1. SENSORY MECHANISMS
Chapter 50

2. Sensory Mechanisms in Mammals
Chapter

3. The body NEVER stops collecting data about the world around it
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.

4. 48.20

5. Picture of brain showing where senses are located

6. Sensations vs Perceptions
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

7. Vocab from the reading Sensory reception Sensory transduction
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. Chemoreceptors
Glucose, water, oxygen, carbon dioxide, amino acids, any necessary chemical substances
Gustatory: taste
Olfactory: smell
Sweet, salty, sour, bitter, umami are the main categories

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 Harper Collins Publishers. Pages

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. Rods and Cones 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
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. Myopia 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

51. The Ear and Equilibrium
Utricle and Saccule
Chambers behind oval window
Utricle opens to semicircular canals- used for equilibrium
Tell brain UP vs DOWN
Help your brain determine your position in space

52. 49.19 a c

53. HOW?? Gravity always pulling down on the hairs
Angle of hairs triggers chain reaction resulting in neurotransmitters to nerve.
Action Potentials in brain interpreted as your angle to earth.