Week 5 Lecture 1 Surface Anatomy of Eye

Overview of Special Senses

• The special senses include vision, hearing, taste, smell, and equilibrium.

• Vision is the primary focus, as it utilizes 70% of sensory receptors in the body.

• 50% of the cerebral cortex is involved in processing visual information.

Anatomy of the Eye

• The eye is a complex structure with parts that extend beyond its visible portion.

  • Eyebrows: Provide shade and prevent perspiration from entering the eyes.

  • Eyelids (Palpebrae): Protect the eye, control light entry, and blink to keep the eye moist.

  • Palpebral Fissure: The space between the superior and inferior palpebrae that allows light to enter.

  • Medial and Lateral Commissures: Points where the eyelids meet.

  • Lacrimal Caruncle: Located at the medial commissure; it produces a whitish oily secretion.

Eyelashes

• Highly innervated hairs that serve as a detection system for foreign objects.

• Trigger reflexive blinking to protect the eye.

Sclera and Conjunctiva

• Sclera: The tough, white outer layer of the eye made of collagen and elastic tissue.

• Conjunctiva: A transparent mucous membrane providing lubrication and protection from infection.

  • Infection of this membrane is known as conjunctivitis.

Iris and Pupil

• Iris: A thin structure containing sphincter muscles that regulate pupil size.

• Pupil: An absence of structure, functioning as the opening allowing light to enter the eye.

Lacrimal Apparatus

• Consists of lacrimal glands and drainage systems for tears.

  • Lacrimal Gland: Located lateral and superior to the eye; releases tears (lacrimal secretions).

  • Tears consist of diluted saline, mucus, antibodies, and lysozyme (an enzyme that destroys bacteria).

  • Tears drain through the lateral lacrimal punctum into two tubes (lateral canaliculi), leading to the lacrimal sac, and then into the nasolacrimal duct which drains into the nasal cavity.

Tears and Emotions

• Emotional crying increases tear production, leading to nasal drainage, causing sniffles.

• Tears serve both a lubricating function and provide antibacterial properties through components like lysozyme.

Extrinsic Eye Muscles

• Six strap-like muscles control the movement of the eyeball.

  • Rectus Muscles (4):

    • Superior Rectus: Moves eye upward.

    • Inferior Rectus: Moves eye downward.

    • Lateral Rectus: Moves eye laterally (outward).

    • Medial Rectus: Moves eye medially (inward).

  • Oblique Muscles (2):

    • Superior Oblique: Allows for upward and lateral eye movement.

    • Inferior Oblique: Allows for downward and lateral eye movement.

Conclusion

• This lecture covered the external anatomy of the eye and functions of various structures.

• Future lectures will delve into the internal structures of the eye and their functions.