Session 6: The Ear Flashcards
What is the sensory nerve supply to the auricle of the external ear and the tympanic membrane?
Auricle is supplied by the auriculotemporal nerve (CNV3) and greater auricular nerve (C2/C3)
Tympanic membrane is supplied by the auriculotemporal nerve but some innervation is supplied via a branch of the vagus nerve (auricular branch)
What is an important posterior relation of the mastoid antrum?
Behind the mastoid antrum and air cells is the sigmoid venous sinus (a dural sinus) and the cerebellum. Infection in the region of the mastoid may spread to involve these structures and allow infection to spread to brain
Name 3 branches from the facial nerve given off in the petrous temporal bone.
Greater petrosal nerve
nerve to stapedius
Chorda Tympani
What is the functional significance of the greater petrosal nerve?
contains preganglionic parasympathetic fibres that are destined for the sphenopalatine ganglion from here the postganglionic fibre are distributed to the lacrimal gland and glands of nose.
What is the function of the nerve to stapedius?
Motor innervation to the stapedius muscle which dampens down movements of the stapes and prevents damage to the inner ear should it be subjected to loud noise.
What is the function of the chorda tympani?
Contains special sensory taste fibres from the anterior 2/3s of the tongue
Explain why sucking a sweet during take off and landing might relieve ear discomfort experienced?
Swallowing opens the Eustachian tube allowing equalisation of pressure from the middle ear to the outside world. During take off and landing the pressure changes are noticeable and increased air pressure inside the middle ear may cause considerable discomfort.
When clearing the ears with a cotton-wool bud stick, why do some people start coughing and a few people even vomit?
The nerve supply to part of the external auditory canal and posterior part of the tympanic membrane is via the auricular branch of the vagus nerve.
Because irritation of the auricular branch is referred along the other branches of the vagus nerve, triggering the gag or cough reflex
between which layers does a perichondrial haematoma occur?
the auricle consists of cartilage overlaid by perichondrium which has blood vessels within it. Haematoma develops between cartilage and perichondrium
What are the implications of a perichondrial haematoma?
The cartilage is avascular and relies on diffusion of gases and nutrients from the perichondrium. The haematoma deprives that part of cartilage from gases and nutrients so begins to necrose.
How is a perichondrial haematoma treated?
Drain it
Without treatment of a perichondrial haematoma what happens?
Necrosis of the underlying cartilage occurs and leads to a cauliflower ear as the normal shape of the auricle is lost.
What causes otitis media with effusion?
it is a chronic accumulation of fluid within the middle ear.
Believed to arise due to Eustachian tube dysfunction, Most commonly seen in young children due to horizontal orientation and narrowness of the tube.
Why does Eustachian tube dysfunction predispose to ear infection?
The tube does not open properly so there is reduced aeration of the middles ear and it cannot equalise with atmospheric pressure.
The mucosal middle ear cells continuously absorb air and as such an increasingly negative pressure is created within the Eustachian tube and middle ear. Negative pressure causes a transudate from the mucosa in the middle ear - effusion. Fluid cannot drain and ideal growth medium for pathogens
What would be the findings of an examination of an eardrum in someone with OME?
Red and inflamed - due to infection
Retracted rather than bulging - due to negative pressure in the middle ear suching eardrum inwards.
