1. Chapter 49 Sensory and Motor Mechanisms

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sensory receptors perform four functions in this process – Sensory transduction, amplification, transmission, and integration

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Two types of sensory receptors exhibit these functions – A stretch receptor in a crayfish Figure 49.2a (a)Crayfish stretch receptors have dendrites embedded in abdominal muscles. When the abdomen bends, muscles and dendrites 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 produces a larger receptor potential and higher requency of action potentials. Muscle Dendrites Stretch receptor Axon Membrane potential (mV) –50 –70 0 0 12 3 45 67 Time (sec) Action potentials Receptor potential Weak muscle stretch –50 –70 0 0 1234567 Time (sec) Strong muscle stretch

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – 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 (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 –50 –70 0 0 1234 567 Time (sec) Action potentials No fluid movement –50 –70 0 01234567 Time (sec) Receptor potential Fluid moving in one direction –50 –70 0 0 1234567 Time (sec) Fluid moving in other direction Membrane potential (mV) “Hairs” of hair cell Neuro- trans- mitter at synapse Axon Less neuro- trans- mitter More neuro- trans- mitter Figure 49.2b

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many sensory receptors are extremely sensitive – With the ability to detect the smallest physical unit of stimulus possible

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Amplification Amplification is the strengthening of stimulus energy – By cells in sensory pathways

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sensory cells without axons – Release neurotransmitters at synapses with sensory neurons

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Integration The integration of sensory information – Begins as soon as the information is received – Occurs at all levels of the nervous system

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some receptor potentials – Are integrated through summation Another type of integration is sensory adaptation – A decrease in responsiveness during continued stimulation

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Sensory Receptors Based on the energy they transduce, sensory receptors fall into five categories – Mechanoreceptors – Chemoreceptors – Electromagnetic receptors – Thermoreceptors – Pain receptors

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mechanoreceptors Mechanoreceptors sense physical deformation – Caused by stimuli such as pressure, stretch, motion, and sound

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The mammalian sense of touch – Relies on mechanoreceptors that are the dendrites of sensory neurons Figure 49.3 Heat Light touch Pain Cold Hair Nerve Connective tissue Hair movement Strong pressure Dermis Epidermis

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Two of the most sensitive and specific chemoreceptors known – Are present in the antennae of the male silkworm moth Figure 49.4 0.1 mm

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electromagnetic Receptors Electromagnetic receptors detect various forms of electromagnetic energy – Such as visible light, electricity, and magnetism

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 enough to 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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, apparently sense Earth’s magnetic field and use the information, along with other cues, for orientation.

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Thermoreceptors Thermoreceptors, which respond to heat or cold – Help regulate body temperature by signaling both surface and body core temperature

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Ciliated receptor cells Cilia Statolith Sensory nerve fibers

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many arthropods sense sounds with body hairs that vibrate – Or with localized “ears” consisting of a tympanic membrane and receptor cells Figure 49.7 1 mm Tympanic membrane

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hearing and Equilibrium in Mammals In most terrestrial vertebrates – The sensory organs for hearing and equilibrium are closely associated in the ear

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exploring the structure of the human ear Figure 49.8 Pinna Auditory canal Eustachian tube Tympanic membrane Stapes Incus Malleus Skull bones Semicircular canals Auditory nerve, to brain Cochlea Tympanic membrane Oval window Eustachian tube Round window Vestibular canal Tympanic canal Auditory nerve Bone Cochlear duct Hair cells Tectorial membrane Basilar membrane To auditory nerve Axons of sensory neurons 1 Overview of ear structure 2 The middle ear and inner ear 4 The organ of Corti 3 The cochlea Organ of Corti Outer ear Middle ear Inner ear

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Cochlea Stapes Oval window Apex Axons of sensory neurons Round window Basilar membrane Tympanic canal Base Vestibular canal Perilymph

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cochlea can distinguish pitch – Because the basilar membrane is not uniform along its length Cochlea (uncoiled) Basilar membrane Apex (wide and flexible) Base (narrow and stiff) 500 Hz (low pitch) 1 kHz 2 kHz 4 kHz 8 kHz 16 kHz (high pitch) Frequency producing maximum vibration Figure 49.10

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Equilibrium Several of the organs of the inner ear – Detect body position and balance

