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Support, Movement, Senses… The Brain… References- chapters 48, 49 © 2014 Pearson Education, Inc. Nervous systems consist of circuits of neurons and supporting cells § By the Cambrian explosion, specialized systems of neurons enabled animals to sense and respond to their environments § The simplest nervous systems (in cnidarians) have neurons arranged in nerve nets- a series of interconnected nerve cells § More complex animals have nerves, in which axons of multiple neurons are bundled together © 2014 Pearson Education, Inc. Figure 49.2 Eyespot Nerve net (a) Hydra (cnidarian) Brain Ventral nerve cord Segmental ganglia (e) Insect (arthropod) © 2014 Pearson Education, Inc. Brain Brain Nerve cords Radial nerve Nerve ring Ventral nerve cord Transverse nerve (b) Sea star (echinoderm) (c) Planarian (flatworm) Ganglia Anterior nerve ring Segmental ganglia Brain Ganglia (d) Leech (annelid) Brain Spinal cord (dorsal nerve cord) Sensory ganglia Longitudinal nerve cords (f) Chiton (mollusc) (g) Squid (mollusc) (h) Salamander (vertebrate) § Bilaterally symmetrical animals exhibit cephalization, clustering of sensory organs at the front end of body § The simplest cephalized animals, flatworms, have a central nervous system (CNS)- consisting of a brain and longitudinal nerve cords § The peripheral nervous system (PNS) consists of neurons carrying information into and out of the CNS © 2014 Pearson Education, Inc. Figure 49.6 Central nervous system (CNS) Brain Spinal cord Cranial nerves Ganglia outside CNS Spinal nerves © 2014 Pearson Education, Inc. Peripheral nervous system (PNS) § Nervous system organization correlates with lifestyle § Sessile molluscs (for example, clams and chitons) have simple systems, whereas more complex molluscs (for example, octopuses and squids) have more sophisticated systems © 2014 Pearson Education, Inc. The Central Nervous System § The spinal cord conveys information to and from the brain and generates basic patterns of locomotion § Spinal cord also produces reflexes independently of the brain § A reflex is the body’s automatic response to a stimulus § Ex: mallet triggers a knee-jerk reflex © 2014 Pearson Education, Inc. Figure 49.7 Cell body of sensory neuron in dorsal root ganglion Gray matter Quadriceps muscle Spinal cord (cross section) Hamstring muscle Key Sensory neuron Motor neuron Interneuron © 2014 Pearson Education, Inc. White matter The Peripheral Nervous System § The PNS transmits information to and from the CNS and regulates movement and the internal environment § In the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNS © 2014 Pearson Education, Inc. § The PNS has two efferent components: the motor system and the autonomic nervous system § Motor system carries signals to skeletal muscles and is voluntary § Autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary © 2014 Pearson Education, Inc. § The autonomic nervous system has sympathetic and parasympathetic divisions § Sympathetic division regulates arousal and energy generation (“fight-or-flight” response) § Parasympathetic division has antagonistic effects on target organs and promotes calming and a return to “rest and digest” functions © 2014 Pearson Education, Inc. Figure 49.9 Parasympathetic division Sympathetic division Constricts pupil of eye Dilates pupil of eye Stimulates salivary gland secretion Inhibits salivary gland secretion Constricts bronchi in lungs Cervical Sympathetic ganglia Relaxes bronchi in lungs Slows heart Accelerates heart Stimulates activity of stomach and intestines Inhibits activity of stomach and intestines Stimulates activity of pancreas Thoracic Inhibits activity of pancreas Stimulates glucose release from liver; inhibits gallbladder Stimulates gallbladder Lumbar Stimulates adrenal medulla Promotes emptying of bladder Promotes erection of genitalia © 2014 Pearson Education, Inc. Inhibits emptying of bladder Sacral Synapse Promotes ejaculation and vaginal contractions The vertebrate brain is regionally specialized § Brain structures are specialized for diverse functions § Forebrain has activities including processing olfactory input, regulating sleep, learning § Midbrain coordinates routing of sensory input § Hindbrain controls involuntary activities, coordinates motor activities © 2014 Pearson Education, Inc. § Comparison of vertebrates shows that relative sizes of particular brain regions vary § These size differences reflect