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CHAPTER 7 Functional Organization of Nervous Systems PowerPoint® Lecture Slides prepared by Stephen Gehnrich, Salisbury University Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview of the Nervous System One of the body’s homeostatic control systems Contains sensors, integrating centers, and output pathways More interneurons in a pathways greater number of interconnections and ability to integrate information Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview of the Nervous System Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.1 Cnidarians Most nervous systems are organized into three functional divisions Afferent sensory, integrating, and efferent motor Cnidarians are an exception Their nervous system is an interconnected web or nerve net Neurons are not specialized into different divisions Neurons carry action potentials in both directions Neurons are not specifically sensory or motor Organism can still perform complex behaviors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cnidarians Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.2a Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.2b Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Nervous System Terms Bilaterally symmetrical – right and left side are mirror images Cephalization – sense organs are concentrated at the anterior end Ganglia – groups of neuronal cell bodies Nuclei – groups of neuronal cell bodies within the brain Brain – an integrating center made up of clusters of nuclei Tracts – bundles of many axons within the CNS Nerve – a bundle of many axons outside of the CNS Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Structure of a Nerve Bundles of myelinated and unmyelinated axons enclosed in several layers of connective tissue Endoneurium – wraps each axon Perineurium – wraps a bundle (fascicle) of axons Epineurium – wraps the entire nerve Mixed nerves – contain both afferent and efferent neurons Each neuron is either afferent (sensory) or efferent (motor) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Structure of a Nerve Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.3 Nervous Systems Across Animal Groups Cephalization occurs in most animals and is more apparent in more complex nervous systems Cnidarians and Echinoderms are exceptions in that they lack cephalization Organisms with more complex nervous systems have more neurons; and therefore, more synapses Increased numbers of synapses allow for more integration of information, and more complex behaviors Since memories are stored in synapses, a complex nervous system also allows for a greater potential for learning Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Nervous Systems Across Animal Groups Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.4 The Vertebrate Central Nervous System High degree of cephalization Unique in having a hollow dorsal nerve cord (spinal cord) Part of the nervous system is encased within cartilage or bone Central nervous system (CNS) – brain and spinal cord Part of the nervous system extends to the periphery of the body Peripheral nervous system (PNS) – nerves outside of the CNS Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Vertebrate Central Nervous System Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.5a Cranial and Spinal Nerves Cranial nerves Exit directly from skull 13 pairs (labeled with roman numerals) Some afferent, some efferent, some mixed Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cranial Nerves Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cranial and Spinal Nerves Spinal nerves Branch from spinal cord Enter and exit between adjacent vertebrae Named based on region of vertebral column from which they emerge Cervical, thoracic, lumbar, sacral, and coccygeal Mixed nerves Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Atlas Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gray and White Matter Brain and spinal cord contain two types of tissue Gray matter – neuronal cell bodies White matter – tracts of axons and their myelin sheaths Spinal chord white matter on surface, gray matter inside Cerebral cortex gray matter on surface, white matter inside Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gray and White Matter Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.5b and Figure 7.10 The CNS Is Isolated and Protected Meninges Layers of connective tissue that surround brain and spinal cord Number of meninges vary across taxa (fish have one, mammals have three) Cerebral spinal fluid (CSF) Fills spaces within the CNS and acts as shock absorber Blood-brain barrier Tight junctions in brain capillary endothelium limit passage of solutes from bloodstream into the CSF Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The CNS Is Isolated and Protected Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.6 The Vertebrate Brain The brain is an extension of the spinal cord Nerve tracts extend between brain and spinal cord It has several cavities called ventricles that contain CSF Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Vertebrate Brain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.7 The Vertebrate Brain Three main regions Rhombencephalon (hindbrain) Reflexes and involuntary behaviors Mesencephalon (midbrain) Coordination of sensory information Relay center in mammals Prosencephalon (forebrain) Integration of olfactory information with other senses Regulation of body temperature, reproduction, eating, emotion Learning and memory in mammals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Brain Size and Morphology Most groups of vertebrates have the same major brain structures, although these structures vary in relative size Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.9 Brain Size and Morphology Mice Cat Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Human Brain Size Much of the variation due to body size Birds and mammals have larger brains than other vertebrates of same size Animals with large brains have more neurons More complex integrating centers and more behaviors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.8 Structure and function of the Mammalian Brain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 7.2 The Parts of the Mammalian Brain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 7.2 Hindbrain (Rhombencephalon) Three regions Pons – located above medulla Pathway between medulla, cerebellum, and forebrain Controls alertness, initiates sleep and dreaming Cerebellum – two hemispheres at back of brain Responsible for motor coordination Contains half of the neurons in the brain Medulla oblongata – located at top of spinal cord Regulates breathing, heart rate, diameter of blood vessels, blood pressure Contains pathways between spinal cord and brain Many cross over (e.g., left to right) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Vertebrate Brain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.7 Midbrain (Mesencephalon) Primary center for coordinating and initiating behavioral responses in fish and amphibians Size and function reduced in mammals Primarily serves as relay center between spinal cord and forebrain Sometimes grouped with the pons and medulla and termed the brainstem Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Forebrain (Prosencephalon) Involved in processing and integrating sensory information, and in coordinating behavior Main regions Cerebrum Thalamus Epithalamus Hypothalamus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cerebrum Outer layer is the cortex Divided into two cerebral hemispheres Left side controls right side of body Right side controls left side of body Neurons pass between the two sides via the corpus callosum Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.10 Hypothalamus Located at base of forebrain Under the thalamus Helps maintain