ,
The width at the center is 2 mm .
Tympanic membaran : have 3 layers , the outer epithelial layer , the middle fibrous layer , the inner mucosal layer .
The tym . mem . have 2 parts ( pars tensa) lower parte which have fibrous layer ,
( pars flaccid ) upper parte without fibrous layer , between them theris anterior and posterior malleolar folds .
Medial wall of the tym . cavity contane :
Promontory which is the bony projection covering the basal turn of the cochlea.
Fenestra ovale occupied by the foot –plat of stapes .
Facial N pass horizontally above oval window .
Ampullry end of the horizontal semicircular canal above 2nd genu of the facial nerve .
Fenestra rotunda closed by mem . posterio-inferior to promontory .
Anterior wall : has 3 opening from abave ,
Canal of huguier for chorda tympani
Canal for tenser tympani muscle
3- Orifice of eust . tube .
Posterior Wall : have Opening as Aditus Connect epitympanum to the mastoid antrum , below aditus is the pyramid via it tendon of stapedus muscle pass .
Ossicles : 3 bones inside the tymp . cavity
Malleus 2- Incus 3- Stapes
Intratympanic muscle : 1-Ten sor tympanic muscle .
2-Stapedius muscle .
Nerve supply of middle ear claft :
Sensory , via tympanic plexus from 9th and 7th cranial nerve
Motor , mendibuler branch of 5th N to the tensor tympani muscle
Stapedial branch of 7th N to stap . Muscle .
Inner Ear : labyrinth
Its lies in the temporal bone ,the osseous labyrinth , has 3 parts , vestibule , bony semicircular canal , cochler
Membaranous labyrinth : consist of communicating sacs and ducts withen the bony labyrinth , as saccule and utricle in the
vestibule , semicircular ducts and cochler duct those sacs containing endolymph .
Organ of corti : neuroeptheial structures arranged alonge the inner edge of the basilar membarane of the membaranous
labyrinth .
Physiology of haering : the ear is divided in to two parts
Conducting parts as ext . ear , tymp . mem, ossiculer chain , Eustachian tube and labyrinthin fluid .
Sensory neural parts as organ of corti , 8th N and central connections .
The acoustic energy collacted by the large area of tymp . memb .applied via the ossiclies to the small area of stapes footplate ,
the ratio of theis areas 14 : 1 , also theres lever action of the ossiculer chain has mechanical advantage of 1.3 : 1 so both of
them give advantage of 18:1 lead to increase in the force applied by staps footplat according to this ratio .
Functional examination of hearing :-
1-Tuning fork tests forks of 256hz and 512hz are commonly used .
A-Rinne test : the patient usually asked to say whether the vibrating fork louder by air conduction (ac) close to the meatus or
by bone conduction (bc) with base of the fork on the mastoid bone , so when the fork becem inaudable by (ac) transferring it
to (bc)if its audable the duration is noted in second , if its not heard by (bc) the order is reversed start by (bc) than (ac) .
Normal subject = (ac) better then (bc) ----rinne +ive
Conductive deafness = (bc) better then(ac) ----rinne –ive
Sensorineural deafness = rinne +ive but often the (bc) not heard .
B-weber test : the fork put on forhead of the patient to see the difference between the two ears , in conductive deafness the
sound is heard in or towards the deaf ear , but in S.N.deafness the sound heard towards better ear .