1. © 2010 Pearson Education, Inc. Lectures by Chris C. Romero, updated by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Chapter 27 Nervous, Sensory, and Motor Systems

2. Biology and Society: Beyond Human Experience Many animals perceive the world in ways we cannot. Bats and porpoises generate ultrasonic sounds in echolocation to –Detect echoes –Determine the size, shape, location, speed, and direction of objects in the environment © 2010 Pearson Education, Inc.

3. Figure 27.00

4. © 2010 Pearson Education, Inc. Many species of fish use electroreception to generate weak electric fields that reveal objects in low-visibility environments. Migratory birds, fish, turtles, amphibians, and bees use magnetoreception to –Detect magnetic fields –Orient their movements relative to Earth’s magnetic fields

5. © 2010 Pearson Education, Inc. AN OVERVIEW OF ANIMAL NERVOUS SYSTEMS The nervous system forms a communication and coordination network throughout an animal’s body. Neurons are nerve cells specialized for carrying electrical signals from one part of the body to another.

6. © 2010 Pearson Education, Inc. Organization of Nervous Systems The nervous system of most animals has two main divisions. –The central nervous system (CNS) consists of the brain and spinal cord (in vertebrates). –The peripheral nervous system (PNS) consists of mostly of nerves that carry signals into and out of the CNS.

7. © 2010 Pearson Education, Inc. A nerve is a communication line made from cable-like bundles of neuron fibers.

8. © 2010 Pearson Education, Inc. The three interconnected functions of the nervous system are carried out by three types of neurons: –Sensory neurons function in sensory input –Interneurons integrate information –Motor neurons function in motor output Effectors perform the body’s responses to motor output.

9. SENSORY INPUT MOTOR OUTPUT Sensory neuron Sensory receptor Effector cells Interneuron INTEGRATION Brain and spinal cord Motor neuron Peripheral nervous system (PNS) Central nervous system (CNS) Figure 27.1

10. © 2010 Pearson Education, Inc. Neurons –Are the functional units of the nervous system –Vary widely in shape –Share some common features

11. Signal direction Dendrites Cell body Nucleus Axon Signal pathway Synaptic terminals Myelin sheath Supporting cell Figure 27.2

12. © 2010 Pearson Education, Inc. The cell body houses –The nucleus –Other organelles

13. © 2010 Pearson Education, Inc. Two types of extensions project from the cell body: –Dendrites, which: –Receive incoming messages from other cells –Convey the information toward the cell body –Axons, which transmit signals toward another neuron or toward an effector

14. © 2010 Pearson Education, Inc. Supporting cells –Outnumber neurons by as many as 50 to 1 –Protect, insulate, and reinforce the neurons The myelin sheath –Forms an insulating material around an axon –Helps increase the speed of the electrical signal

15. © 2010 Pearson Education, Inc. An axon ends in a cluster of branches, each with a bulb-like synaptic terminal that relays signals to –Another neuron or –An effector

16. Signal direction Dendrites Cell body Nucleus Axon Signal pathway Synaptic terminals Myelin sheath Supporting cell Figure 27.2

17. © 2010 Pearson Education, Inc. Sending a Signal through a Neuron A resting neuron has potential energy that can be put to work to send nerve signals from one part of the body to another. This difference in charge (voltage) across the plasma membrane of a resting neuron is the resting potential.

18. © 2010 Pearson Education, Inc. The Action Potential A stimulus is any factor that causes a nerve signal to be generated. A stimulus of sufficient strength can trigger an action potential, a nerve signal that carries information along a neuron. Animation: Resting Potential Animation: Action Potential Blast Animation: Action Potential

19. Neuron interior Figure 27.3-1

20. Neuron interior   Figure 27.3-2

21. Neuron interior     Figure 27.3-3

22. Neuron interior       Figure 27.3-4

23. © 2010 Pearson Education, Inc. Propagation of the Signal An action potential is a localized electrical event. To function as a nerve signal over a distance, this local event must be passed along the neuron. Action potential propagation is like a “domino effect” along a neuron.

