Makindo Medical Notes

Related Subjects: |Anatomy of the Ear |Anatomy of the Oesophagus |Anatomy of the Diaphragm |Anatomy of Large Bowel |Anatomy of Small Bowel |Anatomy of the Biliary system |Anatomy of the Eye |Anatomy of the Larynx |Anatomy of the Ear

👂 Anatomy of the Ear

The ear is a complex organ responsible for hearing 🎧 and balance ⚖️. It is divided into three major sections: the external ear, middle ear, and inner ear. Each section has a unique role in sound conduction and equilibrium.

📌 External Ear

Includes the auricle (pinna) and the external auditory canal, ending at the tympanic membrane.

• Auricle (Pinna):
  • Cartilage covered by skin, shaped to funnel sound waves inward.
  • Landmarks: helix, antihelix, tragus, antitragus, concha, lobule.
  • Clinical Pearl: Auricular haematoma (from trauma) can cause “cauliflower ear” if untreated.
• External Auditory Canal:
  • ~2.5 cm long, lined with ceruminous glands producing cerumen (earwax).
  • Protects against dust, insects, and microbial growth.
  • Clinical Pearl: Otitis externa (“swimmer’s ear”) causes painful, inflamed canal.
• Tympanic Membrane (Eardrum):
  • Thin, cone-shaped membrane vibrating with sound waves.
  • Transfers vibrations to ossicles in the middle ear.
  • Clinical Pearl: Perforated eardrum ➝ conductive hearing loss.

📌 Middle Ear

An air-filled cavity containing the ossicles and the Eustachian tube.

• Ossicles (Malleus, Incus, Stapes):
  • Malleus (“hammer”) attached to tympanic membrane.
  • Incus (“anvil”) bridges malleus and stapes.
  • Stapes (“stirrup”) attached to oval window ➝ sends vibrations into inner ear fluid.
  • Clinical Pearl: Otosclerosis (abnormal stapes fixation) causes progressive conductive hearing loss.
• Eustachian Tube:
  • Connects middle ear ➝ nasopharynx.
  • Equalizes pressure (opens on swallowing/yawning).
  • Clinical Pearl: Blocked tube (e.g., after URTI) ➝ otitis media with effusion (“glue ear”).

📌 Inner Ear

Also called the labyrinth. Contains the cochlea (hearing) and vestibular system (balance). Filled with endolymph and perilymph.

• Cochlea:
  • Spiral structure containing the organ of Corti (sensory hair cells).
  • Converts mechanical vibrations ➝ electrical signals transmitted via cochlear nerve.
  • Clinical Pearl: Noise-induced hearing loss damages high-frequency hair cells first.
• Vestibular System:
  • Semicircular Canals: Detect rotational movement (angular acceleration).
  • Utricle & Saccule: Detect linear acceleration and gravity via otoliths (calcium carbonate crystals).
  • Clinical Pearl: Dislodged otoliths ➝ benign paroxysmal positional vertigo (BPPV).

🧠 Nerve Supply of the Ear

• Cochlear Nerve (CN VIII): Hearing.
• Vestibular Nerve (CN VIII): Balance & spatial orientation.
• Facial Nerve (CN VII): Passes through middle ear; gives chorda tympani branch (taste anterior 2/3 tongue).
• Glossopharyngeal Nerve (CN IX): Sensory to middle ear & Eustachian tube.
• Clinical Pearl: Acoustic neuroma (vestibular schwannoma) ➝ hearing loss, tinnitus, imbalance, facial weakness.

🫀 Vascular Supply

• External Ear: Posterior auricular & superficial temporal arteries.
• Middle Ear: Anterior tympanic (maxillary) & ascending pharyngeal arteries.
• Inner Ear: Labyrinthine artery (branch of AICA or basilar artery).
• Clinical Pearl: Inner ear ischemia ➝ sudden sensorineural hearing loss.

⚡ Functions of the Ear

• Hearing 🎶: Converts sound waves ➝ neural signals ➝ auditory cortex.
• Balance ⚖️: Vestibular system detects movement & orientation, integrated with vision & proprioception.
• Pressure Regulation: Eustachian tube maintains equal air pressure across tympanic membrane.