Anatomy and Physiology Quiz 2
Cerumen Impaction by the Numbers
- 6 % of the general population - 10% of pediatric population - Up to 57% of elderly patients - 36% of cognitively impaired patients- ex- sometimes narrow ear canals -Unilateral impaction found in 75% of cases, with right ear impaction more common than left ear. -Highest prevalence rate in general population is in Nigeria (20%) -Cerumen impaction is the most common ear problems in school- aged children- their cartilage is not as efficient as adults for their is a difference in the mechanism.
The Auricle Structure
-Attaches to the side of the head at about 15-30 degree angle. -Consists of several pieces of cartilage that are held together by ligaments and muscles (vestigial) -No fatty layer truly cartilage -Susceptible to frost bite -Medial cartilage continues Into the external auditory canal -Three muscles are present in human auricle -Important in the hearing ability of animals -- these include people who could wiggle their ears
The Ear Canal - Cerumen
-Cerumen = ear wax -Two types of cells within the EAC contribute to the formation and secretion of cerumen - -Sebaceous glands -Ceruminous glands -Form secretions by passive breakdowns of cells, since they are incapable of producing active secretions -Cerumen typically only found in lateral third portion - or the cartilaginous portion -Differs in consistency based on age and race
External Ear and Sound localization
-Intensity is louder at 90 degrees than at 30 degrees -The maximum time difference between the ears is 760 micropascals. However we are able to pinpoint a sound in front of the head within 1-2 degrees. This corresponds to a time difference of only 13 microseconds. The cells within the auditory system which analyze acoustic information are sensitive to these microchanges.
The Ear Canal Structure
-Lateral 1/3 = cartilaginous portion, a continuation from pinna/auricle - can move and change shape. Chew and talk- anything with the jaw movement will change slightly. -Medial 2/3 = Bony portion. Crossing over into the skull. Temporal bones as your wall - fixed and will not move with any jaw movement
Tympanic Membrane Structure
-Lateral layer = epidermal lining of ear canal - skin -Medial layer = mucosal membrane of the middle ear -Separates the outer ear and the middle ear the whole TM -Lays at 55 degree angle (not perpendicular to the ear canal) -Most concave at the Umbo - part of the eardrum that attaches to the manubrium of the malleus (of the ossicles) -Important landmarks - -Manubrium at 1 o'clock on the right, 11 o'clock on the left -Cone of light- unique reflection of the Umbo when you do otoscopy. 5 o'clock on the right, 7 o'clock on the left
The Auricle Function
-Main purpose- sound collector due to the shape of the ear -500 Hz most effectively collected due to size and shape of pinna -Wavelength of frequencies in this range are smaller than the pinna and cannot pass around it- lower frequencies pass around the ear -Complex resonator- through the ridges and grooves -Wavelength of lower frequencies is too long and will pass around the head -Ridges and depressions on the pinna surface contribute to function as a complex resonator
Interaural Level Difference (ILD)
-Mainly affects high frequencies, 1500 Hz - dampening of the sound on the contralateral side -- volume side difference between the 2 ears - the brain will match the two inputs and see where the sound is coming from. -The difference in intensity of sound between 2 ears -Related to the head shadow effect -Mainly affects high frequencies -Above 1500 Hz -Dimension of the head is greater than the wavelength.
Interaural Time Delay (ITD)
-Mainly affects low frequencies, below 800 Hz, will take longer for a sound to be transmitted to reach the opposite ear. Timing is too close- brain can't equate the differences and to figure out where the sound is coming from. -The difference in arrival time of sound between ears. -Mainly affects low frequencies. -Below 800 Hz -Dimension of the head is smaller than 1/2 wavelength - auditory system can determine phase delays between ears.
