1. For Your Eyes Only

2. The Senses General senses of touch: Temperature, Pressure, Pain
Special senses: Smell, Taste, Sight, Hearing,
Equilibrium

3. The Eye and Vision 70 percent of all sensory receptors are in the eyes
Each eye has over a million nerve fibers
Adult eye is a sphere that measures about 1 inch in diameter
Only see the anterior 1/6 of the eye
Protection for the eye
Most of the eye is enclosed in a bony orbit
A cushion of fat surrounds most of the eye

4. Accessory Structures of the Eye
Eyelids and Eyelashes - both provide protection
Eyelids (fig. 8.1b p. 273) meet at the corners and are called Medial canthus and lateral canthus
Figure 8.1b

5. Accessory Structures of the Eye
Tarsal Glands – (fig. 8.1 a p. 273) modified sebacious (sweat) glands that produce an oily secretion to lubricate the eye
Figure 8.1a

6. Accessory Structures of the Eye
Conjunctiva – delicate membrane that lines the eyelids and covers part of the outer surface of the eyeball (fig. 8.1 a p. 273)
Connects to the surface of the eye and secretes mucus to lubricate the eye
Homeostatic Imbalance:
Conjunctivitis - inflammation of the
conjunctiva and causes reddnes
and irriatation.
Pinkeye – is conjunctivitis caused by a
bacteria or virus and is contagious.

7. Accessory Structures of the Eye
Lacrimal Apparatus
Lacrimal gland – produces lacrimal fluid (tears) and is located in the superior part of the lateral end of eye
Lacrimal canals – drains lacrimal fluid from eyes; Know superior and inferior
Figure 8.1a
Fig. 8.1 b p. 273

8. Accessory Structures of the Eye
Lacrimal sac – (fig. 8.1b p. 273) provides passage of lacrimal fluid towards nasal cavity
Figure 8.1b
p. 273

9. Accessory Structures of the Eye
Nasolacrimal duct – (fig. 8.1b p. 273) empties lacrimal fluid into the nasal cavity
Figure 8.1b

10. Function of the Lacrimal Apparatus
Properties of lacrimal fluid: 1) Dilute salt solution (tears)
2) Contains antibodies and lysozyme (an enzyme that destroys bacteria)
Protects, moistens, and lubricates the eye
Empties into the nasal cavity

11. Extrinsic Eye Muscles
Muscles attach to the outer surface of the eye to produce eye movements
Figure 8.2

12. Extrinsic Eye Muscles
Lateral Rectus - moves eye laterally Medial Rectus - moves eye medially
Superior Rectus - elevates eye Inferior Rectus - Depresses eye 
Figure 8.2

13. Extrinsic Eye Muscles
Inferior Oblique - elevates eye and turns it laterally (rolling your eyes at “MOM”
Superior Oblique - depresses eye and turns it laterally
So the next time you accidently do that, you can say, “ I am sorry, but I had an action potential in my autonomic nervous system and my inferior oblique muscle just contracted
Duck! ‘Cause your mom’s autonomic nervous system will have an action potential as her flexor muscles move to slap your face!
Figure 8.2

14. Structure of the Eye The wall is composed of three tunics
Fibrous tunic – outside layer
Choroid – middle layer
Sensory tunic – inside layer
Figure 8.3a

15. The Fibrous Tunic
Sclera is the white connective tissue layer. Seen anteriorly as the “white of the eye”
Cornea - Transparent, central anterior portion
1) Allows for light to pass through
2) Repairs itself easily
3) The only human tissue that can be transplanted without fear of rejection

16. Choroid Layer Blood-rich nutritive tunic; VASCULAR TUNIC
Dark Pigment prevents light from scattering
Modified interiorly into two structures
Ciliary body – smooth muscle that attaches to the lens by ligaments called Ciliary Zonule

17. Choroid Layer 2) Iris - Pigmented layer that gives eye color.
Circularly and radially arranged smooth
muscles act as a diaphragm of a camera
to allow certain amounts of light.
Dim light: opens to allow light in. Bright light:
closes to keep light out. Think about the
morning when the light hits your eyes?
Pupil – rounded opening in the iris that allows
light into the eye

18. Sensory Tunic (Retina – common name)
The RETINA contains receptor cells (photoreceptors)
1) Rods ) Cones
Signals pass from photoreceptors via a two-neuron chain
1) Bipolar neurons ) Ganglion cells
Signals leave the retina toward the brain through the optic nerve

19. Neurons of the Retina
Figure 8.4

20. Neurons of the Retina and Vision
Rods - Most are found towards the edges of the retina
Allow dim light vision and peripheral vision
Perception is all in gray tones

21. Neurons of the Retina and Vision
Cones - Allow for detailed color vision
Densest in the center of the retina
Need bright light (do you see color at night?)
Fovea centralis – area of the retina with only cones
No photoreceptor cells are at the optic disk, or blind spot

22. Cone Sensitivity
There are three types of cones 1) Blue 2) Green 3) Red
Different cones are sensitive to different wavelengths
Color blindness is the result of lack of one cone type
Blue man
Figure 8.6

23. Lens Lens - Biconvex crystal-like structure
Held in place by a suspensory ligament attached to the ciliary body
Figure 8.3a

24. Internal Eye Chamber Fluids
Aqueous humor - Watery fluid found in chamber between the lens and cornea
Similar to blood plasma
Helps maintain intraocular pressure
Provides nutrients for the lens and cornea
Reabsorbed into venous blood through the canal of Schlemm

25. Internal Eye Chamber Fluids
Vitreous humor - Gel-like substance behind
the lens
Keeps the eye from collapsing
Lasts a lifetime and is not replaced

26. Animal eyes
Tapetum - A reflecting pigment layer lying behind the retina of certain mammals (e.g. cats, dogs)
gives a shining appearance to the eyes when illuminated in the dark.
The role of the tapetum is to reflect light back aiding vision in dim illumination.

27. Animal eyes

28. Animal eyes: Rossi

29. Animal eyes

30. Lens Accommodation
Light must be focused to a point on the retina for optimal vision
The eye is set for distance vision (over 20 ft away)
The lens must change shape to focus for closer objects
Figure 8.9

31. Images Formed on the Retina
Real Image – after accommodation , the real image on the retina is reversed from left to right, upside down, and smaller than the normal object.
Figure 8.10

32. Visual Pathway
1) Photoreceptors of the retina 2) Optic nerve 3)Optic nerve crosses at the optic chiasma
Figure 8.11

33. Visual Pathway 4) Optic tracts 5)Thalamus (axons form optic radiation)
6) Visual cortex of the occipital lobe
Overlapping gives “Binocular” vision with depth perception or 3-D vision
Figure 8.11

34. Eye Reflexes
Internal muscles are controlled by the autonomic nervous system
Bright light causes pupils to constrict through action of radial and ciliary muscles
Viewing close objects causes accommodation
External muscles control eye movement to follow objects
Viewing close objects causes convergence (eyes moving medially)