the relative importance of the particular brain function § Evolution has resulted in a close match between structure and function Lamprey ANCESTRAL VERTEBRATE Shark Ray-finned fish Amphibian Crocodilian Key Forebrain Midbrain Hindbrain © 2014 Pearson Education, Inc. Bird Mammal Figure 49.11b Embryonic brain regions Brain structures in child and adult Telencephalon Cerebrum (includes cerebral cortex, basal nuclei) Diencephalon Diencephalon (thalamus, hypothalamus, epithalamus) Forebrain Midbrain Mesencephalon Midbrain (part of brainstem) Metencephalon Pons (part of brainstem), cerebellum Myelencephalon Medulla oblongata (part of brainstem) Hindbrain Cerebrum Mesencephalon Metencephalon Midbrain Hindbrain Embryo at 1 month © 2014 Pearson Education, Inc. Diencephalon Myelencephalon Midbrain Pons Medulla oblongata Telencephalon Cerebellum Spinal cord Embryo at 5 weeks Spinal cord Child Brainstem Forebrain Diencephalon Arousal and Sleep § The brainstem and cerebrum control arousal and sleep; sleep also regulated by biological clock § Sleep is essential for learning and memory § Some animals have evolutionary adaptations allowing substantial activity during sleep § Dolphins sleep with one brain hemisphere at a time and are therefore able to swim while “asleep” © 2014 Pearson Education, Inc. Biological Clock Regulation § Cycles of sleep and wakefulness are examples of circadian rhythms, daily cycles of biological activity § Such rhythms rely on a biological clock, a molecular mechanism that directs periodic gene expression and cellular activity § Biological clocks are typically synchronized to light and dark cycles © 2014 Pearson Education, Inc. Emotions § Generation and experience of emotions involve many brain structures- the amygdala, hippocampus, thalamus- grouped as the limbic system Thalamus Hypothalamus Olfactory bulb © 2014 Pearson Education, Inc. Amygdala Hippocampus The cerebral cortex controls voluntary movement and cognitive functions § The cerebrum, the largest structure in the human brain, is essential for language, cognition, memory, consciousness, and awareness of our surroundings Skeletal muscle control Sense of touch Frontal lobe Integration of sensory information Parietal lobe Decision making, planning Combining images and object recognition Forming speech Temporal lobe Occipital lobe Hearing © 2014 Pearson Education, Inc. Cerebellum Language comprehension Processing visual stimuli, pattern recognition Figure 49.18 Max Hearing words Seeing words Min Speaking words © 2014 Pearson Education, Inc. Generating words Lateralization of Function § The two hemispheres make distinct contributions to brain function § Left hemisphere more adept at language, math, logic § Right hemisphere stronger at facial and pattern recognition, spatial relations, nonverbal thinking § The two hemispheres work together by communicating through fibers of the corpus callosum © 2014 Pearson Education, Inc. Many nervous system disorders can be explained in molecular terms § Disorders of the nervous system include schizophrenia, depression, drug addiction, Alzheimer’s disease, Parkinson’s disease § Genetic and environmental factors contribute to diseases of the nervous system © 2014 Pearson Education, Inc. The Brain’s Reward System and Drug Addiction § Some drugs are addictive because they increase activity of the brain’s dopamine reward (“pleasure”) system § Cocaine, amphetamine, heroin, alcohol, and tobacco § Drug addiction is characterized by compulsive consumption and an inability to control intake § Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug © 2014 Pearson Education, Inc. Alzheimer’s Disease § Mental deterioration characterized by confusion and memory loss- caused by formation of neurofibrillary tangles and amyloid plaques in the brain § No cure for this disease- some drugs relieve symptoms Amyloid plaque © 2014 Pearson Education, Inc. Neurofibrillary tangle 20 µm Parkinson’s Disease § A motor disorder caused by death of dopaminesecreting neurons in the midbrain § Characterized by muscle tremors, flexed posture, and a shuffling gait § No cure, although drugs and various other approaches may manage symptoms © 2014 Pearson Education, Inc. Senses § The star-nosed mole can catch insect prey in near total darkness in as little as 120 milliseconds § Uses 11 pairs of appendages protruding from its nose to locate and capture prey § Sensory processes convey information about an animal’s environment to its