Anatomy & Physiology of the Auditory System Flashcards
What are the anatomical planes?
- Sagittal
- Coronal
- Tranverse or Horizontal
What does sagittal mean?
Planes separates left from right
What doe coronal mean?
Plane separates front to back
What does transverse mean?
Plane separates top from bottom
What are the anatomical terms of location?
- Superior
- Inferior
- Superficial
- Deep
- Dorsal/Posterior
- Ventral/Anterior
- Cranial
- Rostral
- Caudal
- Proximal
- Distal
- Medial
- Lateral
- Unilateral
- Bilateral
- Contralateral
- Ipsilateral
What does superior and deep mean?
Superior: Toward the surface
Deep: Away from the surface
What does cranial, rostral, and caudal mean?
Cranial: Toward the head
Rostral: Toward the nose
Caudal: Toward the foot or base of the skull
What does proximal, distal, medial, and lateral mean?
Proximal: Toward the point where extremity joins the body
Distal: Toward the end of the extremity
Medial: Toward the midline
Lateral: Away from the midline
Explain the difference between sensation and perception.
Sensation is where our senses receive stimuli from our environment and pass the information to our brain.
Perception is the process of our brain organizing and interpreting the sensory stimuli into our conscious as it relates to our everyday lives.
Explain the difference between “bottom-up” & “top-down” as it relates to sensation & perception.
Sensation is a bottom-up process where information comes from the peripheral system (ears, eyes, nose) to the central system (brain).
Perception is a top-down process, where the central systems act on the information it receives from the periphery system.
Name the cranial nerves that innervate sensory portions of the outer and middle ear.
- Vagus X - carries tactile information from the outer ear and ear canal via Arnold’s nerve
- Glossopharyngeal IX: Carries tactile information from the middle ear, tympanic membrane and Eustachian tube
- Vestibulocochlear VIII: Carries sensory information on hearing and balance from the auditory and vestibular portions of the cochlea
- Facial VII: Carries tactile information from pinna and ear canal
- Trigeminal V: Carries tactile information from outer and middle ear
Name the cranial nerves that innervate the muscles of the middle ear
- Facial VII: Inneravates the stapedius muscle of the middle ear via pyramidal eminence
- Trigeminal V: Mandibular nerve innervates the tensor tympani in the middle ear
List out the parts of the outer ear
- Helix
- Lobe
- Anti-tragus
- Tragus
- Intertragal Insisure
- Conca Cavum
- Crus of Helix
- Concha Symba
- Anti-helix
- Scaphoid Fossa
- Triangular Fossa
What are the main cues in the horizontal plane?
- Interaural Timing Differences (ITDs)
2. Interaural Level Differences (ILDs)
What are the cues for sound localization in the vertical plane?
- Monaural Cue
2. Spectral Peaks & Notches
How are our head and ears able to filter sounds differently?
Depending on the incoming angle of the sound towards the head.
How does Interaural Timing Differences help us localize sounds?
Sounds arrive at each of our ears at slightly different times, and our brain interprets ITDs order of milliseconds to localize sound.
How does Interaural Level Differences help us localize sounds?
Sounds are amplified/attenuated to slightly different levels at each ear
What does ILDs help localize?
HFs sounds
What does ITD help localize?
LFs sounds
What does ITDs mean?
Interaural Timing Differences
What does ILDs mean?
Interaural Level Differences
When does Cone of Confusion occur?
When ITDs & ILDs cues are ambiguous
What solves Cone of Confusion?
Sound localization in the vertical plane
What does the pinna provide to help localize sounds in the vertical plane?
Monaural cues
What helps determine the elevation of sound sources?
Spectral peaks & notches
Define spectral peaks and notches?
High/low points that appear at different frequencies depending on how sound hits the pinna
Explain how the shape of the pinna contributes to sound localization
Sounds coming from different angles in the vertical plane bounce off the structures of the pinna in different ways, creating spectral peaks and notches that the brain interprets as cues for localization in the vertical plane. These pinna reflections also help resolve front-back confusions and other ambiguous locations in the cone of confusion.
Describe the size and shape of the external auditory canal
- Irregular curved tube
- 25mm long
- Ovoid where its greatest diameter is vertically (8-9mm in adults)
- Narrowest point of the EAC is the isthmus
The EAC is tilt ____ and moves ______ to ____.
Upwards, Laterally to medially
List the landmarks of the EAC
- EAC
- TM
- Bone
- Cartilage
What is the function of the EAC?
Funnel sound to the TM and protects the middle & inner ear
What part of the EAC is fixed in diameter?
The bony portion
What part of the Eac is flexible?
The cartilaginous portion
When does the size and shape of the cartilaginous portion of the EAC changes?
With movement of the pinna & mandible
Where is the TM located?
