Lecture 15
Sense Organs I: The Visual System
15-1
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
15-2
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
Fig. 19.10
– Thin mucous membrane
over inner surface of
eyelids and anterior side of
15-3
eyeball
Anatomy of the Eye
Fig. 19.12
• Three coats or tunics
– Fibrous: Consists of sclera and cornea
– Vascular: Consists of choroid, ciliary body, iris
– Neural: Consists of retina
15-4
Anatomy of the Eye
• 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
Fig. 19.12
15-5
Anatomy of the Eye
• Vascular tunic: Middle
– Iris: Controls light
entering pupil; smooth
muscle
– Ciliary muscles: Control
lens shape; smooth
muscle
– Choroid: pigmented layer
that contains melanin
15-6
Anatomy of the Eye
• 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
15-7
Anatomy of the Eye
• Lens
– Held by suspensory
ligaments attached to ciliary
muscles
– Transparent, biconvex
15-8
Focus and Accommodation
Fig. 19.16
• Far vision: 20 feet or more from eye
• Near vision: Closer than 20 feet
– Accommodation
15-9
Review Question
Damage to the retina due to excessive light entering
the eyeball could indicate a problem with the
(a) Iris
(b) Ciliary body
(c) Cornea
(d) Conjunctiva
(e) Choroid
15-10
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.
15-11
Questions?
15-12