Sensory Systems Ch. 39

1. Sensory SystemsCh. 39

2. 6 Billion Worlds • Perception awareness of external and internal environments • Every person’s perception of everything is a little unique • We all vary in our sensory receptors, pathway processing, and application of stimuli • Sensory receptors cells designed to pick up stimulus within a receptive field (type and strength) • Stimuli can trigger a receptor potential which, when strong enough, will start an action potential along an afferent neuron (sensory transduction)

3. The Big Five • Most animals posses 5 types of sensory receptors: • Mechanoreceptors detect pressure and body movement; ears • Photoreceptors detect light; eyes • Chemoreceptors detect specific chemicals; taste buds • Thermoreceptors detect temperature; skin • Nociceptors detect damage; everywhere • Humans have about 15-20 senses: • Gravity, acceleration, balance, pH, O2and CO2 levels, time, etc…

4. Magnitude and Adaptation • Regardless of the sensory receptor, all action potentials are the same size. How do we measure the strength of a stimulus? • Frequency of action potentials; faster = stronger • Number of neurons stimulated; more= stronger • All sensory nerves, except nociceptors, will learn to ignore a stimulus if it remains at a constant strength for enough time (sensory adaptation) • Reason background noise is ignored or why you cant feel your clothing

5. Real Quick…. • Next Wednesday you will do a lab to test your sensory neurons • You will attempt to test how well they function under different stimuli and explain why they may fail you • As part of this lab I want each of you to design your own test to run • By Tuesday, design a sensory test your lab group will do and submit a brief outline • On Wednesday, make sure to bring the material needed to run your experiment. Bring extra material so other groups may also try your idea!

6. Mechanoreceptors: Touch • Touch receptors are located throughout the entire body • The higher the density of receptors the more sensitive an area is • What are the most sensitive parts of the body? • Fingers, lips, and tongue • 2-Point Test test sensitivity by measuring how far way two pins have to be for you to feel both independently • Hair follicles free nerve ends wrap around our body hair and react to movement of the hairs

7. Mechanoreceptors: Balance • 2 Resources: • Proprioceptors sensory neurons in muscle tissue that tell the brain about body position • Measure stretching, contractions, and increasing pressure • Golgi tendon organs monitor stretching of muscles at attachments to bones (tendons)

8. Mechanoreceptors: Balance 2) Vestibular apparatus 3 semicircular canals inside your ear that measure gravity and body movement • Ampulla (end of tube) is filled with sterocilia (sensitive hairs) and fluid (endolymph) • Movement in the head moves the fluid which pushes the hairs • Tubes follow X, Y, and Z axis to give us 3D feedback • Utricle and Saccule area of hair cells with CaCO3stones (otoliths) on tope • Pressure of otoliths tell us if we are upright

9. The Secret of Sound • Sound changes in air pressure caused by vibrations • Pitch depends on frequency • Amplitude (loudness) depends on size of change • Humans 20-20,000 hertz • Not all creatures hear through “ears” • Many invertebrates hear through skin • Insects hearing through exoskeleton or hair cells

10. Mechanoreceptors: Hearing • Human ear is made of 3 parts: • Outer ear part we can see; pinna (ear) funnels sounds into the auditory channel • Pressure pulls and pushes tympanic membrane (ear drum) 2) Middle ear air-filled cavity with three of our smallest bones which transfer tympanic vibrations to oval window (membrane of the inner ear) • Malleus hammer • Incus anvil • Stapes stirrup

11. Mechanoreceptors: Hearing 3) Inner ear fluid-filled cochlea (3.5 cm spiraled tube) transfer oval window vibrations into neuron impulses • Organ of Corti(spiral organ) contains sensory hair cells which react to fluid vibrations • Basilar membrane anchor for hair cells; wide at base and thinner at tip (oval window) • Thin area vibrates at high frequencies • Wide area vibrates at low frequencies • All hair cells send signals along cochlear nerve to the brain

12. The Mystical Eye • Ocellus simplest eye; detects lights but depolarizing when photopigments (retinal, made from vitamin A) absorb light • Compound eye thousands of units (ommatidia) focus light through transparent cells (cornea); great at detecting movement • Single-lens eye lens (cornea) focuses lights while muscles in pupil change its size (small in bright; large in dim); iris blocks light not hitting lens; retina react to light at the back of the eye • Accommodation changing lens to focus on objects

13. Photoreception: Sight • Human eye similar to single-lens eye; clear fluids (aqueous and vitreous humor) fill spaces in eyes and carry nutrients to cells • Why not blood vessels? • Limit our vision • Photoreceptors: • Rods rod shaped; specialized for low light; black and white; respond to a single photon of light • Cones cone shaped; specialized for wavelengths (color); less sensitive than rods • Ciliary body muscle tissue changes shape of lens (not pupil) to focus on objects