brain; muscles carry out movements as instructed by the brain © 2014 Pearson Education, Inc. Sensory receptors transduce stimulus energy and transmit signals to the CNS § All stimuli represent forms of energy § When a stimulus’s input to the nervous system is processed, a motor response may be generated § May involve a simple reflex or elaborate processing © 2014 Pearson Education, Inc. Mole forages along tunnel Mole moves on Food absent OR Mole bites Food present Sensory input Integration Motor output § Sensory pathways have four basic functions in common: § Sensory reception- detection of stimuli by sensory receptors § Transduction- conversion of stimulus energy; magnitude varies with stimuli intensity § Transmission- to the CNS § Integration- brain distinguishes stimuli from different receptors based on where they arrive in the brain © 2014 Pearson Education, Inc. Types of Sensory Receptors § Based on energy transduced, sensory receptors fall into five categories § Mechanoreceptors § Chemoreceptors § Electromagnetic receptors § Thermoreceptors § Pain receptors © 2014 Pearson Education, Inc. Hearing and Equilibrium in Mammals § In most terrestrial vertebrates, sensory organs for hearing and equilibrium are closely associated in the ear § For both senses, settling particles or moving fluid is detected by mechanoreceptors Ciliated receptor cells Cilia Statolith Sensory nerve fibers (axons) © 2014 Pearson Education, Inc. The statocyst is used to sense equilibrium Hearing § Vibrating objects create percussion waves in air, causing tympanic membrane vibration Sensory neurons § The three bones of the middle ear transmit vibrations of moving air to the cochlea § Vibrations create pressure waves in fluid in the cochlea that travel through the vestibular canal © 2014 Pearson Education, Inc. Cochlea Tympanic membrane Hearing § The ear conveys information about § Volume- the amplitude of the sound wave § Pitch- the frequency of the sound wave © 2014 Pearson Education, Inc. Hearing and Equilibrium in Other Vertebrates § Unlike mammals, fishes have only inner ears (near the brain) § Fishes also have a lateral line system that contains mechanoreceptors with hair cells to detect water movement SURROUNDING WATER Lateral line epidermis Side view Lateral line Top view Lateral line canal Water flow Opening of lateral line canal Cross section Nerve Lateral nerve FISH BODY WALL Scale Segmental muscle Water flow Cupula © 2014 Pearson Education, Inc. Supporting cell Nerve fiber Action potentials Sensory hairs Hair cell Diverse visual receptors of animals depend on light-absorbing pigments § Animals use diverse organs for vision, but the underlying mechanism for capturing light is the same, suggesting a common evolutionary origin § Light detectors range from simple clusters of cells that detect direction and intensity of light, to complex organs that form images § Light detectors all contain photoreceptors, cells that contain light-absorbing pigment molecules © 2014 Pearson Education, Inc. Light-Detecting Organs § Most invertebrates have a light-detecting organ § One of the simplest light-detecting organs is that of planarians § A pair of ocelli called eyespots are located near the head § These allow planarians to move away from light and seek shaded locations © 2014 Pearson Education, Inc. Compound Eyes § Insects and crustaceans have compound eyes, which consist of up to several thousand light detectors called ommatidia § Compound eyes are effective at detecting movement § Insects have excellent color vision, and some can see into the ultraviolet range © 2014 Pearson Education, Inc. Single-Lens Eyes § Among invertebrates, single-lens eyes are found in some jellies, polychaetes, spiders, and molluscs § Work like a camera- iris changes the pupil diameter to control how much light enters § Eyes of all vertebrates have a single lens- eye detects color and light, but brain assembles information and perceives an image © 2014 Pearson Education, Inc. Figure 50.17a Retina Choroid Sclera Photoreceptors Retina Suspensory ligament Fovea Neurons Rod Cone Cornea Iris Optic nerve Pupil Aqueous humor Lens Vitreous humor Optic disk Central artery and vein of the retina Optic nerve fibers © 2014 Pearson Education, Inc. Horizontal Amacrine cell cell Bipolar Ganglion cell cell Pigmented epithelium Color Vision § Among vertebrates, most fish, amphibians, and reptiles, including birds, have good color vision § In humans, perception of color is