Ear Flashcards
What are the three divisions of the ear? What structures make up each division?
- External Ear
- Auricle/pinna
- External Acoustic Meatus - Middle Ear
- Tympanic membrane
- Ossicles
- Walls and relations
- Nerves - Internal Ear
- Vestibule
- Semicircular Canals
- Cochlea
What nerve supplies the external surface of the tympanic membrane? The internal surface of the
tympanic membrane?
- Internal Surface: CN IX Glossopharyngeal
- The V3 division of the trigeminal nerve and the Vagus nerve play a role in innervating the external surface of the tympanic membrane.
Which ossicle attaches to the deep surface of the tympanic membrane?
-Malleus
What ossicle attaches to the oval window?
-Stapes
How do the oval and round windows relate to the promontory?
The promontory separates the oval and the round windows.
What is the function of the tensor tympani and the stapedius? What is their innervation?
The tensor tympani and the stapedius mm. both attach to parts of the middle ear to dampen loud sounds. The tensor tympani is innervated by a branch of CN V3, while the stapedius muscle is innervated by nerve to stapedius, a branch of CN VII.
What fiber types are found in the tympanic branch of CN IX? Which fibers stay in the middle ear
and which fibers exit? What nerve exits the tympanic plexus? Describe the course of this nerve to its
target ganglion.
Preganglionic parasympathetic fibers are in the tympanic branch of CN IX. The lesser petrosal nerve exits the tympanic plexus. The lesser petrosal nerve re-enters the temporal bone and then into the middle cranial fossa via the hiatus for the lesser petrosal nerve. From there, it exits foramen ovale to reach the pterygopalatine fossa where it will synapse with the pterygopalatine ganglia.
How does the middle ear relate anatomically to the inner ear (medial/lateral/superior/inferior)?
The middle ear is lateral to the inner ear.
Describe the function of the 2 components of the vestibule.
The vestibule contains 2 membranous structures
- saccule (detects vertical acceleration)
- utricle (detects horizontal acceleration)
What separates the external from the middle ear?
the tympanic membrane
What nerves innervate the external ear?
Several overlapping nerves from both spinal nerves and cranial nerves contribute to sensory innervation of the external ear, including:
- Greater auricular and lesser occipital nerves (from the Cervical plexus)
- Auriculotemporal (V3)
- Auricular branch of CN X
What nerves passes between the malleus and the incus?
The chorda tympani
It passes anteriorly from the Facial nerve between the malleus and incus and just posterior to the tympanic membrane
What is the function of the oval and round window?
Oval window = transmit interpretation of sound. The footplate of the stapes attaches to the membrane covering the oval window and shakes the membrane, which sets in motion fluid waves in the internal ear.
Round window = dissipation of sound. Fluid waves set in motion by oval window go all the way around the cochlea and then hit the round window to stop interpretation of that sound (so can begin interpretation of a new sound).
What structure forms the promontory?
the cochlea pushing into the medial wall (temporal bone) of the middle ear
What is the tympanic plexus and what contributes to it?
A plexus of nerves that forms on the promontory of the middle ear. It is largely composed of preganglionic parasympathetic fibers from CN IX + postganglionic sympathetics from the carotid plexus.
[After CN IX exits skull via jugular foramen, it gives off the tympanic branch containing pregang parasympathetics that enter the middle ear. There it joins with the postgang sympathetics to form the tympanic plexus. The LESSER petrosal nerve arises from this plexus and passes toward pterygopalatine fossa.]
