Anatomy of the Outer Ear

• The ear is responsible for hearing and balance, comprising the outer, middle, and inner ear.
• The inner ear transforms mechanical signals from the middle ear into electrical signals transmitted to the brain and contains receptors for detecting position and movement.

Outer Ear Components

• Consists of the auricle (pinna) and the external auditory canal.

Auricle Function

• Captures sound waves.

Auricle Parts

• Helix, lobule, concha, tragus, antitragus, and antihelix.

Auricle Muscles

• Intrinsic muscles modify morphology, while extrinsic muscles, including the anterior, superior, and posterior auricular muscles, control orientation, innervated by the facial nerve (VII).

Auricle Innervation

• Superficial regions are innervated by the greater auricular nerve (C2, C3) and lesser occipital nerve (C2), along with the auriculotemporal branch of the mandibular nerve (V3).
• Deeper regions are innervated by the auricular branch of the vagus nerve and the auricular branch of the facial nerve.

Auricle Arteries

• Supplied by the posterior auricular artery (from the external carotid artery), anterior auricular branches (from the superficial temporal artery), and the occipital artery.

Auricle Lymphatic Drainage

• Drains into the parotid, mastoid, and deep superior cervical lymph nodes.

External Auditory Canal

• Extends from the concha to the tympanic membrane, with cartilaginous and bony sections. Contains hairs and cerumen-producing glands.

External Auditory Canal Innervation

• Sensory afferents from the auriculotemporal nerve, the auricular branch of the vagus nerve, the auricular branch of the facial nerve, and secondary sensory afferents.

Tympanic Membrane

• Separates the external ear from the middle ear, inserting into the tympanic part of the temporal bone.
• Central concavity where the malleus attaches is called the umbo.
• The lateral process is located at the superior part of the malleus insertion
• Otoscopy reveals a light reflex, known as the luminous triangle.
• Divided into the pars flaccida and pars tensa.
• Sensory innervation to the external surface derives from the auriculotemporal nerve, auricular branch of the vagus nerve, the facial nerve and the glossopharyngeal nerve whereas the internal surface is innervated by the glossopharyngeal nerve.
• Outer ear infection = Otitis Externa "Swimmer's Ear".

Middle Ear

• Located in the temporal bone consisting of the tympanic cavity and the epitympanic recess
• Punction of the middle ear enables the transmission of vibrations to the inner ear via the ossicles (malleus, incus, and stapes).

Middle Ear Limits

• Tegmental wall separates the middle ear from the middle cranial fossa.
• Jugular wall separates the middle ear from the internal jugular vein.
• The lateral wall is composed of the tympanic membrane, while the mastoid wall separates from the mastoid air cells.
• The anterior wall separates the middle ear from the internal carotid artery, featuring openings for the pharyngotympanic tube and the tensor tympani muscle while the medial wall is the labyrinthine wall containing the promontory and oval/round windows.

Mastoid Antrum

• The entrance into the mastoid antrum is posterior to the epitympanic recess.
• Infection of the mastoid antrum and mastoid air cells = Mastoiditis.

Pharyngotympanic Tube Function

• Connects the middle ear to the nasopharynx, equalizing pressure on either side of the tympanic membrane.
• Arterial supply is from the ascending pharyngeal artery (branch of the external carotid artery) and maxillary artery.
• Venous drainage is into the pterygoid venous plexus.
• Innervation of the mucosa is via the tympanic plexus (formed by the tympanic nerve that exits the cranium via the jugular foramen) and the caroticotympanic nerves.

Middle Ear Muscles

• The tensor tympani and stapedius influence ossicular movement.
• Venous drainage of the middle ear is into the pterygoid venous plexus and superior petrosal sinus.

Tensor Tympani Muscle

• Originates from the cartilaginous part of the pharyngotympanic tube and inserts on the superior part of the malleus, innervated by the mandibular nerve, it tenses the eardrum when contracted.

Stapedius Muscle

• Originates from the interior of the pyramidal eminence and inserts on the neck of stapes, innervated by the facial nerve (VII), to retract stapes posteriorly to prevent excess oscillation.

Inner Ear

• Composed of the bony and membranous labyrinths within the petrous part of the temporal bone. The bony labyrinth is lined with periosteum and contains perilymph, while the membranous labyrinth is suspended within, filled with endolymph.
• Transporting information to the brain regarding hearing and balance.
• The cochlear duct is hearing, while semicircular ducts, utricle, and saccule maintain equilibrium.
• Innervated by the vestibulocochlear nerve (VIII).

Bony Labyrinth

• Contains the vestibule, semicircular canals, and cochlea.
• The vestibule connects to the oval window and communicates with the cochlea and semicircular canals and the cochlea contains the vestibular aqueduct.
• Semicircular canals (anterior, posterior, and lateral) at each dilated end form the ampulla.
• The Cochlea spirals 2.5 turns around the modiolus
• The cochlear connects the vestibular duct and tympanic duct to the helicotrema.
• Cochlear canaliculus traverses temporal bone to open into the posterior cranial fossa, connecting cochlea to the subarachnoid space.

Membranous Labyrinth

• Continuous system of ducts and sacs within the bony labyrinth, hosting the endolymph. Includes utricle, saccule, 3 semicircular ducts, and cochlear duct. Participates in hearing and equilibrium.
• Utricle, saccule, and 3 semicircular ducts: organs of equilibrium
• Cochlear duct : organ of hearing

Sensory Receptors

• Inside the macula (saccule) and macula (utricle).
• Crestae are arranged in the ampulla of each of the 3 semicircular ducts.

Vessels

• The bony labyrinth receives irrigation from tympanic branches, stylomastoid branch of the posterior auricular artery, as well as the petrosal branch of the middle meningeal artery.
• Membranous labyrinth receives irrigation from the labyrinthine artery, divided into cochlear branch (supplies cochlea) and vestibular branches (supplies vestibular apparatus.)
• The labyrinths venous drainage is by the vestibular and cochlear veins to form the labyrinthine vein and then to the inferior petrosal sinus or sigmoid sinus.

Innervation

• The facial nerve forms the geniculate ganglion.

Sound Transmission

• Acoustic waves that get into the the external auditory canal reach the tympanic membrane and then gets passed through the ossicles.
• High intensity acoustic that vibrates the tympanic membrane, produces a vibration of low amplitude and high intensity in the oval window and then produces a wave in the fluid that fills the scala vestibuli of the cochlea
• If sounds are very high, the tensor tympani (attached to the malleus) and the stapedius(attached to the stapes) contract.