Chapter 49

1. Chapter 49 Sensory and Motor Mechanisms Brandon Matsnev & Shane Mody

2. Introduction to Sensory Reception Sensations Action potentials that reach the brain via sensory neurons Perception A brain’s interpretation of stimuli

3. Signal transmission(to the nervous system) • Sensory reception: detection of energy of a stimulus by sensory receptors • Extero…outside body ; Intero…inside body *Receptor cells convert the energy of stimuli into changes in membrane potentials and then trasmit signals to the nervous system FOUR FUNCTIONS

4. Signal Transduction • Sensory Transduction • Receptor Potential

5. Amplification • May occur in either • Accessory structures or • The transduction process itself

6. Transmission • Receptors can be either • Sensory neurons themselves or • The intensity of the receptor potential will affect the frequency of action potentials that travel as sensations to the CNS • Separate cells • The strength of the stimulus and receptor potential affect the amount of neurotransmitter released by the receptor at its synapse with a sensory neuron

7. Integration • Sensory adaption

8. Photoreceptors and Vision

9. Types of Photoreceptors Non-image forming Image-forming Compound eyes- of insects and crustaceans; thousands of light detectors (ommatidia); acute movement detection Single-lens eye- lights enters through pupil; lens focuses light onto retina; muscle moves lens forward and backward Eye cup- of planarians; light enters cup and stimulates the photoreceptors through an opening where there is no screening pigment

11. Rod Cells and Cone Cells Rod Cells Cone Cells 6 million Distinguish colors in daylight • Human retina contains 125 million • Sensitive to light • Do not distinguish colors • See at night (only in black and white)

12. Rod Cells and Cone Cells How light is interpreted…structure • Rod and cone cells consist of folded membranes … embedded visual pigments have retinal, bounded to opsin • rods contain own opsin, which, combined with retinal, makes up pigment rhodopsin

14. Color vision is more complicated - Results from the presence of three subclasses (red, green, and blue) in retina; collectively known as photopsins • Absorption spectra for these pigments overlap, brain’s interpretation depends on… Ex. → red and green cones stimulated, we may see orange or yellow, depending on which cones are more strongly stimulated * Color blindness is due to deficiency or absence of types of photopsin

15. The Retina’s Role

16. The Retina’s Role - Lateral inhibition- sharpens edges, enhances contrast; after rod or cone stims. H cell, light appears lighter and dark, darker

17. The Retina’s Role • Ganglion cells form optic nerves • Optic nerves from two eyes meet at optic chiasm • Nerve tracts create reverse effect on sides of brain

18. hearing and equilibrium

23. Lateral line System Andthe inner ear • Detect pressure waves in fishes and amphibians • Within chambers in IE sensory hairs stim. By movement of otoliths • Vibrations of water caused by sound waves

24. Lateral line System Andthe inner ear • Lateral line system- contains mechanoreceptors that detect low-frequency waves • water enter LLS through pores • Neuromasts (receptor units) has hair cells, whose hair bends from pressure, enabling them to transduce energy • Help fish perceive movement

25. Gravity Sensors • Statocysts- function in equilibrium, contain statoliths • Gravity causes statoliths to settle in low part of chamber, stim. hair cells in that location

26. Taste and Smell • Gustation – another word for taste • Olfaction – another word for smell Both dependent on chemoreceptors that detect specific chemicals in environment

27. Taste and Smell: Animals Animals use senses to do a variety of things • Attract mates • Mark territory • Navigate

28. Terrestrial Animals • Taste is detection of chemicals found in a solution • Smell is detection of chemicals carried throughout the air Aquatic Animals • No distinction between taste and smell for animals under water

29. Receptor cells for taste are modified epithelial cells organized into taste buds Taste in Humans

30. 5 Taste perceptions Sour Sweet Salty Bitter Umami Each type of taste receptor can be stimulated by a broad range of chemicals, but is most responsive to a particular type of substance

31. Smell In Humans Olfactory Receptor Cells – neurons that line the upper portion of the nasal cavity and send impulses along their axons directly to the olfactory bulb of the brain. The receptive ends of cells contain cilia that extend into the layer of mucus coating the nasal cavity.

32. Humans can distinguish over thousands of different odors Each olfactory receptor cell expresses only one or at most a few OR genes Cells with different odorant selectivities are interspersed in the nasal cavity. But odors sort themselves out in the olfactory bulb.

33. Do Smell and Taste Interact? • Although the receptors and brain pathways for both are independent they do interact. • Mostly what we smell is taste. That is why when your nose is stuffed its harder to taste things

34. Skeleton Three Main Functions of Skeletons • Support • Protection • Movement Three Main Types • Hydrostatic Skeleton • Exoskeleton • Endoskeleton

35. Hydrostatic Skeletons Consist of fluid held under pressure in a closed body compartment Hydrostatic Skeletons found in • Flatworms • Cnidarians • Nematodes • Annelids

36. Hydrostatic Skeletons are well suited for aquatic life They cushion internal organs from shocks and provide support for crawling and burrowing.

