S7) Functional Anatomy and Disorders of the Ear Flashcards
What is the ear?
The ear is the organ of hearing and balance (equilibrium)
Different pathologies can involve the three different areas of the ear.
Identify these
- External ear
- Middle ear
- Inner ear
Identify 6 signs/symptoms of ear disease
- Otalgia (ear pain)
- Tinnitus (ear ringing)
- Discharge
- Vertigo - feel world spinning (rotation is key) even though they are still
- Hearing loss (conductive vs sensorineural)
- Facial nerve palsy - facial nerve runs through petrous bone so close to ear
Within which bone of the skull do we find the parts of the ear?
Temporal bone
Identify the four components of the temporal bone
- Squamous part
- Petromastoid part
- Tympanic plate
- Styloid process
What is referred pain?
Referred pain is pain felt in a part of the body other than its actual source
What is the significance of otalgia?
- Otalgia can sometimes be referred pain
- Due to the diverse sensory innervation of the ear, sources outside of the ear that share similar nerve innervation may present with otalgia e.g. laryngeal cancers, TMJ, disease of oropharynx
State the components and function of the external ear
- Components: pinna, external auditory meatus (2-3cm), lateral surface of tympanic membrane
- Function: collects, transmits and focuses sound waves onto the tympanic membrane
What does the pinna of the external ear consist of and what is its role?
The pinna consist of cartilage, skin and fatty tissue
- collects, transmits and focuses sound waves onto the tympanic membrane
Label the following surface features of the external ear:
- Helix
- Antihelix
- Concha
- Tragus
- External auditory meatus
- Lobule
Identify 4 causes of pinna abnormalities
- Congenital
- Inflammatory
- Infective
- Traumatic
When do pinna haematomas occur?
- Secondary to blunt injury to the pinna
- Common in contact sports
How do pinna haematomas occur?
- Accumulation of blood between cartilage and perichondrium
- Deprives the cartilage of its blood supply
- Causes pressure necrosis of tissue
How are pinna haematomas treated?
- Prompt drainage
- Measures to prevent re‐accumulation and re‐apposition of two layers
- apply tamponade so that the perichondrium is stuck to the cartilage
What happens to untreated/poorly treated pinna haematomas?
Untreated or poorly treated leads to fibrosis and new asymmetrical cartilage development → ‘cauliflower deformity’ of the ear as it develops asymmetrically and this is not reversible
How long is the external acoustic meatus?
2.5 cm
Describe the structure of the external acoustic meatus (ear canal)
- Consists of a a cartilaginous (outer 1/3) and bony part (inner 2/3)
- Skin-lined cul-de-sac
- Sigmoid shape
- keratinised, stratified squamous epithelium
- outer third is moveable
Describe the anatomical location of the external acoustic meatus
- Free outer border provides an attachment for external ear cartilage
- Medially, it fuses with the petrous part of the temporal bone
Identify 4 functions of the external acoustic meatus
- Arrangement of hairs and production of wax (cartilaginous part)
- Prevent objects entering deeper into ear canal
- Aids in desquamation and skin migration out of canal
- Skin lining secretes cerumen to protect meatal skin
What are the components of ear wax?
- Discarded cells of meatal skin
- Cerumen (modified sebum)
Describe the structure, location and function of the tympanic membrane
- Structure: fibrous structure, translucent
- Location: apex points medially
- Function: allows visualisation of some structures within the ear (malleus)
Identify two common conditions involving external acoustic meatus
Where are the middle and inner ear found?
The petrous part of the temporal bone contains the middle and inner ear
Describe the anatomical relations of the petrous part of the temporal bone
Upper surface forms part of the floor of the middle and posterior cranial fossae:
- Internal acoustic meatus pierces the part forming the posterior cranial fossa
- ICA and carotid canal are found in its inferior surface (irregular)
What is the middle ear?
The middle ear (aka tympanic cavity) is an air-filled cavity between the tympanic membrane and the inner ear, containing three ossicles lined with respiratory epithelium (psueodstratified)
tube at the bottom called the pharyngotympanic tube connects with the nasopharynx which allows it to equilibrate with atmospheric pressure in nasopharynx
Identify the 3 ossicles in the middle ear
- Malleus
- Incus
- Stapes
The ossicles lie in the upper part of the tympanic cavity.
