1. Anatomy & Physiology of the Ear


Masters Medicine (ENT) Flashcards on 1. Anatomy & Physiology of the Ear, created by t.whittingham on 16/01/2016.
Flashcards by t.whittingham, updated more than 1 year ago
Created by t.whittingham about 8 years ago

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The Auditory Process Converts sound waves (air vibrations) into vibrations within the inner ear (fluid vibrations). -> These fluid vibrations then excite receptor cells in the inner ear and cause impulses in the auditory nerve. -> The nerve impulses travel to the auditory cortex and are perceived by the brain as sound.
Function of the external ear Collection & transmission of sound.
Function of the middle ear Amplification of sound. Transfers sound from air into fluid-membrane waves in the inner ear.
Function of the inner ear. Conversion of sound to nerve impulses (cochlea). Balance function (Vestibular labyrinth)
Components of the Outer Ear (2) 1. Pinna 2. External Auditory Canal (External Auditory Meatus)
Pinna Visible part of ear. Acts as a funnel to collect sound -> directs it to the auditory canal. Skin closely adherent to cartilage.
External Auditory Meatus (External Auditory Canal) Resonating tube -> transmits sound to eardrum. Extends from the pinna to the eardrum. Approximately 24mm long. Outer 1/3 = cartilage Inner 2/3 = bone
Function of wax in the Ear Canal Protects ear -> traps dust & particles. Self-cleaning -> moves laterally (outwards) - migrates skin from surface of eardrum and deep external meatus.
Physiology of the external ear 1. Collection + Localisation of sound -> detects sound source e.g. left/right - differential volume & sound shadowing effect of head - ear trumpet effect. 2. Resonance -> ear canal & pinna act like wind instrument. -> speech frequencies resonate in ear canal & amplify.
Components of the Middle Ear (4) 1. Tympanic Membrane 2. Tympanic Cavity 3. Ossicles 4. Eustachian Tube Middle ear cavity = inside temporal bone of the skull.
Tympanic Membrane (Eardrum) Separates ear canal from middle ear cavity -> functionally part of middle ear. Approximately 1cm diameter. Function = transmits sound from air to ossicles in middle ear.
3 layers of the Tympanic Membrane 1. Outer layer = squamous epithelium (normal skin - continuous with ear canal). 2. Middle layer = fibrous, with radial & circular fibers to stiffen ear drum. 3. Inner layer = mucous membrane.
Tympanic Cavity Small cavity surrounding the bones of the middle ear. Bound by the: - Oval window - Round window - Promontory
Ossicular Chain Whole system acts as a vibrating membrane with attached bony levers working a small piston to pump sound into fluid of inner ear. 1. Malleus 2. Incus 3. Stapes
Malleus Also called the hammer. Largest of the ossicles. Vibration of tympanic membrane moves whole malleus.
Incus Also called Anvil. Acts as a lever transferring vibration from malleus to the stapes.
Stapes Stirrup shaped bone. Attaches to long process of incus. Smallest bone in the human body. Footplate lies in oval window of cochlea - transmits vibrations into inner ear.
Stilleto-Heel Effect Size ratio of tympanic membrane to oval window = approximately 20:1. = Middle ear amplifier.
Eustachian Tube Ventilates & drains middle ear cavity. Opens into back of nasal cavity (nasopharynx). - 1/3 bone, 2/3 cartilage. - Closed at rest, opens with yawning & swallowing.
Muscles of the Middle Ear 1. Tensor Tympani Muscle 2. Stapedius
Tensor Tympani Muscle Attaches to upper end of handle of malleus. Protects ear against sudden loud sound -> dampens sounds.
Stapedius muscle The smallest skeletal muscle in the human body. Stiffens stapes as reflex against loud noise.
Nerves of the Middle Ear 1. Chorda Tympani Nerve = crosses middle ear - transfers taste fibers from tongue & sends fibers to salivary glands in mouth. 2. Facial Nerve (C.N. VII)
Glue Ear Build up of mucus in middle ear cavity & eustachian tube -> prevents ear drum from vibrating properly -> causes conductive hearing loss.
Treatment of Glue Ear 1. Grommets = small tube inserted into ear - helps drain fluid and maintain ear pressure. 2. T-Tubes = long stay ventilation tube - bigger version of grommet.
Tympanometry Objective test of middle-ear function. Tests mobility of ear drum & conduction bones by creating variations of ear pressure in ear canal.
Acute Otitis Media Inflammatory disease of the middle ear -> dysfunction of the eustachian tube. Difference to Glue Ear = also includes other symptoms.
Perforated Ear Drum Hole in ear drum -> pressure leaks through hole -> eardrum doesn't vibrate properly.
Attic Perforation Perforation in the superior part of the eardrum.
Cholesteatoma An uncommon abnormal collection of skin cells inside the ear. Associated with chronic infection. Can lead to erosion of ossicles, inner ear damage, facial nerve damage & in extreme cases, meningitis or brain abscess.
Causes of conductive hearing loss (6) 1. Wax 2. Perforations 3. Glue Ear 4. Chronic Infection 5. Scarring 6. Damaged Ossicles
Inner Ear - 2 main functional parts 1. Cochlear system = dedicated to hearing 2. Vestibular system = dedicated to balance
Bony Labyrinth One of the hardest bones in the body - protects nervous system. - Oval window = way in - Round window = way out Composed of 3 parts: 1.Cochlea 2. Vestibule 3. Semicircular Canals
Membranous Labyrinth. Collection of fluid-filled tubes inside the bony labyrinth. Separated from bony labyrinth by fluid called Perilymph.
Cochlea Spinal-shaped cavity. Receives vibrations from Stapes. Ascending passage = scala vestibuli Descending passage = scala tympani
Cochlear Duct (Scala Media) Lies between the Scala Vestibuli & Scala Tympani. Filled with Endolymph.
Basiliar Membrane & Reissner's Membrane Flexible - respond to vibrations travelling up the Scala Vestibuli. Movement of membranes send vibrations back down to the Scala Tempani.
Organ of Corti Situated on the basiliar membrane. Stimulated as the basiliar membrane vibrates -> sends nerve impulses to the brain via the cochlear nerve. Nerve impulses are generated by hair cells within the Organ of Corti.
Tonotopic Organization Low frequency sound are detected at the apex (top of cochlea) High frequency sound detected at basal turn (base of cochlea)
Pure Tone Audiometry Key hearing test used to identify hearing threshold levels of individual -> can determine degree, type & configuration of hearing loss. Normal hearing threshold = less than 20dB HL in young healthy adults with no ear disease & no family history of deafness or noise trauma.
Sensorineural Hearing Loss Type of hearing loss in which the root cause lies in the inner ear. Most common cause = age-related (presbycusis). Second most common cause = noise-induced hearing loss.
Vestibular Labyrinth The sensory system that provides the leading contribution about the sense of balance and spatial orientation -> for the purpose of coordinating movement with balance. Components: 1. Otolithic Organs (Utricule & Saccule). 2. Semicircular Canals.
Utricle & Saccule Sense linear accelerations and gravity. Maintain head & body position. Initiate reflexes to keep head upright.
Semicircular Canals 3 in each ear. Detects rotational movements.
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