Chapter 49

1. Chapter 49 Sensory and Motor Mechanisms

2. Overview: Sensing and Acting • Bats use sonar to detect their prey • Moths, a common prey for bats • Can detect the bat’s sonar and attempt to flee Figure 49.1

3. Both of these organisms • Have complex sensory systems that facilitate their survival • The structures that make up these systems • Have been transformed by evolution into diverse mechanisms that sense various stimuli and generate the appropriate physical movement

4. Concept 49.1: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system • Sensations are action potentials • That reach the brain via sensory neurons • Once the brain is aware of sensations • It interprets them, giving the perception of stimuli

5. Sensations and perceptions • Begin with sensory reception, the detection of stimuli by sensory receptors • Exteroreceptors • Detect stimuli coming from the outside of the body • Interoreceptors • Detect internal stimuli

6. Functions Performed by Sensory Receptors • All stimuli represent forms of energy • Sensation involves converting this energy • Into a change in the membrane potential of sensory receptors

7. Sensory receptors perform four functions in this process • Sensory transduction, amplification, transmission, and integration

8. Weakmuscle stretch Strongmuscle stretch Muscle Dendrites Receptor potential –50 –50 –70 –70 Stretchreceptor Membranepotential (mV) Action potentials 0 0 Axon –70 –70 4 5 1 2 6 7 0 0 1 2 3 4 5 6 7 3 Time (sec) Time (sec) stretch, producing a receptor potential in the stretch receptor. The receptor potential triggers action potentials in the axon of the stretch receptor. A stronger stretch producesa larger receptor potential and higherrequency of action potentials. (a) Crayfish stretch receptors have dendrites embedded in abdominal muscles. When the abdomen bends, muscles and dendrites Figure 49.2a • Two types of sensory receptors exhibit these functions • A stretch receptor in a crayfish

9. Fluid moving inone direction Fluid moving in other direction No fluidmovement “Hairs” ofhair cell Neuro-trans-mitter at synapse Moreneuro-trans-mitter Lessneuro-trans-mitter –50 –50 Axon –50 Receptor potential –70 –70 –70 Membranepotential (mV) Membranepotential (mV) Membranepotential (mV) Action potentials 0 0 0 –70 –70 –70 5 6 7 1 2 3 4 0 0 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Time (sec) Time (sec) Time (sec) (b) Vertebrate hair cells have specialized cilia or microvilli (“hairs”) that bend when sur-rounding fluid moves. Each hair cell releases an excitatory neurotransmitter at a synapse with a sensory neuron, which conducts action potentials to the CNS. Bending in one direction depolarizes the hair cell, causing it to release more neurotransmitter and increasing frequency Figure 49.2b • A hair cell found in vertebrates of action potentials in the sensory neuron. Bending in the other direction has the opposite effects. Thus, hair cells respond to the direction of motion as well as to its strength and speed.s

10. Sensory Transduction • Sensory transduction is the conversion of stimulus energy • Into a change in the membrane potential of a sensory receptor • This change in the membrane potential • Is known as a receptor potential

11. Many sensory receptors are extremely sensitive • With the ability to detect the smallest physical unit of stimulus possible

12. Amplification • Amplification is the strengthening of stimulus energy • By cells in sensory pathways

13. Transmission • After energy in a stimulus has been transduced into a receptor potential • Some sensory cells generate action potentials, which are transmitted to the CNS

14. Sensory cells without axons • Release neurotransmitters at synapses with sensory neurons

15. Integration • The integration of sensory information • Begins as soon as the information is received • Occurs at all levels of the nervous system

16. Some receptor potentials • Are integrated through summation • Another type of integration is sensory adaptation • A decrease in responsiveness during continued stimulation

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

18. Mechanoreceptors • Mechanoreceptors sense physical deformation • Caused by stimuli such as pressure, stretch, motion, and sound

19. Cold Light touch Pain Hair Heat Epidermis Dermis Hair movement Nerve Strong pressure Connective tissue • The mammalian sense of touch • Relies on mechanoreceptors that are the dendrites of sensory neurons Figure 49.3

20. Chemoreceptors • Chemoreceptors include • General receptors that transmit information about the total solute concentration of a solution • Specific receptors that respond to individual kinds of molecules

21. 0.1 mm • Two of the most sensitive and specific chemoreceptors known • Are present in the antennae of the male silkworm moth Figure 49.4

22. Electromagnetic Receptors • Electromagnetic receptors detect various forms of electromagnetic energy • Such as visible light, electricity, and magnetism

23. Some snakes have very sensitive infrared receptors • That detect body heat of prey against a colder background Figure 49.5a (a) This rattlesnake and other pit vipers have a pair of infrared receptors,one between each eye and nostril. The organs are sensitive enoughto detect the infrared radiation emitted by a warm mouse a meter away. The snake moves its head from side to side until the radiation is detected equally by the two receptors, indicating that the mouse is straight ahead.

24. Many mammals appear to use the Earth’s magnetic field lines • To orient themselves as they migrate Figure 49.5b (b) Some migrating animals, such as these beluga whales, apparentlysense Earth’s magnetic field and use the information, along with other cues, for orientation.

