Anatomy and Physiology of the Ear Flashcards
What sections is the ear separated into?
- External
- Middle
- Inner
What type of epithelium is found in the external auditory canal?
Stratified keratinised epithelium (skin) - with elastic cartilage
What are the features of the lateral 1/3 of the auditory canal?
- Made of skin and cartilage
- Skin contains ceruminous and sebaceous glands (produce wax)
- Protective barrier and disinfectant
What are the features of the medial 2/3 of the auditory canal?
- Made of skin and bone
- No hairs or cilia
- Doesn’t produce wax
Describe the cycle of skin renewal
Skin of external ear canal is constantly bine shed and renewed. It grows from the umbo of the tympanic membrane outwards.
The skin is shed in the lateral 1/3rd of the canal and becomes trapped in the wax as part of the cleaning mechanisms
What are four conditions that can affect the external ear?
- Pinna haematoma
- Otitis externa
- Fungal OE
- Foreign body
What is pinna haematoma?
Trauma common during sports where shearing forces can lead to separation of the anterior auricular perichondrium from the underlying cartilage. As a result, blood vessels and be torn.
If not drained early, the haematoma can lead to necrosis. This can stimulate new and asymmetrical cartilage growth resulting in ‘cauliflower ear’.
What is otitis externa?
Inflammation (redness and swelling) of the ear canal with discharge (usually self-limiting). If it becomes chronic, there is lots of oedema in the canal walls, narrowing the canal.
What are the three layers of the tympanic membrane?
- Outer layer continuous with skin of EAC
- Middle fibrous layer
- Inner layers of resp epithelium (ciliated columnar epithelium with goblet cell)
What structures are found in the middle ear?
- Tympanic membrane
- Ossicles
- Nerves
What are ossicles?
Small bones of the middle that conduct sound waves from the tympanic membrane to the inner ear
What condition can disrupt conduction through the ossicles?
Trauma or bony sclerosis (otosclerosis)
What is the type of epithelium in the middle ear?
Ciliated columnar with goblet cells and therefore capable of producing mucous (glue ear)
How does the middle ear connect to the mastoid system?
Via aditus to mastoid antrum
How does the middle ear connect to the nasopharynx?
Via eustacian tube
What nerves innervate the middle ear?
Facial nerve and it’s branch (chorda tympani)
What are the anatomical relations of the middle ear?
- Meninges
- Middle cranial fossa
- Facial nerve
- Mastoid cavity
- Inner ear
- Sigmoid sinus/internal jugular vein
What two conditions can affect the middle ear?
Otitis media and Cholesteatoma
What can occur with otitis media?
Perforation can occur through the tympanic membrane if large enough pressure is built up
Effusion - presence of bubbles of gas, making it harder to equalise the ear
What can be used to treat OM with effusion?
Grommets - small ventilation tube inserted in the eardrum to balance pressure on either side
What is Cholesteatoma?
- Abnormal growth that develops behind the eardrum
- Nothing to do with cholesterol
- Skin in middle ear: keratinised squamous epithelium in wrong place
- Can be congenital or acquired
- Causes problems because they grow and are destructive
What nerve innervates the upper half of the pinna?
Mandibular division of the trigeminal nerve (CN V3)
What nerve innervated the lower half of the pinna?
Greater auricular nerve (C2, 3)
What nerve innervates the anterior half of the external auditory canal?
Facial nerve (CN VII)
What nerve innervates the posterior half of the eternal auditory canal?
Arnolds nerve (auricular branch of vagus nerve (CN X)
What nerve innervates the middle ear?
Tympanic branch of the glossopharyngeal nerve (CN IX) –> Jacobsons nerve
What is otalgia?
Ear pain
What are secondary causes of otalgia wrt nerves that innervate the ear?
Referred pain:
• C2/3 – arthritis/cervical spondylosis, soft tissue injury
• CN V – Dental, TMJ dysfunction, nasopharyngeal disease
• CN IX – oropharyngeal inflammation/infection, tongue base malignancy
• CN X – laryngeal/pharyngeal malignancy
What are the different structures of the inner ear?
- Bony and membranous labyrinth which contains fluid: perilymph and endolymph
- Cochlear: organ of corti (hearing organ)
- Peripheral vestibular apparatus: utricle, saccule, semicircular canals
- Vestibulocochlear nerve (CN VIII)
Describe a simplified process of hearing
- Function of middle ear is to transduce vibration into nervous impulses
- Foot of stapes vibrates in oval window
- Causes pressure waves through fluid filled cochlear
- This is detected by hair cells in organ of corti
- Transmitted to brainstem (junction of pons and medulla) by CN VIII
What nerve is responsible to send signals to and from the ear and brain?
Vestibulocochlear nerve (CN VIII)
What structures in the inner ear are important for balance?
- Semi-circular canals
- Saccule
- Utricle
Why are the semicircular canals important for maintaining balance?
Detects head rotation
What is the vestibule-occular reflex?
Its what makes you able to fix your visions on an object when your head is moving
Why is the saccule important for maintaining balance?
Detect linear acceleration in vertical plane
Why is the utricle important for maintaining balance?
Detects linear acceleration in horizontal plane
