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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 49 Nervous Systems Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Overview: Command and Control Center • The human brain contains about 100 billion neurons, organized into circuits more complex than the most powerful supercomputers • A recent advance in brain exploration involves a method for expressing combinations of colored proteins in brain cells, a technique called “brainbow” • This may allow researchers to develop detailed maps of information transfer between regions of the brain © 2011 Pearson Education, Inc. Figure 49.1 Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells • Each single-celled organism can respond to stimuli in its environment • Animals are multicellular and most groups respond to stimuli using systems of neurons © 2011 Pearson Education, Inc. • The simplest animals with nervous systems, the cnidarians, have neurons arranged in nerve nets • A nerve net is a series of interconnected nerve cells • More complex animals have nerves © 2011 Pearson Education, Inc. • Nerves are bundles that consist of the axons of multiple nerve cells • Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring © 2011 Pearson Education, Inc. Figure 49.2 Radial nerve Nerve net Nerve ring Eyespot Brain Nerve cords Transverse nerve Brain Ventral nerve cord Segmental ganglia (a) Hydra (cnidarian) (b) Sea star (echinoderm) (c) Planarian (flatworm) (d) Leech (annelid) Brain Brain Ventral nerve cord Segmental ganglia (e) Insect (arthropod) Ganglia Anterior nerve ring Brain Longitudinal nerve cords Ganglia (f) Chiton (mollusc) (g) Squid (mollusc) Spinal cord (dorsal nerve cord) (h) Salamander (vertebrate) Sensory ganglia Figure 49.2a Radial nerve Nerve net (a) Hydra (cnidarian) Nerve ring (b) Sea star (echinoderm) • Bilaterally symmetrical animals exhibit cephalization, the clustering of sensory organs at the front end of the body • Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS) • The CNS consists of a brain and longitudinal nerve cords © 2011 Pearson Education, Inc. Figure 49.2b Eyespot Brain Brain Nerve cords Ventral nerve cord Transverse nerve Segmental ganglia (c) Planarian (flatworm) (d) Leech (annelid) • Annelids and arthropods have segmentally arranged clusters of neurons called ganglia © 2011 Pearson Education, Inc. Figure 49.2c Ganglia Brain Ventral nerve cord Segmental ganglia (e) Insect (arthropod) Anterior nerve ring Longitudinal nerve cords (f) Chiton (mollusc) • Nervous system organization usually 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 © 2011 Pearson Education, Inc. Figure 49.2d Brain Brain Ganglia (g) Squid (mollusc) Spinal cord (dorsal nerve cord) Sensory ganglia (h) Salamander (vertebrate) • In vertebrates – The CNS is composed of the brain and spinal cord – The peripheral nervous system (PNS) is composed of nerves and ganglia © 2011 Pearson Education, Inc. Organization of the Vertebrate Nervous System • The spinal cord conveys information from and to the brain • The spinal cord also produces reflexes independently of the brain • A reflex is the body’s automatic response to a stimulus – For example, a doctor uses a mallet to trigger a knee-jerk reflex © 2011 Pearson Education, Inc. Figure 49.3 Quadriceps muscle Cell body of sensory neuron in dorsal root ganglion Gray matter White matter Hamstring muscle Spinal cord (cross section) Sensory neuron Motor neuron Interneuron • Invertebrates usually have a ventral nerve cord while vertebrates have a dorsal spinal cord • The spinal cord and brain develop from the embryonic nerve cord • The nerve cord gives rise to the central canal and ventricles of the brain © 2011 Pearson Education, Inc. Figure 49.4 Central nervous system (CNS) Brain Peripheral nervous system (PNS) Cranial nerves Spinal cord Ganglia outside CNS Spinal nerves Figure 49.5 Gray matter White matter Ventricles • The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid • The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord as well as to provide nutrients and remove wastes © 2011 Pearson