The medial end of the EAC
How is the TM positioned and why is it positioned that way?
At angle to increase surface area for vibrations
Describe the size and shape of the TM.
- Cone-shaped
- Center pulled inward by 2mm
The shape of the TM aids in?
Producing a catenary level that amplifies sound vibrations
List the landmarks of the TM
- Annulus
- Short process of the malleus
- Pars flaccida
- Posterior fold
- Junction of incus and stapes
- Pars tensa
- Light reflex
- Umbo
- Handle of the malleus
- Anterior fold
What is the Isthmus?
The narrowest bend of the EAC where the cartilaginous portion of the canal meets the bony portion.
What is the annulus
- Thich fibrocartilaginous rim of the TM
- Has an horseshoe shape with an opening at the superior end near the pars flaccida
- Connected to a groove in the bony wall of the canal
What is the function of the Annulus?
Hold the TM in place
What is the pars flaccida?
- Small superior section
- Tissue of the TM that contains few internal fibers
- Loose
What does the pars tensa contain?
- Contains rest of the TM
- Contains internal fibers that hold tension over the TM
What are the tissues of the TM?
1, Outer Layer
- Middle Layer
- Inner Layer
The outer layer of the TM contains?
Epidermal epithelium
Which layer is continuous with the EAC?
Outer layer (Epidermal Epithelium)
The middle layer of the TM contains?
Collagen fibers that makes the TM springy
The inner layer of the TM contains?
Muscosal epithelium that is continuous with middle ear lining
List the collagen fibers of the TM
Radical & Concentric fibers
What causes cerumen to be produced in our EAC
The cartilaginous portion of EAC containing hair follicles, and the secretions of the ceruminous and aprocrine glands mixed with dead skin cells and other debris of the canal, produces cerumen
What part of the EAC can cerumen be found?
Lateral portion of the EAC
What are the glands that produce cerumen?
Ceruminous & Apocrine Glands
Explain how the mass and stiffness of an object affect its resonant frequency
Objects with heavier mass will produce lower pitches, while objects that are stiffer produce higher pitchers.
Describe the resonant property of the outer ear
The EAC is like a Helmholtz resonator that amplifies high-frequency sounds
What does the size and shape of the head, pinna, and ear canal all contribute to?
Some amplification to sound traveling through the outer ear allows us to plot the contribution as a transfer function.
What does the transfer function indicates?
1, Concha amplifies sound by 10dB at 5kHz.
- The pinna amplifies sounds by 3-4dB from 3-4kHz.
- Ear canal & TM amplify sounds by 10dB from 2-3KHz.
What affects the resonance of the outer ear system?
- Head
- Pinna
- Ear canal
- Placement of the TM
When we put all the information together we receive from the transfer function, we can infer that?
We get about 15-20dB of gain from 2-5kHz which is important for speech
What are the congenital abnormalities of the outer ear and their meaning?
- Microtia: Small, under-developed pinna
- Anotia: Complete absence of a pinna and canal opening
- Stenosis: Very narrow ear external ear canal
- Atresia: Complete lack of an external ear canal
- Preauricular Ear Pit: Small hole in the skin anterior to the pinna
- Preauricular Skin Tag: Small mound of extra skin/tissues anterior to the pinna
Congenital malformations of the external ear usually associate with?
CHL
Which outer ear abnormalities are common?
Preauricular Ear Pit & Skin Tag
What are the acquired abnormalities of the outer ear and their meaning?
- Perichondrial Hematoma: Known as cauliflower or wrestler’s ear caused by trauma to the tissues of the pinna
- Melanoma: Rare but serious since it spreads to other tissues
- Basal Cell Carcinoma: Affects the basal layers of the epidermis and tends to affect areas exposed frequently to the sun.
- Squamous Cell Carcinoma: Most common type of ear cancer. Affects the squamous cells of the epidermis
- Exostosis: Acquired bony growth in the EAC. Known as swimmers or sufers ear.
What are the three types of skin cancer found on the outer ear?
- Melanoma
- Squamous Cell Carcinoma
- Basal Cell Carcinoma
What are the healthy landmarks that can be noted during otoscopy?
- Cone of Light
- Umbo
- Short process of malleus
What are signs of pathology that can be noted during otoscopy?
- Absence of healthy TM landmarks
- Perforation in the TM
- Signs of infection: bacterial, fungal, redness, swelling, puss
- Stenosis (narrow canal)
- Impacted Cerumen or other objects
Describe best practices for performing otoscopy on a patient
- Point otoscope slightly upward
- Pull the pinna in a superior-posterior direction to straighten out the canal.
- BRACE!
What is the correlation between fitting a hearing aid and it interacting with ear canal’s natural resonance.
