ANATOMY AND PHYSIOLOGY OF THE EAR Yard Doc

ANATOMY AND PHYSIOLOGY OF THE EAR Yard. Doc. Dr. Müzeyyen Doğan

Learning goal and objectives of the lesson Learning goal of the lesson: The learner should know the basic anatomic structures and physiology of external, middle and inner ear Learning objectives of the lesson the learner will be able to: n identify the anatomic structures of the external, middle and inner ear n identify the physiology of the hearing n identify the physiology of the balance Skill objectives the learner will be able to ear examination

OUTER EAR n n Consists of the auricle and EAM Skin-lined apparatus Approximately 2. 5 cm in length Ends at tympanic membrane

OUTER EAR n n Auricle is mostly skinlined cartilage External auditory meatus n n Cartilage: ~40% Bony: ~60% S-shaped Narrowest portion at bony-cartilage junction

Anatomy and Physiology n EAC is related to various contiguous structures n n n Tympanic membrane Mastoid Glenoid fossa Cranial fossa Infratemporal fossa

Anatomy and Physiology n n n Squamous epithelium Bony skin – 0. 2 mm Cartilage skin n n 0. 5 to 1. 0 mm Apopilosebaceous unit

The Middle Ear: n n n A cleft within the temporal bone Lining is mucous membrane Tympanic Membrane separates it from EAC Eustachian tube connects it to nasopharynx Also Connected to Mastoid Air Cells

Middle Ear Structures 1 - Malleus 2 - Incus --Ossicles 3 - Stapes 4 - Tympanic Membrane (Eardrum) 5 - Round Window 6 - Eustachian Tube

Middle Ear Muscles 1. The Stapedius Attaches to Stapes, Contracts in Response to Loud sounds, chewing, speaking; Facial (VIIth cranial) nerve 2. The Tensor Tympani Helps open Eustachian tube

Ligaments of Middle Ear n Function n restrict and confine the effect of ossicles to act as a lever n restrict movements to reduce the chance of damage to the inner ear n prevents distortion to sound

Middle Ear Functions n Impedance Matching n Filtering n Acoustic Reflex

Impedance Matching n The middle ear allows the impedance matching of sound traveling in air to acoustic waves traveling in a system of fluids and membranes in the inner ear

Acoustic Reflex n The movement of the ossicles may be stiffened by two muscles, the stapedius and tensor tympani, which are under the control of the facial nerve and trigeminal nerve, respectively. These muscles contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. This is called the acoustic reflex

Middle Ear Transmits Energy by Two Pathways:

MECHANISMS OF MIDDLE-EAR GAIN Acoustic Coupling Ossicular Coupling • • Area Difference (TM to footplate) Lever Action (Malleus to Incus)

Acoustic Coupling n The collected pressure of sound vibration that strikes the tympanic membrane is therefore concentrated down to this much smaller area of the footplate, increasing the force but reducing the velocity and displacement, and thereby coupling the acoustic energy.

Anatomy and Physiology • Ossicular Amplifier System

MIDDLE-EAR GAIN n The ossicles are classically supposed to mechanically convert the vibrations of the eardrum, into amplified pressure waves in the fluid of the cochlea (or inner ear) with a lever arm factor of 1. 3. Since the area of the eardrum is about 17 fold larger than that of the oval window, the sound pressure is concentrated, leading to a pressure gain of at least 22.

Function of Middle Ear n Conduction n n Protection n Creates a barrier that protects the middle and inner areas from foreign objects Middle ear muscles may provide protection from loud sounds Transducer n n n Conduct sound from the outer ear to the inner ear Converts acoustic energy to mechanical energy Converts mechanical energy to hydraulic energy Amplifier n n 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)

Ear

INNER EAR : n Cochlea – hearing n Vestibule – static equilibrium n Semicircular canals – dynamic equilibrium

OHC vs. IHC Function n n Vestibulocochlear nerve – cranial nerve VIII Audible range: 20 -- 20, 000 hertz Ossicles amplify sound 22 X Some nerve fibers cross over to opposite side of brain

Hair Cells n n n Outer Hair Cells Inner Hair Cells OHC movie

OCH Cilia Theory: Tip-links <<<IHC OHC >>>

Equilibrium – Balance Static equilibrium – maintenance of body posture relative to gravity while the body is still. Dynamic equilibrium – maintenance of the body posture (mainly the head) in response to sudden movements. Tracking a moving object.

Static Equilibrium Inside the vestibule are two chambers : utricle and saccule. Regions of hair cells and supporting cells called maculae. Otoliths – “ear rocks”

Dynamic Equilibrium Semicircular canals In ampulla is the crista ampullaris – contains hair cells and supporting cells covered by a gelatinous mass called the cupula. Neurological connections between eyes and semicircular canals – for tracking Nystagmus