24. Axon Action potential   Figure 27.4-1

25. Axon Action potential       Figure 27.4-2

26. Axon Action potential         Figure 27.4-3

27. © 2010 Pearson Education, Inc. Action potentials are –All-or-none events –The same no matter how strong or weak the stimulus that triggers them

28. © 2010 Pearson Education, Inc. Passing a Signal from a Neuron to a Receiving Cell A synapse is a relay point –Between two neurons or –Between a neuron and an effector cell Synapses come in two varieties: –Electrical –Chemical

29. © 2010 Pearson Education, Inc. Chemical synapses –Have a narrow gap, the synaptic cleft, separating a synaptic terminal of the sending neuron from the receiving cell –Rely on neurotransmitters, chemicals that carry information from one nerve cell to another kind of cell Blast Animation: Signal Transmission at Synapses Animation: Synapse Blast Animation: Signal Amplification in Neurons

30. SYNAPSE Synaptic terminal of sending neuron Dendrite of receiving neuron Sending neuron Vesicles Action potential arrives. Neurotransmitter is released into synaptic cleft. Neurotransmitter binds to receptor. Neurotransmitter molecules Ion channels Receiving neuron Synaptic cleft Synaptic terminal Vesicle fuses with plasma membrane. Neurotransmitter Receptor Ion channel opens and triggers or inhibits a new action potential. Ion channel closes. Neurotransmitter is broken down and released. Ions Figure 27.5

31. SYNAPSE Sending neuron Vesicles Action potential arrives. Neurotransmitter is released into synaptic cleft. Neurotransmitter binds to receptor. Neurotransmitter molecules Ion channels Receiving neuron Synaptic cleft Synaptic terminal Vesicle fuses with plasma membrane. Figure 27.5a

32. Neurotransmitter Receptor Ion channel opens and triggers or inhibits a new action potential. Ion channel closes. Neurotransmitter is broken down and released. Ions Figure 27.5b

33. © 2010 Pearson Education, Inc. Chemical synapses can process extremely complex information. A neuron may receive input from hundreds of other neurons via thousands of synaptic terminals.

34. Receiving cell body Dendrites Myelin sheath Axon Synaptic terminals SEM Figure 27.6

35. Receiving cell body Dendrites Myelin sheath Axon Synaptic terminals Figure 27.6a

36. Synaptic terminals SEM Figure 27.6b

37. © 2010 Pearson Education, Inc. Neurotransmitters A variety of small molecules can act as neurotransmitters: –Amines, derived from amino acids that affect sleep, mood, attention, and learning –Peptides, short chains of amino acids that include endorphins, which decrease pain perception

38. © 2010 Pearson Education, Inc. Drugs and the Brain Many drugs, such as caffeine, nicotine, and alcohol, act at synapses by increasing or decreasing the normal effect of neurotransmitters. Prescription drugs used to treat psychological disorders alter the effects of neurotransmitters.

39. THE HUMAN NERVOUS SYSTEM: A CLOSER LOOK Although there is remarkable uniformity in the way nerve cells function, there is great variety in how nervous systems as a whole are organized. Vertebrate nervous systems are diverse in –Structure –Level of sophistication © 2010 Pearson Education, Inc.

40. The Central Nervous System Vertebrate central nervous systems –Integrate information coming from the senses –Transmit signals that produce responses –Consist of the –Brain, the master control center of the nervous system –Spinal cord, a jellylike bundle of nerve fibers inside the spinal column

41. Central nervous system (CNS) Peripheral nervous system (PNS) Brain Spinal cord Figure 27.7

42. © 2010 Pearson Education, Inc. The brain and spinal cord –Contain spaces –Are filled with cerebrospinal fluid, a liquid that –Cushions the CNS –Helps supply the CNS with nutrients, hormones, and white blood cells Also protecting the brain and spinal cord are layers of connective tissues called meninges.

43. Brain Cerebrospinal fluid Meninges Spinal cord (cross section) Figure 27.8

44. © 2010 Pearson Education, Inc. The Peripheral Nervous System The vertebrate peripheral nervous system is divided into two functional components: –The somatic nervous system –The autonomic nervous system

45. PERIPHERAL NERVOUS SYSTEM Somatic nervous system (voluntary) Autonomic nervous system (involuntary) Parasympathetic division (rest and digest) Sympathetic division (fight or flight) Voluntary leg muscles Involuntary heart muscle LM   Figure 27.9

46. Voluntary leg muscles Figure 27.9a

47. Involuntary heart muscle LM Figure 27.9b

48. © 2010 Pearson Education, Inc. The somatic nervous system –Carries signals to and from skeletal muscles –Mainly responds to external stimuli

49. © 2010 Pearson Education, Inc. The autonomic nervous system –Regulates the internal environment –Controls –Smooth and cardiac muscles –Organs and glands of the digestive, cardiovascular, excretory, and endocrine systems

50. © 2010 Pearson Education, Inc. The autonomic nervous system contains two sets of neurons with opposing effects on most organs: –The parasympathetic division primes the body for digesting food and resting. –The sympathetic division prepares the body for intense, energy- consuming activities.

