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

2. General Sensation and Orbital Region: Topic Objectives
Be able to identify the four basic conditions necessary for sensation
Be able to apply the characteristics of sensation to unique clinical and pathological conditions
Distinguish how sensory intensity is coded in action potentials and how processing enhances signal identification
Apply referred pain signals to specific organs or internal areas of the body
Be able to identify all structures of the eye and orbit.
Be able to apply the cardinal directions to eye movement and in identifying the causes of basic palsies and nerve involvement.
Be able to compare the physiological reasons for emmetropia , myopia, hyperopia, presbyopia, cataract and glaucoma.
Be able to contrast field of vision vs. optic field, and the effect of lesions to optic nerve, optic chiasma, and optic tract

3. 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)

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

5. Reversing X pattern; notice shading.

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

7. Which dark line is larger?
Assumption: perspective

8. Face Recognition

9. 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

10. 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

11. 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

12. Lateral Inhibition - -

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

14. Distribution of Cutaneous Receptors

15. Sensitivity of Skin due to Receptive Fields

16. Cutaneous Receptors

18. Proprioceptors

19. 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

20. Relationship of Stretch to AP

21. Referred Pain
Illustrates projection.

22. General Pathway of Perception

23. Orbital Region

24. Accessory Structures of the Eye

25. Eyelid

26. Lacrimal Apparatus

27. Outer Eye

28. Superficial Orbit

29. Extrinsic Ocular Muscles

33. Arrangement of Posterior Orbit
Trochlear
Optic Nerve
Occulomotor
Abducens

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

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

36. Eye Anatomy

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

40. (90% of glaucomas)

41. Iris controls amount of light entering the eye.
Parasympathetic fibers via the oculomotor nerve and ciliary ganglion
Sympathetic fibers via the superior cervical ganglion through the internal carotid plexus

42. Distant Vision

43. Near Vision (Accomodation)

44. Near and Far-sightedness

45. 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.

46. Increase lens opacity with age.
Cataract

47. Retina Cellular Arrangement

48. Special Areas of Retina

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

50. Photoreceptors: Cones and Rods
Three populations of cones

51. Rod’s and Cone’s Photopigments

52. Retinal Bleaching

53. Light Signal Transduction

54. Visual Processing