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Chapter 49 Sensory and Motor Mechanisms PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Both organisms have complex sensory systems that facilitate survival • These systems include diverse mechanisms that sense stimuli and generate appropriate movement 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 • The brain interprets sensations, giving the perception of stimuli Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Sensations and perceptions begin with sensory reception, detection of stimuli by sensory receptors • Exteroreceptors detect outside stimuli • Interoreceptors detect internal stimuli Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Functions Performed by Sensory Receptors • All stimuli represent forms of energy • Sensation involves converting energy into change in the membrane potential of sensory receptors • Functions of sensory receptors: sensory transduction, amplification, transmission, and integration Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The stretch receptor in a crayfish is an example of a sensory receptor Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-2a Weak muscle stretch Muscle Stretch receptor Membrane potential (mV) Dendrites Strong muscle stretch –50 Receptor potential –50 –70 –70 Action potentials 0 0 –70 –70 Axon 0 1 2 3 4 5 6 7 Time (sec) 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 0 1 2 3 4 5 6 7 Time (sec) in the axon of the stretch receptor. A stronger stretch produces a larger receptor potential and higher frequency of action potentials. • Another sensory receptor is the hair cell, which detects motion in the vertebrate ear and lateral line systems of fishes and amphibians Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-2b No fluid movement “Hairs” of hair cell Fluid moving in one direction More neurotransmitter Neurotransmitter at synapse Less neurotransmitter –50 –50 –70 Action potentials 0 –70 Membrane potential (mV) –50 Receptor potential Membrane potential (mV) Membrane potential (mV) Axon Fluid moving in other direction –70 0 Vertebrate hair cells have specialized cilia or microvilli (“hairs”) that bend when surrounding fluid moves. Each hair cell releases an excitatory neurotransmitter 0 –70 –70 0 1 2 3 4 5 6 7 Time (sec) –70 0 1 2 3 4 5 6 7 Time (sec) 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 0 1 2 3 4 5 6 7 Time (sec) neurotransmitter and increasing frequency 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. Sensory Transduction • Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptor • This change in membrane potential is called a receptor potential Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Many sensory receptors are very sensitive, able to detect the smallest physical unit of stimulus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Amplification • Amplification is the strengthening of stimulus energy by cells in sensory pathways Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Transmission • After energy has been transduced into a receptor potential, some sensory cells generate action potentials, which are transmitted to the CNS • Sensory cells without axons release neurotransmitters at synapses with sensory neurons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Integration • Integration of sensory information begins when information is received • Integration occurs at all levels of the nervous system • Some receptor potentials are integrated through summation • Another integration is sensory adaptation, decreased responsiveness during stimulation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Sensory Receptors • Based on energy transduced, sensory receptors fall into five categories: – Mechanoreceptors – Chemoreceptors – Electromagnetic receptors – Thermoreceptors – Pain receptors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mechanoreceptors • Mechanoreceptors sense physical deformation caused by stimuli such as pressure, stretch, motion, and sound • The sense of touch in mammals relies on mechanoreceptors that are dendrites of sensory neurons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-3 Heat Light touch Pain Cold Hair Epidermis Dermis Hypodermis Nerve Connective tissue Hair movement Strong pressure Chemoreceptors • General chemoreceptors transmit information about the total solute concentration of a solution • Specific chemoreceptors respond to individual kinds of molecules • The antennae of the male silkworm moth have very sensitive specific chemoreceptors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 0.1 mm LE 49-4 Electromagnetic Receptors • Electromagnetic receptors detect electromagnetic energy, such as light, electricity, and magnetism • Some snakes have very sensitive infrared receptors that detect body heat of prey against a colder background Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-5 Eye Infrared receptor 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. Some migrating animals, such as these beluga whales, apparently sense Earth’s magnetic field and use the information, along with other cues, for orientation. • Many mammals appear to use Earth’s magnetic field lines to orient themselves as they migrate 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pain Receptors • In humans, pain receptors, or nociceptors, are a class of naked dendrites