14. Rods and Cones • 120 million rods and 6 million cones • Fovea area at back of the eye where the lens focuses light; high conc. Of cones • Peripheral visioninput from area outside fovea; high conc. rods • Photoreception: • Outer membrane discs react to light • Internal segment processes cells activity • Axon of cell absorbs/releases glutamate to start impulse

15. Rods and Rhodopsin • Rhodopsin retinal protein in rods; part of G-protein pathway • Inactive (cis-form) releases glutamate into synapse • Active (trans-form) deceases glutamate release by closing Na+ channels and hyperpolarizing the cell • Rods work opposite of regular neurons; stimulation decreases neurotransmitter release

16. Vision and The Retina • 6 types of neurons make of the retina: 1 and 2) Rods and Cones 3) Bipolar cells send impulse from rods/cones to ganglion cells 4) Ganglion cells receive info from all over the retina and form optic nerve (blind spot) 5) Horizontal cells receive input laterally along excitation point 6) Amacrine cells send lateral information on to ganglions from bipolar cells • Lateral inhibition horizontal/amacinecells inhibit impulses outside area of light on retina; allow better detph

17. Cones and Color Vision • Most mammals have only 2 types of cones but humans/primates have 3 • Each type has a different photopsins(retinal + opsin proteins) • S-type 445nm (blue light) • M-type 535nm (green light) • L-type 570nm (red light) • All three have ranges that overlap so all visible light can be detected

18. Our Wonderful 3D World • 3D space comes from our brains receiving 2 sets of visual stimulus (2 eyes) • Optic chiasm part of image from left and right eye are shared but slightly different positions • Test this by altering which eye is open • Communication between each hemisphere in the brain allows the merging of the data to make 3D images • The greater the difference between data, the closer the object appears and the more 3D it is

19. Chemoreceptors: Taste • Taste is a crucial survival tool • Organisms taste through their mouth, feet, antenna, or even their whole body • Analyzing the chemical make of the material tells the organism the possible benefits or dangers of consuming it • 5 basic tastes: • Sweet sugars • Salty salts • Sour acids • Bitter bases and toxins • Umami protein (glutamate)

20. The Buds • Taste in many mammals comes from the tongue moist, enzyme recreating muscular tissue • Taste buds (papillae) chemoreceptors for the 5 tastes; react to specific chemicals • Salivary glands release a watery enzyme solution; used to help break down material and dissolve particles to be tasted • Taste leads to emotional responses due to connections with the limbic system

21. Chemoreceptors: Smell • Sent is a powerful communication method in many species • Small amount of particles are needed to get reactions • Easily dispersed by the wind • Pheromone communication through sent in insects/animals • Dead ants release a pheromone that tells other ants to remove its body • If pheromone sprayed on live ant, he will be kicked out of the colony (thought to be dead)

22. The Olfactory • Smell in humans is detected by olfactory bulbs in our nose • Directly linked to the brain…why? • Most mammals their nose comes first; faster the nose response the safer they are • Sensory hairs covered in mucus (help dissolve particles in air) react to different classes of chemicals • Taste and smell have a strong connection; often the smell of something is close to how you will taste it • Smell is our first memory maker; babies remember the smell of their parents months before their voice, touch, or even face

23. Nociceptors: Temperature • Thermoreceptors detect temperature in the environment and the body • Tool: infrared pit organs in snakes; find blood for mosquitoes • Safety: reflex protects us from damaging tissue • Homeostasis: hypothalamus regulates body temp.; causes sweating or shivering • Most mammals organize temps into groups from 8oCto 52oC

24. Nociceptors: Pain • Nociceptors are located throughout the entire body except the brain • Natural defense against tissue damage; pain stops our desire to continue a destructive act • 2 types of pain: • Glutamate-releasing cells sharp pain in specific areas • Substance-P releasing cells dull aching pain over a general area • Endorphins natural painkillers released by the CNS that limit Substance-P reaction

25. Supersenses: Magnetoreceptors and Electroreceptors • Magnetoreceptors detect the magnetic field of the Earth/magnetic material • Tool: used by migrating species to guide them across great distances • Field of the Earth varies in location but is relatively constant • Electroreceptors detect electrical fields • Passive Tool: used by sharks to locate prey in unclear water or under sand • Active Tool: attack prey with electrical impulse from glands; electric eel

26. Homework • Suggested Homework: • Test Your Knowledge • Actual Homework: • Discuss the Concepts #3 • Interpret the Data • Due Tuesday • Essay!!! • Explain a sense that humans do not possess (not magnetic or electroreception) • Citation and reference pages must be done correctly or you get a 0! • Due Tuesday • Test!! • Tuesday; Ch. 17, 37, 38, and 39