51. © 2010 Pearson Education, Inc. The Human Brain The brain, the most sophisticated computer, consists of –Up to 100 billion intricately organized neurons –Many more supporting cells

52. © 2010 Pearson Education, Inc. The brain is divided into three regions: –The hindbrain –The midbrain –The forebrain

53. Forebrain Cerebrum Thalamus Hypothalamus Pituitary gland Cerebral cortex Pons Medulla oblongata Cerebellum Spinal cord Midbrain Hindbrain Figure 27.10

54. Table 27.1

55. © 2010 Pearson Education, Inc. The brainstem –Consists of the hindbrain (medulla oblongata and pons) and the midbrain –Serves as a sensory filter, selecting which information reaches higher brain centers The cerebellum, another part of the hindbrain, is a planning center for body movements.

56. © 2010 Pearson Education, Inc. The forebrain contains the most sophisticated integrating centers in the brain: –The thalamus, which relays information to the cerebral cortex –The hypothalamus, with many regulatory functions –The cerebrum, the largest and most sophisticated part of the brain

57. © 2010 Pearson Education, Inc. The Cerebral Cortex The cerebrum consists of right and left cerebral hemispheres interconnected by the corpus callosum.

58. Left cerebral hemisphere Corpus callosum Medulla oblongata Cerebellum Thalamus Right cerebral hemisphere Figure 27.11

59. © 2010 Pearson Education, Inc. The cerebral cortex –Is a highly folded layer of tissue that forms the surface of the cerebrum –Helps produce our most distinctive human traits

60. © 2010 Pearson Education, Inc. The right and left cerebral hemispheres –Have four lobes –Are specialized for different mental tasks in a phenomenon known as lateralization Higher mental activities occur in association areas of the brain.

61. Frontal lobe Parietal lobe Temporal lobe Occipital lobe Frontal association area Speech Smell Hearing Auditory association area Visual association area Vision Reading Taste Speech Somatosensory association area otor cortex M So sensory ma to Figure 27.12

62. © 2010 Pearson Education, Inc. Evidence from brain surgery patients indicates that patterns of lateralization are not fixed.

63. Figure 27.13

64. In 1848, a railroad accident to a man named Phineas Gage –Propelled a three-foot-long spike through his head but –Caused significant changes in his personality. © 2010 Pearson Education, Inc. Brain Trauma

65. Figure 27.14

66. © 2010 Pearson Education, Inc. Neurological Disorders Neurological disorders can also affect brain function. –Major depression is extreme and persistent sadness and loss of interest in pleasurable activities. –Bipolar disorder involves extreme mood swings. –Alzheimer’s disease causes mental deterioration.

67. Depressed person Area of decreased brain activity Healthy person Figure 27.15

68. Depressed person Area of decreased brain activity Figure 27.15a

69. Healthy person Figure 27.15b

70. © 2010 Pearson Education, Inc. THE SENSES Sensory structures –Gather information –Pass it on to the CNS

71. © 2010 Pearson Education, Inc. Sensory Input Sensory input is the process of using receptors to –Sense the environment –Send information about it to the CNS to be integrated and acted upon Sensory transduction is the conversion of a stimulus signal to an electrical signal by a sensory receptor cell.

72. © 2010 Pearson Education, Inc. Sensory Transduction Receptor potentials –Are changes in membrane potentials caused by sensory stimuli –Vary in intensity, depending on the strength of the stimulus

73. Sugar molecule (stimulus) Receptor Membrane of sensory receptor cell Signal transduction pathway Sensory receptor cell Receptor potential Ion channels Sugar molecule Taste bud Sensory receptor cells Sensory neuron Neurotransmitter Action potential (to brain) Figure 27.16

74. Taste bud Sugar molecule (stimulus) Receptor Membrane of sensory receptor cell Signal transduction pathway Sensory receptor cell Receptor potential Ion channels Sugar molecule Sensory receptor cells Sensory neuron Neurotransmitter Action potential (to brain) Figure 27.16a

75. © 2010 Pearson Education, Inc. Sensory adaptation –Causes some sensory receptors to be less sensitive when they are stimulated repeatedly –Keeps the body from continuously reacting to normal background stimuli

76. © 2010 Pearson Education, Inc. Types of Sensory Receptors Sensory receptors can be grouped into five categories, which work in various combinations to produce the five human senses. A section of human skin reveals why the surface of our body is sensitive to such a variety of stimuli.