in the epidermis • They respond to excess heat, pressure, or chemicals released from damaged or inflamed tissues 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 perception of body equilibrium are related in most animals Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hearing and Equilibrium in Mammals • In most terrestrial vertebrates, sensory organs for hearing and equilibrium are closely associated in the ear Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-8 Middle ear Inner ear Outer ear Semicircular canals Stapes Middle ear Incus Skull bones Auditory nerve, to brain Malleus Pinna Tympanic Auditory membrane canal Eustachian tube Tympanic membrane Oval window Cochlea Round window Eustachian tube Tectorial membrane Hair cells Bone Cochlea duct Vestibular canal Basilar membrane Axons of To auditory sensory neurons nerve Auditory nerve Tympanic canal Organ of Corti 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 strike the round window Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-9 Cochlea Stapes Vestibular canal Oval window Perilymph Apex Base Round window Tympanic canal Axons of sensory neurons Basilar membrane • Pressure waves in the canal cause the basilar membrane to vibrate, bending its hair cells • This bending of hair cells depolarizes their membranes, sending action potentials that travel via the auditory nerve to the brain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The cochlea can distinguish pitch because the basilar membrane is not uniform along its length • Each region vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-10 Cochlea (uncoiled) Basilar membrane Apex (wide and flexible) 500 Hz (low pitch) 1 kHz 2 kHz 4 kHz 8 kHz 16 kHz (high pitch) Base (narrow and stiff) Frequency producing maximum vibration Equilibrium • Several organs of the inner ear detect body position and balance: the utricle, saccule, and semicircular canals Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-11 Semicircular canals Ampulla Flow of endolymph Flow of endolymph Vestibular nerve Cupula Hairs Hair cell Vestibule Nerve fibers Utricle Saccule Body movement Hearing and Equilibrium in Other Vertebrates • Like other vertebrates, fishes and amphibians have inner ears near the brain • Most fishes and aquatic amphibians also have a lateral line system along both sides of their body • The lateral line system contains mechanoreceptors with hair cells that respond to water movement Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-12 Lateral line Lateral line canal Scale Neuromast Epidermis Segmental muscles of body wall Opening of lateral line canal Lateral nerve Cupula Sensory hairs Supporting cell Nerve fiber Hair cell Concept 49.3: The senses of taste and smell are closely related in most animals • Gustation (taste) and olfaction (smell) are dependent on chemoreceptors that detect specific chemicals in the environment • Taste receptors of insects are in sensory hairs called sensilla, located on feet and in mouthparts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Number of action potentials in first second of response LE 49-13b Chemoreceptors 50 30 10 0 0.5 M NaCl Meat 0.5 M Sucrose Stimulus Honey Taste in Humans • In humans, receptor cells for taste are modified epithelial cells organized into taste buds • Five taste perceptions: sweet, sour, salty, bitter, and umami (elicited by glutamate) • Transduction in taste receptors occurs by several mechanisms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-14 Taste pore Sugar molecule Sensory receptor cells Taste bud Tongue Sensory neuron G protein Adenylyl cyclase Sugar Sugar receptor ATP cAMP Protein kinase A SENSORY RECEPTOR K+ CELL Synaptic vesicle Ca2+ Neurotransmitter Sensory neuron Smell in Humans • Olfactory receptor cells are neurons that line the upper portion of the nasal cavity • Binding of odorant molecules to receptors triggers a signal transduction pathway, sending action potentials to the brain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-15 Brain Olfactory bulb Nasal cavity Bone Odorant Epithelial cell Odorant receptors Chemoreceptor Plasma membrane Odorant Cilia Mucus 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vision in Invertebrates • Most invertebrates have a light-detecting organ • One of the simplest is the eye cup of planarians, which provides information about light intensity and direction but does not form images 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 singlelens eyes of invertebrates Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Structure of the Eye • Main parts of the vertebrate eye: – The sclera: white outer layer, including cornea – The choroid: pigmented layer – The conjunctiva: covers outer surface of sclera – The iris: regulates the pupil – The retina: contains photoreceptors – The lens: focuses light on the retina Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-18 Sclera Choroid Retina Ciliary body Fovea (center of visual field) Suspensory ligament Cornea Iris Optic nerve Pupil Aqueous humor Lens Vitreous humor Central artery and vein of the retina Optic disk (blind spot) • Humans and other mammals focus light by changing the shape of the lens Animation: Near and Distance Vision Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-19 Front view of lens and ciliary muscle Choroid Lens (rounder) Retina Ciliary muscle