Describe the articulations of its synovial joints
- The handle of the malleus is attached to the tympanic membrane but its body articulates with the body of the incus
- The incus then articulates wit the stapes
- The stapes then articulates with the bony labyrinth of the inner ear at the oval window
Describe the structure and function of the 3 ossicles of the middle ear
- Structure: connected via synovial joints
- Function:
I. Relay vibrations from the tympanic membrane to the oval window of the cochlea (inner ear)
II. Transmit vibration from an air medium to a fluid‐medium
Movement in the middle ear is tampered by two muscles tensor tympani and stapedius.
What is their role?
Tensor tympani and stapedius muscles contract if potentially excessive vibration due to loud noise (protective; acoustic reflex)
Identify and describe any pathology involving the ossicles
- In otosclerosis, ossicles can become fused at articulations, between the base plate of stapes and oval window
- Sound vibrations cannot be transmitted, causing deafness
- can be genetic or environmental
- conductive hearing loss
What are the roles of the mucous membrane and pharyngotympanic tube in terms of pressure in the middle ear?
- Mucous membrane continuously reabsorbs air in middle ear causing negative pressure
- Eustachian tube equilibrates pressure of middle ear with atmospheric pressure, also allowing for ventilation and drainage of mucus from the middle ear
Describe the physiological cause of ‘ear popping’
- The pharyngotympanic tube is usually closed
- It intermittently opens when pulled by the attached palate muscles when swallowing/yawning
What is posterior to the middle ear and why is this clinically significant?
- Posteriorly, the middle ear communicates with the mastoid air cells via the mastoid aditus and antrum
- This connection provides a potential route for infection (mastoiditis)
Where is the mastoid antrum found?
The cavity of the mastoid antrum (a prolongation of the middle ear cavity) extends into the mastoid process and communicates with air cells
Describe the pathophysiology of Otitis media with effusion (glue ear)
- Otitis media with effusion is a build up of fluid and negative pressure in middle ear
- Caused by Eustachian tube dysfunction (not infection), this results in fluid and negative pressure build up in the ear → can predispose to infection and decreases mobility of TM and ossicles (affecting hearing)
→ negative pressure pulls the membrane but also pulls fluid across into the middle ear cavity
How can otitis media with effusion be resolved?
- Most resolve spontaneously in 2‐3 months, but some may persist
- Require grommets (tympanostomy tube) to ventilate middle ear and equilibrium of pressure
What is acute otitis media and what are its symptoms?
- Acute otitis media is an acute middle ear infection which is more common in infants & children
- Symptoms: otalgia, red/bulging TM, loss of normal landmarks, temperature (non-specific) can see red and bulging tympanic membrane
mostly viral
common bacterial cause is strep pneumonia
The pharygotympanic tube is shorter and more horizontal in infants.
What are the implications of this for infants?
- Easier passage for infection from the nasopharynx to the middle ear
- Tube can block more easily, compromising ventilation and drainage of middle ear, increasing risk of middle ear infection
Identify 4 types of complications resulting from acute otitis media
- Tympanic membrane perforation due to increased pressure and pus putting pressure on membrane (heal itself)
- Facial nerve involvement
- Mastoiditis
- Intracranial complications: meningitis, sigmoid sinus thrombosis, brain abscess
Identify the important anatomical relations of the ear
- you could have a really bad infection that eats through the bone and that can spread into the venous sinus, causing a thrombosis in the vein
In terms of the anatomical relations of the ear, explain how mastoiditis might occur
- Middle ear cavity communicates via mastoid antrum with mastoid air cells
- Provides a potential route for middle ear infections to spread into the mastoid bone (mastoid air cells)
ear appears red and pushed forward
Describe the anatomical relationship of the facial nerve with the middle ear and the significance of this
- Facial nerve and one of its branches, the chorda tympani, runs through middle ear cavity.
- Hence, facial nerve may be involved in pathology involving the middle ear
What is a cholesteatoma?
