The Special Senses

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the retina

Optic disc

(blind spot)

Optic nerve

Posterior pole

Fovea centralis

Macula lutea

Retina

Choroid

Sclera

Ora serrata

(a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball.

Ciliary body

Ciliary zonule

(suspensory

ligament)

Cornea

Iris

Anterior pole

Pupil

Anterior

segment (contains

aqueous humor)

Lens

Scleral venous

sinus

Posterior segment

(contains vitreous humor)

Slide 17

Fibrous Layer

Outermost layer; dense avascular connective tissue

Two regions: sclera and cornea

Sclera

Opaque posterior region

Protects and shapes eyeball

Anchors extrinsic eye muscles

Slide 18

Fibrous Layer

2. Cornea:

Transparent anterior 1/6 of fibrous layer

Bends light as it enters the eye

Sodium pumps of the corneal endothelium on the inner face help maintain the clarity of the cornea

Numerous pain receptors contribute to blinking and tearing reflexes

Slide 19

Vascular Layer (Uvea)

Middle pigmented layer

Three regions: choroid, ciliary body, and iris

Choroid region

Posterior portion of the uvea

Supplies blood to all layers of the eyeball

Brown pigment absorbs light to prevent visual confusion

Slide 20

Vascular Layer

2. Ciliary body

Ring of tissue surrounding the lens

Smooth muscle bundles (ciliary muscles) control lens shape

Capillaries of ciliary processes secrete fluid

Ciliary zonule (suspensory ligament) holds lens in position

Slide 21

Vascular Layer

3. Iris

The colored part of the eye

Pupil—central opening that regulates the amount of light entering the eye

Close vision and bright light—sphincter papillae (circular muscles) contract; pupils constrict

Distant vision and dim light—dilator papillae (radial muscles) contract; pupils dilate

Changes in emotional state—pupils dilate when the subject matter is appealing or requires problem-solving skills

Slide 22

Figure 15.5

Iris (two muscles)

• Sphincter pupillae

• Dilator pupillae

Sphincter pupillae

muscle contraction

decreases pupil size.

Dilator pupillae

muscle contraction

increases pupil size.

Sympathetic +

Parasympathetic +

Slide 23

Sensory Layer: Retina