Anatomy - Ear and Auditory Pathway

External ear and middle ear

Mainly concerned with the transfer of sound into the inner ear

Inner ear

Contains the organ for equilibrium as well as the organ for hearing

Tympanic membrane

Separates the external ear from the middle ear

Auricle (Pinna)

Shell-like structure that collects sound. Composed of elastic cartilage covered by a very thin skin

Helix

Elevated margin of the auricle

Antihelix

Another elevated margin inferior to the helix

Concha

The deepest depression of the auricle

Tragus

Tongue-like opening overlapping the opening of the EAM

Antitragus

Another elevation opposite the tragus

Lobule

Only non-cartilaginous portion that consists of fibrous tissue, fat, and blood vessels

External Auditory Meatus (EAM)

An ear canal that leads inward through the tympanic part of the temporal bone. From the auricle → tympanic membrane. Adults: 2–3 cm. Slightly s-shaped canal

Outer (Lateral) Cartilaginous

Skin continuous with the auricular skin. Contains sebaceous (ceruminous glands) that produce earwax (cerumen). Angled downward and forward

Inner (Medial) Bony

Lined with thin skin continuous with the external layer of the tympanic membrane

Auricular branch of vagus nerve (CN X), Sensory branch of facial nerve (CN VII)

The external auditory meatus is mainly innervated by what nerves?

Posterior Auricular & Superficial Temporal

Provides circulation to the external ear

Superficial parotid, Mastoid, Deep cervical, Superficial cervical

Lymphatic drainage of the external ear is from what lymph nodes?

Greater Auricular Nerve (Cervical Plexus)

Innervates the medial surface (back of the ear) and the posterior part of the lateral surface (front of the ear)

Auriculotemporal Nerve (Mandibular Branch of CN V)

Innervates the anterior aspect of the lateral surface of the auricle. Includes the concha's rim, the helix's crus, and the tragus

Greater auricular nerve

The lobule senses the least amount of pain due to its singular innervation from the?

Auricular Hematoma (Cauliflower Ear)

Failed adhesion between skin and cartilage. Facilitated by application of pressure via a bolster

Tympanic membrane

Has a diameter of approximately 1 cm. A thin, oval, semi-transparent membrane at the middle end of the external auditory meatus. Forms a partition between the external auditory meatus and the tympanic cavity of the middle ear. Extremely sensitive to pain

Pars flaccida

A thin membrane superior to the lateral process of the mallus. Lacks the radial and circular fibers present in the remainder of the membrane

Pars tensa

Radial and circular fibers present in the remainder of the membrane known as?

Auriculotemporal Nerve (Mandibular Branch of CN V), Auricular Branch of Vagus Nerve (CN X)

Innervates the lateral surface of the tympanic membrane

Tympanic Plexus of Glossopharyngeal Nerve (CN IX)

Supplies the inner or medial aspect of the tympanic membrane

Otoscope

Used to visualize the external ear (i.e., external auditory meatus and tympanic membrane)

Tympanic membrane perforation

Leads to significant hearing loss and patient needs to undergo tympanoplasty and use a cartilage graft due to the extent of the perforation

Middle Ear

An air-containing cavity within the petrous part of the temporal bone. Lined with a mucous membrane

Tympanic Cavity

Thought of as a six-sided box which has a roof, floor, anterior and posterior walls, and medial and lateral walls

Tegmental wall

What is the roof the tympanic cavity that separates the tympanic cavity from the dura

Membranous wall

The lateral wall of the tympanic cavity composed of the tympanic membrane and handle of the malleus

Jugular wall

The floor of the tympanic cavity. A layer of bone that separates the tympanic cavity from the superior bulb of the jugular vein

Labyrinthine wall

The medial wall of the tympanic cavity. Stapes attached to the oval window, promontory of the cochlea, and round window

Carotid wall

The anterior wall of the tympanic cavity. Eustachian tube or pharyngotympanic tube and carotid canal

Mastoid wall

The posterior wall of the tympanic cavity where the aditus that opens to the mastoid antrum can be seen

Malleus, Incus, Stapes

What are the ossicles content of the tympanic cavity?

Stapedius, Tensor tympani

What are the muscles content of the tympanic cavity?

