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
- Hearing loss (conductive vs sensorineural)
- Facial nerve palsy
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
State the components and function of the external ear
- Components: pinna, external auditory meatus, 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?
The pinna consist of cartilage, skin and fatty tissue
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
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
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
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
Identify two common conditions affecting the tympanic membrane
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
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
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), can predispose to infection and decreases mobility of TM and ossicles (affecting hearing)
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
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)
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
- Facial nerve involvement
- Mastoiditis
- Intracranial complications: meningitis, sigmoid sinus thrombosis, brain abscess
Identify the important anatomical relations of the ear
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)
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
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
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
Identify and describe the components of the inner ear
Fluid-filled tubes:
- Cochlea (bony labyrinth surrounding cochlear duct)
- Vestibular apparatus (bony labyrinth surrounding saccule & utricle and contents)
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
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
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:
