1. General Sensation and Vision
Orbital Region
General Sensation and Vision

2. Generalized Sensation Physiology
Sensation –state of awareness of external and internal conditions of the body
Four conditions for sensation:
1. Adequate stimulus
2. Adequate receptor (transducer)
3. Conduction
4. Translation (interpretation)

3. Brain’s Assumption in Translating
Assumption: Source of light is from above

4. Reversing X pattern; notice shading.

5. How many triangles?
Assumption: Straight lines should connect.

6. Which dark line is larger?
Assumption: perspective

7. Characteristics of Sensation
Modality –ability to interpret nerve impulses differently
Projection –referral of sensation to point of origin
Adaptation –decrease in sensitivity of receptors to continued stimulation
Phasic (fast)
Tonic (slow)
Some receptors never adapt (pain, cold, etc.)
Afterimage –persistence of sensation after stimulus ceases

8. Classification of Receptors
Type of Sensory Information Relayed
Exteroreceptors, Enteroreceptors, Proprioceptors
Type of Stimulus Transduced
Mechanoreceptors, Thermoreceptors, Chemoreceptors, and Nociceptors
Complexity of Receptor
Simple structure (usually single cell) –most general senses
Complex structure (many cells) –special senses

9. Receptor Physiology
Stimulation of a receptor leads to the generation of a receptor (generator) potential in its membrane.
These are usually excitatory, and are similar to the EPSPs found in neurons
If the receptor potential reaches the threshold potential for the sensory neuron; it fires an AP into the CNS
Strength of the stimulus is therefore encoded by the number of AP generated
Sensations may be sharpened through Lateral Inhibition

10. Lateral Inhibition - -

11. General Senses Cutaneous –skin receptors
Proprioception –sense of body position
Nociception –pain perception (chemoreceptors that perceive locally secreted warning hormones (prostaglandins))

12. Distribution of Cutaneous Receptors

13. Sensitivity of Skin due to Receptive Fields

14. Cutaneous Receptors

16. Proprioceptors

17. Muscle sensors Muscle spindles (Intrafusal fibers:
-senses degree of length of muscle fibers and the rate of change in length
Golgi Tendon organs –sense tension within tendon

18. Relationship of Stretch to AP

19. Referred Pain
Illustrates projection.

20. General Pathway of Perception

21. Orbital Region

22. Accessory Structures of the Eye

23. Eyelid

24. Lacrimal Apparatus

25. Outer Eye

26. Extrinsic Ocular Muscles

27. Arrangement of Posterior Orbit
Trochlear -to sup. oblique
Optic Nerve
Occulomotor -to sup. rectus, med. rectus, inf. rectus, inf. oblique, and levator palpebrae superioris
Abducens -to lateral rectus

28. Action and Innervation of Ocular Muscles

29. Action and Innervation of Ocular Muscles
Which cranial nerve and muscle is injured?

30. Orbital Blood Supply Ophthalmic Middle Meningeal to Cavernous sinus
Internal Carotid
Facial v.

31. Eye Anatomy

32. Aqueous Humor Flow
(Canal of Schlemm)
Glaucoma results from inadequate drainage of Aqueous Humor leading to increase pressure in the eye.

33. Iris controls amount of light entering the eye.

34. Distant Vision

35. Near Vision (Accomodation)

36. Near and Far-sightedness

37. Astigmatism and Presbyopia
Astigmatism –results from imperfections in the resolving structures in the eye (lens and/or cornea)
Presbyopia is the loss of near vision with age; resulting from a decrease in elasticity of the lens.

38. Increase lens opacity with age.
Cataract

39. Retina Cellular Arrangement

40. Special Areas of Retina

41. Blind Spot
Optic Disc (blind spot)
Optic N.

42. Photoreceptors: Cones and Rods
Three populations of cones

43. Rod’s and Cone’s Photopigments

44. Retinal Bleaching

45. Light Signal Transduction

46. Visual Processing