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 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
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)
Identify the structures observed in this otoscopic view of a normal external ear and lateral surface of the tympanic membrane:
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
label a normal acoustic meatus
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