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

26. 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

27. Concept 49.2: The mechanoreceptors involved with hearing and equilibrium detect settling particles or moving fluid • Hearing and the perception of body equilibrium • Are related in most animals

28. Ciliatedreceptor cells Cilia Statolith Sensory nerve fibers Sensing Gravity and Sound in Invertebrates • Most invertebrates have sensory organs called statocysts • That contain mechanoreceptors and function in their sense of equilibrium Figure 49.6

29. Tympanicmembrane 1 mm • Many arthropods sense sounds with body hairs that vibrate • Or with localized “ears” consisting of a tympanic membrane and receptor cells Figure 49.7

30. Hearing and Equilibrium in Mammals • In most terrestrial vertebrates • The sensory organs for hearing and equilibrium are closely associated in the ear

31. 1 2 Overview of ear structure The middle ear and inner ear Incus Semicircularcanals Skullbones Stapes Middleear Outer ear Inner ear Malleus Auditory nerve,to brain Pinna Tympanicmembrane Cochlea Eustachian tube Auditory canal Ovalwindow Eustachian tube Tympanicmembrane Tectorialmembrane Hair cells Roundwindow Cochlear duct Bone Vestibular canal Auditory nerve Axons of sensory neurons Basilarmembrane To auditorynerve Tympanic canal Organ of Corti 4 3 The organ of Corti The cochlea • Exploring the structure of the human ear Figure 49.8

32. 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

33. Cochlea Stapes Axons ofsensoryneurons Oval window Vestibularcanal Perilymph Apex Base Roundwindow Tympaniccanal Basilar membrane • These vibrations create pressure waves in the fluid in the cochlea • That travel through the vestibular canal and ultimately strike the round window Figure 49.9

34. 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

35. Cochlea(uncoiled) Apex(wide and flexible) Basilarmembrane 500 Hz(low pitch) 1 kHz 2 kHz 4 kHz 8 kHz 16 kHz(high pitch) Frequency producing maximum vibration Base(narrow and stiff) • The cochlea can distinguish pitch • Because the basilar membrane is not uniform along its length Figure 49.10

36. Each region of the basilar membrane vibrates most vigorously • At a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex

37. Equilibrium • Several of the organs of the inner ear • Detect body position and balance

38. Each canal has at its base a swelling called an ampulla, containing a cluster of hair cells. The semicircular canals, arranged in three spatial planes, detect angular movements of the head. When the head changes its rateof rotation, inertia prevents endolymph in the semicircular canals from moving with the head, so the endolymph presses against the cupula, bending the hairs. Flowof endolymph Flowof endolymph Vestibular nerve Cupula Hairs Haircell Nervefibers Vestibule Utricle Body movement Saccule The hairs of the hair cells project into a gelatinous cap called the cupula. The utricle and saccule tell the brain which way is up and inform it of the body’s position or linear acceleration. Bending of the hairs increases the frequency of action potentials in sensory neurons in direct proportion to the amount of rotational acceleration. • The utricle, saccule, and semicircular canals in the inner ear • Function in balance and equilibrium Figure 49.11

39. Hearing and Equilibrium in Other Vertebrates • Like other vertebrates, fishes and amphibians • Also have inner ears located near the brain

40. Most fishes and aquatic amphibians • Also have a lateral line system along both sides of their body

41. Lateralline Opening of lateralline canal Lateral line canal Scale Epidermis Neuromast Lateral nerve Segmental muscles of body wall Cupula Sensoryhairs Supporting cell Hair cell Nerve fiber • The lateral line system contains mechanoreceptors • With hair cells that respond to water movement Figure 49.12

42. Concept 49.3: The 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

43. The taste receptors of insects are located within sensory hairs called sensilla • Which are located on the feet and in mouthparts

44. EXPERIMENT Insects taste using gustatory sensilla (hairs) on their feet and mouthparts. Each sensillum contains four chemoreceptors with dendrites that extend to a pore at the tip of the sensillum. To study the sensitivity of each chemoreceptor, researchers immobilized a blowfly (Phormia regina) by attaching it to a rod with wax. They then inserted the tip of a microelectrode into one sensillum to record action potentials in the chemoreceptors, while they used a pipette to touch the pore with various test substances. To brain Chemo-receptors Sensillum Microelectrode To voltagerecorder RESULTS Each chemoreceptor is especially sensitive to a particular class of substance, but this specificity is relative; each cell can respond to some extent to a broad range of different chemical stimuli. Pore at tip Pipette containingtest substance Chemoreceptors 50 Number of action potentials in first second of response 30 CONCLUSION Any natural food probably stimulates multiple chemoreceptors. By integrating sensations, the insect’s brain can apparently distinguish a very large number of tastes. 10 0 Honey 0.5 MSucrose 0.5 MNaCl Meat Figure 49.13 Stimulus

45. 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)

46. Taste pore Sugar molecule Taste bud Sensoryreceptorcells Sensoryneuron Tongue 1 A sugar molecule binds to a receptor protein on the sensory receptor cell. Sugar Adenylyl cyclase G protein Sugarreceptor 2Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A. ATP cAMP Proteinkinase A 3Activated protein kinase A closes K+ channels in the membrane. SENSORYRECEPTORCELL K+ 4 The decrease in the membrane’s permeability to K+ depolarizes the membrane. Synapticvesicle —Ca2+ 5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell. Neurotransmitter 6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter. Sensory neuron • Transduction in taste receptors • Occurs by several mechanisms Figure 49.14

47. Smell in Humans • Olfactory receptor cells • Are neurons that line the upper portion of the nasal cavity

48. Brain Action potentials Odorant Olfactory bulb Nasal cavity Bone Epithelial cell Odorantreceptors Chemoreceptor Plasmamembrane Cilia Figure 49.15 Odorant Mucus • When odorant molecules bind to specific receptors • A signal transduction pathway is triggered, sending action potentials to the brain

49. Concept 49.4: Similar mechanisms underlie vision throughout the animal kingdom • Many types of light detectors • Have evolved in the animal kingdom and may be homologous

50. Vision in Invertebrates • Most invertebrates • Have some sort of light-detecting organ