Cholesteatoma is a rare abnormal skin growth (sac or cyst of skin cells) growing into into middle ear, behind the tympanic membrane
due to increasing pressure in middle ear cavity due to some chronic dysfunction in the Eustachian tube
Identify 3 possible symptoms of cholesteatoma
- Causes painless, often smelly otorrhea (ear discharge)
- Might cause hearing loss
- Might potentially cause more serious neurological complications
Describe the growth and development of a cholesteatoma
- Secondary to chronic ET dysfunction or chronic/recurring ear infections
- Not malignant but slowly grows and expands, eroding into structures e.g. ossicles, mastoid bone, cochlea
- it can destroy bone eg petrous bone or cochlea*
Describe the formation of the inner ear (labyrinth)
- The inner ear consist of a series of canals hollowed out of the petrous bone (bony labyrinth) which surround a series of ducts (membranous labyrinth)
- The ducts of the membranous labyrinth are shaped to form the utricle, saccule, semicircular ducts and cochlear duct
inner ear is needed for balance and hearing
so any issues within the inner ear will present with balance problems unlike the others
Identify and describe the components of the inner ear
Fluid-filled tubes:
- Cochlea (bony labyrinth surrounding cochlear duct which is full of fluid ) - where AP are generated
- Vestibular apparatus (bony labyrinth surrounding saccule & utricle and contents)
-semicircular canals (3) anterior posterior and latera generate AP - all of these are fluid filled and continuous. these structure stimulate our sense of balance
Describe the fluid found in the inner ear
- Perilymph is found between the membranous and bony labyrinth
- Endolymph fills the ducts of the membranous labyrinth
What is the function of the cochlea of the inner ear?
The cochlea, containing the spiral organ of Corti, converts vibration into an electrical signal (action potential) which is perceived as sound
- oval window moves when the ossicles move → waves of fluid sent to the cochlea duct → sensed by stereocilia → generate action potentials
What is the function of the vestibular apparatus of the inner ear?
The vestibular apparatus is involved in maintaining our sense of position and balance also generates action potentials
full of fluid
any problems here will result in issues with balance
In 4 steps, describe how the vestibular apparatus maintain our sense of position and balance
⇒ Stereocilia in utricle and saccule respond to rotational acceleration & the static pull of gravity
⇒ Stereocillia in semicircular ducts respond to rotational acceleration in three different planes
⇒ Movement of head & body moves inner ear fluid, causing sterecilia to bend
⇒ Bending generates an action potential which is relayed to vestibular part of CN XIII and is perceived as our sense of position and balance
The cochlea is our organ of hearing. It is fluid filled tube.
Describe how it functions
- Movements at the oval window set up movements of the fluid in the cochlea
- Waves of fluid cause movement of special sensory cells (stereocilia) within the cochlear duct which generate action potentials in CN VIII
In 5 steps, explain how we hear
⇒ Auricle and external auditory canal focuses and funnels sound waves towards TM which vibrates
⇒ Vibration of the ossicles sets up vibrations/movement in cochlear fluid
⇒ Sensed by stereocilia (nerve cells) in the cochlear duct
⇒ Movement of the stereocilia in organ of Corti trigger action potentials in cochlear part of CN VIII
⇒ Primary auditory cortex make senses of the input
Identify 3 diseases of the inner ear
- Meniere’s Disease
- Benign Paroxysmal Positional Vertigo
‐ Labrynthitis
Identify 4 symptoms of pathology of the inner ear
- Vertigo
- Hearing loss (sensorineural)
- Tinnitus
- Nystagmus (involuntary eye movement)
How does one examine a patient presenting with hearing loss?
- Inspection of external ear and surrounding areas
- Otoscopy
- Gross hearing assessment
- Tuning forks (Weber’s and Rinne’s test)
- Referral for more formal audiometry testing
Conductive hearing loss arises from pathology involving the external or middle ear.
Provide 4 examples
- Wax
- Otitis media
- Glue ear
- Otosclerosis
Sensorineural hearing loss arises from pathology involving the inner ear structures or CN VIII.
Provide 4 examples
- Presbycusis (most common type in >55 year olds)
- Meniere’s Disease
- Acoustic neuroma
- Ototoxic medications
What is the purpose of Rinne’s and Weber’s testing?
Rinne’s and Weber’s testing helps differentiate between a conductive and sensorineural hearing loss
What is an acoustic neuroma?
An acoustic neuroma (aka vestibular schwannoma) is a benign brain tumour of the Schwann cells developing on the vestibulocochlear nerve, impairing hearing and balance
What is Meniere’s disease?
