External Ear Anatomy Flashcards
Externally visible part of the external ear:
Pinna/Auricle
Identify the covered structures:
What is the helix of the ear?
The free margin of the auricular helix
Appropriate directional terminology:
Lateral = cranial = internal = concave
Appropriate directional terminology:
Medial = caudal = external = convex
What is the structure of the auricular cartilage? What is its function?
- Elastic / fibroelastic cartilage that is tubular proximally and flared distally (relative to the skull)
- Supports the externally visible part of the ear
- Collects & funnels sound to the middle ear
How does the auricular cartilage attach to the bony skull?
Via the annular cartilage
What is the scutiform cartilage?
To redirect the muscles controlling the movement of the ear; acts as a fulcrum -> improves mobility of auricular cartilage
What leads the external entrance into the tympanic bulla?
(bony) External Acoustic Meatus
What is the “tubular part” of the auricular cartilage?
The cartilaginous part of the external acoustic meatus
Function
- rim / free margin/edge of the pinna that aourrounds the scapha
- forms the apex (where the lateral and medial borders of the helix meet)
What species have the cutaneous marginal pouch?
Carnivores
What is the function of the tragus?
Directs sound toward ear drum; slightly covers / protects the ear canal
Purpose of the intertragic and pretragic incisures?
use to guide otoscope into the ear
Where does the ear canal begin and end?
Begins where auricular cartilage narrows toward a tubular shape (near cochlea) and ends @ tympanic membrane (eardrum)
What overlaps the vertical part of the ear canal?
The parotid salivary gland - avoid during sx!
What are the 3 portions of the horizontal part of the ear canal?
- tubular portion of auricular cartilage
- annular cartilage
- osseous portion extending from skull
What is the composition of the ear canal?
Stratified squamous epithelium
- sebaceous and ceruminous glands => ear wax!
- sparse hair follicles
What are the 4 major divisions of extrinsic muscles of the external ear and their functions?
- Rostral (embedded with scutiform cartilage, which redirects the action of rostral mm.)
- Caudal
- Dorsal (fix scutiform cartilage in place so other muscles can act upon it)
- Ventral (“depress” pinnae)
Where do most arteries supplying the external ear branch from?
the external carotid artery
Which artery branch in the dog supplies the majority of the external ear?
Caudal auricular artery
which is a br. of external carotid a.
What is the significance of the 3 large arterial branches positioned along the medial surface of the external ear?
Rostral, Intermediate and Caudal Auricular brr.
Supply the lateral surface of the pinna
their branches pass through foramina in the auricular cartilage to supply the lateral surface of the pinna (and dermis of ear canal)
Clinical significances of the large central vein and 2 peripheral arteries on the medial surface of the ruminant ear?
- Tattooing procedure (for breed registeries, tagging, brucellosis, etc.) can be wrecked by clamping into the vein -> ink does not go in
- Knowledge of their location is imperative for injections
Where to do SQ injection or place IV in ruminant ear?
Clinical significance of the marginal ear veins // peripheral veins in the pig?
Great for small-volume blood draws (1-3cc)
What nerve supplies motor function to the external ear? What can a defect in this branch lead to?
The auricular part of the auriculopalpebral nerve of the facial nerve. Defect => ear droop
What nerves (4) carry sensory information from the ear?
- Auricular part of the mandibular nerve of the trigeminal nerve (CN V - V3)
- Facial nerve (CN VII)
- Vagus nerve (CN X)
- C2 - second cervical nerve
