Lecture on Senses: Eye and Ear

Overview

• Focus on special senses: vision (eye), equilibrium, and hearing (ear).
• Special senses use complex sensory organs compared to general senses (pain, temperature, etc.).

The Eye

Accessory Structures

• Eyelids (Palpebrae): Protect, lubricate the eye; medial and lateral canthus.
• Lacrimal Caruncle: Soft tissue at eye corner.
• Conjunctiva: Thin epithelium; includes palpebral (on eyelid) and ocular (on eye surface) conjunctiva.
• Lacrimal Apparatus: Includes lacrimal gland, lacrimal ducts, lac sac, and nasolacrimal duct; produces tears containing lysozyme.

Anatomy of the Eye

• Three Layers:
  • Fibrous Layer: Sclera and cornea; provides protection and refraction.
  • Vascular Layer: Iris, ciliary body, choroid; provides nutrients, regulates light.
  • Neural Layer (Retina): Contains photoreceptors (rods and cones) for image processing.
• Eye Cavities:
  • Posterior Cavity: Contains vitreous humor.
  • Anterior Cavity: Contains aqueous humor; divided into anterior and posterior chambers.

Focusing and Vision

• Cornea and Lens: Key structures for light refraction and focus.
• Accommodation: Ciliary body alters lens shape for focusing on near or distant objects.
• Vision Clarity: 20/20 vision as a standard; myopia (nearsightedness) and hyperopia (farsightedness) issues.

The Ear

Ear Structure

• External Ear: Auricle directs sound waves; ends at tympanic membrane (eardrum).
• Middle Ear: Contains auditory ossicles (malleus, incus, stapes); transmits vibrations.
• Inner Ear: Contains cochlea (hearing), vestibule, and semicircular canals (equilibrium).

Hearing Process

1. Sound waves vibrate the tympanic membrane.
2. Vibration moves auditory ossicles.
3. Stapes at the oval window transfers vibrations to endolymph in cochlea.
4. Hair cells in cochlea convert mechanical vibrations to electrical signals.

Additional Notes

• Pediatric ear tubes relieve pressure and prevent infections in children.
• Hearing declines with age due to damage to hair cells and ossification.

Conclusion

• This lecture complements the lab work on the anatomy of the eye and ear.
• Next topic will be the endocrine system.