1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Slides prepared by Stephen Gehnrich, Salisbury University 6 C H A P T E R Sensory Systems (3)

2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Photoreception  Ability to detect visible light  A small proportion of the electromagnetic spectrum from ultraviolet to near infrared  Ability to detect this range of wavelengths supports idea that animals evolved in water  Visible light travels well in water; other wavelengths do not

3. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Photoreceptors  Range from single light- sensitive cells to complex, image-forming eyes  Two major types of photoreceptor cells:  Ciliary photoreceptors  Have a single, highly folded cilium  Folds form disks that contain photopigments  Rhabdomeric photoreceptors  Apical surface covered with multiple outfoldings called microvillar projections  Microvillar projections contain photopigments  Photopigments  Molecules that absorb energy from photons Phylogeny of Photoreceptors

4. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Vertebrate Photoreceptors  Vertebrates have ciliary photoreceptors  Rods  Cones  Both have inner and outer segments  Inner and outer segments connected by a cilium  Outer segment contains photopigments  Inner segment forms synapses with other cells

5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 6.1 Characteristics of Rods and Cones

6. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 6.30 Diversity in Rod and Cone Shape  Diverse shapes of rods and cones among vertebrates  Shape does not determine properties of photoreceptor  Properties of photoreceptor depend on its photopigment

7. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Eye  Eyespots  Cells or regions of a cell that contain photosensitive pigment  For example, protist Euglena  Eyes are complex organs  Detect direction of light  Light-dark contrast  Some can form an image

8. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 6.33a Types of Eyes Flat sheet eyes  Some sense of light direction and intensity  Often in larval forms or as accessory eyes in adults Limpet Patella

9. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 6.33b Types of Eyes  Cup-shaped eyes (e.g., Nautilus)  Retinal sheet is folded to form a narrow aperture  Discrimination of light direction and intensity  Light-dark contrast  Image formation  Poor resolution Nautilus

10. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 6.33c Types of Eyes  Vesicular Eyes (present in most vertebrates)  Lens in the aperture improves clarity and intensity  Lens refracts light and focuses it onto a single point on the retina  Image formation  Good resolution

11. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 6.33d Types of Eyes  Convex Eye (annelids, molluscs, arthropods)  Photoreceptors radiate outward  Convex retina

12. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Compound Eyes of Arthropods  Composed of ommatidia (photoreceptor)  Each ommatidium has its own lens  Images formed in two ways  Apposition compound eyes  Ommatidia operate independently  Each one detects only part of the image  Afferent neurons interconnect to form an image  Superposition compound eyes  Ommatidia work together to form image  Resolving power is increased by reducing size and increasing the number of ommatidia

13. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Structure of The Vertebrate Eye  Sclera  “White” of the eye  Cornea  Transparent layer on anterior  Iris  Two layers of pigmented smooth muscle  Pupil  Opening in iris allows light into eye  Lens  Focuses image on retina  Ciliary body  Muscles that change lens shape  Aqueous humor  Fluid in the anterior chamber  Vitreous humor  Gelatinous mass in the posterior chamber  Retina  Layer of photoreceptor cells  Choroid  Pigmented layer behind retina  Tapetum  Layer in the choroid of nocturnal animals that reflects light

14. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Vertebrate Retina  Arranged into several layers  Rods and cones are are in the retina and their outer segments face backwards  Other cells are in front of rods and cones  Bipolar cells, ganglion cells, horizontal cells, amacrine cells  Axons of ganglion cells join together to form the optic nerve  Optic nerve exits the retina at the optic disk (“blind spot”)

15. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cephalopod Eye and Retina  Photoreceptors are on the surface of the retina  Project forward  Supporting cells are located between photoreceptor cells  No other layers of cells associated with photoreceptors  Axons of photoreceptors form optic nerve

16. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 6.38a,b Convergence in the Vertebrate Retina

17. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 6.40 Lateral Inhibition in the Retina

18. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Brain Processes the Visual Signal  Action potentials from retina travel to brain  Optic nerves  optic chiasm  optic tract  lateral geniculate nucleus  visual cortex  Binocular vision  Eyes have overlapping visual fields  Binocular zone  Combine and compare information from each eye to form a three-dimensional image  Depth perception

19. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Color Vision  Detecting different wavelengths of visible light  Requires photopigments with different light sensitivities  Most mammals: see two (dichromatic) colors  Humans: see three (trichromatic) colors  Birds, reptiles and fish: see three, four (tetrachromatic), or five (pentachromatic) colors Retina and brain compare output from each type of receptor and infer the color

20. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Thermoreception  Central thermoreceptors  Located in the hypothalamus and monitor internal temperature  Peripheral thermoreceptors  Monitor environmental temperature  Warm-sensitive  Cold-sensitive  Thermal nociceptors – detect painfully hot stimuli  ThermoTRPs  Thermoreceptor proteins  TRP ion channel

21. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 6.43 Specialized Thermoreception  Specialized organs for detecting heat radiating objects at a distance  Pit organs  Pit found between the eye and the nostril of pit vipers  Can detect 0.003°C changes (humans can detect only 0.5°C changes)

22. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Magnetoreception  Ability to detect magnetic fields  For example, migratory birds, homing salmon  Neurons in the olfactory epithelium of rainbow trout contain particles that resemble magnetite  Responds to magnetic field