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The utricle, saccule, and semicircular canals in the inner ear – Function in balance and equilibrium Figure 49.11 The semicircular canals, arranged in three spatial planes, detect angular movements of the head. Body movement Nerve fibers Each canal has at its base a swelling called an ampulla, containing a cluster of hair cells. When the head changes its rate of rotation, inertia prevents endolymph in the semicircular canals from moving with the head, so the endolymph presses against the cupula, bending the hairs. The utricle and saccule tell the brain which way is up and inform it of the body’s position or linear acceleration. The hairs of the hair cells project into a gelatinous cap called the cupula. Bending of the hairs increases the frequency of action potentials in sensory neurons in direct proportion to the amount of rotational acceleration. Vestibule Utricle Saccule Vestibular nerve Flow of endolymph Cupula Hairs Hair cell

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hearing and Equilibrium in Other Vertebrates Like other vertebrates, fishes and amphibians – Also have inner ears located near the brain

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most fishes and aquatic amphibians – Also have a lateral line system along both sides of their body

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The lateral line system contains mechanoreceptors – With hair cells that respond to water movement Figure 49.12 Nerve fiber Supporting cell Cupula Sensory hairs Hair cell Segmental muscles of body wall Lateral nerve Scale Epidermis Lateral line canal Neuromast Opening of lateral line canal Lateral line

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The taste receptors of insects are located within sensory hairs called sensilla – Which are located on the feet and in mouthparts

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 49.13 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. Number of action potentials in first second of response CONCLUSION Any natural food probably stimulates multiple chemoreceptors. By integrating sensations, the insect’s brain can apparently distinguish a very large number of tastes. To brain Chemo- receptors Pore at tip Pipette containing test substance To voltage recorder Sensillum Microelectrode 50 30 10 0 0.5 M NaCl Meat 0.5 M Sucrose Honey Stimulus Chemoreceptors 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.

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Taste pore Sugar molecule Sensory receptor cells Sensory neuron Taste bud Tongue G protein Adenylyl cyclase —Ca 2 + ATP cAMP Protein kinase A Sugar Sugar receptor SENSORY RECEPTOR CELL Synaptic vesicle K+K+ Neurotransmitter Sensory neuron Transduction in taste receptors – Occurs by several mechanisms Figure 49.14 4The decrease in the membrane’s permeability to K + depolarizes the membrane. 5Depolarization opens voltage-gated calcium ion (Ca 2+ ) channels, and Ca 2+ diffuses into the receptor cell. 6The increased Ca 2+ concentration causes synaptic vesicles to release neurotransmitter. 3Activated protein kinase A closes K + channels in the membrane. 2Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A. 1A sugar molecule binds to a receptor protein on the sensory receptor cell.

47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Smell in Humans Olfactory receptor cells – Are neurons that line the upper portion of the nasal cavity

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When odorant molecules bind to specific receptors – A signal transduction pathway is triggered, sending action potentials to the brain Brain Nasal cavity Odorant Odorant receptors Plasma membrane Odorant Cilia Chemoreceptor Epithelial cell Bone Olfactory bulb Action potentials Mucus Figure 49.15

49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vision in Invertebrates Most invertebrates – Have some sort of light-detecting organ

51. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Light Light shining from the front is detected Photoreceptor Visual pigment Ocellus Nerve to brain Screening pigment Light shining from behind is blocked by the screening pigment One of the simplest is the eye cup of planarians – Which provides information about light intensity and direction but does not form images Figure 49.16

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Two major types of image-forming eyes have evolved in invertebrates – The compound eye and the single-lens eye

53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Compound eyes are found in insects and crustaceans – And consist of up to several thousand light detectors called ommatidia Figure 49.17a–b Cornea Crystalline cone Rhabdom Photoreceptor Axons Ommatidium Lens 2 mm (a) The faceted eyes on the head of a fly, photographed with a stereomicroscope. (b) The cornea and crystalline cone of each ommatidium function as a lens that focuses light on the rhabdom, a stack of pigmented plates inside a circle of photoreceptors. The rhabdom traps light and guides it to photoreceptors. The image formed by a compound eye is a mosaic of dots produced by different intensities of light entering the many ommatidia from different angles.

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Single-lens eyes – Are found in some jellies, polychaetes, spiders, and many molluscs – Work on a camera-like principle

55. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Vertebrate Visual System The eyes of vertebrates are camera-like – But they evolved independently and differ from the single-lens eyes of invertebrates

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Structure of the Eye 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

57. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – The iris, which regulates the pupil – The retina, which contains photoreceptors – The lens, which focuses light on the retina

58. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The structure of the vertebrate eye Figure 49.18 Ciliary body Iris Suspensory ligament Cornea Pupil Aqueous humor Lens Vitreous humor Optic disk (blind spot) Central artery and vein of the retina Optic nerve Fovea (center of visual field) Retina Choroid Sclera

59. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Humans and other mammals – Focus light by changing the shape of the lens Figure 49.19a–b Lens (flatter) Lens (rounder) Ciliary muscle Suspensory ligaments Choroid Retina Front view of lens and ciliary muscle Ciliary muscles contract, pulling border of choroid toward lens Suspensory ligaments relax Lens becomes thicker and rounder, focusing on near objects (a) Near vision (accommodation) (b) Distance vision Ciliary muscles relax, and border of choroid moves away from lens Suspensory ligaments pull against lens Lens becomes flatter, focusing on distant objects

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sensory Transduction in the Eye Each rod or cone in the vertebrate retina – Contains visual pigments that consist of a light- absorbing molecule called retinal bonded to a protein called opsin

62. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rods contain the pigment rhodopsin – Which changes shape when it absorbs light Figure 49.20a, b Rod Outer segment Cell body Synaptic terminal Disks Inside of disk (a) Rods contain the visual pigment rhodopsin, which is embedded in a stack of membranous disks in the rod’s outer segment. Rhodopsin consists of the light-absorbing molecule retinal bonded to opsin, a protein. Opsin has seven  helices that span the disk membrane. (b) Retinal exists as two isomers. Absorption of light converts the cis isomer to the trans isomer, which causes opsin to change its conformation (shape). After a few minutes, retinal detaches from opsin. In the dark, enzymes convert retinal back to its cis form, which recombines with opsin to form rhodopsin. Retinal Opsin Rhodopsin Cytosol H C C H2CH2C C H2CH2C C H CH 3 H C C H C C C C C C C H H H H O H H3CH3C H C CH2CH2C C H2CH2CC H H C C H C C C C H H H C C C H O trans isomer cis isomer Enzymes Light

63. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Processing Visual Information The processing of visual information – Begins in the retina itself

64. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Absorption of light by retinal – Triggers a signal transduction pathway Figure 49.21 EXTRACELLULAR FLUID Membrane potential (mV) 0 – 40 – 70 Dark Light – Hyper- polarization Time Na + cGMP CYTOSOL GMP Plasma membrane INSIDE OF DISK PDE Active rhodopsin Light Inactive rhodopsinTransducinDisk membrane 2Active rhodopsin in turn activates a G protein called transducin. 3Transducin activates the enzyme phos- phodiesterae (PDE). 4Activated PDE detaches cyclic guanosine monophosphate (cGMP) from Na + channels in the plasma membrane by hydrolyzing cGMP to GMP. 5The Na+ channels close when cGMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes. 1Light isomerizes retinal, which activates rhodopsin.

65. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the dark, both rods and cones – Release the neurotransmitter glutamate into the synapses with neurons called bipolar cells, which are either hyperpolarized or depolarized

66. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the light, rods and cones hyperpolarize – Shutting off their release of glutamate The bipolar cells – Are then either depolarized or hyperpolarized Figure 49.22 Dark Responses Rhodopsin inactive Na + channels open Rod depolarized Glutamate released Bipolar cell either depolarized or hyperpolarized, depending on glutamate receptors Light Responses Rhodopsin active Na + channels closed Rod hyperpolarized No glutamate released Bipolar cell either hyperpolarized or depolarized, depending on glutamate receptors

67. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Three other types of neurons contribute to information processing in the retina – Ganglion cells, horizontal cells, and amacrine cells Figure 49.23 Optic nerve fibers Ganglion cell Bipolar cell Horizontal cell Amacrine cell Pigmented epithelium Neurons Cone Rod Photoreceptors Retina Optic nerve To brain

68. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Signals from rods and cones – Travel from bipolar cells to ganglion cells The axons of ganglion cells are part of the optic nerve – That transmit information to the brain Figure 49.24 Left visual field Right visual field Left eye Right eye Optic nerve Optic chiasm Lateral geniculate nucleus Primary visual cortex

69. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most ganglion cell axons lead to the lateral geniculate nuclei of the thalamus – Which relays information to the primary visual cortex Several integrating centers in the cerebral cortex – Are active in creating visual perceptions

70. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 49.5: Animal skeletons function in support, protection, and movement The various types of animal movements – All result from muscles working against some type of skeleton

71. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

72. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

73. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Annelids use their hydrostatic skeleton for peristalsis – A type of movement on land produced by rhythmic waves of muscle contractions Figure 49.25a–c (a) Body segments at the head and just in front of the rear are short and thick (longitudinal muscles contracted; circular muscles relaxed) and anchored to the ground by bristles. The other segments are thin and elongated (circular muscles contracted; longitudinal muscles relaxed.) (b) The head has moved forward because circular muscles in the head segments have contracted. Segments behind the head and at the rear are now thick and anchored, thus preventing the worm from slipping backward. (c) The head segments are thick again and anchored in their new positions. The rear segments have released their hold on the ground and have been pulled forward. Longitudinal muscle relaxed (extended) Circular muscle contracted Circular muscle relaxed Longitudinal muscle contracted Head Bristles

74. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exoskeletons An exoskeleton is a hard encasement – Deposited on the surface of an animal Exoskeletons – Are found in most molluscs and arthropods

75. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endoskeletons An endoskeleton consists of hard supporting elements – Such as bones, buried within the soft tissue of an animal Endoskeletons – Are found in sponges, echinoderms, and chordates

76. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

77. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The human skeleton Figure 49.26 1 Ball-and-socket joints, where the humerus contacts the shoulder girdle and where the femur contacts the pelvic girdle, enable us to rotate our arms and legs and move them in several planes. 2 Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane. 3 Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side. key Axial skeleton Appendicular skeleton Skull Shoulder girdle Clavicle Scapula Sternum Rib Humerus Vertebra Radius Ulna Pelvic girdle Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges 1 Examples of joints 2 3 Head of humerus Scapula Humerus Ulna Radius

78. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Physical Support on Land In addition to the skeleton – Muscles and tendons help support large land vertebrates

79. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 49.6: Muscles move skeletal parts by contracting The action of a muscle – Is always to contract

80. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Skeletal muscles are attached to the skeleton in antagonistic pairs – With each member of the pair working against each other Figure 49.27 Human Grasshopper Biceps contracts Triceps relaxes Forearm flexes Biceps relaxes Triceps contracts Forearm extends Extensor muscle relaxes Flexor muscle contracts Tibia flexes Extensor muscle contracts Flexor muscle relaxes Tibia extends

81. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vertebrate Skeletal Muscle Vertebrate skeletal muscle – Is characterized by a hierarchy of smaller and smaller units Figure 49.28 Muscle Bundle of muscle fibers Single muscle fiber (cell) Plasma membrane Myofibril Light band Dark band Z line Sarcomere TEM 0.5  m I band A band I band M line Thick filaments (myosin) Thin filaments (actin) H zone Sarcomere Z line Nuclei

82. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

83. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

84. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Skeletal muscle is also called striated muscle – Because the regular arrangement of the myofilaments creates a pattern of light and dark bands

85. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

86. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Sliding-Filament Model of Muscle Contraction According to the sliding-filament model of muscle contraction – The filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments

87. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As a result of this sliding – The I band and the H zone shrink Figure 49.29a–c (a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bands and H zone are relatively wide. (b) Contracting muscle fiber. During contraction, the thick and thin filaments slide past each other, reducing the width of the I bands and H zone and shortening the sarcomere. (c) Fully contracted muscle fiber. In a fully contracted muscle fiber, the sarcomere is shorter still. The thin filaments overlap, eliminating the H zone. The I bands disappear as the ends of the thick filaments contact the Z lines. 0.5  m Z H A Sarcomere

88. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

89. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Myosin-actin interactions underlying muscle fiber contraction Figure 49.30 Thick filament Thin filaments Thin filament ATP ADP P i Cross-bridge Myosin head (low- energy configuration) Myosin head (high- energy configuration) + Myosin head (low- energy configuration) Thin filament moves toward center of sarcomere. Thick filament Actin Cross-bridge binding site 1Starting here, the myosin head is bound to ATP and is in its low- energy confinguration. 2 The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration. P 1The myosin head binds to actin, forming a cross- bridge. 3 4 Releasing ADP and ( i ), myosin relaxes to its low-energy configuration, sliding the thin filament. P 5 Binding of a new mole- cule of ATP releases the myosin head from actin, and a new cycle begins.

90. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Role of Calcium and Regulatory Proteins A skeletal muscle fiber contracts – Only when stimulated by a motor neuron

91. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When a muscle is at rest – The myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin Figure 49.31a Actin Tropomyosin Ca 2+ -binding sites Troponin complex (a) Myosin-binding sites blocked

92. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings For a muscle fiber to contract – The myosin-binding sites must be uncovered This occurs when calcium ions (Ca 2+ ) – Bind to another set of regulatory proteins, the troponin complex Figure 49.31b Ca 2+ Myosin- binding site (b) Myosin-binding sites exposed

93. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The stimulus leading to the contraction of a skeletal muscle fiber – Is an action potential in a motor neuron that makes a synapse with the muscle fiber Figure 49.32 Motor neuron axon Mitochondrion Synaptic terminal T tubule Sarcoplasmic reticulum Myofibril Plasma membrane of muscle fiber Sarcomere Ca 2+ released from sarcoplasmic reticulum

94. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The synaptic terminal of the motor neuron – Releases the neurotransmitter acetylcholine, depolarizing the muscle and causing it to produce an action potential

95. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Action potentials travel to the interior of the muscle fiber – Along infoldings of the plasma membrane called transverse (T) tubules The action potential along the T tubules – Causes the sarcoplasmic reticulum to release Ca 2+ The Ca 2+ binds to the troponin-tropomyosin complex on the thin filaments – Exposing the myosin-binding sites and allowing the cross-bridge cycle to proceed

96. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ACh Synaptic terminal of motor neuron Synaptic cleft T TUBULE PLASMA MEMBRANE SR ADP CYTOSOL Ca 2  P2P2 Cytosolic Ca 2+ is removed by active transport into SR after action potential ends. 6 Review of contraction in a skeletal muscle fiber Figure 49.33 Acetylcholine (ACh) released by synaptic terminal diffuses across synaptic cleft and binds to receptor proteins on muscle fiber’s plasma membrane, triggering an action potential in muscle fiber. 1 Action potential is propa- gated along plasma membrane and down T tubules. 2 Action potential triggers Ca 2+ release from sarco- plasmic reticulum (SR). 3 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments. 5 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. 4 Tropomyosin blockage of myosin- binding sites is restored; contraction ends, and muscle fiber relaxes. 7

97. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neural Control of Muscle Tension Contraction of a whole muscle is graded – Which means that we can voluntarily alter the extent and strength of its contraction

98. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There are two basic mechanisms by which the nervous system produces graded contractions of whole muscles – By varying the number of fibers that contract – By varying the rate at which muscle fibers are stimulated

99. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Figure 49.34 Spinal cord Nerve Motor neuron cell body Motor unit 1 Motor unit 2 Motor neuron axon Muscle Tendon Synaptic terminals Muscle fibers

100. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A motor unit – Consists of a single motor neuron and all the muscle fibers it controls Recruitment of multiple motor neurons – Results in stronger contractions

101. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A twitch – Results from a single action potential in a motor neuron More rapidly delivered action potentials – Produce a graded contraction by summation Figure 49.35 Action potential Pair of action potentials Series of action potentials at high frequency Time Tension Single twitch Summation of two twitches Tetanus

102. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tetanus is a state of smooth and sustained contraction – Produced when motor neurons deliver a volley of action potentials

103. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Muscle Fibers Skeletal muscle fibers are classified as slow oxidative, fast oxidative, and fast glycolytic – Based on their contraction speed and major pathway for producing ATP

104. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of skeletal muscles

105. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Types of Muscle Cardiac muscle, found only in the heart – Consists of striated cells that are electrically connected by intercalated discs – Can generate action potentials without neural input

106. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In smooth muscle, found mainly in the walls of hollow organs – The contractions are relatively slow and may be initiated by the muscles themselves In addition, contractions may be caused by – Stimulation from neurons in the autonomic nervous system

107. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 49.7: Locomotion requires energy to overcome friction and gravity Movement is a hallmark of all animals – And usually necessary for finding food or evading predators Locomotion – Is active travel from place to place

108. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Swimming Overcoming friction – Is a major problem for swimmers Overcoming gravity is less of a problem for swimmers – Than for animals that move on land or fly

109. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Locomotion on Land Walking, running, hopping, or crawling on land – Requires an animal to support itself and move against gravity

110. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diverse adaptations for traveling on land – Have evolved in various vertebrates Figure 49.36

111. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Flying Flight requires that wings develop enough lift – To overcome the downward force of gravity

112. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONCLUSION For animals of a given body mass, swimming is the most energy- efficient and running the least energy- efficient mode of locomotion. In any mode, a small animal expends more energy per kilogram of body mass than a large animal. Flying Running Swimming 10 –3 10 3 10 6 1 10 –1 10 10 2 1 Body mass(g) Energy cost (J/Kg/m) CONCLUSION This graph compares the energy cost, in joules per kilogram of body mass per meter traveled, for animals specialized for running, flying, and swimming (1 J = 0.24 cal). Notice that both axes are plotted on logarithmic scales. RESULTS Physiologists typically determine an animal’s rate of energy use during locomotion by measuring its oxygen consumption or carbon dioxide production while it swims in a water flume, runs on a treadmill, or flies in a wind tunnel. For example, the trained parakeet shown below is wearing a plastic face mask connected to a tube that collects the air the bird exhales as it flies. EXPERIMENT The energy cost of locomotion – Depends on the mode of locomotion and the environment Figure 49.37 Comparing Costs of Locomotion

113. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animals that are specialized for swimming – Expend less energy per meter traveled than equivalently sized animals specialized for flying or running