Ear

EARLecturer:

JIM CALUAG, M.D.

ANATOMY

PART 1:

The EAR• The Organ of

Hearing and Balance

• Attached to Temporal Bone

5 PARTS OF THE TEMPORAL BONE

ANATOMIC SUBDIVISIONS

EXTERNAL EAR• Outside the Head• Made up of Pinna

and EAC• Land Marks:

1. Helix and Anti Helix

2. Tragus & Anti-tragus

3. Conchae and Lobule

4. Meatus and Canal

• Canal is divided into Outer Soft Tissue and Inner Bony Part

• Junction is the ISTHMUS which is the Anatomical Constriction

MIDDLE EAR• Wedge-shaped cavity with 6 walls

boundaries1. Superior – TEGMEN TYMPANI2. Inferior – JUGULAR BULB3. Medial – OVAL and ROUND

WINDOWS; LATERAL SEMI-CIRCULAR CANAL and BONY PROMONTORY

4. Lateral – EAR DRUM3 layers: Outer epithelium Middle Fibrous Inner Mucosal

5. Anterior – TENSOR TYMPANI; Internal Carotid Artery; EUSTACHIAN TUBE (37mm Length)

6. Posterior – FACIAL CANAL (decending portion turns downward to exit into the Stylomastoid foramen)

• 2 branch of Nerve in this decending part:1. Stapedius Muscle

– attached to the stapes (the Horshoe in the illustration)2. Chorda tympani – attached to the ear drum

• a.k.a. Tympanic Membrane;

• Pearly white, pearly gray in color divided into Pars Flaccida & Pars Tensa by Maleolar fold

• PARS FLACCIDA-retracts when ET is Blocked & Bulges if there is Middle Ear Effusion

Ear Drum

Eustachian Tube• Partly bony (always

open) & Partly cartilagenous (closed at the pharyngeal end EXCEPT when swallowing or Yawning)

• The ET Lumen is opened by:1. Contraction of TENSOR & VELI PALATINI

• Tensor Veli Palatini – innervated by the mandibular branch of CN V from the Otic Ganglion

• Levator Veli Palatini – innervated by CN X

• Tensor Tympani – arises from the Cartilagenous end of ET.ACTION: to draw the handle of the malleus inward innervated by the motot root of CN V

• Stapedius muscle – lies in the posterior part of the middle ear below the aditus attached to the head of the stapesACTION: to draw the head of the stapes outward and downward, innervated by CN VII

• Ossicular Chain – suspended in the Middle ear cavity forming a chain for conduction of vibrations from the drum to the oval window

• MALLEUS, INCUS AND STAPES• Deeper Auricular Branches of

the Internal Maxillary Artery –Blood Supply of the Middle Ear

• Nerve Supply – Auriculotemporal branch of CN V, Auricular branch of CN X and Tympanic Branch of CN IX

INNER EAR• a.k.a. Labyrinth• With Bony and Membranous Part

Osseous Labyrinth

• Hard Bony Shell• Mediately situated in the middle

ear space• 2 parts:

1. COCHLEA-lies infront of the vestibule. Resembles a snail

shell of 2 ½ turns w/ its Central Conical Axis (MODIOLUS)2. SEMICIRCULAR CANAL

• 3 openings of Cochlear Canal:1. ROUND WINDOW2. The COCHLEAR AQUEDUCT3. OPENIND OF THE VESTIBULE

Membranous Labyrinth• Filled with endolymph in the

bony labyrinth• Consists of 2 Sacs:

UTRICLE & SACCULE containing sensory epithelium innervated by the vestibular part of CN VIII

• Ends Organ of Hearing are found in the Cochlear Duct

• COCHLEAR DUCT – a spiral tube superiorly bounded by the Reissner’s membrane and inferiorly by the Basilar Membrane

• SCALA VESTIBULI – above the Cochlear Duct (Perilymph)• SCALA TYMPANI – below the Cochlear duct (Perilymph)

Perilymph EndolymphVOLUME 78.3 cu.mm 2.76 cu.mm.Na+Content 310 mg/100ml 15mg/100mlK+ Content 30mg/100ml >600mg/100mlCHON 70-100mg/100ml 20-30mg/100mlPH 7.2 7.5

• INTERNAL AUDITORY LABYRINTH – blood supply to the Cochlea

• ORGAN of CORTI – Epithelial structure on top of the basilar membrane divided by a tunnel composed of 2 rows of Rods (Rods of CORTI)

• Tectorial Membrane - forms of the superior surface of the Organ of Corti made up of fine, colorless fibers in a transparent matrix with a hair cells embedded in it

• Spiral Ganglion of Corti –has an average of 31,000 ganglion cells, each inner hair cell has an innervation from 2 or more nerve fibers.