Bony portion
-May not reach full maturation until end of third year of life. -Formed by 3 main structures- -Tympanic portion of the temporal bone. -Floor, anterior walls and inferior posterior wall -Squamous portion of the temporal bone -Roof and portion of the posterior wall -Condyle of the mandible (jaw) -Inferior- anterior wall at the temperomandibular joint- jaw and temporal bone joint
Outer Ear Pathologies
-Otitis Externa -Otomycosis -Perichondrial Hematoma -Exostoses -Osteoma -Carcinoma (Basal cell and/or squamous cell) -Canal cholesteatoma -Furunculosis
Outer Ear Acoustics
-The signal entering the ear canal does not equal the signal reaching the tympanic membrane. -There is shift both in phase and amplitude with the input vs. output. -Outpit is 6 dB gain and shifted by a quarter of a wave. The combined effect of alterations by the pinna and the ear canal is 20 dB -- from coming into the external ear (hitting the pinna) to the TM of the signal - not linear - does not have an impact as much in lower frequencies but more in higher frequencies because of the combined effect of the resonance of the ear canal (2,700) and the pinna (5000) -When you put them together - a wider range - 2,000-5,000 range is intentional - consonants, soft sounds here, hearing loss occurs first for humans
The Middle Ear Overview
-The tympanic cavity houses the whole middle ear. -Structures- tympanic membrane, the ossicles, the eustachian tube, -Function- transmit sound from acoustic energy (outer ear) to mechanical (vibrational energy) -Pathway- Tympanic membrane to ossicles- malleus to ossicles- incus, to ossicles- stapes to the oval window of the cochlea. *The stapes footplate connects to the oval window of the cochlea
The Ear Canal Structure Nerve Supply
-Trigeminal (V) -Facial (VII) -Glossopharyngeal (IX) -Vagus (X) -Stimulation of the medial portion of the canal can result- ear mold impressions - in a coughing reflex due to this nerve innervation -Ear canal is covered by an epidermal lining (skin) -Forms the most lateral layer of the tympanic membrane at the medial end of the external auditory canal.
Outer Ear Clinical Topics
-otoscopy - assessment of the outer ear and tymapnic membrane -Ear mold impressions -Cerumen impaction -Failure of the self-cleaning mechanism -Can cause pain -otalgia, conductive hearing loss, itching, tinnitus, vertigo -More common in those that wear hearing aids or earplugs -under-diagnosed and under-treated ~8 million cerumen removal procedures per year, within the scope of practice of audiologists, dependent on state licensure. Diagnosed by otoscopy
The Outer Ear Structure
2 main structures- -Pinna/auricle -External auditory canal/meatus -Most lateral component- pinna -Most medial component- tympanic membrane
The Outer Ear Function
2 major functions- 1. Sound collector -Collects acoustic energy -Funnels the energy toward the middle ear -Signal that enters the ear is NOT the same as the signal that is passed on to the middle ear. 2. Protector- ear wax (Cerumen) comes into play -Ceruminous secretions of hair follicles and glands have anti-fungal and antibacterial properties. -Secretions prevent growth of infections -Protects against foreign bodies entering the ear canal. -Barrier to protect sensitive structures of middle and inner ear.
The Ear Canal Primary Function
Acoustic Resonator -Signal that enters the canal is NOT the same as the signal that reaches the eardrum. -EAC is tube closed on one end- quarter wave resonator. -Length of EAC is 2.5 - 3 cm -Best boosts frequencies with wavelengths of 10-12 cm = 3,500- 4,000 Hz -10 - 15 dB amplification of sounds in the 3,000- 4,000 Hz range - absolute perfect ear quarter wave resonator - frequency in this range is a little wider because it is not perfect -EAC resonates a slightly wider range than of frequencies than if it were truly a tube closed on one end.
The Ear Canal Structure Adult
Dimensions- -2.5 cm to 3 cm in length -0.75 cm diameter -Hourglass S- shape; larger at orifice- opening, narrows in diameter to the isthmus, widens again towards the TM Shape- -Cylindrical - evenly shaped S shaped tube -Superior/posterior in cartilaginous portion to inferior/anterior in bony portion
The Ear Canal Structure Pediatric
Dimensions- -Variable, shorter and narrower Shape- -Cylindrical, straighter in shape
The Ear Canal Secondary Function
Directional Effects -Works along with the auricle Head Shadow Effect- the effect of the head on the transmission of sound. -Unequal effect on frequency -Dependent on wavelength- -Not as impactful of low frequencies- 250 Hz -6,000 Hz - is disrupted to the waves - transmission of higher frequencies is impeded on the contralateral side of sound input
Middle Frequencies
Is known as the transition zone 1000-1500 Hz -Both ITD and IID are used on some level - the two combined could assist in sound localization
Movement of the Ossicles
Malleus will pivot with the vibration of the tympanic membrane. Cause incus and cause stapes (stapes footplate) to project into pistol like motion, to the cochlea causing a traveling wave. This leads to the interpretation of sound.
The Ear Canal Function
Protection against infection and foreign bodies. -Physical shape of ear canal protect the middle ear and inner ear from external temperature changes. -Cerumen allows for the ear to utilize a self-cleaning mechanism -Cerumen migration occurs at 0.5 - 1 mm/day -Keeps the ear canal free of shred skin, keratinocytes and dried cerumen -Impaired migration leads to cerumen impaction when it isnt migrating effectively. -Self- cleaning system becomes less effective with age - cerumen impaction very common in the geriatric population and often requires removal. -Due to growth of ear hair -Age related effects on cartilaginous portion
The Auricle Function Continued
Sound locator -Comparison of signal between the two ears allows for location to be determined -Front vs. back -Up vs. down -Left vs. right -Interaural time difference (ITD) and Interaural intensity difference (IID), Duplex theory - includes both of them
Less dense portions of the temporal bone
Squamous- roof and part of posterior wall of external auditory meatus (ear canal) Mastoid- projects down to form mastoid process - area behind your ear where you put the bone oscillator Tympanic- floor, anterior wall, part of posterior wall of external auditory meatus. Petrous- houses inner ear and contains the internal auditory canal.
Bone of the Outer Ear
Temporal Bone Temporal bone is one of the strongest bones
The ossicles are suspended in the middle ear cavity by multiple ligaments and two muscles:
Tensor Tympani - innervated by CN V Stapedius- innervated by CN VII
Auditory System Overview
The stato-acoustic organ may be divided into- -External -Middle -Inner
Atresia
•Absence or abnormal narrowing of the external auditory canal •Bilateral or unilateral •Causes •Often congenital •Prevalence •1 in every 10,0000 to 20,000 births •Right ear more commonly affected than the left ear •Treatment •Evaluation by audiologist and speech language pathologist •Surgical interventions for ear canal and tympanic membrane reconstruction, known as atresia repair •Requires consistent follow-up for ear cleanings every 6-12 months •Bone anchored hearing aids or traditional hearing aids may be appropriate
The Middle Ear- Acoustics
•Acoustic Impedance •Impedance = the opposition to the flow of energy or the reluctance to accept energy •Resistance factor = The loss of energy caused by friction, independent of frequency • Mass Reactance = Mass of the object or system, directly proportional to frequency •Greater resistance to high-frequency sounds •Stiffness Reactance = Stiffness of the object or system, inverse relationship with frequency •Greater resistance to low-frequency sounds •The middle ear cavity is considered a stiff system that naturally attenuates low- frequency sounds
The Eustachian Tube Age Differences
•Adults: •2x as long •45 degree angle •Children: •1/2 as long •Flat, up to 10 degrees •Lengthens and becomes more vertical over time
Outer Ear Clinical Implications Overview
•All disorders of the outer ear can cause CONDUCTIVE hearing loss •Conductive hearing loss = an impairment of the transmission of sound from the environment to the cochlea- mismatch •Not all disorders of the outer ear will result in hearing loss •BUT all hearing loss from outer ear disorders will have a conductive component •Maximum conductive loss = 60 dB •Unilateral or bilateral
The Ossicles Overview
•Also known as Ossicular Chain •Series of three bones suspended in the middle ear cavity •Transmit vibrations of a sound wave from the tympanic membrane to the oval window of the cochlea
Microtia
•Congenital deformity resulting in an underdeveloped pinna •Unilateral or bilateral •Unilateral more common than bilateral •Classified by category ( Type 1 to Type 4) •Type 4 = Anotia - no pinna •Occurrence: 1-5 in every 10,000 live births •Causes •Unknown in most cases, typically occurs in the first few weeks of pregnancy •Potential genetic link •CDC found factors increase the risk: •Mother with diabetes •Mother who eats low carb diet •Does not have an impact on the internal structures of the ear •Diagnosis •Visible at birth •CT scan •Treatment •Dependent on the level of involvement •Surgical reconstruction of pinna •Typically done between age 4 and 10 years old •Bone-anchored hearing aids to bypass the dysfunction of the outer ear