Education, Inc. • The brain and spinal cord contain – Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons – White matter, which consists of bundles of myelinated axons © 2011 Pearson Education, Inc. Glia • Glia have numerous functions to nourish, support, and regulate neurons – Embryonic radial glia form tracks along which newly formed neurons migrate – Astrocytes induce cells lining capillaries in the CNS to form tight junctions, resulting in a blood-brain barrier and restricting the entry of most substances into the brain © 2011 Pearson Education, Inc. Figure 49.6 CNS PNS Neuron VENTRICLE Cilia Astrocyte Oligodendrocyte Schwann cell Microglial cell Ependymal cell 50 m Capillary LM Figure 49.6a CNS PNS Neuron VENTRICLE Cilia Astrocyte Oligodendrocyte Schwann cell Microglial cell Capillary Ependymal cell 50 m Figure 49.6b LM 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 © 2011 Pearson Education, Inc. • The PNS has two efferent components: the motor system and the autonomic nervous system • The motor system carries signals to skeletal muscles and is voluntary • The autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary © 2011 Pearson Education, Inc. Figure 49.7 Central Nervous System (information processing) Peripheral Nervous System Efferent neurons Afferent neurons Sensory receptors Autonomic nervous system Motor system Control of skeletal muscle Internal and external stimuli Sympathetic Parasympathetic Enteric division division division Control of smooth muscles, cardiac muscles, glands • The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions • The sympathetic division regulates arousal and energy generation (“fight-or-flight” response) • The parasympathetic division has antagonistic effects on target organs and promotes calming and a return to “rest and digest” functions © 2011 Pearson Education, Inc. • The enteric division controls activity of the digestive tract, pancreas, and gallbladder © 2011 Pearson Education, Inc. Figure 49.8 Sympathetic division Parasympathetic division Action on target organs: Action on target organs: 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 Thoracic Stimulates activity of pancreas Inhibits activity of pancreas Stimulates gallbladder Stimulates glucose release from liver; inhibits gallbladder Lumbar Stimulates adrenal medulla Promotes emptying of bladder Promotes erection of genitalia Inhibits emptying of bladder Sacral Synapse Promotes ejaculation and vaginal contractions Figure 49.8a Parasympathetic division Sympathetic division Action on target organs: Action on target organs: Constricts pupil of eye Dilates pupil of eye Stimulates salivary gland secretion Inhibits salivary gland secretion Constricts bronchi in lungs Slows heart Stimulates activity of stomach and intestines Stimulates activity of pancreas Stimulates gallbladder Cervical Sympathetic ganglia Figure 49.8b Parasympathetic division Sympathetic division Relaxes bronchi in lungs Accelerates heart Inhibits activity of stomach and intestines Thoracic Inhibits activity of pancreas Stimulates glucose release from liver; inhibits gallbladder Lumbar Stimulates adrenal medulla Promotes emptying of bladder Promotes erection of genitalia Inhibits emptying of bladder Sacral Synapse Promotes ejaculation and vaginal contractions Concept 49.2: The vertebrate brain is regionally specialized • Specific brain structures are particularly specialized for diverse functions • These structures arise during embryonic development © 2011 Pearson Education, Inc. Figure 49.9a Figure 49.9b Brain structures in child and adult Embryonic brain regions Telencephalon Cerebrum (includes cerebral cortex, white matter, 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 Midbrain Hindbrain Metencephalon Diencephalon Diencephalon Midbrain Myelencephalon Pons Medulla oblongata Spinal cord Forebrain Telencephalon Embryo at 1 month Embryo at 5 weeks Cerebellum Spinal cord Child Figure 49.9ba Mesencephalon Metencephalon Midbrain Hindbrain Diencephalon Myelencephalon Spinal cord Forebrain Telencephalon Embryo at 1 month Embryo at 5 weeks Figure 49.9bb