Lecture 16: Anatomy and Histology of the Ear Flashcards
What composes the external ear?
Auricle to Tympanic Membrane
What composes the middle ear?
Tympanic Membrane to Oval Window
What composes the inner ear?
Oval Window to Internal Acoustic Meatus
What type of cartilage is the external ear mostly made up of?
Elastic Cartilage
What supplies the external ear?
Posterior Auricular Artery (from ECA)
Superficial Temporal Artery (from ECA)
What provides sensory innervation to the external ear?
- Facial Nerve
- Cervical Plexus: Lesser Occipital and Greater Auricular Nerves
- Auriculotemporal Nerve (V3)
- Vagus/Glossopharyngeal Nerve
What innervates the superior part/roof of the external acoustic meatus?
Facial Nerve
What innervates the posterior part of the external acoustic meatus?
Greater Auricular Nerve (Cervical Plexus)
What innervates the anterior part of the external acoustic meatus?
Auriculotemporal Nerve (V3)
What innervates the inferior part/floor of the external acoustic meatus?
Vagus: Arnold Nerve
-plays a role in the cough reflex
What glands make ear wax?
Ceruminous Glands
What is the composition of the external acoustic meatus?
Outer ⅔: Soft CT and Cartilage (similar to external ear)
-where you can see ceruminous and sebaceous glands + hair follicles
Inner ⅓: Just skin and bone
Where is the cone of light?
Anterior, inferior quadrant of Tympanic Membrane
What makes up the roof of the middle ear?
Tegmental Wall (from Temporal Bone) -Separates ear from brain/middle cranial fossa
What makes up the floor of the middle ear?
Jugular Wall
-Separates ear from bulb of Internal Jugular Vein
What makes up the lateral wall of the middle ear?
Membranous Wall (going to external ear)
What makes up the medial wall of the middle ear?
What is found at this wall?
Labyrinthine Wall (Oval and Round Windows)
- Lateral Semicircular Canal
- Facial Canal and Nerve
- Promontory of Labyrinthine Wall
What makes up the posterior wall of the middle ear?
Mastoid Wall
-Separates tympanic cavity from mastoid air cells and facial canal
What can be found at the anterior wall of the middle ear?
Pharyngotympanic Tube
Tensor Tympanic Muscle
-Separates Tympanic Cavity from Internal Carotid Artery
What does the pharyngotympanic tube connect?
Middle ear to nasopharynx
What does the pharyngotympanic tube do?
Equalize pressure
What two muscles expand the pharyngotympanic tube?
Levator Veli Palatini Muscle
Tensor Veli Palatini Muscle
What type of epithelium is found on the pharyngotympanic tube?
Pseudo-stratified Epithelium
What three bones make up the auditory ossicles in the middle ear?
What pharyngeal arches are they from?
Malleus (PA 1)
Incus (PA 1)
Stapes (PA 2)
What does the auditory ossicles do?
Transmit sound from the air to the fluid filled concha
What does the Tensor Tympani Muscle do?
What nerve innervates it?
Dampens loud sounds by pulling on handle of malleus
Innervated by CN V3
What does the Stapedius Muscle do?
What nerve innervates it?
Dampens vibrations and limits excess movement of stapes bone (at the neck)
Innervated by CN VII
Where is the bony labyrinth located?
Petrous Region of Temporal Bone
What separates bony labyrinth with membranous labyrinth?
Perilymph
What lymph is found in membranous labyrinth?
Endolymph
What sections are found in the membranous labyrinth?
What do they do?
Semicircular Canals: Equilibrium
Utricle and Saccule: Acceleration
Cochlear Duct: Hearing
Sensory Cells
What is kinocilium?
Specialized hair cells that can be displaced and result in depolarization or hyper polarization of the hair cells
What are the three sections of the Cochlear Duct?
What lymph does each section contain?
- Scala Vestibule - Perilymph
- Scala Media - Endolymph
- Scala Tympani - Perilymph
What makes up the roof and floor Scala Media?
Roof: Vestibular Membrane
Floor: Basilar Membrane
What is found in the Basilar membrane?
Organ of Corti
What is Organ of Corti composed of?
Hair cells (sensory)
Support Cells
Pillar Cells
What is the ratio of outer hair cells to inner hair cells?
3:1
Where is stereocilia found?
Overlying tectorial membrane, which is extending from spiral lamina
What is the function of the external ear?
Directs sound waves to external auditory meatus
What is the function of the middle ear?
- Takes sound waves and turns them into physical energy that pushes against auditory ossicles and then pushes on the oval window
- Controls pressure in the middle ear via Pharyngotympanic Tube
What is the function of the inner ear?
- Transform sound waves to the brain
2. Balance
How does sound move in the inner ear?
- Stapes moves oval window, causing the perilymph to change pressure in Scala Vestibule.
- This disturbs endolymph in scala media and displaces basilar membrane.
- Stereocilia in hair cells is distorted. Organ of Corti cells are distorted and initiates a signal via CN VIII.
- Perilymph in Scala Tympani takes the pressure and it exits via round window.
What are the three canals in the semicircular canals and what is their axis?
Anterior: Sagittal Plane
Lateral: Transverse Plane
Posterior: Coronal Plane
What is displaced by fluid motion within semicircular canal?
Cupulla: has hair cells with stereocilia
What covers hair cells in the vestibule?
Otolithic Membrane
What does the utricle sense?
Horizontal Acceleration
What does the saccule sense?
Vertical Acceleration
Where is perilymph drained to?
Subarachnoid Space
Where is endolymph drained to?
Venous Sinuses of Dura Mater
How does elastic cartilage get its nutrients?
Periochondrium
What pathologies are associated with external ear?
Cauliflower Ear
Wrestling
What is mastoiditis?
Infection of mastoid cells that can spread into cranial fossa
How can the tympanic membrane be damaged?
- Medial Ear pressure from fluid
2. External Trauma
What is Otitis Media?
Infection of the middle ear (can be viral, bacterial, fungal, etc). The ear is filled with fluid or pus.
Tympanic membrane is red and bulged
What is Ménière’s Syndrome?
Increased endolymph that leads to abnormal signaling.
Can cause dizziness, vertigo, and possible hearing loss
What can cause conductive hearing loss?
Problems with outer or middle ear
What can cause sensorineural hearing loss?
Damage to inner ear or auditory nerve
What can cause central hearing loss?
Problems in CNS
Why do young children suffer from otitis media more than adults?
Pharyngotympanic tube is at a more shallow angle, allowing for less drainage and pressure equalization of the inner ear