Chorda tympani (branch of CN VII), Tympanic plexus of CN IX

What are the nerves content of the tympanic cavity?

Ossicles

The first bones to be ossified during development. Essentially mature at birth. Form a mobile, osseous bridge from the tympanic membrane to the oval window. Joints between the ossicles are of the synovial type

Malleus

Largest ossicle. Latin word for hammer. Functions as a lever, with the longer of its two processes and its handle attached to the tympanic membrane

Head

Part of the malleus that articulates with the incus

Neck

Part of the malleus that lies against the pars flaccida

Handle

Part of the malleus that is embedded in the tympanic membrane with its tip at the umbo, which is why the malleus moves with the tympanic membrane

Umbo

The central point of maximum depression at the tympanic membrane

Incus

Second largest ossicle. Latin word for anvil. Located between and articulates with the malleus and the stapes. Has a body and two limbs

Body

Part of the incus that articulates with the head of the malleus

Long limb (process)

Part of the incus that lies parallel to the handle of the malleus, and its interior end articulates with the stapes by way of the lenticular process. Only has a single nutrient vessel, while other portions of the ossicular chain are supplied by two or more sources

Short limb

Part of the incus that is connected by a ligament to the posterior wall of the tympanic cavity

Stapes

Smallest ossicle and smallest bone in the body. Latin word for stirrup. Composed of a head, neck, two limbs, and a base

Head

Part of the stapes that articulates with the long process of the incus

Neck

Part of the stapes that receives the insertion of the stapedius muscle

Base (Footplate)

Part of the stapes that fits into the oval window

Chorda Tympani Nerve

Branch of the facial nerve (CN VII). Carries taste fibers at the anterior 2⁄3 of the tongue. Also carries secretomotor fibers for the submandibular and sublingual salivary glands

Tympanic Plexus of CN IX

Branches of the tympanic plexus of the glossopharyngeal nerve provide innervation to the mucosa of the middle ear and adjacent pharyngotympanic (Eustachian) tube

Pharyngotympanic (Eustachian) Tube

Connects the tympanic cavity to the nasopharynx. Functions to equalize ear pressure from the middle ear with the atmospheric pressure to balance the pressure on both sides of the tympanic membrane. Balance allows the tympanic membrane to move easily. The tube is a drainage route for serous secretion of the mucous membrane lining the middle ear

Levator veli palatini (LVP), Tensor veli palatini (TVP)

The pharyngotympanic tube opened through the combination of contractions from what muscles?

Otitis media

Patients with cleft palate are prone to _________ since their LVP and TVP are very weak for them to open the pharyngotympanic tube properly. Thus, serous secretions of the mucous membrane lining the middle ear will accumulate, thereby introducing bacterial growth

Otitis medial with effusion (OME)

A collection of non-infected fluid accumulating in the middle ear space as a result of a cold, sore throat, or upper respiratory infection. The accumulation of fluid leads to the blockade and not necessarily the inflammation of the middle ear

Inner Ear

Contains the vestibulocochlear organ. Concerned with the reception of sound and the maintenance of balance. Situated on the petrous part of the temporal bone, medial to the middle ear

Bony Labyrinth

The space within the otic capsule that is filled with perilymph. Inside, it contains the membranous labyrinth, composed of sacs and ducts filled with endolymph

Vestibule

The central part that lies posterior to the cochlea and anterior to the semicircular canals. The saccule and utricle are lodged here

Anterior, Lateral, Horizontal

What are the three semicircular canals?

Cochlea

Opens to the anterior part of the vestibule. Consists of a central bony pillar called the modiolus. Around the modiolus, a hollow bony tube makes two and a half spiral turns

Modiolus

Contains canals for blood vessels. Distributes the branches of the cochlear nerve

Promontory

The first basal turn of the cochlea is responsible for the promontory. Seen in the medial wall of the middle ear

Osseous Spiral Lamina

A spiral ledge that winds around the modiolus. Projects into the interior part of the canal, partially dividing it

Basilar Membrane

Stretches from the spiral lamina to the outer bony wall, thus dividing the cochlear canal into the: Scala vestibuli (above), Scala tympani (below)