77. Heat PainCold Light touch (Hair) Epidermis Dermis Nerve to CNS Hair movement Strong pressure Figure 27.17

78. © 2010 Pearson Education, Inc. Pain receptors respond to stimuli causing injury or disease. Thermoreceptors detect heat or cold. Mechanoreceptors are stimulated by various forms of mechanical energy.

79. © 2010 Pearson Education, Inc. Chemoreceptors respond to chemicals in the external environment or body fluids. Electromagnetic receptors are sensitive to energy of various wavelengths, including light.

80. © 2010 Pearson Education, Inc. Vision Human eyes are able to –Detect a multitude of colors –Form images of faraway objects –Respond to minute amounts of light energy

81. © 2010 Pearson Education, Inc. Structure of the Human Eye The human eye consists of –A tough outer covering, the sclera –A transparent cornea in front of the lens –An iris with a center opening, the pupil –The retina, at the back of the eyeball, where photoreceptors respond to light The optic nerve connects the retina to the brain

82. © 2010 Pearson Education, Inc. Two fluid-filled chambers make up the bulk of the eye. –The large chamber is filled with vitreous humor. –The small chamber contains aqueous humor.

83. Sclera Muscle Ligament Cornea Iris Pupil Aqueous humor Lens Vitreous humor Blind spot Optic nerve Retina Choroid Figure 27.18

84. © 2010 Pearson Education, Inc. The iris –Regulates the size of the pupil –Lets light shine onto the lens The lens of the eye changes shape and refracts light, which focuses light onto the retina. Function of the Human Eye Animation: Near and Distance Vision

85. Near vision Choroid Retina Lens Muscle contracted Ligaments slacken Light from a near object Distance vision Muscle relaxed Ligaments pull on lens Light from a distant object Figure 27.19

86. © 2010 Pearson Education, Inc. Photoreceptors The human retina contains two types of photoreceptors. –Rods: –Are extremely sensitive to light –Perceive only shades of gray –Are distributed at the outer edges of the retina

87. © 2010 Pearson Education, Inc. –Cones: –Are less sensitive to light –Perceive colors –Are distributed at the center of focus on the retina Rods and cones detect light using an array of membranous disks containing visual pigments.

88. Cell body Synaptic terminals Membranous disks containing visual pigments Cone Rod Figure 27.20

89. © 2010 Pearson Education, Inc. Rods and cones are stimulus transducers that –Absorb light –Generate receptor potentials Other retinal neurons –Integrate these receptor potentials –Generate action potentials that travel along the optic nerve to the brain

90. Optic nerve fibers Retina NeuronsPhotoreceptors ConeRod To brain Optic nerve Retina Figure 27.21

91. © 2010 Pearson Education, Inc. Vision Problems and Corrections The most common visual problems are –Nearsightedness, the inability to focus on distant objects –Farsightedness, the inability to focus on near objects –Astigmatism, blurred vision caused by a misshapen lens or cornea

92. Shape of normal eyeball Point of focus Retina Lens Corrective lens Point of focus Point of focus Point of focus Shape of normal eyeball Corrective lens (a) A nearsighted eye (eyeball too long)(b) A farsighted eye (eyeball too short) Figure 27.22

93. Shape of normal eyeball Point of focus Retina Lens Corrective lens Point of focus (a) A nearsighted eye (eyeball too long) Figure 27.22a

94. Point of focus Point of focus Shape of normal eyeball Corrective lens (b) A farsighted eye (eyeball too short) Figure 27.22b

95. © 2010 Pearson Education, Inc. Hearing The Structure of the Human Ear The ear is composed of –The outer ear –The middle ear –The inner ear

96. Outer earMiddle ear Inner ear Pinna Auditory canal Eardrum (a) Ear structure Eustachian tube Stirrup Anvil Hammer Skull bones Eardrum Eustachian tube Cochlea Auditory nerve, to brain (b) The middle and inner ears Figure 27.23