Suspensory ligaments Near vision (accommodation) Lens (flatter) Distance vision • The human retina contains two types of photoreceptors: rods and cones • Rods are light-sensitive but don’t distinguish colors • Cones distinguish colors but are not as sensitive Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sensory Transduction in the Eye • Each rod or cone contains visual pigments consisting of a light-absorbing molecule called retinal bonded to a protein called opsin • Rods contain the pigment rhodopsin, which changes shape when absorbing light Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-20 Rod Outer segment Disks Inside of disk Cell body cis isomer Light Enzymes Synaptic terminal Cytosol Retinal Rhodopsin Opsin trans isomer Processing Visual Information • Processing of visual information begins in the retina • Absorption of light by retinal triggers a signal transduction pathway Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-21 Light Active rhodopsin INSIDE OF DISK EXTRACELLULAR FLUID PDE Plasma membrane Inactive rhodopsin Transducin Disk membrane Membrane potential (mV) 0 Dark Light cGMP –40 GMP Na+ Hyperpolarization –70 Time CYTOSOL Na+ • In the dark, rods and cones release the neurotransmitter glutamate into synapses with neurons called bipolar cells • Bipolar cells are either hyperpolarized or depolarized • In the light, rods and cones hyperpolarize, shutting off release of glutamate • The bipolar cells are then either depolarized or hyperpolarized Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-22 Dark Responses Light Responses Rhodopsin inactive Rhodopsin active Na+ channels open Na+ channels closed Rod depolarized Rod hyperpolarized Glutamate released No glutamate released Bipolar cell either depolarized or hyperpolarized, depending on glutamate receptors Bipolar cell either hyperpolarized or depolarized, depending on glutamate receptors • Three other types of neurons contribute to information processing in the retina: ganglion cells, horizontal cells, and amacrine cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-23 Retina Optic nerve To brain Retina Photoreceptors Neurons Cone Rod Amacrine cell Optic nerve Ganglion fibers cell Horizontal cell Bipolar cell Pigmented epithelium • Signals from rods and cones travel from bipolar cells to ganglion cells • Axons of ganglion cells form the optic nerves that transmit sensations from the eyes to the brain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-24 Left visual field Left eye Optic nerve Optic chiasm Lateral geniculate nucleus Primary visual cortex Right visual field Right eye • Most ganglion cell axons lead to the lateral geniculate nuclei of the thalamus • The thalamus relays information to the primary visual cortex • Several integrating centers in the cerebral cortex are active in creating visual perceptions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 49.5: Animal skeletons function in support, protection, and movement • The various animal movements result from muscles working against a skeleton Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endoskeletons • An endoskeleton consists of hard supporting elements, such as bones, buried in soft tissue • Endoskeletons are found in sponges, echinoderms, and chordates Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • A mammalian skeleton has more than 200 bones • Some are fused; others are connected at joints by ligaments that allow freedom of movement Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-26_6 Key Axial skeleton Appendicular skeleton Shoulder girdle Sternum Rib Humerus Skull Examples of joints Head of humerus Scapula Clavicle Scapula 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. Vertebra Radius Ulna Humerus Pelvic girdle Carpals Ulna Phalanges Metacarpals Femur Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane. Patella Tibia Fibula Ulna Radius Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side. Tarsals Metatarsals Phalanges Physical Support on Land • In addition to the skeleton, muscles and tendons help support large land vertebrates 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 • Skeletal muscles are attached in antagonistic pairs, with each member of the pair working against each other Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-27 Human Grasshopper Extensor muscle relaxes Biceps contracts Biceps relaxes Extensor muscle contracts Forearm extends Triceps contracts Flexor muscle contracts Forearm flexes Triceps relaxes Tibia flexes Tibia extends Flexor muscle relaxes Vertebrate Skeletal Muscle • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The myofibrils are composed to two kinds of myofilaments: – Thin filaments consist of two strands of actin and one strand of regulatory protein – Thick filaments are staggered arrays of myosin molecules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Skeletal muscle is also called striated muscle because the regular arrangement of myofilaments creates a pattern of light and dark bands • Each unit is a sarcomere, bordered by Z lines • Areas that contain the myofilments are the I band, A band, and H zone Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-28 Muscle Bundle of muscle fibers Single muscle fiber (cell) Nuclei Plasma membrane Myofibril Light Z line band Dark band Sarcomere TEM I band A band M line 0.5 µm I band Thick