Introduction
The human ear is not only responsible for hearing but also plays a crucial role in maintaining balance. Anatomically, it is divided into three main parts: the external ear, middle ear, and internal ear. Each part has distinct structures and specialized functions that contribute to our auditory and vestibular systems.
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External Ear
The external ear gathers sound waves from the environment and directs them towards the tympanic membrane.
Pinna (Auricle)
- Lateral Surface: Collects sound waves.
- Applied Aspects: Visible part, varies in size/shape.
- Nerve Supply: Greater auricular and auriculotemporal nerves.
- Arterial Supply: Posterior auricular and superficial temporal arteries.
- Venous & Lymphatic Drainage: Drains into pre- and post-auricular lymph nodes.
External Auditory Meatus
- Cartilaginous Part: Lateral 1/3rd, flexible.
- Bony Part: Medial 2/3rd, fixed.
- Arterial Supply: Deep auricular branch of maxillary artery.
- Nerve Supply: Auriculotemporal and vagus nerves.
Tympanic Membrane (Eardrum)
Introduction
Thin, semi-transparent membrane separating the external and middle ear.
Layers
- Outer cutaneous
- Middle fibrous
- Inner mucous
Parts
- Pars tensa
- Pars flaccida
Surfaces
- Lateral (convex): Faces external meatus
- Medial (concave): Faces middle ear cavity
Blood Supply & Nerve Supply
- Arterial: Deep auricular, anterior tympanic arteries
- Venous Drainage: External jugular system
- Nerve: Auriculotemporal, auricular branch of vagus, glossopharyngeal
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Middle Ear (Tympanic Cavity)
Introduction
An air-filled cavity in the temporal bone involved in sound conduction.
Communications
- Nasopharynx via Eustachian tube
- Mastoid air cells
- Internal ear via round and oval windows
Contents
- Ear ossicles
- Muscles
- Tympanic plexus
Subdivisions
- Epitympanum
- Mesotympanum
- Hypotympanum
Boundaries
- Roof: Tegmen tympani
- Floor: Jugular wall
- Anterior Wall: Carotid wall
- Posterior Wall: Mastoid wall
- Medial Wall: Labyrinthine wall
- Lateral Wall: Membranous wall (tympanic membrane)
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Ear Ossicles
Small bones that amplify sound:
- Malleus (hammer)
- Incus (anvil)
- Stapes (stirrup)
They transmit vibrations from the tympanic membrane to the inner ear.
Intratympanic Muscles & Applied Aspects
- Tensor Tympani: Tenses the tympanic membrane, innervated by mandibular nerve
- Stapedius: Stabilizes stapes, innervated by facial nerve
Blood and Nerve Supply of Middle Ear
- Arterial Supply: Anterior tympanic artery, stylomastoid artery
- Venous & Lymphatic Drainage: Pterygoid venous plexus and deep cervical nodes
- Nerve Supply: Tympanic plexus (glossopharyngeal), facial and sympathetic fibers
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Internal Ear (Labyrinth)
Bony Labyrinth
- Cochlea: Hearing organ
- Vestibule: Balance; connects cochlea and semicircular canals
- Semicircular Canals: Detect angular motion
Membranous Labyrinth
- Cochlear Duct (Scala media)
- Saccule and Utricle: Detect linear motion
- Utriculo-saccular Duct: Connects both sacs
- Semicircular Ducts: End in ampullae, detect movement
- Receptors: Hair cells in maculae and cristae
- Innervation: Vestibulocochlear nerve (CN VIII)
Functions of the Ear
- Hearing: Via cochlea and auditory pathway
- Balance: Via vestibular apparatus (utricle, saccule, semicircular canals)
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