Meniere’s disease is a condition of the inner ear which causes vertigo (dizziness with spinning sensation), hearing loss and tinnitus (ear ringing)
What is labyrinthitis?
Vestibular neuritis is an inner ear infection wherein the labyrinth becomes inflamed causing vertigo, hearing loss, nystagmus (involuntary eye movement), tinnitus and the feeling of pressure in the ear
Identify the structures observed in this otoscopic view of a normal external ear and lateral surface of the tympanic membrane:
list the nerves that carry general sensation to the ear
- cervical spinal nerves (C2/C3)
- vagus
- trigeminal
- glossoopharyngeal
how can problems from the pharynx or larynx be interpreted as pain in the ear
pain comes in from body tissue that shares same sensory innervation to the ear and so it comes off as referred pain
what is perichondritis
inflammation of perichondrium that overlies the cartilage pinna and it also provides blood supply
- pain is swollen, read and painful
- treated with antibiotics
what is epithelial migration
skin inside the external acoustic meatus moves laterally towards the ear canal and is a form of self cleaning
label a normal acoustic meatus
what is Otitis externa
- inflammation of ear canal
- ear discomfort and pain, can be a discharge
- can be susceptible to bacteria infection
- malignant otitis externa → life threatening when the bacteria starts to penetrate the bone in the ear
what is acute otitis media?
- infection inside the middle ear, usually viral and self resolving
- the tympanic membrane is bulging
- due to increased pressure
what is otitis media with effusion?
- underlying problem is not infection
- tympanic membrane becomes retracted and sucked in towards the middle ear cavity
- this is due to increasing negative pressure
- can see fluid by middle ear cavity (this area should only be air filled)
describe the order as to how we hear
- auricle + external auditory Canal focuses and funnels sound waves → tympanic membrane which vibrates
- ossicles vibrate and amplify → send vibrations to cochlear fluid
- stereocillia in cochlear duct sense vibrations
- sterocillia moves and trigger action potential in CN VIII
- primary auditory complex
what is prebycusis
- older people
- sensorineural hearing loss (to do with the cochlea)
- can be corrected with hearing aids
benign paroxysmal positional vertigo
- only effects the vestibular apparatus - effected balance and feels like spinning
- vertigo only
- short lived episodes triggered by movement of head
- due to crystals inside the tubes which can move and cause fluid to move which moves stereo cilia which generates AP making it seem like we are moving but head is actually still.
What is Menieres disease
- issues to do with the cochlea and the vestibular apparatus
- vertigo, hearing loss and tinnitus
- describe fullness and nausea and vomiting
- long lasting
- recovery in between episodes
- hearing may deteriorate over time
acute labrynthitis vs acute vestibular neuronitis
- viral infection made its way to inner ear
- AL → whole inner ear structures are effected = hearing loss and vomiting and vertigo
- AVN → no hearing disturbances and sudden onset
when is a tuning fork tests used
helps to determine if its the inner ear or the middle ear
- webers and rinnes test
what is conductive hearing loss
- pathology involving external or middle ear
- wax
- acute otitis media
- otitis media with effusion
- otosclerosis
sensorineural hearing loss
- pathology of the inner ear or CN VIII
- presbycusis - age related hearing loss
- noise - related hearing loss (bilateral and gradual)
- Menieres disease
- ototoxic medications
- acoustic neuroma - grows on the vestibulocochlear nerve and van cause unilateral hearing loss
what is the function of the external + middle ear compared to the inner ear
- external and middle: convey sound vibration to inner ear
- inner ear: converts vibration into action potential
what is the difference between the round and oval window
- the oval window is where the cochlea meets the stapes that creates an action potential
- round window is found under the ovl window, it is a space that allows fluid to expand in the oval window, this means the stapes can generate waves in the fluid
which nerves carry somatic sensation from the external ear
cervical c2,c3
vagus
mandibular division of trigeminal nerve
(glossopharangeal carries sensory from MIDDLE ear via the tympanic branch
which branches of the facial nerve arise from the petrous part of the temporal bone
- chorda tympani (middle ear, taste for anterior 2/3 tongue, parasympathetic from sublingual and submandibular)
- **nerve to the stapedius **
3.** greater petrosal nerve **(parasympathetic to the face and neck, lacrimal gland, makes nasal mucus)
what is the most common cause for otitis externa
pseudomonas aeruginosa
