Anatomy of the Ear Stefan Sivkov Dept of

Anatomy of the Ear Stefan Sivkov Dept. of Anatomy, Histology and Embryology

Major Divisions of the Ear Peripheral Mechanism Outer Ear Middle Ear VIII Inner Cranial Ear Nerve Central Mechanism Brain

External ear, Auris externa Auricula Meatus acusticus externus Middle ear, Auris media Cavitas tympani Membrana tympanica Ossicula auditus Tuba auditiva Inner ear, Auris interna Labyrinthus membranaceus - Labyrinthus vestibularis - Labyrinthus cochlearis Labyrinthus osseus - Vestibulum - Canales semicirculares ossei - Cochlea - Meatus acusticus internus

Outer Ear Pinna Preauricular Tags Pinna Preauricular Pits EAM Cerumen External Auditory Meatus Function EAM resonance

Function of Outer Ear n n n Collects sound Localization Resonator Protection Sensitive (earlobe)

Pinna The visible portion that is commonly referred to as "the ear" n Helps localize sound sources n Directs sound into the ear n Each individual's pinna creates a distinctive imprint on the acoustic wave traveling into the auditory canal n

External Auditory Meatus n Extends from the pinna to the tympanic membrane – About 26 mm in length and 7 mm in diameter in adult ear. – Size and shape vary among individuals. n n Protects the eardrum Resonator n The net effect of the head, pinna, and ear canal is that sounds in the 2, 000 to 4, 000 Hz region are amplified by 10 to 15 d. B. – Provides about 10 decibels (d. B) of gain to the eardrum at around 3, 300 Hertz (Hz). – Sensitivity to sounds greatest in this frequency region – Noises in this range are the most hazardous to hearing

Outer ear Tissues: elastic cartilage covered with skin A. Meatus acusticus externus besides the hair follicles and fat glands contains: Glandulae ceruminosae – modified sweat glands on the lateral wall of the canal. Сerumеn (ear wax) combination of wax and fat glands secret and desquamated epithelial cells.

Middle Ear Tympanic Cavity Tympanic Membrane Ossicles Middle Ear Muscles Eustachian Tube Mastoid

Function of Middle Ear n Conduction – Conduct sound from the outer ear to the inner ear n Protection – Creates a barrier that protects the middle and inner areas from foreign objects – Middle ear muscles may provide protection from loud sounds n Transducer – Converts acoustic energy to mechanical energy – Converts mechanical energy to hydraulic energy n Amplifier – Transformer action of the middle ear – only about 1/1000 of the acoustic energy in air would be transmitted to the inner-ear fluids (about 30 d. B hearing loss)

Tympanic cavity • • • Volume – 1. 5 ml Form – flatten drum Structure – six walls: - Lateral - Medial - Anterior - Posterior - Superior - Inferior

Lateral wall

Tympanic Membrane Separates outer ear from middle ear n Barrier from foreign objects n Cone-shaped in appearance n – about 17. 5 mm in diameter Vibrates in response to sound waves. n The membrane movement is incredibly small – as little as one-billionth of a centimeter n

Tympanic membrane Two parts: Pars flaccida – upper, thin, loose Pars tensa – lower, tense Three layers: 1. Outer, cutaneous – continuation of the canal skin. No hairs and glands. 2. Middle, fibrous – elastic fibers. 3. Inner, mucous – tympanic cavity lining

Medial wall, paries labyrinthicus Most complex. On this wall are distinguished: -fenestra vestibuli -fenestra cochleae -promontorium -prominentia canalis semicircularis lateralis - prominentia canalis facialis Superior wall, paries tegmentalis Separates tympanic from cranial cavity. Children less than 2 years – infections of the middle ear can pass to the cranial cavity.

Inferior wall, paries jugularis Separates tympanic cavity from fossa jugularis Anterior wall, paries caroticus Separates tympanic cavity from canalis caroticus -canalis musculotubularis Posterior wall, paries mastoideus Composed of: • Styloid complex of Procter • Antrum mastoideum • Fossa incudis

Auditory (Eustachian) tube Connects tympanic cavity with pharynx Two openings: • ostium pharyngeum tubae • ostium tympanicum tubae. Two parts: • bony • cartilagenous Function: • Equalizes pressure on both sides of tympanic membrane for optimal hearing.

Ossicles n Malleus (hammer) n Incus (anvil) n Stapes (stirrup) smallest bone of the body

Inner Ear Vestibular semicircular canals utricle and saccule Auditory Cochlear traveling wave Vestibular traveling wave pathologies

Inner ear Two compartments: (а) Bony labyrinth and (b) Membraneous labyrinth. Bony labyrinth: complex cavity in dense bone (pars petrosa) Parts of the bony labyrinth: a. Vestibulum. b. Semicircular canals. c. Cochlea.

Bony labyrinth. Labyrinthus osseus Vestibulum and semicircular canals

Vestibulum Two walls: External and internal. External wall has • Fenestra vestibuli. Internal wall has: • Recessus ellipticus • Recessus sphericus • Recessus cochlearis • Maculae cribrosae superior, medius, inferior

Openings into vestibulum a. Fenestra vestibuli. b. Fenestra cochleae. c. Openings (5) of the semicircular canals d. Aqueductus vestibuli

Semicircular canals 3: anterior, posterior and lateral. Have ampulla and crus. Canalis semicircularis lateralis –horizontal. - eminentia canalis semicircularis lateralis on the medial wall of tympanic cavity. Canalis semicircularis anterior –frontal. - eminentia arcuata on pars petrosa of os temporale. Canalis semicircularis posterior –sagittal

Labyrinthus osseus. Cochlea Meatus acusticus internus

Охлюв • Cone-shaped: base and apex. • Canalis spiralis cochleae - promontorium, on the medial wall of tympanic cavity. • Modiolus - canales longitudinales modioli. • Lamina spiralis ossea -hamulus Divides canalis spiralis cochleae into: • Scala tympani • Scala vestibuli

Labyrinthus membranaceus

Function of Inner Ear n Converts mechanical sound waves to neural impulses that can be recognized by the brain for: – Hearing – Balance

Membraneous labyrinth. Labyrinthus membranaceus • Closed system of sacs and ducts underling the bony labyrinth. • Filled with endolymph. • Two parts: vestibular & cochlear.

Vestibular labyrinth Composed of : • Two bags - sacculus et utriculus • Three ductus semicirculares • One ductus endolymphaticus.

Cristra ampullaris

Balance Linear motion n Rotary motion n

Sensory cells (Epitheliocytus pilosus)

Macula utriculi (sacculi) Otoliths. Statoconia

Static balance Maculae react to gravitational forces and participate in maintaining the static balance.

Dynamic balance Cristae ampullares react to rotatory movements and paticipate in dynamic balance.

Cochlea The cochlea resembles a snail shell and spirals for about 2 3/4 turns around a bony column n Within the cochlea are three canals: – Scala Vestibuli – Scala Tympani – Scala Media n

Cochlear labyrinth Spiral canal - ductus cochlearis. Occupies scala media of the spiral canal. Has two blind ends - cecum vestibulare and cecum cupulare. Has three walls: • paries vestibularis • paries externus • paries tympanicus- organ of Corti, basal membrane

Organ of Corti n End organ of hearing

Organ of Corti

Sensory cells of the organ of Corti