filaments (myosin) Thin filaments (actin) Z line H zone Sarcomere Z line The Sliding-Filament Model of Muscle Contraction • According to the sliding-filament model, filaments slide past each other longitudinally, producing more overlap between thin and thick filaments • As a result of sliding, the I band and H zone shrink Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-29 0.5 µm Z H A Sarcomere Relaxed muscle fiber Contracting muscle fiber Fully contracted muscle fiber I • The sliding of filaments is based on interaction between 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-30–4 Thick filament Thin filaments Thin filament Myosin head (low-energy configuration) Thick filament Thin filament moves toward center of sacomere. Actin Myosin head (lowenergy configuration) Cross-bridge binding site Myosin head (highenergy configuration) Cross-bridge The Role of Calcium and Regulatory Proteins • A skeletal muscle fiber contracts only when stimulated by a motor neuron • When a muscle is at rest, myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-31 Tropomyosin Ca2+-binding sites Actin Troponin complex Myosin-binding sites blocked. Ca2+ Myosinbinding site Myosin-binding sites exposed. • For a muscle fiber to contract, myosin-binding sites must be uncovered • This occurs when calcium ions (Ca2+) bind to a set of regulatory proteins, the troponin complex Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The stimulus leading to contraction of a muscle fiber is an action potential in a motor neuron that makes a synapse with the muscle fiber Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-32 Motor neuron axon Mitochondrion Synaptic terminal T tubule Ca2+ released from sarcoplasmic reticulum Sarcoplasmic reticulum Myofibril Plasma membrane of muscle fiber Sarcomere • The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine • Acetylcholine depolarizes the muscle, causing it to produce an action potential Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Action potentials travel to the interior of the muscle fiber along transverse (T) tubules • The action potential along T tubules causes the sarcoplasmic reticulum to release Ca2+ • The Ca2+ binds to the troponin-tropomyosin complex on the thin filaments • This binding exposes myosin-binding sites and allows the cross-bridge cycle to proceed Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-33 Synaptic terminal of motor neuron Synaptic cleft PLASMA MEMBRANE T TUBULE SR ACh Ca2+ CYTOSOL Ca2+ Neural Control of Muscle Tension • Contraction of a whole muscle is graded, which means that the extent and strength of its contraction can be voluntarily altered • There are two basic mechanisms by which the nervous system produces graded contractions: – Varying the number of fibers that contract – Varying the rate at which fibers are stimulated Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In a vertebrate skeletal muscle, each branched muscle fiber is innervated by one motor neuron • Each motor neuron may synapse with multiple muscle fibers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-34 Spinal cord Motor unit 1 Motor unit 2 Synaptic terminals Nerve Motor neuron cell body Motor neuron axon Muscle Muscle fibers Tendon • 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 • A twitch results from a single action potential in a motor neuron • More rapidly delivered action potentials produce a graded contraction by summation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-35 Tension Tetanus Summation of two twitches Single twitch Action potential Time Pair of action potentials Series of action potentials at high frequency • Tetanus is a state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials 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 • These categories are based on their contraction speed and major pathway for producing ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Types of Muscle • Cardiac muscle, found only in the heart, consists of striated cells electrically connected by intercalated discs • Cardiac muscle can generate action potentials without neural input Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In smooth muscle, found mainly in walls of hollow organs, contractions are relatively slow and may be initiated by the muscles themselves • Contractions may also be caused by stimulation from neurons in the autonomic nervous system 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Swimming • Overcoming friction is a major problem for swimmers • Overcoming gravity is easier for swimmers than for animals that move on land or fly 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 • Diverse adaptations for locomotion on land have evolved in vertebrates Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Flying • Flight requires that wings develop enough lift to overcome the downward force of gravity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparing Costs of Locomotion • The energy cost of locomotion depends on the mode of locomotion and the environment • Animals specialized for swimming expend less energy per meter traveled than equivalently sized animals specialized for flying or running Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 49-37 Flying Running 102 10 1 Swimming 10–1 10–3 1 103 Body mass (g) 106 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings