1. Lecture 02 – Sensory Organs (Part 2 – The Human Eye)
Genalin Lagman Taguiam

2. Course Outcomes
On the completion of the week’s activity, the students should be able to
Describe the structures and functions of the eye
Describe the conduction of light waves from the exterior to the brain

3. Accessory Structures of the Eye
EYEBROWS
Help to shade and protect the eyes
EYELIDS
Protect and lubricate the eyes by reflex blinking
Supported by cranial nerve V

4. Accessory Structures of the Eye
CONJUNCTIVA
Mucosa that lines the eyelids and covers the anterior eyeball surface
Lubricates the eyeball surface with its mucus

5. Accessory Structures of the Eye
LACRIMAL APPARATUS
consists of the
lacrimal gland
Produces a saline solution containing mucus, lysozyme, and antibodies
lacrimal canaliculi
lacrimal sac
nasolacrimal duct

6. Accessory Structures of the Eye
EXTRINSIC EYE MUSCLES

7. Accessory Structures of the Eye
CONTROLLING CRANIAL NERVES

8. Structure of the Eyeball
Outermost fibrous layer
consists of
SCLERA
Protects the eye and gives it shape
CORNEA
Allows light to enter the eye

9. Structure of the Eyeball
Iris that control the size of pupil

10. Structure of the Eyeball
What causes the pupils to dilate (mydriasis) and to constrict (miosis)?

11. Structure of the Eyeball
What causes the pupils to dilate (mydriasis) and to constrict (miosis)?
There are two types of muscle that control the size of the iris:
the iris sphincter, composed of circularly arranged muscle fibers,
and the iris dilator, composed of radially arranged muscle fibers.
The former is innervated by the parasympathetic nervous system;
the latter by the sympathetic nervous system.
Sympathetic stimulation of the adrenergic receptors causes the contraction of the radial muscle and subsequent dilation of the pupil.
Conversely, parasympathetic stimulation causes contraction of the circular muscle and constriction of the pupil.

12. Structure of the Eyeball
Sensory layer (or RETINA)
Consists of neural layer that contains photoreceptors (rods and cones), bipolar cells and ganglion cells
Ganglion cell axons form the optic nerve which exits via the optic disc (blind spot)

13. Structure of the Eyeball
Sensory layer (or RETINA)

14. Structure of the Eyeball
Sensory layer (or RETINA)
outer segment of the photoreceptors that contain the light-absorbing pigment in membrane-bounded discs

15. Structure of the Eyeball
Blind spot

16. Structure of the Eyeball
Fovea centralis

17. Structure of the Eyeball
The anterior segment
filled with aqueous humor
formed by capillaries in the ciliary processes and drained into the scleral venous sinus

18. Structure of the Eyeball
The posterior segment
contains vitreous humor
Help support the eyeball and keep the retina in place

19. Structure of the Eyeball
The biconvex lens
Suspends within the eye by the ciliary zonule attached to the ciliary body
Only adjustable refractory structure of the eye

20. Physiology of Vision Light
Made up of those wavelengths of the electromagnetic spectrum that excite the photoreceptors
Refracted (bent) when passing from 1 transparent medium to another of different density

21. Physiology of Vision

22. Physiology of Vision Concave lenses disperse light
Convex lenses converge light and bring its rays to a focal point
The greater the lens curvature, the more light bends

23. Physiology of Vision Cornea accounts for the most refraction
but lens allows active focusing for different distances

24. Physiology of Vision
Focusing for close-up/ near vision requires the following reflex activities of the eye
Accommodation (bulging of the lens)
Pupillary constriction (mioisis)
Convergence of the eyeballs
All three reflexes are controlled by cranial nerve III

25. Physiology of Vision
Accommodation

26. Physiology of Vision
Pupillary constriction (mioisis) P

27. Physiology of Vision
Convergence of the eyeballs

28. Physiology of Vision Rods Cones Respond to low-intensity light
Provide night and periphery vision
Cones
Are bright-light, high discrimination receptors
Provide for color vision

29. Physiology of Vision During light adaptation In dark adaptation
Photopigments are bleached and rods are inactivated
Then, as cones decrease their light sensitivity, high acuity vision ensues
In dark adaptation
Cones cease functioning
Visual acuity decreases

30. Physiology of Vision
Visual pathway to the brain begins with the optic nerve fibers (ganglion cell axons) from the retina
At the optic chiasma, fibers from the medial half of each retina cross over and continue on in the optic tracts to the thalamus

31. Physiology of Vision
Thalamic neurons project to the visual cortex via the optic radiation
Fibers also project from the retina to the midbrain pretectal nuclei and superior colliculi and to the suprachiasmatic nucleus of the hypothalamus

32. References
Marieb, E.N. (2010). Human anatomy and physiology (8th Ed.). San Francisco, Pearson.
Marieb, E.N. (2006). Human anatomy and physiology (7th Ed.). San Francisco, Pearson.
Tortora, G. J. (2006). Principles of anatomy and physiology. (11th. Ed.). New Jersey, John Wiley and Sons, Inc.