1. Sensory Systems

2. Overview • Lots of sensation or sensory systems • Whole fields of Psychology are associated with this area • Examples • Visual system • Auditory system • Tactile system • Olfactory and Taste system • others

3. Systems overview • Systems have some type of receptor system • Receptor systems are designed to convert some outside stimulus to a electrical-chemical signal • Is called transduction • The electrical-chemical signal is used by the nervous system

4. Receptor systems • Usually lack axons • Usually form synapses with dendrites of other sensory neurons • Messages are carried on different pathways to specific areas of the brain • Detect small ranges of energy levels • Visual system: 400 to 700 nm • Auditory system: 20 to 20,000 Hz

5. Receptor systems • Some systems are more complicated than others • Visual system versus touch system • Visual system was initially part of brain systems • Has become more specialized and moved • Allows more processing of information • Increases survival.

6. The Eye

7. Some structures • Pupil: Is basically a hole • Iris: Is a muscle that controls the size of the hole • Cornea: • Is it clear transparent membrane that covers the pupil and Iris • Focuses approximately 75% of visual information onto the retina • Lens: Focuses the remaining 25% of light onto the fovea of the retina

8. Rods and Cones • Two types of photoreceptors are located within the retina • Rods: 120 million • Light sensitive (not color) • Found in periphery of retina • Low activation threshold • Cones: 6 million • Are color sensitive • Found mostly in fovea Source: http://insight.med.utah.edu/Webvision /imageswv/rodcoEM.jpeg 6.8

9. Retinal Circuitry Adapted from Dowling, J.E., and Boycott, B.B. Proceedings of the Royal Society of London, B., 1966, 166, 80-111. 6.9

10. Primary Visual Pathway • Information from each visual field crosses over at the optic chiasm and projects to the opposite side of the primary visual cortex 6.10

11. Visual Cortex 6.11

12. Summary of Visual Cortex • V4: responds to color (and form perception) • Lesions of V4 impair color perception • V5: responds to movement • TEO: involved in color discrimination, 2-d pattern discrimination • TEO projects to area TE • TE: neurons here respond to 3-d objects (a face or a hand) 6.12

13. Auditory system • Is less sophisticated than the visual system • Designed to transduce frequencies of sound into hearing

14. Divisions of the Ear • Outer ear: • Channel to tympanic membrane • Middle ear: • Ossicles • Inner ear: • Cochlea

15. The Cochlea • The cochlea is formed from three chambers: • Hair cells within the organ of Corti transduce sound waves into nerve impulses 7.15

17. Auditory Pathways • Afferent pathways: • Through cochlear nuclei • To superior olivary nuclei • To inferior colliculus • To medial geniculate • To auditory cortex • Efferent pathway: • Olivocochlear bundle 7.17

18. Touch / Pain • Three different sensations are reported to the brain by receptors localized within skin 7.18

19. Temperature • Is detected by warmth and cold receptors • Receptor activation is relative to the baseline temperature • The receptors lie at different levels of the skin (cold are close to the surface of the skin)

20. Touch and Pain • Touch involves perception of pressure and vibration of an object on the skin • Pacinian corpuscles detect deformation of the skin • Pain is associated with skin tissue damage • Nociceptors detect pain

21. Morphology of Skin Epidermis Dermis 7.21

22. The dorsal columns carry precise information related to touch The spinothalamic tract carries pain and temperature signals (poorly localized) 5-10 cortical maps of the body surface Somatosensory Pathways 7.22

23. Other systems • Taste • Vestibular

24. Conclusions • Lots of systems • Each has a specific purpose • When damage occurs, usually multiple systems are impacted. • Creates specific symptomatology • Can be used to identify locations of brain or system damage