Lecture on the Ear

Anatomy of the Ear

• Three Parts of the Ear: External ear, middle ear, inner ear.

External Ear

• Components:
  • Pinna (auricle): Collects and delivers sound to the ear canal.
  • External auditory canal (meatus): Channels sound to the tympanic membrane.
• Tympanic Membrane:
  • Also known as the eardrum.
  • Tightly drawn, sensitive to air vibrations.
  • Frequency of air compressions determines pitch of sound.

Middle Ear

• Structure:
  • Air pocket within the petrous portion of the temporal bone.
  • Contains the tympanic cavity.
• Ear Ossicles (Bones):
  • Malleus (Hammer): Attached to the tympanic membrane.
  • Incus (Anvil): Articulates with malleus and stapes.
  • Stapes (Stirrup): Fits into the oval window.
• Function:
  • Transmits vibrations from the eardrum to the oval window.
  • Communicates with nasopharynx via Eustachian tube—aids in pressure equalization.

Eustachian Tube

• Connects middle ear to nasopharynx.
• Equalizes air pressure between middle ear and external atmosphere.
• Problems can lead to eardrum rupture (e.g., during flights).
• Otitis Media: Inflammation, common in children due to anatomy, can cause earache.

Inner Ear

• Bony Labyrinth: Contains cochlea, vestibule, and semicircular canals, filled with perilymph.
• Membranous Labyrinth: Filled with endolymph, high in potassium concentration.

Cochlea

• Organ of Hearing:
  • Vibrations from stapes create fluid waves in cochlea.
  • Organ of Corti: Contains hair cells that convert sound waves into nerve impulses.
• Hair Cells:
  • Respond to sound frequency.
  • High frequencies affect early cochlea, low frequencies affect further up.

Vestibule

• Components:
  • Utricle: Monitors horizontal accelerations and head position.
  • Saccule: Monitors vertical accelerations.
  • Contains otoliths (calcium carbonate crystals) that provide sensory input based on head position and movement.

Semicircular Canals

• Function:
  • Monitors rotational movements of the head in three dimensions.
  • Contains semicircular ducts filled with endolymph.

Hair Cells Mechanism

• Stereocilia: Bending opens/closes potassium channels, influencing neurotransmitter release.
• Vestibular Processing: Head movement displaces endolymph, bending hair cells and sending impulses to the brain.

Nerve Connections

• Vestibular Cochlear Nerve (Cranial Nerve VIII):
  • Transmits auditory and balance information to the brain.
  • Synapses in the brainstem and routes to the auditory cortex in the temporal lobe.

Clinical Notes

• Excessive noise exposure can damage hair cells, leading to hearing loss.
• Allergies can affect Eustachian tube functionality, impacting pressure equalization.

Practical Component

• Mention of lab dissections of temporal bones for visualizing ear structures.

These notes summarize the lecture on the structure and function of the ear, covering the external, middle, and inner ear components, mechanisms of hearing and balance, and clinical considerations.