Tympanic Membrane Structure Shape and Size
•Delicate, membrane boundary separating the outer and middle ear •Shape: Concave and cone-like •Displaced inward 2mm at tip of the cone = Umbo •At 55 degree angle •Size: •Adult: 8-9mm horizontal diameter, 9-10mm vertical diameter, .1mm thick •Child: Starts at 140 degree angle almost laying flat on the canal floor, and straightens over time •Very thin and highly compliant
1. Area differential between the TM and Stapes Footplate
•Largest contributor to the transformer action •Force that is applied over the tympanic membrane is directed toward a smaller structure (the stapes footplate) and thus increasing the force per unit area •Area of the TM = 55 mm2 •Area of the stapes footplate = 3.2 mm2 •Size Ratio = 55:3.2 or 17:1 •Total area of TM is closer to 83 mm2, but only 2/3 vibrates effectively and is considered 17:1 = 24.65dB
Collapsed Canals
•Lateral portion of the ear canal elongates to form an oval over time- tall and narrow- putting pressure on the pinna you get collapsed canals- when you put headphones in •Cartilaginous portion weakens and breaks down over time, becoming less effective and upholding the structure •Occurs when pressure is applied to the auricle •Can result in a false high frequency conductive hearing loss •Can be corrected by insert headphones •More common in geriatric population and pediatric populations •Found in 41% of elderly nursing home residents (Schaw and Goldbaum, 1980) •90% bilateral prevalence •Potentially more common in older white males -Inserts hold the ear canal open vs. supra-aural - the headphones are closed
The lever action of the ossicular chain
•Lever = manubrium of the malleus + long process of the incus •Lever moves as a unit •Provides a gain in force that is proportional to the ratio of the manubrium to the long process of the incus •Manubrium of the malleus > long process of the incus •= 1.3: 1 gain (~ 2.5dB)
The Eustachian Tube Function
•Main function: Controls the pressure of the head •"Ears pop" •Opening of the eustachian tube occurs when the levator veli palatini and tensor veli palatini muscles are activated •Opens when: •Chewing •Yawning •Pressure changes, such as flying •Valsalva Maneuver = forceful opening of the eustachian tube •Failure of the eustachian tube to open appropriately à infection, fluid, aural fullness
The Ossicles Structure
•Malleus, incus and stapes are the three smallest bones in the human body! •Size does not change over the lifetime •Connected with a ligament array
Middle Ear Anatomy- Tympanic Cavity
•Mastoid antrum: Posterior to epitympanum •Epitympanic recess (attic): Superior to TM •Mesotympanum: Medial to TM •Hypotympanum: Below TM
The Middle Ear Acoustics
•Middle ear = Dampens low frequency sounds •Hearing sensitivity across the frequency range of human hearing is not uniform •Most sensitive in the mid-frequency range •= The signal that enters the ear canal is very different than the signal that reaches the cochlea •Outer ear = Boosts 2000-7000 Hz range (up to 15 dB) •Middle ear resonance ~ 900 Hz •800 - 1200Hz •The resonance of the ossicles ~ 2kHz
The Middle Ear Transformer- Total
•Middle ear functions as an acoustic transformer or impedance-matching devices to improve the transmission flow of energy from a region of low impedance to one of high impedance •Components •Area differential = 17x boost •Lever Effect = 1.3x boost •Buckling Effect = 2x boost •Total Effect •An increase in energy at the oval window of 40:1 •Approximately 32 dB increase •** Frequency dependent and will vary dependent on specific dimensions and functions of individual middle ear systems
The Malleus "Hammer"
