--- title: "Anatomy of Inner Ear" description: "Notes on Anatomy of Inner Ear, covering the bony and membranous labyrinths." source: "The ENT Resident" author: "Dr. Mausumi Das" canonical_url: "https://www.theentresident.com/ent-notes-lectures/inner-ear-anatomy" categories: ["Otology"] video: "https://www.youtube.com/watch?v=NP7DXq2NHAE" image: "https://media.theentresident.com/og-images/inner-ear-anatomy.png" --- # Anatomy of Inner Ear Notes on Anatomy of Inner Ear, covering the bony and membranous labyrinths. Watch the full video lecture on YouTube: https://www.youtube.com/watch?v=NP7DXq2NHAE ## Anatomy of the Inner Ear The **inner ear**, also known as the **labyrinth**, is a key sensory structure responsible for hearing and balance. It consists of: - A **bony labyrinth** - A **membranous labyrinth** - **Two fluids**: *endolymph* (inside the membranous labyrinth) and *perilymph* (between bony and membranous labyrinth) --- ### πŸ— Components of the Inner Ear The inner ear is divided into: - **Vestibule** - **Semicircular Canals** (3) - **Cochlea** --- ### 🦴 Bony Labyrinth #### πŸ”Ή **Vestibule** - Central part of the labyrinth - **Lateral wall**: contains the *oval window* - **Medial wall**: contains two recesses: - *Spherical recess* - *Elliptical recess* >What does the Spherical and Elliptical recess lodge in it? - **Aqueduct of vestibule**: transmits the endolymphatic duct - Receives **5 openings** from the semicircular canals #### πŸ”Ή **Semicircular Canals** - 3 canals: **lateral**, **posterior**, **superior** - Lie at **right angles** to each other - Each has: - **Ampullated end** (opens into vestibule) - **Non-ampullated end** (some join to form a **common crus**) #### πŸ”Ή **Cochlea** - **2.5 turns** around the central bony axis: **modiolus** - Houses **3 compartments**: - **Scala vestibuli** (above) - **Scala tympani** (below) - **Scala media** (central) β€” contains **endolymph** - The **helicotrema** at the apex connects scala vestibuli and tympani - Promontory on the medial wall of the middle ear = basal turn of cochlea --- ### πŸ’§ Fluids of the Inner Ear - **Endolymph**: inside membranous labyrinth (scala media) - **Perilymph**: between bony and membranous labyrinth (scala vestibuli & tympani) >Check out my post on Inner ear fluids to learn more about Perilymph and Endolymph. --- ### 🎼 Functional Anatomy of the Cochlea - **Scala media** (membranous cochlea) is triangular in cross-section: - **Basilar membrane** β†’ houses **Organ of Corti** - **Reissner's membrane** β†’ separates from scala vestibuli - **Stria vascularis** β†’ lateral wall; secretes endolymph - **Sound conduction**: - Stapes footplate β†’ scala vestibuli β†’ helicotrema β†’ scala tympani β†’ round window - Pressure differences vibrate **basilar membrane** - Stimulates **Organ of Corti** β†’ transduces mechanical to electrical signals --- ### 🧬 Membranous Labyrinth | Structure | Location | Sensory Epithelium | Function | | --- | --- | --- | --- | | Cochlear duct | Inside cochlea | Organ of Corti | Hearing | | Utricle | Vestibule | Macula | Linear acceleration | | Saccule | Vestibule | Macula | Linear acceleration | | Semicircular ducts | Inside canals | Crista ampullaris | Angular acceleration | | Endolymphatic duct/sac | Vestibular aqueduct | β€” | Endolymph regulation | πŸ”Έ *Ductus reuniens*: connects cochlear duct to saccule πŸ”Έ *Utriculosaccular duct*: connects utricle and saccule πŸ”Έ *Endolymphatic sac*: surgically important in **MΓ©niΓ¨re's disease** --- ### 🩸 Blood Supply of the Inner Ear **Arterial Supply** β€” via **Labyrinthine artery** (Branch of **AICA** or sometimes **Basilar artery**) - **Anterior Vestibular Artery** β†’ utricle, superior & lateral semicircular canals - **Common Cochlear Artery** β†’ - **Main Cochlear Artery** β†’ ~80% cochlear supply - **Vestibulocochlear Artery** β†’ - *Cochlear branch* β†’ ~20% cochlear supply - *Posterior Vestibular Artery* β†’ saccule, posterior semicircular canal **Venous Drainage:** - **Internal auditory vein** - **Vein of cochlear aqueduct** - **Vein of vestibular aqueduct** β†’ Drain into **inferior petrosal sinus** and **lateral sinus** --- ### πŸ“Œ Clinical Highlights - **Footplate of stapes** is closely related to the **saccule**. - In **MΓ©niΓ¨re's disease**, a distended saccule may press against it. - **Organ of Corti**, **macula**, and **crista ampullaris** are the key sensory zones. - **Von BΓ©kΓ©sy's theory** explains basilar membrane motion and wave propagation. --- ### πŸ“ Summary Table | Structure | Location | Sensory Epithelium | Function | | --- | --- | --- | --- | | Cochlear duct | Inside cochlea | Organ of Corti | Hearing | | Utricle | Vestibule | Macula | Linear acceleration | | Saccule | Vestibule | Macula | Linear acceleration | | Semicircular ducts | Inside canals | Crista ampullaris | Angular acceleration | | Endolymphatic duct/sac | Vestibular aqueduct | β€” | Endolymph regulation | --- ## About This Note This free ENT note on Anatomy of Inner Ear was written by Dr. Mausumi Das and is paired with a corresponding video lecture. 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