97. Fig. 27-23a Outer ear Middle ear Inner ear Pinna Auditory canal Eardrum (a) Ear structure Eustachian tube Figure 27.23a

98. © 2010 Pearson Education, Inc. The outer ear –Consists of the pinna and the auditory canal –Collects sound waves –Passes sound waves to the eardrum, a sheet of tissue that separates the outer ear from the middle ear

99. © 2010 Pearson Education, Inc. In the middle ear, the vibrating eardrum passes the sound waves to three small bones that relay the sound to the inner ear. The Eustachian tube –Conducts air between the middle ear and back of the throat –Allows air pressure to stay equal on either side of the eardrum

100. Stirrup Anvil Hammer Skull bones Eardrum Eustachian tube Auditory nerve, to brain (b) The middle and inner ears Cochlea Figure 27.23b

101. © 2010 Pearson Education, Inc. The inner ear consists of fluid-filled channels in the bones of the skull. One of the channels, the cochlea, contains the organ of Corti, which –Is the actual hearing organ –Includes hair cells, the receptor cells of the ear

102. Cross section through cochlea Organ of Corti Overlying membrane Hair cells Supporting cells Sensory neurons Basilar membraneTo auditory nerve and brain Auditory nerve Fluid Bone Figure 27.24

103. Cross section through cochlea Organ of Corti Auditory nerve Fluid Bone Figure 27.24a

104. Overlying membrane Hair cells Supporting cells Sensory neurons Basilar membrane To auditory nerve and brain Figure 27.24b

105. © 2010 Pearson Education, Inc. When we hear, sound waves –Are collected by the outer ear –Are transmitted indirectly to the cochlea, which causes –Hair cells in the organ of Corti to bend –Nerve cells to send signals to the brain Function of the Human Ear

106. Outer earMiddle ear Inner ear Cochlea Pinna Auditory canal Ear- drum Hammer, anvil, stirrup One vibration Concentration in middle ear Organ of Corti stimulated Time Amplitude Pressure Figure 27.25

107. © 2010 Pearson Education, Inc. Louder sounds cause –Greater movement of the hair cells –More action potentials

108. © 2010 Pearson Education, Inc. Deafness, the loss of hearing, can be caused by –Middle ear infections –Injury, such as a ruptured eardrum –Overexposure to loud noises Hearing Problems

109. © 2010 Pearson Education, Inc. MOTOR SYSTEMS Movement –Is one of the most distinctive features of animals –Relies upon an interplay of organ systems The nervous system issues commands to the muscular system. The muscular system exerts the forces that make animals move by acting on the skeletal system.

110. © 2010 Pearson Education, Inc. The Skeletal System The skeletal system provides –Anchoring –Support –Protection of internal organs

111. © 2010 Pearson Education, Inc. Organization of the Human Skeleton All vertebrates have an endoskeleton, situated among soft tissues, and consisting of –Bones, hard supporting elements –Cartilage at points of flexibility

112. Skull Shoulder girdle Clavicle Scapula Sternum Ribs Humerus Vertebra Ulna Radius Pelvic girdle Carpals Metacarpals Phalanges (curled under) Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges Figure 27.26

113. Skull Shoulder girdle Clavicle Scapula Sternum Ribs Humerus Vertebra Ulna Radius Pelvic girdle Carpals Metacarpals Phalanges (curled under) Figure 27.26a

114. Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges Figure 27.26b

115. © 2010 Pearson Education, Inc. The axial skeleton –Supports the axis of the body –Includes the skull, vertebral column, and rib cage The appendicular skeleton is made up of the bones of the –Limbs –Shoulders –Pelvis

116. © 2010 Pearson Education, Inc. Much of the versatility of our skeleton comes from three types of movable joints: –Ball-and-socket joints in the shoulder and hip –Hinge joints that permit movement in a single plane –Pivot joints that allow rotation The bones of the skeleton are held together at movable joints by strong fibrous ligaments.

