ENT Flashcards
Describe the physiology of the outer ear
the outer ear is air-filled, composed of auricle and auditory canal
Describe the physiology of the middle ear
the middle ear is air-filled and consists of the tympanic membrane (eardrum) and a chain of bones (auditory ossicles) called the malleus, incus, and stapes
Describe the physiology of the inner ear
The inner ear is fluid-filled and consists of three semicircular canals and the cochlea (a spiral-shaped series of three tubular canals containing the organ of Corti/organ of sound)
How do all three parts of the ear work to enable us to hear sound?
The outer ear functions to direct sound waves into the auditory canal
Sound waves traveling through air amplified by tympanic membrane
Sound waves must be converted into pressure waves in fluid in inner ear (cochlea)
Describe the physiology of the cochlea in the inner ear
consists of a series of ducts called the scala vestibuli, scala tympani and scala media
What is the organ of Corti?
The organ of Corti contains inner and outer hair cells, which are the sites of auditory transduction
The bodies of the hair cells are in contact with auditory nerve fibres, and the cilia of the hair cells are in contact with the tectorial membrane
What happens when the hair cells in the inner ear are depolarised?
excitatory neurotransmitter is released to activate afferent cochlear auditory nerves
What happens when the hair cells in the inner ear are hyperpolarised?
afferent cochlear auditory nerves are inhibited
What is the vestibular system?
The vestibular system is used to maintain equilibrium or balance by detecting angular and linear accelerations of the head
What detects the angular rotation of the head in the vestibular system?
Semicircular canals. Mad up of the superior, posterior and horizontal
What detects the liner accelerations of the head in the vestibular system?
detected by the otolithic organs. Made up of the saccule and utricle
Describe how the hair cell causes depolarisation and activation of the nerve fibre
Each hair cell has 50 to 70 small cilia called stereocilia, plus one large cilium, the kinocilium
When the stereocilia bend in the direction of the kinocilium, ion channels open to cause membrane depolarization and activation of the nerve fibre
Describe how the hair cell causes hyperpolarisation and inhibition of the nerve fibre
Each hair cell has 50 to 70 small cilia called stereocilia, plus one large cilium, the kinocilium
Bending the stereocilia backward to the kinocilium closes the ion channel causing membrane hyperpolarization and inhibition of the nerve fibre
What are the three groups of ear infections?
- Outer ear inflammation (otitis externa): conductive hearing loss
- Middle ear inflammation (otitis media): conductive hearing loss
- Inner ear inflammation (labyrinthitis): sensorineural hearing loss causing ‘inner ear dizziness’
What is Otitis Externa ususally caused by?
Bacterial :
Pseudomonas aeruginosa
Proteus mirabilis
Staphlococcus aureus
Fungal:
Candida
Aspergillus