Organs - The Ear (External) Flashcards
What are the two parts of the external ear?
1) Auricle
2) External acoustic meatus
What is the function of the auricle?
To capture sound waves and direct them towards the external acoustic meatus.
What is the structure of the auricle?
Inferiorly - lobule - only part not supported by cartilage.
Outer curvature - helix.
Second innermost curvature that runs parallel to the helix - antihelix.
The antihelix separates into an inferoanterior and superoposterior crus.
The hollow depression in the centre of the ear - concha that directs sound to the external acoustic meatus
Immediately anterior to the beginning of the external acoustic meatus is the tragus. Opposite the tragus is the anti-tragus.
Clinical relevance: auricular haematoma
Collection of blood between the cartilage of the ear and the overlying perichondrium. It usually occurs as a result of trauma, commonly seen in contact sports.
The accumulation of blood can disrupt the blood supply to the cartilage and required prompt drainage. Untreated causes can result in avascular necrosis of the cartilage, resulting in a ‘cauliflower ear’ deformity.
What is the basic overview of the external acoustic meatus?
It is sigmoid-shaped tube that extends from the deep part of the concha to the tympanic membrane.
The walls of the external 1/3 are formed by cartilage, whereas the inner 2/3 are formed by the temporal bone.
What is the path of the external acoustic meatus?
Initially - superoanteriorly.
Then a slight superoposterior direction.
The ends by running in an inferoanterior direction.
What are the features of the tympanic membrane?
The tympanic membrane lies at the distal end of the external acoustic meatus.
It is made of connective tissue with skin on the outside and mucous membrane on the inside. The membrane is connected to the surrounding temporal one by a fibrocartilagenous ring.
The translucency of the tympanic membrane allows the structure within the middle ear to be observed during otoscopy.
On the inner surface of the membrane, the handle of malleus attaches to the tympanic membrane, at a point called the umbo of tympanic membrane.
The handle of malleus continues superiorly, and at its highest point, a small projection called the lateral process of the malleus can be seen. The parts moving away from the lateral process are called the anterior and posterior malleolar folds.
Clinical relevance - perforation of the tympanic membrane
It is susceptible to perforation by trauma and infection.
An infection of the middle ear (otitis media) causes pus and fluid to build up behind the tympanic membrane. This causses and increased pressure within the middle ear, and eventually the eardrum can rupture.
In some cases, the tympanic membrane can heal itseld, but in larger perforations surgical grafting may be required.
What is the vasculature of the external ear?
Provided by branches of the external carotid artery:
1) Posterior auricular artery
2) Superficial temporal artery
3) Occipital artery
4) Maxillary artery (deep auricular branch) - supplies deep aspect of the external acoustic meatus and tympanic membrane only.
Venous drainage is via veins following the arteries listed above.
What is the innervation of the external ear?
Skin of the auricle - greater auricular nerve (branch of the cervical plexus).
Skin of the auricle - lesser occipital nerve (branch of the cervical plexus)
Auriculotemporal nerve (branch of the mandibular nerve) - innervated the deeper aspect of the auricle and external acoustic meatus.
Some individuals can complain of an involuntary cough when cleaning their ears - this is due to stimulation of the auricular branch of the vagus nerve (the vagus nerve is also responsible for the cough reflex).
What are the lymphatics of the external ear?
1) Superficial parotid
2) Mastoid
3) Upper deep cervical
4) Superficial cervical
nodes