Resonance depends on the pinna to funnel sound into an open ear canal. Hearing aids will disrupt the natural resonance of the outer ear system. For BTEs, since the microphone is behind the pinna, one will lose 5-10 dB of gain, and ITC HAs will seal off the ear canal loosing around 10 dB of gain from the natural ear canal resonance. This causes the resonant peaks to shift from HF - LF and cause occlusion
Define 3 standard real-ear measures.
- Real-ear Unaided Response (REUR): Patient is not wearing HA, just measuring their natural ear canal resonance
- Real-ear Aided response (REAR): Patient wears HA and measures the output of the HA while it is in the patient’s ear.
- Real-ear Insertion Gain (REIG): Amount of gain provided by the HA. Aka, difference between REUR & REAR
List the structures that makes up the tympanic cavity
- Epitympanic Recess
- Jugular Wall
- Membranous (Lateral) Wall
- Carotid (Anterior) Wall
- Mastoid (Posterior) Wall
- Labyrinthine (Medial) Wall
The roof of Epitympanic Recess is…
A thin plate of bone called Tegmen Tympani
What forms the Jugular wall?
The tympanic plate of the temporal bone
What runs through the Jugular Wall?
- Glossopharyngeal Nerve
- Jugular vein
What does the Memnranous Wall contain?
Mostly the TM
What does the Carotid Wall contain and where is it located?
- Tensor Tympani: Superior portion
- Carotid Artery: Helps separate tympanic cavity
- Eustachian tube: Inferior to tensor tympanic
What does the Carotid Wall seperate?
The tympanic cavity from the carotid artery
What forms the lateral wall of the attic?
Bony portion above the tympanic membrane
What forms the Mastoid Wall?
The mastoid bone
What does the Mastoid Wall contain?
- Chorda Tympani
- Pyramidal Eminence
- Tympanic Aditus
- Tympanic Antrum
What is the pyramidal eminence?
A hallow tube that contains the stapedius muscle and its tendon
What does the superior portion of the Posterior Wall have?
An opening called Tympanic Aditus
What does the tympanic cavity of the posterior wall connect to?
Tympanic antrum
The Labyrinthine Wall contains…..
- The promontory
- The oval window
- The round window
- The prominence of the facial nerve
- The prominence of the lateral semicircular canal
The Labyrinthine Wall is formed by?
The basal turn of the cochlea
What is the Promontory and where is located?
A large round protrudence in the center of the medial wall
What forms the Promontory?
The basal turn of the Cochlea
The grooved surface on the Promontory are?
Nerves that form the tympanic plexus
What fits inside the oval window?
The footplate of the stapes
Where is the round window located?
Inferior to the oval window near the promontory
What is the Facial Nerve Prominence?
A canal that house the facial nerve
Where is the Facial Nerve Prominence located?
Superior to the oval window
Where does the facial nerve run?
From the Labyrinthine Wall - Mastoid Wall
What is the chorda tympani?
A branch of the facial nerve
Where is the Semicircular Canal Prominence located?
Superior/Posterior to the facial nerve prominence
Near the Antrum
How do you know if you’re looking at a sagittal view of the ear?
If you see the Eustachian tube
How do you know if you’re looking at a coronal view of the ear?
The ear canal is running in a particular direction
Am I looking outside or inside the body?
How do you know you’re inside the body (medially) but looking out?
You see the TM with the ossicles
How do you know you’re outside the body (laterally) looking in?
You’‘ll see a curvy ear canal with TM
Describe the shape of the ossicles and how they are suspended in the middle ear
Ossicles are small and very light weight, thus making it easy to move.
The ossicle suspensions are due to the rotational axes created by the position of the ossicles. Balanced ligament suspension is organized in a way that allows the mass to be centered. So it moves easily when sound is present & stop immediately when sound is not present
What are the two muscles that are connected to the osscles?
- Tensor Tympani
- Stapedius
Where does the middle ear muscles tendons attach to the ossciles?
- Tensor Tympani: Malleus
- Stapedius: Stapes
What innervates the tensor tympani
Trigeminal Nerve V
What innervates the stapedius muscle?
Facial Nerve VII
What are the two function of the Eustachian tube?
- Allows fluid to drain out of the middle ear
2. Equalizes air pressure in the tympanic cavity
List one type of Eustachian tube dysfunction
When you have a cold due to the swelling and mucus in the nasopharynx closes off the Eustachian tube. Causes a LF HL.
List another type of Eustachian tube dysfunction
Patulous Eustachian Tube is where the ET stays intermittently open. Leads to perception of self-generated sounds
What are the three impedance matching mechanisms of the middle ear?
- Area Ratio Transformer
- Lever Action of the Ossicular Chain
- Caternary Lever
What is impedance mismatch?
When sound travels from one medium to another (mechanical - fluid), there is an abrupt change in reactance and resistance that causes HF sound to bounce off while LF sounds get absorbed.
