Lecture 9 -- Ear Anatomy

What is the external auditory meatus?

= Ear canal = The space running inside the cartilages to the tympanic membrane.

Ring-like.

List out three groups of muscles of the external ear and their functions.

Pre-auricular - Move ear forward

Ventral auricular - Move ear ventrally

Post auricular - Move ear caudally and medially

What is the name of the muscle? Where does it originate and insert to? What is its function?

Parotidoauricularis

Runs over the parotid and goes up the auricular cartilage

When this muscle contracts, the ear is pulled out and down

Describe the MOTOR neurone supply to the external ear.

Motor:

Rostral auricular nerve of facial nerve → Supply the rostral ear muscles

Caudal auricular nerve of facial nerve → Supply the caudal ear muscles

Great auricular nerve from C2 → Supply the caudal ear muscles

Describe the SENSORY neurone supply to the external ear.

Small rostral part + deep ear canal: Auricular-temporal branches of mandibular trigeminal

Rest of the outside of ear: Cervical spinal nerve

Inside of the ear canal → Internal auricular branch of the facial nerve

Identify the nerve supply

Which nerve, if paralyzed, causes the ears to be stuck in a backwards position?

Facial nerve

→ Rostral auricular nerve of facial nerve innervate the rostral ear muscles, which is responsible for pulling the ear forward

→ If facial nerve is paralysed, the ear will be stuck in backwards position

What is the middle ear?

A cavity that lies within the temporal bone.

What forms the ventral floor of the middle ear?

Tympanic bulla.

What lies laterally to the middle ear?

Tympanic membrane (eardrum).

What lies medially and dorsally to the middle ear?

Petrous temporal bone that house the inner ear

Identify the structure below.

What is tympanic bulla?

Air filled ventral part of the cavity in middle ear

Chorda tympani

Splits off from the main branch in middle ear

How do the auditory tubes run?

Runs from the wall of nasopharynx to the middle ear cavity

What is the function of the auditory tube?

When swallowing/ yawning, the opening of the auditory tube = osita is forced to open → Air enters + move into the middle ear cavity → Allow to equalize pressure on either side of the eardrum.

In which animals is the guttural pouch found?

Odd-toed ungulates (horses, tapirs, rhinos).

What is the guttural pouch?

An air-filled ventral diverticulum of the auditory tube.

What divides the guttural pouch ventrally into medial and lateral compartments?

Stylohyoid bone

P.S. Medial is large 2/3 vs Lateral 1/3 + The sylohyoid bone only divide the ventral part of the pouch into medial and lateral compartment = Dorsal part communicates freely

What are the suspected functions of the guttural pouch?

NOT KNOWN

?Regulation of internal carotid artery pressure and cooling blood flow to the head?

Where guttural pouch can be found?

Dorsal - Skull and C1 = Locate at the back of the head

Ventral - Pharynx and retropharyngeal lymph node

Medial - Meidan septum

Lateral - Pterygoid muscle, parotid and mandibular salivary glands

What is the opening of the guttural pouch?

Ostia

What can be appreciated within the medial and lateral compartment of the guttural pouch?

Medial compartment:

1. Internal carotid artery

2. Cranial cervical ganglion

3. Glossopharyngeal and vagus nerve

4. Accessory nerve

5. Hypoglossal nerve

6. Longus capitus muscle

Lateral compartment:

1. External carotid artery

2. Maxillary artery

3. Facial nerve

4. Mandibular trigminal nerve

Where is the Ostia located?

Dorsal to most pouch when head horizontal

→ Only drain when head is down and horse swallows

What are common diseases of the guttural pouch?

Tympany (air distension), empyema (bacterial infection), mycosis (fungal infection).

What is the name of the lateral surgical approach to the guttural pouch?

Viborg's Triangle

Cranial border - Caudal mandible
Caudal border - Tendon of insertion of sternocephalicus
Ventral border - Linguofacial vein

What are the symptoms relate to the structures affected?

1. Nosebleed

   → Internal/ external carotid artery

2. Nasal discharge

   → Infection of the guttural pouch

3. Nerve dysfunction

   → Laryngeal paralysis = Vagus nerve

   → Homers syndrome (Drooping eyelid; constricted pupil)

   → Facial asymmetry

4. Swelling

How guttural pouch disease can be diagnosed?

Endoscopy and radiography