Membranous Labyrinth

Consists of a series of communicating sacs and ducts that are suspended in the bony labyrinth. Contains endolymph

Endolymph

A water fluid similar in composition to the intracellular fluid. Differs from the composition of the perilymph, which is similar to the extracellular fluid

Ductus reuniens

The two divisions of the membranous labyrinth are connected by the _________, located between the saccule and the cochlear duct

Vestibular Labyrinth

Responsible for balance. Contains the following: Utricle, Saccule Utriculosaccular duct, Semicircular ducts (3), Endolymphatic duct

Maculae

Specialized areas of sensory epithelium. Sensitive to the orientation of the head to gravity and linear acceleration or deceleration, such as forward motion and head bobbing movements during walking

Utricular macula

Oriented in the horizontal plane. Responsible for the forward and backward movements

Saccular macula

Oriented in the vertical plane. Responsible for the up and down movements in relation to gravity (not nodding movements)

Utriculosaccular Duct

Connects the utricle and saccule

Semicircular ducts

Have the same configuration as the semicircular canals, although much smaller in diameter. Arranged at right angles to each other so that all three planes are represented

Ampullary crest

Sensors of rotational acceleration or deceleration of the head. Records the movements of the endolymph in the ampulla resulting from the rotation of the head in the plane of the duct

Endolymphatic duct

Storage reservoir for excess endolymph formed by the blood capillaries in the membranous labyrinth

Cochlear Duct

A spiral tube closed at one end. Triangular in cross-section. Firmly suspended across the cochlear canal between the spiral ligament on the external wall of the cochlear canal and the osseous spiral lamina of the modiolus

Helicotrema

Spanning the entire canal in this manner, the endolymph-filled cochlear duct divides the perilymph-filled spiral canal into two channels. These channels are continuous at the apex of the cochlea, called the

Spiral organ of corti

The receptor for auditory stimulus is this structure which is situated on the basilar membrane, overlaid by the gelatinous tectorial membrane

Scala Vestibuli

Contains perilymph that is high in sodium and low in potassium. Located above the scala media.

Scala tympani

Contains perilymph that is high in sodium and low in potassium. Located below the scala media.

Scala Media

Contains endolymph that is low in sodium and high in potassium

Vestibuli (Reissner’s Membrane)

Separates scala vestibuli and scala media

Basilar membrane

Separates scala media and scala tympani

Helicotrema

The scala tympani and scala vestibuli join together at the apex of the cochlea to form the?

Spiral organ of Corti

Found within the scala media resting above the basilar membrane. Even if it is located in the scala media, it is actually filled with perilymph and protected by the reticular membrane (or lamina) from the endolymph which is toxic to the hair cells

Stria Vascularis

Maintains the chemical composition of the endolymph and its positive electrical potential

Cochlear division of vestibulocochlear nerve (CN VIII)

The hair cells of the spiral organ are innervated by the?

Outer Hair Cells

Function as receptor cells that transduce mechanical movement into an electrochemical signal to stimulate the auditory nerve

Cuticular plate

The apical portion of the outer hair cells includes a thickened region called the?

Reticular lamina

Forms a barrier from the endolymph in the scala media due to its ionic composition being toxic to the hair cells

Stereocilia

Hair-like structures that deflect mechanical disturbances. Rooted in the cuticular plate of each hair cell and projecting through the reticular lamina are bundles of actin filaments called the?

Movement of stereocilia → Opening of ion channels → Release of neurotransmitters → Propagation of the auditory signal to the vestibulocochlear nerve

Trace the auditory signal transmission from the stereocilia

Presbycusis

The gradual deterioration of hearing overtime which is most common among the elderly

Base of the cochlea

High-pitched or frequency sounds stimulate the hair cells where?

Apex of the cochlea

Low-pitched or frequency sounds stimulate the hair cells where?

Central Auditory Pathway

Pathway on how will the sound reach the brain for interpretation. Same as the cochlea, it is tonotopically arranged

Cochlear nerve → transmits electrical signal toward the cochlear nucleus (level of brainstem) → superior olivary complex → lateral lemniscus → inferior colliculus → medial geniculate body→ auditory complex (Brodmann area 41, 42)

Trace the central auditory pathway starting from the cochlear nerve.