SENSORY MECHANISMS

1. SENSORY MECHANISMS Chapter 50

2. Sensory Mechanisms in Mammals Chapter 50.1-50.4

3. Sense  brain  action React to the environment we are in Link the immediate stimulus to a memory We may interpret more to a stimulus than is really there. The body NEVER stops collecting data about the world around it

4. 48.20

5. Picture of brain showing where senses are located

6. Action potential from a sense neuron Brain’s interpretation of the sensation Color, smell, sound, taste, texture Created by the brain…do not really exist in the outside world Sensations vs Perceptions

7. Vocab from the reading • Sensory reception • Sensory receptors • Exteroreceptors • Interoreceptors • Sensory transduction • Receptor potential • Amplification • Transmission • Integration • Sensory adaptation

8. Sensory Transduction

9. Mechanoreceptors • Pressure, touch, stretch, motion, sound

10. Hair cells detect motion • Hair is really cilia or microvilli • Vertebrate ears

11. Pain receptors • “naked” dendrites (branches of neurons) • Called nociceptors • Vital to survival

12. Thermoreceptors • Register changes in external and internal temperatures • Posterior hypothalamus is the body’s “thermostat”

13. Glucose, water, oxygen, carbon dioxide, amino acids, any necessary chemical substances Gustatory: taste Olfactory: smell Sweet, salty, sour, bitter, umami are the main categories Chemoreceptors

14. Electromagnetic receptors • Visible light, electricity, magnetic pull We think whales know migration patterns by sensing the earth’s magnetic field photoreceptor Infrared receptor

15. Specialized sense organs “Ampullae of Lorenzini” • Detect electrical fields created by other fish • Can find a ray buried in the sand

16. VISION

17. When light enters a vertebrate eye, it travels through the jelly and strikes the photoreceptors of the retina. But the neurons of the retina are actually pointed backward. It is as if we are gazing at our own brain. Light has to make its way through several layers of neurons and a web of capillaries before it finally gets to the nerve endings that can detect it. Once light strikes the backward pointing photoreceptors of the retina, the photoreceptors then have to send their signals back up through the layers of the retina toward the front of the eye… This achitecture is, as the evolutionary biologist George Williams has bluntly put it, “stupidly designed.” Zimmer, C. Evolution: The Triumph of an Idea. 2001. Harper Collins Publishers. Pages 128-129

18. Vertebrates have Single Lens Eyes • Brain “sees”, NOT the eyes Ms. Bjelko’s Eye Taken in 2004 FOVEA: spot with most cone cells OPTIC DISC: blind spot

20. Focus and Lens Shape • The thicker the lens, the more sharply the light is bent as it enters the eye • Ciliary muscles contract to accommodate vision of close objects, making lens thicker

21. Visual pigments • CONES • Retinal (similar to vitamin A in structure) bonded to opsin (membrane protein) • RODS • Retinal bonded to a different opsin protein form Rhodopsin

22. How does this work molecularly? LIGHT Rhodopsin Retinal changes shape and separates from opsin Bright light “bleaches” rhodopsin (the process above) and rods stop working temporarily. Causes cones to take over. Cause of temporary blindness going from very dark to very light places.

23. Black and white vision at molecular level (highly simplified!!!) • Light induced shape change in rhodopsin starts a G protein linked chain reaction that • Releases glutamate (neurotransmitter) to bipolar cells in retina. • What happens next depends on the type of glutamate receptor on the bipolar cell.

24. Color vision (highly simplified) • 3 types of cones and corresponding opsins in retina- TOGETHER CALLED PHOTOPSINS • red, green, blue • The wavelength of light each specializes in overlap so we can see shades and other colors. • APPLICATION: Color blindness is genetic- sex linked- absence/deficiency of 1+ photopsin

25. 125mill in humans Monochrome More sensitive to light Allow vision at night 6mill in humans Colors Less sensitive to light More light needed to stimulate Rods and Cones Which species will have more rod cells? a. nocturnal animal b. diurnal animal

26. Strange Fact • Color vision exists in ALL CLASSES of vertebrates, but NOT ALL SPECIES • Good Color Vision: most fish, birds, amphibians, reptiles, primates • Limited Color vision: cats, most mammals (b/c they are nocturnal)

27. Path of Light through the Eye

28. The eye is like a camera. Images appear upside down AND backwards on the retina. Brain fixes it.

29. How your brain interprets the messages from your eyes.

30. Emmetropia- normal vision Upside down image lands on retina

31. Image forms in front of retina “nearsighted” Can see clearly at short distances Corrected with diverging lenses Myopia

32. Hyperopia Image forms behind the retina “farsighted”- can see clearly at long distances Corrected with converging lenses

33. Taste and Smell

34. Chemical conversations • Much of the animal kingdom communicates via chemicals instead of sound. • Pheromones • Scent marking territories

35. Defining Terms • Taste (olfaction)- detection of chemicals in solutions • Smell (gustation)- detection of chemicals in air • Animals in aquatic environments- no functional difference between taste and smell

36. Taste: Basic Mechanism • Molecule from food dissolves in liquid on tongue • Molecule reaches specific proteins in receptor cell membranes (modified epithelial cells in groups called taste buds) • Triggers depolarization of membrane • Neurotransmitters released • Visual on next page

37. Taste: Basic Mechanism

38. All Taste Buds LOOK the same • 4 different taste perceptions • 1 more being studied: umami • Meat or cheese flavor depending on the source you read.

39. Smell: Basic Mechanism • Chemicals detected by cilia on olfactory receptor cells (in layer of mucus in upper nasal cavity. • Molecule binds to specific receptor molecules on plasma membrane • Triggers G protein signaling pathway involving adenylyl cyclase and 2nd messenger cAMP • CAMP opens Na+ channels, depolarizing membrane

40. Smell: Basic Mechanism Olfactory bulb

41. Smell and Taste are Linked • Most of the thousands of smells we identify are based on a few primary odors that match up to the 4/5 taste perceptions • Lack of smell causes lack of sense of taste

42. Hearing and Equilibrium

43. Parts of the Ear • Fill in the labels on the drawing you were provided as we go through the functions of each part

45. Hearing is a mechanical system that works like a Rube Goldberg machine. 18 steps for a machine to drop coins in a bank

46. Many little steps to get a sound wave from your environment to your inner ear where it can be interpreted by your brain.

47. HOW do you hear? 1 • Sound waves in the air travel down the outer ear canal • Hit the ear drum/ tympanic membrane • Vibrations on ear drum, passed to the malleus, incus, and stapes in that order • Stapes transfers the vibrations to oval window (membrane on cochlea) • Vibrations produce pressure waves in the fluid of the cochlea. • 

48. HOW do you hear? 2 • Pressue wave in cochlea eventually strikes the round window • Pressure waves in vestibular canal push down on cochlear duct and basilar membrane • Basilar membrane vibrates up and down and hair cells brush against tectorial membrane at the frequency of the vibrations • Ion channels open in hair cells as they touch letting K+ in • Membrane depolarizes, neurotransmitter is released

49. HOW do you hear? 3 • Neuron carries sensations to brain via auditory nerve • Sound detected by frequency of impulses in nerve • Volume determined by amplitude of sound wave (higher the amplitude, more frequent impulses to nerve) • Pitch determined by frequency of sound wave (short high frequency waves= high pitches, long, low freqency waves = low pitches

50. How well do we hear compared to other mammals? • Human: 20-20,000hz • Dog: up to 40,000 hz • Bats: higher than 40,000hz