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  1. Lecture 15 Sense Organs I: The Visual System

  2. Visual System • Eye • Accessory structures • Eyebrows, eyelids, eyelashes, lacrimal (tear) glands • Optic nerve (II) • Sensory information travels along optic nerve to thalamus then to occipital lobe

  3. Accessory Structures of Eye • Eyebrows • Prevent running perspiration into eyes • Shade • Eyelids or palpebrae • Protect and lubricate • Lacrimal caruncle has sebaceous and sweat glands • Extrinsic eye muscles (6) • Lacrimal apparatus • Lacrimal gland (facial nerve VII) • Conjunctiva • Thin mucous membrane over inner surface of eyelids and anterior side of eyeball Fig. 19.10

  4. Anatomy of the Eye • Three coats or tunics • Fibrous: Consists of sclera and cornea • Vascular: Consists of choroid, ciliary body, iris • Neural: Consists of retina Fig. 19.12

  5. Fibrous tunic: Outer Sclera: White outer layer, maintains shape, protects internal structures, provides muscle attachment point, continuous with cornea Cornea: No blood vessels, transparent, allows light to enter eye and refracts (bends) light Anatomy of the Eye Fig. 19.12

  6. Vascular tunic: Middle Iris: Controls light entering pupil; smooth muscle Ciliary muscles: Control lens shape; smooth muscle Choroid: pigmented layer that contains melanin Anatomy of the Eye

  7. Retina: Inner Contains neurons sensitive to light Macula lutea & Fovea centralis: Area of greatest visual acuity Optic disc: Blind spot Cavities Anterior: Aqueous humor Posterior: Vitreous humor Anatomy of the Eye

  8. Lens Held by suspensory ligaments attached to ciliary muscles Transparent, biconvex Anatomy of the Eye

  9. Focus and Accommodation • Far vision: 20 feet or more from eye • Near vision: Closer than 20 feet • Accommodation Fig. 19.16

  10. Review Question Damage to the retina due to excessive light entering the eyeball could indicate a problem with the • Iris • Ciliary body • Cornea • Conjunctiva • Choroid

  11. Points to Remember • Accessory eye structures protect and lubricate the eye. • There are 3 basic layers to the eye: fibrous tunic, vascular tunic and neural tunic. • Image formation on retina by bending of light rays through cornea and lens. • To view close objects, the lens increases its curvature.

  12. Questions?