117. JOINTS Ball-and-socket (example: shoulder) Hinge (example: elbow flexing) Pivot (example: elbow rotation) Head of humerus Scapula Humerus Ulna Radius Figure 27.27

118. Ball-and-socket (example: shoulder) Head of humerus Scapula Figure 27.27a

119. Hinge (example: elbow flexing) Humerus Ulna Figure 27.27b

120. Pivot (example: elbow rotation) Ulna Radius Figure 27.27c

121. © 2010 Pearson Education, Inc. The Structure of Bones Bones –Are covered with a connective tissue membrane –Have cartilage at their ends that cushions the joints –Are served by blood vessels and nerves

122. Cartilage Spongy bone (contains red bone marrow) Compact bone Central cavity Yellow bone marrow Fibrous connective tissue Blood vessels Cartilage Figure 27.28

123. © 2010 Pearson Education, Inc. The central cavity of a long bone contains yellow bone marrow, which is mostly stored fat. The end of a long bone contains red bone marrow, a specialized tissue that produces blood cells.

124. © 2010 Pearson Education, Inc. Skeletal Diseases and Injuries The human skeleton –Is quite strong and provides reliable support, but –Is susceptible to disease and injury

125. © 2010 Pearson Education, Inc. Arthritis –Is an inflammation of the joints –Affects one out of every seven people in the United States Rheumatoid arthritis –Is an autoimmune disease –Usually begins between ages 40 and 50 –Affects more women than men

126. © 2010 Pearson Education, Inc. Osteoporosis –Makes bones thinner and more porous –Is most common in women after menopause

127. © 2010 Pearson Education, Inc. Bones are rigid but not inflexible. If a force applied to a bone exceeds its capacity to bend, the result is a broken bone or fracture. The treatment of a fracture involves –Putting the bone back into its natural shape –Immobilizing it until the body’s natural bone-building cells can repair the fracture

128. Figure 27.29

129. © 2010 Pearson Education, Inc. The Muscular System The muscular system is made of all the skeletal muscles in the body. Skeletal muscles –Are attached to the skeleton –Pull on bones to produce movements Tendons connect muscles to bones. Antagonistic pairs of muscles produce opposite movements.

130. Biceps contracted Biceps relaxed Triceps contracted Triceps relaxed Tendon Figure 27.30

131. © 2010 Pearson Education, Inc. The Cellular Basis of Muscle Contraction Skeletal muscle is made up of a hierarchy of smaller and smaller parallel strands. Blast Animation: Anatomy of Muscle

132. Muscle Nuclei Bundle of muscle fibers Single muscle fiber (cell) Myofibril Light band Light band Dark band Sarcomere Dark band Light band Light band Thick filaments (myosin) Thin filaments (actin) Sarcomere TEM Figure 27.31

133. Muscle Nuclei Bundle of muscle fibers Single muscle fiber (cell) Myofibril Light band Dark band Light band Figure 27.31a

134. Dark band Light band Light band Thick filaments (myosin) Thin filaments (actin) Sarcomere TEM Dark band Sarcomere Myofibril Light band Light band Figure 27.31b

135. © 2010 Pearson Education, Inc. Each skeletal muscle cell, or fiber –Contains bundles of myofibrils –Is called striated, because the myofibrils exhibit alternating light and dark bands when viewed with a light microscope A sarcomere –Is the region between two dark, narrow lines called Z lines –Is the functional unit of muscle contraction

136. © 2010 Pearson Education, Inc. A myofibril is composed of two kinds of filaments: –Thin filaments, made mostly of the protein actin –Thick filaments, made mostly of the protein myosin A sarcomere contracts when its thin filaments slide across its thick filaments.

137. Sarcomere Dark band Relaxed muscle Contracting muscle Fully contracted muscle Figure 27.32

138. © 2010 Pearson Education, Inc. In the sliding-filament model, the key events are the binding between –Parts (called heads) of the myosin molecules in the thick filaments –Specific sites on actin molecules in the thin filaments Contraction requires energy supplied by ATP.

139. Thick filament (myosin) Thin filament (actin) Myosin head (low-energy configuration) ATP ATP binds to a myosin head, which is then released from an actin filament. Figure 27.33-1

140. Thick filament (myosin) Thin filament (actin) Myosin head (low-energy configuration) ATP ADP+ P Myosin head (high-energy configuration) ATP binds to a myosin head, which is then released from an actin filament. The breakdown of ATP cocks the myosin head. Figure 27.33-2

141. Thick filament (myosin) Thin filament (actin) Myosin head (low-energy configuration) ATP ADP+ P Myosin head (high-energy configuration) ATP binds to a myosin head, which is then released from an actin filament. The breakdown of ATP cocks the myosin head. The myosin head attaches to an actin binding site. Figure 27.33-3