37. Exoskeletons They are hard encasements deposited on the surface of an animal Exoskeletons are found on • Mollusks • Clams • Arthropods

38. Jointed exoskeleton of arthropods is a cuticle Cuticle – a non living coat secreted by the epidermis • About 30 – 50% of it consists of Chitin

39. Endoskeletons Consist of hard supporting elements such as bones buried within the soft tissue of the animal Endoskeletons found in • Echinoderms • Chordates • Mammals

40. Mammalian skeleton is built from more then 200 bones, some fused together and others connected at joints by ligaments. • Axial Skeleton Appendicular Skeleton • Skull - limb bones • Vertebral Column - pectoral and pelvic girdles • Rib Cage

41. Human Grasshopper Extensormusclerelaxes Bicepscontracts Tibiaflexes Flexormusclecontracts Tricepsrelaxes Forearmflexes Extensormusclecontracts Tibiaextends Bicepsrelaxes Forearmextends Flexormusclerelaxes Triceps contracts Muscles • The action of a muscle • Is always to contract • Skeletal muscles are attached to the skeleton in antagonistic pairs • The pair is working against each other

42. Muscle Bundle ofmuscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Myofibril Z line Lightband Dark band Sarcomere TEM 0.5 m A band I band I band M line Thickfilaments(myosin) Thinfilaments(actin) H zone Z line Z line Sarcomere • Vertebrate skeletal muscle • Is characterized by a ladder of smaller and smaller units • A skeletal muscle consists of a bunch of long fibers • Running parallel to the length of the muscle • A muscle fiber • Is itself a bundle of smaller myofibrils set longitudinally

43. The Myofibrils • Two kinds of myofilaments • Thin filaments, consisting of two strands of actin and one strand of regulatory protein • Thick filaments, staggered arrays of myosin molecules • Skeletal muscle - striated muscle • Because the regular collection of the myofilaments creates a pattern of light and dark bands

44. 0.5 m (a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bandsand H zone are relatively wide. Z H A Sarcomere (b) Contracting muscle fiber. During contraction, the thick andthin filaments slide past each other, reducing the width of theI bands and H zone and shortening the sarcomere. (c) Fully contracted muscle fiber. In a fully contracted musclefiber, the sarcomere is shorter still. The thin filaments overlap,eliminating the H zone. The I bands disappear as the ends ofthe thick filaments contact the Z lines. Sliding-filament model of muscle contraction • The filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments

45. The sliding of filaments • The interaction between the actin and myosin molecules of the thick and thin filaments • The top of a myosin molecule • Binds to an actin filament • Forming a cross-bridge and pulling the thin filament toward the center of the sarcomere • Myosin-actin interactions underlying muscle fiber contraction

46. Thick filament Thin filaments 1 Starting here, the myosin head is bound to ATP and is in its low-energy confinguration. 5 Binding of a new mole- cule of ATP releases the myosin head from actin, and a new cycle begins. Thin filament Myosin head (low-energy configuration) The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration. ATP 2 ATP Cross-bridge binding site Thick filament P Actin Thin filament moves toward center of sarcomere. Myosin head (high-energy configuration) ADP Myosin head (low-energy configuration) P i 1 The myosin head binds toactin, forming a cross-bridge. 3 ADP + Cross-bridge ADP P i P i Releasing ADP and ( i), myosinrelaxes to its low-energy configuration, sliding the thin filament. 4 P

47. Tropomyosin Ca2+-binding sites Actin Troponin complex (a) Myosin-binding sites blocked Calcium and Regulatory Proteins • A skeletal muscle fiber contracts • Only when stimulated by a motor neuron • When a muscle is at rest • The myosin-binding sites on the thin filament are blocked by the narrow protein tropomyosin • For a muscle fiber to contract • The myosin-binding sites must be uncovered • when calcium ions (Ca2+) Bind to another set of regulatory proteins, the troponin complex

48. Motorneuron axon Mitochondrion Synapticterminal T tubule Sarcoplasmicreticulum Ca2+ releasedfrom sarcoplasmicreticulum Myofibril Sarcomere Plasma membraneof muscle fiber • The stimulus going to the contraction of a skeletal muscle fiber Is an action potential in a motor neuron that makes a synapse with the muscle fiber

49. Acetylcholine (ACh) released by synaptic terminal diffuses across synapticcleft and binds to receptor proteins on muscle fiber’s plasma membrane, triggering an action potential in muscle fiber. 1 Synapticterminalof motorneuron PLASMA MEMBRANE Synaptic cleft T TUBULE Action potential is propa- gated along plasma membrane and down T tubules. 2 ACh SR 4 Action potential triggers Ca2+ release from sarco- plasmic reticulum (SR). 3 Ca2 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. Tropomyosin blockage of myosin- binding sites is restored; contraction ends, and muscle fiber relaxes. 7 Ca2 CYTOSOL Cytosolic Ca2+ is removed by active transport into SR after action potential ends. 6 ADP P2 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments. 5 Contraction In A Skeletal Muscle Fiber

50. Two basic mechanisms - nervous system produces graded contractions • By varying the number of fibers that contract • By varying the rate at which muscle fibers are stimulated In a vertebrate skeletal muscle Each branched muscle fiber is innervated by only one motor neuron Each motor neuron May synapse with multiple muscle fibers