PART II:

PHYSIOLOGY

AUDITORY SYSTEM• Conducts acoustic energy to the inner

ear where it is converted to impulses in the Auditory nerve

• Impulses are processed in the higher centers of the auditory chain from the Cochlea to the superior olive; to the lateral lemniscus; to the Superior Colliculus to the medial geniculate body, to the Auditory Complex

• Sound waves travels the ear canal causes the ear drum to vibrate which causes vibration of the ossicles resulting to Perilymphatic Motion

• IMPEDANCE MATCHING – process by which acoustic energy in the airborne sound is transformed to Vibratory energy in the Cochlea

• The Stapedius and the Tensor tympani contracts to protect the inner ear against over stimulation by Stiffening the OSSICLES

• Movement of the Footplate of the stapes results to Perilymphatic motion using hair cells distortion giving rise to an electrical potential that triggers the nerve impulse

VESTIBULAR SYSTEM• Controls movements of the Body in space• Otolith Organs – sensitive to linear acceleration and aids in

postural balance• Semicircular Canal – responds to angular acceleration and aids in

the coordination of head and eye movements.• Receptor Units – hair cells located in the CRISTAE of Semicircular

Canal and Maculae of Otolith Organs• Due to Inertia, movement of endolymph causes displacement of

the hair cells opposite to the direction of the acceleration stimulus.• Stimulation of the Vestibular Organs creates a neural excitation

that travels via the vestibular nerve to the 4 vestibular nuclei in the brain

• NYSTAGMUS – is a Reflex Eye Movement elicited upon stimulation of the semicircular canals

• UTRICLE – important in orientation to gravity and linear acceleration and controls movement needed to maintain an upright posture in the presence of a displacing linear force

PART IIIEMBRYOLOGY AND

CONGENITAL ANOMALY

EMBRYOLOGY• EXTERNAL EAR – modification of the

surface ectoderm• MIDDLE EAR – an air sinus and

develops as an outpouching of the pharynx

• Cochlea – develops parallel with the middle ear and Ossicles

DEVELOPMENT OF THE EXTERNAL AND MIDDLE EAR

• 9 – 10 DAYS AOG (at 4 mm size of the EMBRYO) the Tube Tympanic recess forms an expanded cavity with the lateral extentions of the 1st, 2nd and 3rd branchoal arches with the 1st and 2nd pouches

• The Lateral part becomes the middle ear and pharyngeal midline structures become the Eustachian Tube

• The Auditory meatus develops and thickening of the ectoderm at the upper end of the 2nd external pharyngeal cleft

• Circular area of contact between the ectodermal meatal plug and the ectodermal tubotympanic recess becomes the tympanic membrane

• The cartilagenous otic capsule conceals the inner ear and later becomes petrous bone

• Anterior to the tubo tympanic recess- Meckles Cartilage (1st Arch) it’s upper part forms the Malleus and Incus

• Posterior to the Tubo tympanic recess- Reichert’s Cartilage (2nd Arch) gives rise to the Stapes, the Stylohyoid ligament and the Upper body of the hyoid

• The bony canal develops as an extention of the tympanic ring by intramembranous ossification.

• 3 layers of the Drum:outer ectodermmiddle mesoderminner endoderm

• Irritation of the Auricular branch of CN X may cause reflex coughing, vomiting or Sneezing because it is the only somatic afferent branch of formerly known as ALDERMAN’S NERVE

• The mastoid Antrum presents the posterior extension of the Middle Ear

• The ossicles are extramucosal and secondarily incorporated to the M.E. by formation of attic recesses

DEVELOPMENT OF INNER EAR• Develops as an ectodermal thickening on the

lateral surface of the head at the level of the 4th ventricle in embryos of 4mm in size (9-10days)

• 14 – 15 days (6mm size) –Endolymphatic ducts• 37 days (15mm size) – Semicircular Canal• CRISTAE – derived from the Ampullae of the