•Most lateral bone of the ossicular chain •Three segments: •Head - large bulb-shaped portion that projects up from the manubrium into the epitympanic process •Posterior surface contains an articular facet that connects to the Incus •Neck - A constriction in the bone located between the manubrium and the head •Also includes a small projection for the point of attachment of the tensor tympani muscle •Manubrium - Attached firmly to the medial side of the tympanic membrane
The Stapes "Stirrup"
•Most medial bone of the ossicular chain •Smallest bone in human body •Four Segments: •Head/Neck: Contains a concave articular facet that forms the point of connection to the incus •Two crura: Anterior and posterior, connect the footplate to the head/neck •Footplate: Covered by a thin later of cartilage and fastened to the bony wall of the oval window of the cochlea by the annular ligament
Stenosis
•Narrowing of the ear canal •Causes •Congenital •Result of multiple ear infections •Clinical presentations •Narrowed canal during otoscopy •Cerumen impaction likely •Conductive hearing loss •Treatment options •Surgical intervention to expand the ear canal using a stent •Reoccurrence occurs in small percentage of patients •Improvements in air conduction thresholds
Tympanic Membrane - 3 layers-
•Outer/lateral layer: Extension of epidermal lining of the EAC •Middle layer: Fibrous material that supports the tympanic membrane •Not evenly distributed à pars flaccida and pars tensa •Pars Flaccida (Schrapnell's Membrane) •Less density of supportive fibers, appearing thinner and more flaccid •Superior 1/9th of TM •Pars Tensa •High density of supportive fibers, creating a stiffer membrane more ideal for sound transmission •Remaining 8/9th of TM •Inner/medial layer: Membranous lining of the middle ear space •Tympanic Annulus: peripheral fibrocartilaginous ring of the tympanic membrane
The buckling effect of the curved membranous structure of the TM
•TM curves from its attachment to the rim of the EAC at both ends to the point where the manubrium attaches to the TM (the Umbo) •The curve results in greater movement of the curved membranes and less movement for the manubrium •Smaller displacement of the manubrium 🡪 a boost in force •= 2:1 boost
The Middle Ear Transformer
•The acoustic signal that reaches the eardrum travels through the air to the fluid-filled inner ear •Air = Low-impedance medium •Fluid = Significantly greater impedance • = "Impedance Mismatch" •Middle ear therefore must function as a transformer to overcome the impedance mismatch •Combination of three mechanisms: 1. Area differential between the TM and Stapes footplate 2. The lever action of the ossicular chain 3. The buckling effect of the curved membranous structure of the TM
The Incus "Anvil"
•The middle bone of the ossicular chain •Three segments: •Body •Anterior surface of the body is an articular facet that serves as the contact point for the connection of the incus to the malleus •Short Process = 5mm long •Arise at right angle from the body •Long Process = 7mm long •Medial end is covered with cartilage and articulates with the head of the stapes
The Ossicles Function
•The ossicles collectively transmit sound from the tympanic membrane to the cochlea •Air-filled ear canal to the fluid-filled cochlea
Tympanic Membrane Function
•Transmit sound from the external auditory canal to the ossicular chain or ossicles
The Eustachian Tube Structure AKA Auditory Tube
•Tube that connects the middle ear cavity to the naso-pharynx •In adults, the eustachian tube is at a 45 degree angle •First 1/3 = 12mm, bony •Typically patent •Second 2/3 = 18-24mm, cartilaginous •Typically closed, but opens at times •Isthmus = The connection between the bony and cartilaginous portions •Narrowest point in the tube (1-2mm) •Normal width = 3-6mm
The Middle Ear Cavity Overview
•Two main areas: •Tympanic cavity proper: Large area in the lower portion of the cavity •Epitympanum/attic: Small upper area •Boundaries •Lateral: TM and squamous portion of temporal bone •Superior: Tegmen tympani, separating the middle ear space from the cranium •Inferior: Tympanic plate of the temporal bone •Anterior: Carotid Wall, eustachian tube, and tensor tympani •Medial: Temporal bone, including the promontory housing the cochlea