based on three types of cones (photoreceptors), each with a different visual pigment: red, green, or blue § Mammals that are nocturnal usually have a high proportion of rods (photoreceptors that differentiate objects in low light) in the retina © 2014 Pearson Education, Inc. § Abnormal color vision results from alterations in the genes for one or more photopsin proteins § In 2009, researchers studying color blindness in squirrel monkeys made a breakthrough in gene therapy © 2014 Pearson Education, Inc. The senses of taste and smell rely on similar sets of sensory receptors § In terrestrial animals, § Gustation (taste) is dependent on the detection of chemicals called tastants; In mammals, there are five taste perceptions: sweet, sour, salty, bitter, umami § Olfaction (smell) is dependent on the detection of odorant molecules § In aquatic animals there is no distinction between taste and smell § Taste receptors of insects are in sensory hairs located on feet and in mouth parts © 2014 Pearson Education, Inc. The physical interaction of protein filaments is required for muscle function Muscle § Muscle activity is a response to input from the nervous system § Vertebrate skeletal muscle moves bones and the body Bundle of muscle fibers Nuclei Single muscle fiber (cell) Plasma membrane § Glycolysis and aerobic respiration generate the energy (ATP) needed to sustain muscle contraction © 2014 Pearson Education, Inc. Myofibril § Amyotrophic lateral sclerosis (ALS), formerly called Lou Gehrig’s disease, interferes with the excitation of skeletal muscle fibers; this disease is usually fatal © 2014 Pearson Education, Inc. Nervous 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 © 2014 Pearson Education, Inc. Figure 50.31 Spinal cord Motor unit 1 Motor unit 2 Synaptic terminals Nerve Motor neuron cell body Motor neuron axon Muscle Muscle fibers Tendon © 2014 Pearson Education, Inc. Other Types of Muscle § In addition to skeletal muscle, vertebrates have cardiac muscle and smooth muscle § Cardiac muscle, found only in the heart, consists of striated cells electrically connected by intercalated disks § Smooth muscle is found mainly in walls of hollow organs such as those of the digestive tract § 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 © 2014 Pearson Education, Inc. Skeletal systems transform muscle contraction into locomotion Human forearm (internal skeleton) § Skeletons function in support, protection, and movement Flexor muscle Triceps Extension Biceps Triceps © 2014 Pearson Education, Inc. Extensor muscle Flexion § The skeleton provides a rigid structure to which muscles attach Biceps Grasshopper tibia (external skeleton) Key Contracting muscle Extensor muscle Flexor muscle Relaxing muscle Types of Skeletal Systems § The three main types of skeletons are § Hydrostatic skeletons (lack hard parts) § Exoskeletons (external hard parts) § Endoskeletons (internal hard parts) © 2014 Pearson Education, Inc. § The skeletons of small and large animals have different proportions, underlying function § In mammals and birds, the position of legs relative to the body is very important in determining how much weight the legs can bear © 2014 Pearson Education, Inc. Types of Locomotion § Most animals are capable of locomotion- active travel from place to place § In locomotion, energy is expended to overcome friction and gravity © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. § Air poses relatively little resistance for land locomotion § Maintaining balance is a prerequisite to walking, running, or hopping § Crawling poses a different challenge; a crawling animal must exert more energy to overcome friction © 2014 Pearson Education, Inc. Swimming § In water, friction is a bigger problem than gravity § Fast swimmers usually have a sleek, torpedo-like shape to minimize friction § Animals swim in diverse ways § Paddling with their legs as oars § Jet propulsion § Undulating their body and tail from side to side, or up and down © 2014 Pearson Education, Inc. Flying § Active flight requires that wings develop enough lift to overcome the downward force of gravity § Many flying animals have adaptations that reduce body mass § Ex: birds have no urinary bladder or teeth, and have relatively large bones with air-filled regions © 2014 Pearson Education, Inc. Energy cost (cal/kg ・ m) (log scale) Figure 50.UN01a Flying Running 102 10 1 Swimming 10-1 10-3 © 2014 Pearson Education, Inc. 1 103 Body mass (g) (log scale) 106