Cerebrum Diencephalon Midbrain Pons Medulla oblongata Cerebellum Spinal cord Child Figure 49.9c Left cerebral hemisphere Right cerebral hemisphere Cerebral cortex Corpus callosum Cerebrum Basal nuclei Cerebellum Adult brain viewed from the rear Figure 49.9d Diencephalon Thalamus Pineal gland Hypothalamus Brainstem Midbrain Pituitary gland Pons Medulla oblongata Spinal cord Arousal and Sleep • The brainstem and cerebrum control arousal and sleep • The core of the brainstem has a diffuse network of neurons called the reticular formation • This regulates the amount and type of information that reaches the cerebral cortex and affects alertness • The hormone melatonin is released by the pineal gland and plays a role in bird and mammal sleep cycles © 2011 Pearson Education, Inc. Figure 49.10 Eye Reticular formation Input from touch, pain, and temperature receptors Input from nerves of ears • Sleep is essential and may play a role in the consolidation of learning and memory • Dolphins sleep with one brain hemisphere at a time and are therefore able to swim while “asleep” © 2011 Pearson Education, Inc. Figure 49.11 Key Low-frequency waves characteristic of sleep High-frequency waves characteristic of wakefulness Location Left hemisphere Right hemisphere Time: 0 hours Time: 1 hour Biological Clock Regulation • Cycles of sleep and wakefulness are examples of circadian rhythms, daily cycles of biological activity • Mammalian circadian rhythms rely on a biological clock, molecular mechanism that directs periodic gene expression • Biological clocks are typically synchronized to light and dark cycles © 2011 Pearson Education, Inc. • In mammals, circadian rhythms are coordinated by a group of neurons in the hypothalamus called the suprachiasmatic nucleus (SCN) • The SCN acts as a pacemaker, synchronizing the biological clock © 2011 Pearson Education, Inc. RESULTS Wild-type hamster Wild-type hamster with SCN from hamster Circadian cycle period (hours) Figure 49.12 hamster hamster with SCN from wild-type hamster 24 23 22 21 20 19 Before procedures After surgery and transplant Emotions • Generation and experience of emotions involve many brain structures including the amygdala, hippocampus, and parts of the thalamus • These structures are grouped as the limbic system • The limbic system also functions in motivation, olfaction, behavior, and memory © 2011 Pearson Education, Inc. Figure 49.13 Thalamus Hypothalamus Olfactory bulb Amygdala Hippocampus • Generation and experience of emotion also require interaction between the limbic system and sensory areas of the cerebrum • The structure most important to the storage of emotion in the memory is the amygdala, a mass of nuclei near the base of the cerebrum © 2011 Pearson Education, Inc. Figure 49.14 Nucleus accumbens Happy music Amygdala Sad music Figure 49.14a Nucleus accumbens Happy music Figure 49.14b Amygdala Sad music Concept 49.3: The cerebral cortex controls voluntary movement and cognitive functions • The cerebrum, the largest structure in the human brain, is essential for awareness, language, cognition, memory, and consciousness • Four regions, or lobes (frontal, temporal, occipital, and parietal), are landmarks for particular functions © 2011 Pearson Education, Inc. Figure 49.15 Frontal lobe Motor cortex (control of skeletal muscles) Somatosensory cortex (sense of touch) Parietal lobe Prefrontal cortex (decision making, planning) Sensory association cortex (integration of sensory information) Visual association cortex (combining images and object recognition) Broca’s area (forming speech) Temporal lobe Occipital lobe Auditory cortex (hearing) Wernicke’s area (comprehending language) Cerebellum Visual cortex (processing visual stimuli and pattern recognition) Language and Speech • Studies of brain activity have mapped areas responsible for language and speech • Broca’s area in the frontal lobe is active when speech is generated • Wernicke’s area in the temporal lobe is active when speech is heard • These areas belong to a larger network of regions involved in language © 2011 Pearson Education, Inc. Figure 49.16 