Sensory and Motor Mechanisms

1. Sensory and Motor Mechanisms Chapter 49

2. Sensing and Acting • Bats use sonar to detect their prey • Moths can detect the bat’s sonar and attempt to flee • Both of these organisms have complex sensory systems that facilitate their survival

3. Types of Sensory Receptors • Based on the energy they transduce, sensory receptors fall into five categories • Mechanoreceptors • Chemoreceptors • Electromagnetic receptors • Thermoreceptors • Pain receptors

4. Mechanoreceptors • Mechanoreceptors sense physical deformation • Caused by stimuli such as pressure, stretch, motion, and sound • The mammalian sense of touch • Relies on mechanoreceptors that are the dendrites of sensory neurons

5. Figure 49.4 Mechanoreception by a hair cell

6. Chemoreceptors • General receptors that transmit information about the total solute concentration of a solution • Specific receptors that respond to individual kinds of molecules • EX: Taste, Smell

7. Figure 49.5 Chemoreceptors in an insect: Female silk moth Bombyx mori releasing pheromones; SEM of male Bombyx mori antenna

8. Figure 49.x1 Chemoreceptors: Snake tongue

9. Electromagnetic Receptors • Electromagnetic receptors detect various forms of electromagnetic energy • Such as visible light, electricity, and magnetism • Some snakes have very sensitive infrared receptors • That detect body heat of prey against a colder background

10. Figure 49.6 Specialized electromagnetic receptors: Rattle snake with infrared recpters, beluga whale pod

11. Figure 49.6bx Beluga whale pod • Many mammals appear to use the Earth’s magnetic field lines • To orient themselves as they migrate

12. Thermoreceptors • Thermoreceptors, which respond to heat or cold • Help regulate body temperature by signaling both surface and body core temperature

13. Pain Receptors • In humans, pain receptors, also called nociceptors • Are a class of naked dendrites in the epidermis • Respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissues

14. The mechanoreceptors  hearing and equilibrium detect settling particles or moving fluid • Hearing and the perception of body equilibrium are related in most animals • Three regions of the human ear • The outer ear • The middle ear • The inner ear

15. Ear Structure • The outer ear external pinna and the auditory canal • Collects sound and directs it to the tympanic membrane (eardrum)

16. Middle Ear • Three small bones malleus (hammer), the incus (anvil) and stapes (stirrup) collect vibrations • The eustacian tube equalizes air pressure between the outer and middle ear

17. Cochlea Stapes Axons ofsensoryneurons Oval window Vestibularcanal Perilymph Apex Base Roundwindow Tympaniccanal Basilar membrane The Cochlea • Snail shaped structure organ of corti

18. Hearing • Vibrating objects create percussion waves in the air • That cause the tympanic membrane to vibrate • The three bones of the middle ear • Transmit the vibrations to the oval window on the cochlea • These vibrations create pressure waves in the fluid in the cochlea • That travel through the vestibular canal and ultimately strike the round window

19. The pressure waves in the vestibular canal • Cause the basilar membrane to vibrate up and down causing its hair cells to bend • The bending of the hair cells depolarizes their membranes • Sending action potentials that travel via the auditory nerve to the brain

20. Figure 49.18 How the cochlea distinguishes pitch

21. Figure 49.19 Organs of balance in the inner ear

22. Senses of Taste and Smell • Are closely related in most animals • The perceptions of gustation (taste) and olfaction (smell) • Are both dependent on chemoreceptors that detect specific chemicals in the environment

23. Taste in Humans • The receptor cells for taste in humans • Are modified epithelial cells organized into taste buds • Five taste perceptions involve several signal transduction mechanisms • Sweet, sour, salty, bitter, and umami (elicited by glutamate)

24. Figure 49.2 Sensory transduction by a taste receptor

25. Smell in Humans • Olfactory receptor cellsAre neurons that line the upper portion of the nasal cavity • When odorant molecules bind to specific receptors • A signal transduction pathway is triggered, sending action potentials to the brain

26. Olfaction in Humans

27. Vision in the Animal Kingdom • Two major types of image-forming eyes have evolved in invertebrates • The compound eye and the single-lens eye • Compound eyes are found in insects and crustaceans • And consist of up to several thousand light detectors called ommatidia • Single-lens eyes • Are found in some jellies, polychaetes, spiders, and many molluscs • Work on a camera-like principle

28. Simplest Eye • The eye cup of planarians provides information about light intensity and direction but does not form images

29. Figure 49.8 Compound eyes (a)

30. Vertebrate Eyes • Camera-like they evolved independently and differ from the single-lens eyes of invertebrates • The main parts of the vertebrate eye are • The sclera, which includes the cornea • The choroid, a pigmented layer • The conjunctiva, that covers the outer surface of the sclera • The iris, which regulates the pupil • The retina, which contains photoreceptors • The lens, which focuses light on the retina

31. Structure of the Human Eye

32. Focusing of the Mammalian Eye

33. Photoreceptors • The human retina contains two types of photoreceptors • Rods are sensitive to light but do not distinguish colors • Cones distinguish colors but are not as sensitive

34. Figure 49.13 From light reception to receptor potential: A rod cell’s signal-transduction pathway

35. The effect of light on synapses between rod cells and bipolar cells

36. Figure 49.15 The vertebrate retina

37. Neural pathways for vision

38. The Human Skeleton • Functions in support, protection, & movement • Animal movements result from muscles working against some type of skeleton • The mammalian skeleton is built from more than 200 bones • Some fused together and others connected at joints by ligaments that allow freedom of movement

39. The Human Skeleton

40. Muscles contraction Move Skeletal Parts • The action of a muscle always to contract • Skeletal muscles are attached to the skeleton in antagonistic pairs • With each member of the pair working against each other

41. Vertebrate Skeletal Muscle • Is characterized by a hierarchy of smaller and smaller units • A skeletal muscle consists of a bundle of long fibers • Running parallel to the length of the muscle • A muscle fiber • Is itself a bundle of smaller myofibrils arranged longitudinally • Skeletal muscle is also called striated muscle • Because the regular arrangement of the myofilaments creates a pattern of light and dark bands

42. The myofibrils are composed to 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 • Each repeating unit is a sarcomere • Bordered by Z lines • The areas that contain the myofilments • Are the I band, A band, and H zone

43. Skeletal Muscle

44. The sliding-filament model of muscle contraction • The filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments • As a result of this sliding • The I band and the H zone shrink • The sliding of filaments is based on • The interaction between the actin and myosin molecules of the thick and thin filaments • The “head” of a myosin molecule binds to an actin filament • Forming a cross-bridge and pulling the thin filament toward the center of the sarcomere

45. The sliding-filament model of muscle contraction

46. One hypothesis for how myosin-actin interactions generate the force for muscle contraction

47. Hypothetical mechanism for the control of muscle contraction

48. Review of skeletal muscle contraction

49. Types of Skeletons • The three main functions of a skeleton are • Support, protection, and movement • The three main types of skeletons are • Hydrostatic skeletons, exoskeletons, and endoskeletons

50. Hydrostatic Skeletons • A hydrostatic skeleton • Consists of fluid held under pressure in a closed body compartment • This is the main type of skeleton • In most cnidarians, flatworms, nematodes, and annelids • Annelids use their hydrostatic skeleton for peristalsis • A type of movement on land produced by rhythmic waves of muscle contractions