142. Thick filament (myosin) Thin filament (actin) Myosin head (low-energy configuration) ATP ADP+ P Myosin head (high-energy configuration) ATP binds to a myosin head, which is then released from an actin filament. The breakdown of ATP cocks the myosin head. The myosin head attaches to an actin binding site. The power stroke slides the actin (thin) filament toward the center of the sarcomere. As long as ATP is available, the process can be repeated until the muscle is fully contracted. Figure 27.33-4

143. Thick filament (myosin) Thin filament (actin) Myosin head (low-energy configuration) Myosin head (high-energy configuration) ATP binds to a myosin head, which is then released from an actin filament. The breakdown of ATP cocks the myosin head. ATPADP+ P ATP Figure 27.33a

144. The myosin head attaches to an actin binding site. The power stroke slides the actin (thin) filament toward the center of the sarcomere. As long as ATP is available, the process can be repeated until the muscle is fully contracted. Figure 27.33b

145. © 2010 Pearson Education, Inc. Motor Neurons: Control of Muscle Contraction Motor neurons –Can branch to a number of muscle fibers –Stimulate muscles to contract A neuromuscular junction is the connection between –A motor neuron –Muscle fibers associated with that neuron

146. © 2010 Pearson Education, Inc. A motor unit consists of –A neuron –All the muscle fibers it controls Motor units may consist of –Just one muscle fiber or –Up to hundreds of muscle fibers The strength of a muscle contraction depends on the number of motor units activated.

147. Spinal cord Motor neuron cell body Nerve Muscle Tendon Bone Muscle fibers (cells) Nuclei Motor unit 2 Motor unit 1 Motor neuron axon Neuromuscular junctions Figure 27.34

148. The Process of Science: How Do New Sense Arise? Observation: Two species of electric fish use special ion channel proteins in muscle cells to generate electric fields. Question: Did different ion channel proteins evolve in these two species? Hypothesis: Ion channel genes of the two electric species had mutated in unique ways. © 2010 Pearson Education, Inc.

149. Experiment: The DNA sequence of the genes in the two electric fish was determined and compared to a closely related but non- electric fish. Results: A single ion channel gene duplicated in the common ancestor, into forms a and b. –The a form mutated differently in the two electric fish species. –The b form retained its muscle functions in electric and non-electric fishes.

150. Location of gene function Muscle Electric organ African species Electric fish Gene b Gene a (mutation 1) a (mutation 2) ba and b none Electric fishNonelectric fish South American species Figure 27.35

151. © 2010 Pearson Education, Inc. Stimulus and Response: Putting It All Together An animal’s nervous system connects sensations derived from environmental stimuli to responses carried out by its muscles.

152. Figure 27.36

153. Evolution Connection: Seeing UV Many birds can see ultraviolet light, which seems to be important in –Social communication –Food gathering © 2010 Pearson Education, Inc.

154. Researchers have discovered that a single amino acid change in the pigment protein rhodopsin converted it to a UV-detecting form. This is another example of a large scale change that can be traced to a small change: a single mutation.

155. Figure 27.37

156. INTEGRATION Figure 27.UN01

157. SENSORY INPUT Figure 27.UN02

158. MOTOR OUTPUT Figure 27.UN03

159. Sensory receptor Effector SENSORY INPUT MOTOR OUTPUT INTEGRATION Peripheral nervous system (PNS) Central nervous system (CNS) Figure 27.UN04

160. Incoming signal Dendrites Cell body Axon Myelin (speeds signal transmission) Synaptic terminal Action poten tial signal Figure 27.UN05

161. NERVOUS SYSTEM Central Nervous System (CNS) Peripheral Nervous System (PNS) Spinal cord: nerve bundle that communicates with body Somatic nervous system: voluntary control over muscles Autonomic nervous system: involuntary control over organs Parasympathetic division: rest and digest  Sympathetic division: fight or flight  Brain Figure 27.UN06

162. BRAIN Forebrain (sophisticated integration) Midbrain Hindbrain Brainstem (filters motor and sensory input) Thalamus  Hypothalamus  Cerebrum  Pons  Medulla oblongata  Cerebellum (coordinates movement)  Figure 27.UN07

163. Stimulus Receptor potential Action potential Sensory receptor cell Sensory neuron CNS Figure 27.UN08

164. Outer earMiddle earInner ear Eardrum Bones Organ of Corti (inside cochlea) Figure 27.UN09