Semicircular Canals• ORGAN OF CORTI – derived from Cochlear duct

DEVELOPMENT OF THE TEMPORAL AND MASTOID BONE• the Temporal Bone is separated into 3

parts:PETROUS BONESQUAMOUS BONETYMPANIC BONE

• It is pneumatized by the extension of the epithelial sac from the middle ear to the bone marrow

• 3 degrees of Temporal Bone pneumatization:Pneumatic Bone (well-pneumatized)Diploic Bone (partially pneumatized)Sclerotic bone (not pneumatized)

• Union of the Squamous and Petrous bone forms the mastoid process and the antrum (entrance to this antrum is through the Aditus

CONGENITAL ANOMALIES

EXTERNAL EAR• Maldevelopment of the

1st and 2nd Arches• MACROTIA – abnormally

large ear• MICROTIA – abnormally

small ear

• Lop Ear – excessive protrusion

BEFORE AFTER

MIDDLE EAR• Ossicular chain maybe congenitally

deformed, disrupted or fixed• Common deformities include a missing

part of the Incus and fixation of the Stapes

• Stapedectomy and Prosthesis replacement re-establish hearing if the stapes is fixed

INNER EAR• MICHEL’S DEAFNESS - Total lack of development of the

inner ear, Autosomal Dominant• MONDINI’S DEAFNESS – partial aplasia of the inner ear

resulting in a flattened cochlea with only 1 ½ turns associated with dysgenesis of the organ of Corti, Autosomal Dominant

• SCHEIBE’S DEAFNESS – the bony labyrinth is fully develop but the cochlear duct and the saccule is represented by undifferentiated cells, Autosomal Recessive

• ALEXANDER’S DEAFNESS – aplasia of the Cochlear duct in which the Organ of Corti and Adjacent ganglion cells are severely affected resulting to High Frequency SNHL

INNER EAR• WAARDENBURG’S

DISEASE - there’s lateral displacement of the Lacrimal points and medial canthus, hyperplasia of eyebrow, flat nasal root and mild severe SNHL

• ALBINISM – characterized by severe- profound SNHL maybe Autosomal dominant, recessive or sex-linked

• Onychodystrophy – affected siblings have small, short fingernails, toenails and SNHL probably a recessive trait

• Usher’s Syndrome – presents with progressive retinitis pigmentosa and moderate-severe SNHL, recessive transmission

• TRISOMY 13-15 D – includes low set of ears, undifferentiated pinna, absence of external and middle ears, cleft lip and palate, aplasia of the optic nerve, microphthalmia and colobama iridis

• TRISOMY 18 E – includes flexion of the index finger over the 3rd finger, a prominent occiput, micronathia, low sets of ear and malformed pinna, patient dies in infancy

• RUBELLA – in the 1st trimester results in SNHL pathology shows aplasia of the Saccule and the Organ of Corti and patients may also suffer from other defects such as cardiac anomalies, blindness and retardation

• KERNICTERUS – results from RH blood incompatibility of the blood of the parents characterized by Bilirubin deposition in the brain, there’s jaundice, retardation, cerebral palsy and SNHLTX : Post partum exchange transfusion

• CRETINISM – thyroid disease associated with deafness referred to as Endemic Cretinism. Presents with mixed hearing loss

• HURLER’S SYNDROME – results in skeletal deformity, dwarfism, retardation, blindness and profound SNHL transmitted as a recessive trait or it may be sex-linked

• KLIPPEL-FEIL SYNDROME – skeletal defect such as fusion of the cervical vertebra, Spina Bifida, Scoliosis, Torticollis associated with vestibular dysfunction and profound SNHL. Autosomal Recessive

• ALSTROM’S DISEASE – features of Obesity, DM, Retinitis pigmentosa and progressive deafness

Klippel-feil

• CROUZON’S DISEASE – craniofacial dysostosis is presented by premature closure of the cranial suture, short upper lip, protruding lower lip, exophthalmos, hook nosed. Atresia of the external meatus and mixed deafness. Autosomal dominant.

• RICHARD’S-RUNDELL SYNDROME- features of ataxia, hypogonadism, mental deficiencies & severe SNHL which is total by 5-6 years of age.

• ALPORT’S DISEASE – a progressive glomerulonephritis that usually begins in childhood, progressive S.N.H.L. increases as the renal malfunction worsens

The end…