Functional Anatomy and Disorders of the Ear Flashcards
The ear can be broadly categorised into what 3 parts?
External
Middle
Inner
What is otalgia?
Ear pain
Can sometimes be referred pain from another site of the body
Diverse sensory innervation of the ear = sources outside of the ear that share similar nerve innervation may present with otalgia e.g. laryngeal cancers
What is tinnitus?
Ringing/buzzing
Damage and loss of the tiny sensory hair cells in the cochlea of the inner ear.
What is vertigo?
Feels like the room is spinning when it is not
Within which bone of the skull do we find parts of the ear?
Petrous part of the temporal bone
What is the main function of the external ear?
Collects, transmits and focuses sounds waves into the tympanic membrane
Describe the anatomy of the external ear
Shaped by cartilage
External acoustic meatus = sigmoid shape
Pinna
Lateral surface of tympanic membrane
Discuss some possible abnormalities of the pinna
Congenital
Inflam
Infective = reactivation of varicella-zoster virus in the geniculate ganglion - shingles can effect facial N giving ipsilateral facial palsy (Ramsey Hunt syndrome)
Traumatic = cauliflower deformities (bleeding between tissues, cartilage effects, shape distorted)
Pinna haematoma = blood between cartilage and perichondrium - deprives cartilage of blood supply and pressure necrosis of tissue – prompt drainage needed = untreated leads to fibrosis and new asymmetrical cartilage devel
Outline the structure of the external acoustic meatus
Skin-lined
S shaped = have to pull ear up and back when examining
Cartilaginous (outer 1/3) and bony (inner 2/3) parts
Cartilaginous = glands for wax, hairs for protection
How long is the external acoustic meatus?
2.5cm
What are the common conditions involving the external acoustic meatus?
Wax = can become impacted and stop vibrations reacting TM
Otitis externa = inflam, may have exudate (causes = infect, eczema) AKA swimmers ear
Describe some common abnormalities of the tympanic membrane
Perforation = trauma, pressure on the inside of TM
Bulging secondary to otitis media
What does a normal tympanic membrane look like?
Pale grey semitransparent ovoid cone shaped disc located at the end of the external auditory canal
What normal structures can be seen when visualising the tympanic membrane?
Incus
Umbo
Pars tensa
Cone of light
Manubrium of malleus
Short process of malleus
Pars flaccida
Describe the anatomy of the middle ear
Full of air
3 ossicles = translate vibrations from tympanic membrane to inner ear = transmit vibration from air to water
1) Malleus
2) Incus
3) Stapes (smallest bone in the body)
Connected via synovial joints
What is the role of the ossicles?
Relay vibrations from tympanic membrane to the cochlea via the oval window
Amplify vibrations
What muscles are involved in the acoustic reflex?
Tensor tympani
Stapedius – supplied by facial N
Muscles contract to dampen any potentially excessive vibration due to loud noice
What is hyperacoustis?
Facial N problem = loose stapedius that contracts to prevent excessive vibration
Sensitivity to loud noises
What is otosclerosis?
Fusion of the ossicles at articulations – particularly at base plate of stapes and oval window
Sound vibrations cannot be transmitted
Gradual hearing loss
What is the eustachian tube?
Prevents -ve pressure getting to large = allows equilibration of pressure within middle ear cavity with that of the atmosphere
Also allows for ventilation of and drainage of mucus from the middle ear
How is -ve pressure generated in the middle ear?
Mucous membrane continuously reabsorbing air
Describe otitis media with effusion (glue ear)
Build up of transudate fluid and -ve pressure in middle ear = retracted tympanic mem
Due to eustachian tube dysfunction
Decreases mobility of tympanic mem = affecting hearing
Treat = resolve spontaneously, insert grommets to equilibrate pressure
What is acute otitis media?
Middle ear infection
More common in infants/children = due to eustachian tube being shorter and more horizontal = easier for infect to track from back of the throat to middle ear
Red +/- bulging TM = loss of normal landmarks
What are the potential complications of acute otitis media?
TM perforation
Facial N involvement
Mastoiditis
Intracranial complications = meningitis, brain abscess
What is mastoiditis?
Inflam of mastoid process
= middle ear cavity communicated via mastoid antrum with mastoid air cells = potential route for middle ear infections to spread into the mastoid bone
How does mastoiditis present?
Ear pushed forward
Bone swollen, red
Outline the important relationship the middle ear has with the facial N
Chorda tympani runs through middle ear cavity
Facial N may be involved in middle ear pathology
What is cholesteatoma?
Abnormal skin growth into middle ear behind TM
Can erode through ossicles
Present = painless smelly discharge, top of TM crusting (sac that is eroding into middle ear cavity)
Describe the anatomy of the inner ear
Filled with liquid
Cochlea = converts vibration into electrical signal perceived as sounds
Vestibular apparatus = maintains our sense of position and balance
Outline the stages of ‘how we hear’
Auricle and external auditory canal focuses and funnels sound waves towards tympanic membrane which vibrates
Vibration of the ossicles (stapes at the oval window) sets up vibrations/movement in cochlear fluid
Sensed by stereocilia (nerve cells) in the cochlear duct (part called the spiral organ of Corti)
Movement of the stereocilia in organ of Corti trigger action potentials in cochlear part of CN VIII
Primary auditory cortex (make sense of the input)
What makes up the vestibular apparatus?
3 Semicircular ducts in diff planes - fluid filled
Saccule + Utricle = hair cell that sense motion of fluid
Fluid filled series of channels that respond to position and rotation
Maintain sense of balance
Name some diseases of the inner ear
Meniere’s Disease = too much fluid in the cochlear duct and vestibular apparatus, issue with drainage, fullness, cant hear, ringing, episodes of vertigo
Benign Paroxysmal Positional Vertigo = short bursts of vertigo, crystals in vestibular apparatus fluid, movement dislodges crystals, moves fluid, moves stereocilia, sensation of movement
Labrynthitis = inner ear infect
What signs and symptoms present with inner ear pathology
Vertigo
Hearing loss and tinnitus
Nystagmus
How can hearing loss be assessed?
Whispering word
Webers test
Rinne test
What is the difference between conductive and sensorineural hearing loss?
Conductive = pathology in external or middle ear
Sensorineural = pathology in inner ear, or CN, or CNS
What is presbyacusis?
Sensorineural hearing loss
Most common type in >55
Old-aged related hearing loss, both ears
In someone with normal hearing, what will be louder, bone or air conduction?
air
Outline the air conduction pathway of sound
ear canal –> TM –> ossicles –> cochlea –> CN8 Vestibulocochlear N
Outline the bone conduction pathway of sound
vibrations of skull bones –> cochlear –> CN8 Vestibulocochlear N
What is conductive deafness?
deafness due to ear canal, TM or middle ear
bone conduction = better hearing
What is sensorineural deafness?
deafness due to the cochlear, Vestibulocochlear N or brain
air conduction = better hearing BUT both reduced
Outline the webers test
assess = compares sensitivity of both cochlear
tap tuning fork, place tuning fork on top of head, sound better on one side or another?
sound via bone conduction
- normal = sound equal
- unilateral sensorineural deafness = quieter in 1 ear
- unilateral conductive deafness = louder in 1 ear (due to removal of background noise)
Outline the rinne test
assess = compares air and bone conduction
tap tuning fork, place over mastoid process, then place in front of ear – which one was loudest?
- normal = loudest in front of ear (air provides best sound conduction)
- conductive = bone conduction louder
- sensorineural = air conduction louder
Name the 3 ossicles
1) Malleus
2) Incus
3) Stapes (smallest bone in the body)
Which nerves are involved in carrying general somatic sensation from the external ear?
Cervical nerve (C2)
Mandibular division of trigeminal nerve
Vagus nerve
