1. General Sensation & Vision
Exercise 23 & 24
General Sensation
&
Vision

2. Sensory Receptors Structures specialized to respond to stimuli
Activation of sensory receptors results in depolarizations that trigger impulses to the CNS
The realization of these stimuli, sensation and perception, occur in the brain

3. Receptor Classification by Stimulus Type
Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch
Thermoreceptors – sensitive to changes in temperature
Photoreceptors – respond to light energy (e.g., retina)
Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry)
Nociceptors – sensitive to pain-causing stimuli
Receptor Classification by Stimulus Type

4. Receptor Class by Location: Exteroceptors
Respond to stimuli arising outside the body
Found near the body surface
Sensitive to touch, pressure, pain, and temperature
Include the special sense organs

5. Simple Receptors: Unencapsulated
Table

6. Simple Receptors: Encapsulated
Table

7. Simple Receptors: Encapsulated
Table

8. Adaptation of Sensory Receptors
Adaptation occurs when sensory receptors are subjected to an unchanging stimulus
Receptor membranes become less responsive
Receptor potentials decline in frequency or stop

9. Chemical Senses
Chemical senses – gustation (taste) and olfaction (smell)
Their chemoreceptors respond to chemicals in aqueous solution
Taste – to substances dissolved in saliva
Smell – to substances dissolved in fluids of the nasal membranes

10. Eye and Associated Structures
70% of all sensory receptors are in the eye
Most of the eye is protected by a cushion of fat and the bony orbit
Accessory structures include eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic eye muscles

11. Palpebrae (Eyelids)
Figure 15.5b

12. Extrinsic Eye Muscles
Figure 15.7a, b

13. Structure of the Eyeball
Figure 15.8a

14. Pupil Dilation and Constriction
Figure 15.9

15. Sensory Tunic: Retina
Figure 15.10a

16. Anterior Segment
Figure 15.12

17. Focusing for Distant Vision
Light from a distance needs little adjustment for proper focusing
Far point of vision – the distance beyond which the lens does not need to change shape to focus (20 ft.)
Figure 15.17a

18. Focusing for Close Vision
Figure 15.7b

19. Problems of Refraction
Figure 15.18

20. Astigmatism

21. Visual Pathways
Figure 15.23

22. Terms Accommodation Emmetropia: normal vision Myopia: near-sigthedness
Hyperopia: far-sightedness
Presbyopia: “old vision”
Glaucoma: intraocular pressure imbalance
Cataract: clouding of the lens
Conjunctivitis: inflammation of the conjunctiva

23. The Retina

28. Retina