Ear Anatomy and Physiology Flashcards
What are the 3 areas of the ear?
- External
- Middle
- Inner
What is the pinna?
- Stratified keratinised epithelium (skin)
- Elastic cartilage
What is the external ear canal made of?
Lateral 1/3rd made of skin and cartilage:
- Skin containing ceruminous and sebaceous glands (producing wax)
- Thick hairs on the outside, become finer on the inside
- Protective barrier and disinfectant
Medial 1/3rd made of skin and bone
- No hairs or cilia
- Doesn’t produce wax
How do the lateral and medial 1/3 of external ear canal differ?
Lateral 1/3rd made of skin and cartilage:
- Skin containing ceruminous and sebaceous glands (producing wax)
- Thick hairs on the outside, become finer on the inside
- Protective barrier and disinfectant
Medial 1/3rd made of skin and bone
- No hairs or cilia
- Doesn’t produce wax
How does skin grow in the external ear canal?
Skin is constantly being shed and renewed:
- Grows from the umbo of the tympanic membrane outwards
- Is shed in the lateral 1/3rd of canal and trapped in wax as part of cleaning mechanism
What can wax or other mechanical obstruction of the external ear canal cause?
Wax or other mechanical obstruction cause minimal hearing loss when compared with other problems in other parts of the ear
What are some examples of clinical problems of the ear canal?
- Earwax
- Pinna haematoma
- Cauliflour ear
- Otitis externa
- Fungal infection
- Foreign body
What are the 3 layers of the tympanic membrane?
- Outer layer is continuous with skin of external ear canal
- Middle fibrous layer
- Inner layer of respiratory epithelium (ciliated columnar epithelium with goblet cells)
How long is the external earn canal in adults?
4cm
How large is the diameter of the tympanic membrane?
1cm in diameter
What does the tympanic membrane seperate?
Separate the middle ear from the external ear
Where are ossicles found?
Middle ear
What is the function of ossicles?
- Conduct sound waves from tympanic membrane to inner ear
- Play an important role in sound conduction
- Much more important than tympanic membrane
- Disruption can be from trauma or bony sclerosis (otosclerosis)
What kind of epithelium is the middle ear lined with?
Lined with same continuous respiratory epithelium that forms inner layer of tympanic membrane:
- Capable of producing mucus
What nerve is found in the middle ear?
Middle ear contains the facial nerve
What are some important anatomical relations of the middle ear?
- Middle cranial fossa
- Internal carotid artery
- Sigmoid sinus and internal jugular vein
What are the 6 segments of the facial nerve?
- Intracranial
- Meatal (internal auditory meatus)
- Labyrinthine
- Tympanic (fallopian tube)
- Mastoid
- Extratemporal
What does the facial nerve innervate?
The facial nerve is the motor supply to the muscles of facial expression:
- Stapedius
- Posterior belly of digastric
- Stylohyoid
Where does taste come from?
Taste comes from the anterior 2/3rds of tongue from the chorda tympani
What nerve is used for taste?
Chorda tympani, which is a branch of the facial nerve
What are examples of middle ear clinical problems?
- Otitis media
- Tympanic membrane perforation
- Otitis media with effusion (OME)
- Grommets
- Cholesteatoma
What are some possible complications of ottitis media and cholesteatoma?
- Remember anatomical relations
- Meninges
- Middle cranial fossa
- Facial nerve
- Mastoid cavity
- Inner ear
- Sigmoid sinus/internal jugular vein
Cholesteatoma - pathology
- Misnomer, nothing to do with cholesterol
- To do with skin of the middle ear
- Keratinised squamous epithelium in the wrong place
- Cause problems because they grow and are destructive
What nerves innervate the ear?
- Jacobsons nerve
- Tympanic branch of glossopharyngeal nerve (CN IX)
- Sensation to middle ear
- Arnolds nerve
- Auricular branch of vagus nerve (CN X)
- Sensation to posterior half of external ear canal
- Facial nerve (CN VII)
- Anterior half of external ear canal
- Mandibular branch of trigeminal nerve (CN V3)
- Pinna (upper half)
- Greater auricular nerve (C2/3)
- Pinna (lower half)