The middle ear plays an essential role in hearing as?
An impedance matching system
What do the three aspect of the middle ear mechanically do?
Amplify sound vibrations so it can efficiently transfer from the ear canal to the fluid-filled cochlea
What part of the middle ear has a low impedance and a high impedance?
Low Impedance: Ear Canal
High Impedance: Fluid-filled Cochlea
How much does the Impedance Matching System account for amplification?
33 dB of amplification
What is the role of the Area Ratio Transformation?
As the middle ear transfers the force of vibrations from the large TM to the small oval window, the sound pressure level increases by 25 dB
How much amplification does the Area Ratio Transformation provide?
25 dB
What is the role of the Lever Action of the Ossicular Chain?
The mallleus and incus move around a balanced point. But, the manubrium is longer than the long process of the incus, so there is an increase in sound pressure of 2 dB
How much amplification does the Lever Action of the Ossicular Chain provide?
2 dB
What is the role of the Catenary Lever?
The outer rim of the TM is attached to the canal wall by the annulus, the center of the TM is attached at the umbo. Displacement occurs between the annulus and the umbo. This difference creates another lever action that increases sound pressure by 6dB.
Describe what freqencies are affect by the middle ear transfer function
If there is an increase in stiffness, low frequency transmissions are limited.
If there is an increase in mass, high frequency transmissions are limited.
Gain from the middle ear is concentrated around?
Mid-frequecnies
Middle ear peaks around?
1kHz
What is the major component of the middle ear impedance?
The middle ear stiffness
What is the minor component of the middle ear impedance?
The middle ear mass
The middle ear is a ____ dominated system. It is sensitive to ______________.
Stiffness-dominated system, changes in the stiffness of the TM and ossicles
How does a tympanometer work?
- A probe tip with ports for air pump, speaker, and microphone is placed in the ear
- Pressure is this placed in the ear canal from +200 daPa - -400daPa through the air pump while a tone is played via the speaker
- The microphone records the amount of energy being reflected back off of the TM
Why is 226 Hz tone used in adults?
Since the adult ear is a stiffness dominated system, many middle ear pathologies cause an increase in stiffness. Using 226 Hz is a sensitive measure to identify abnormal middle ear functions since it provides us with the energy that gets reflected off the TM.
What are the physiological characteristics of the acoustic reflex?
- The acoustic reflex pathway is bilateral
- Reflex activates in response to low and mid frequencies
- Stapedius contractions increase with increasing sound intensity
How does the acoustic reflexes inform us of site lesion for retrocochlear pathology?
Ipsilateral & contralateral reflexes inform us about the different neural pathways
How does Wideband measures differ from conventional immittance?
With conventional immittance, we only measure energy, while wideband measures allow us to incorporate the frequency spectrum & static pressure. We can determine what gets absorbed and reflected, and know which frequency gets absorbed by the ME. Lastly, wideband does not require pressurization of the ear canal which is helpful for newborns and young babies
What were the findings of Merchant et al. (2021) as they relate to the diagnostic advantage of wideband measures?
The statistical model she used revealed that wideband measures improved sensitivity and specificy for differentiating clear ears from normal ears.
What are the characteristics of a normal tymp?
- Peaks around 0
- Pressure at either side of the TM is normal or equivalent
- Also known as Type-A
What are the characteristics of an abnormal tymp?
Flat Tymp:
- Peak is absent
- TM mobility is minimal at all pressures
- Caused by fluid in the ear
- Type B
Negative Pressure Tymp:
- Peak occurs at negative pressure
- Peak is off centered
- Indicates ET cannot equalize pressure in the ME
- Common during colds or end stages of ear infections
- Type C
Explain what happens with the middle ear when pressure gets more negative, postive, or equal
Negative / Positive: ME Stiffens
Equal: Moves freely (0)
What does the peak acoustic admittance mean on a tympanogram?
It is where the pressure value at the middle ear transfers maximum acoustic energy to the cochlea
What can abnormally large ear canal volume indicate from tympanometry providing measure of ear canal volume?
TM perforation or tubes
Since the acoustic reflex pathway is bilateral, once ___ sounds is presented _____
Loud, to one ear, it will contract the stapedius muscle in both ears.
What are the acoustic reflex stimulus/probe configurations?
- Stimulus in left ear, measurement probe in left ear = Left Ipsilateral
- Stimulus in right ear, measurement probe in right ear = Right Ipsilateral
- Stimulus in the left ear, measurement probe in the right ear = Left contralateral
- Stimulus in the right ear, measurement probe in the left ear = Right contralateral
Under which naming convention will we test the acoustic nerve?
Right v Left
Under which naming convention will we test the facial nerve?
Ipsilateral v Contralateral