Max Hearing words Seeing words Min Speaking words Generating words Lateralization of Cortical Function • The two hemispheres make distinct contributions to brain function • The left hemisphere is more adept at language, math, logic, and processing of serial sequences • The right hemisphere is stronger at pattern recognition, nonverbal thinking, and emotional processing © 2011 Pearson Education, Inc. • The differences in hemisphere function are called lateralization • Lateralization is partly linked to handedness • The two hemispheres work together by communicating through the fibers of the corpus callosum © 2011 Pearson Education, Inc. Information Processing • The cerebral cortex receives input from sensory organs and somatosensory receptors • Somatosensory receptors provide information about touch, pain, pressure, temperature, and the position of muscles and limbs • The thalamus directs different types of input to distinct locations © 2011 Pearson Education, Inc. • Adjacent areas process features in the sensory input and integrate information from different sensory areas • Integrated sensory information passes to the prefrontal cortex, which helps plan actions and movements • In the somatosensory cortex and motor cortex, neurons are arranged according to the part of the body that generates input or receives commands © 2011 Pearson Education, Inc. Figure 49.17 Frontal lobe Parietal lobe Jaw Tongue Leg Hip Trunk Neck Head Knee Hip Genitalia Toes Tongue Pharynx Primary motor cortex Abdominal organs Primary somatosensory cortex Figure 49.17a Knee Hip Toes Jaw Tongue Primary motor cortex Figure 49.17b Leg Hip Trunk Neck Head Genitalia Tongue Pharynx Abdominal organs Primary somatosensory cortex Frontal Lobe Function • Frontal lobe damage may impair decision making and emotional responses but leave intellect and memory intact • The frontal lobes have a substantial effect on “executive functions” © 2011 Pearson Education, Inc. Figure 49.UN01 Evolution of Cognition in Vertebrates • Previous ideas that a highly convoluted neocortex is required for advanced cognition may be incorrect • The anatomical basis for sophisticated information processing in birds (without a highly convoluted neocortex) appears to be the clustering of nuclei in the top or outer portion of the brain (pallium) © 2011 Pearson Education, Inc. Figure 49.18 Human brain Cerebrum (including cerebral cortex) Thalamus Midbrain Hindbrain Cerebellum Avian brain to scale Cerebrum (including pallium) Avian brain Cerebellum Hindbrain Thalamus Midbrain Concept 49.4 Changes in synaptic connections underlie memory and learning • Two processes dominate embryonic development of the nervous system – Neurons compete for growth-supporting factors in order to survive – Only half the synapses that form during embryo development survive into adulthood © 2011 Pearson Education, Inc. Neural Plasticity • Neural plasticity describes the ability of the nervous system to be modified after birth • Changes can strengthen or weaken signaling at a synapse © 2011 Pearson Education, Inc. Figure 49.19 N1 N1 N2 N2 (a) Synapses are strengthened or weakened in response to activity. (b) If two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses. Memory and Learning • The formation of memories is an example of neural plasticity • Short-term memory is accessed via the hippocampus • The hippocampus also plays a role in forming long-term memory, which is stored in the cerebral cortex • Some consolidation of memory is thought to occur during sleep © 2011 Pearson Education, Inc. Long-Term Potentiation • In the vertebrate brain, a form of learning called long-term potentiation (LTP) involves an increase in the strength of synaptic transmission • LTP involves glutamate receptors • If the presynaptic and postsynaptic neurons are stimulated at the same time, the set of receptors present on the postsynaptic membranes changes © 2011 Pearson Education, Inc. Figure 49.20 Ca2 PRESYNAPTIC NEURON Na Mg2 Glutamate NMDA receptor (open) NMDA receptor (closed) Stored AMPA receptor POSTSYNAPTIC NEURON (a) Synapse prior to long-term potentiation (LTP) 1 2 3 (b) Establishing LTP 3 1 2 Depolarization (c) Synapse exhibiting LTP 4 Action potential Figure 49.20a PRESYNAPTIC NEURON Glutamate Ca2 Na Mg2 NMDA receptor (open) POSTSYNAPTIC NEURON Stored AMPA receptor (a) Synapse prior to long-term potentiation (LTP) NMDA receptor (closed) Figure 49.20b Mg2 1 AMPA receptor NMDA receptor 3 2 Na Ca2 (b) Establishing LTP Figure 49.20c 3 1 AMPA receptor NMDA receptor 2 Depolarization (c) Synapse exhibiting LTP 4 Action potential Stem Cells in the Brain • The adult human brain contains neural stem cells • In mice, stem cells in the brain can give rise to neurons that mature and become incorporated into the adult nervous system • Such neurons play an essential role in learning and memory © 2011 Pearson Education, Inc. Figure 49.21 Concept 49.5: Nervous system disorders can be explained in molecular terms • Disorders of the nervous system include schizophrenia, depression, drug addiction, Alzheimer’s disease, and Parkinson’s disease • Genetic and environmental factors contribute to diseases of the nervous system © 2011 Pearson Education, Inc. Figure 49.22 Genes shared with relatives of person with schizophrenia 12.5% (3rd-degree relative) 25% (2nd-degree relative) 50% (1st-degree relative) 100% 40 30 20 Child Fraternal twin Identical twin Full sibling Parent Half sibling 0 Uncle/aunt Nephew/ niece Grandchild 10 Individual, general population First cousin Risk of developing schizophrenia (%) 50 Relationship to person with schizophrenia Schizophrenia • About 1% of the world’s population suffers from schizophrenia • Schizophrenia is characterized by hallucinations, delusions, and other symptoms • Available treatments focus on brain pathways that use dopamine as a neurotransmitter © 2011 Pearson Education, Inc. Depression • Two broad forms of depressive illness are known: major depressive disorder and bipolar disorder • In major depressive disorder, patients have a persistent lack of interest or pleasure in most activities • Bipolar disorder is characterized by manic (high-mood) and depressive (low-mood) phases • Treatments for these types of depression include drugs such as Prozac © 2011 Pearson Education, Inc. Drug Addiction and the Brain’s Reward System • The brain’s reward system rewards motivation with pleasure • Some drugs are addictive because they increase activity of the brain’s reward system • These drugs include cocaine, amphetamine, heroin, alcohol, and tobacco • Drug addiction is characterized by compulsive consumption and an inability to control intake © 2011 Pearson Education, Inc. • Addictive drugs enhance the activity of the dopamine pathway • Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug © 2011 Pearson Education, Inc. Figure 49.23 Nicotine stimulates dopaminereleasing VTA neuron. Inhibitory neuron Dopaminereleasing VTA neuron Opium and heroin decrease activity of inhibitory neuron. Cocaine and amphetamines block removal of dopamine from synaptic cleft. Cerebral neuron of reward pathway Reward system response Alzheimer’s Disease • Alzheimer’s disease is a mental deterioration characterized by confusion and memory loss • Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brain • There is no cure for this disease though some drugs are effective at relieving symptoms © 2011 Pearson Education, Inc. Figure 49.24 Amyloid plaque Neurofibrillary tangle 20 m Parkinson’s Disease • Parkinson’s disease is a motor disorder caused by death of dopamine-secreting neurons in the midbrain • It is characterized by muscle tremors, flexed posture, and a shuffling gait • There is no cure, although drugs and various other approaches are used to manage symptoms © 2011 Pearson Education, Inc. Figure 49.UN02 Brain Spinal cord (dorsal nerve cord) Sensory ganglia Nerve net Hydra (cnidarian) Salamander (vertebrate) Figure 49.UN03 CNS VENTRICLE Ependymal cell Cilia PNS Astrocyte Oligodendrocyte Schwann cells Capillary Neuron Microglial cell Figure 49.UN04 Cerebral cortex Cerebrum Forebrain Thalamus Hypothalamus Pituitary gland Midbrain Hindbrain Pons Medulla oblongata Cerebellum Spinal cord Figure 49.UN05