homeostasis Body temperature, thirst, hunger, reproduction, etc. Interacts with autonomic nervous system Regulates secretion of pituitary hormones Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Limbic System A network of connected structures that lie between the cortex and the rest of the brain Influences emotions, motivation, memory Sometimes called the “emotional brain” Includes hypothalamus and other parts Amygdala – aggression and fear responses Hippocampus – converts short-term memory to longterm memory Olfactory bulbs – sense of smell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Limbic System Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.11 Thalamus and Epithalamus Thalamus Large grouping of gray matter above hypothalamus Part of the reticular formation Receives input from limbic system and all senses except olfaction Relays information to cortex Acts as a filter by blocking some afferent signals Epithalamus Located above the thalamus Pineal complex – Establishes circadian rhythms and secretes melatonin Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Vertebrate Brain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.7 Cortex Integrates and interprets sensory information and initiates voluntary movements Has taken over many of the midbrain functions of lower vertebrates Isocortex (outer layer) necessary for cognition and higher brain functions More folded in more advanced mammals Gyri (singular: gyrus) = folds Sulci (singular: sulcus) = grooves Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cortex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.12b Cortex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cortical Layers Six anatomically distinct layers Differ in shape and density of neurons Variable number of connections within each layer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.13 Cortical Lobes Lobes named according to their function or overlying bones of the skull Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.14a,b Topology of the Cerebral Cortex Each region of the cortex corresponds to a specific part of the body that it controls by motor output, or from which it receives sensory input Size of the brain region devoted to different parts of the body varies widely Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.? Topology of the Cerebral Cortex (somatosensory) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.15 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Association Areas of the Cerebrum Receive information from adjacent areas and further process and integrate the information Size of these areas is larger in animals with more complex behaviors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Peripheral Nervous System Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.16 Peripheral Nervous System Divisions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.16 Autonomic Nervous System “Involuntary nervous system” Involved in homeostasis Branches of the Autonomic Nervous System Sympathetic Most active during periods of stress or physical activity “Fight-or-flight” system Parasympathetic Most active during periods of rest “Resting and digesting” system Enteric Independent of other two systems Affects digestion by innervating the organs of the alimentary canal Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Maintaining Homeostasis Balancing of the sympathetic and parasympathetic systems Three mechanisms for regulating autonomic function Dual innervation Most organs receive input from both systems Antagonistic action One system stimulates while the other inhibits Basal tone Even under resting conditions autonomic neurons carry APs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Dual Innervation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.17 Antagonistic Action Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 7.3 Similarities in Autonomic Pathways Pathways contain two neurons in series Preganglionic May synapse with many postganglionic neurons and intrinsic neurons Postganglionic Neurotransmitter is released at the effector organ from varicosities The pre- and postganglionic neurons synapse with each other in the autonomic ganglia Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Similarities in Autonomic Pathways Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.18 Differences in Autonomic Pathways • Differences between the sympathetic (S) and parasympathetic (PS) branches Preganglionic cell body location S – thoracic and lumbar regions of spinal cord PS – hindbrain and sacral region of spinal cord Ganglia location S – chain that runs close to spinal cord PS – close to the effector Number of postganglionic neurons that synapse with a single preganglionic neuron S – ten or more P – three or fewer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Differences in Autonomic Pathways • Neurotransmitter released at the effector organ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.19 Only Sympathetic Innervation • Some effectors receive only sympathetic innervation Adrenal medulla Sweat glands Arrector pili muscles in the skin Kidneys Most blood vessels Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.20 Sympathetic vs. Parasympathetic Systems Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 7.4 Regulation of the Autonomic System Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.21 Autonomic Reflex Arcs Most autonomic changes occur via simple neural circuits that do not involve conscious centers of the brain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.22 Integrative Functions of Nervous Systems Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Animal Behaviors • Three categories Reflex behaviors Involuntary and simple Rhythmic behaviors Underlie locomotion, breathing, and the function of the heart Voluntary behaviors Most complex and diverse Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Reflex Arcs Least complex integrated responses Can involve as few as two neurons (monosynaptic) or more than two (polysynaptic) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.23 and Figure 7.25 Convergence and Divergence in Reflex Arcs • Neurons in reflex arcs can be arranged in two ways: Convergence – allows spatial summation Divergence – can amplify signals Some reflex arcs have both convergence and divergence Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.24 Rhythmic Behaviors Governed by pattern generators Groups of neurons that produce self-sustaining, rhythmic depolarizations Pacemaker cell A cell generates spontaneous depolarizations that control the firing of all the cells in the network Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Swimming Behavior in the Leech Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.26 Tetrapod Locomotion Involves pattern generators and reflexes The brainstem initiates the process and regulates speed The spinal cord acts as a pattern generator Afferent signals are sent back to the CNS The cortex is involved with guiding locomotion in complex environments The cerebellum coordinates locomotion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Tetrapod Locomotion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.27 Voluntary Movements Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.28 Learning and Memory Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Learning and Memory Most animals can learn and form memories due to the plasticity of the nervous system Learning Process of acquiring new information Memory Retention and retrieval of information Plasticity Changes in synaptic and neuronal function in response to stimuli Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Invertebrate Learning and Memory Well studied in the sea slug, Aplysia (~20,000 neurons) Habituation Decline in response to a stimulus after repeated exposure Allows animal to ignore unimportant stimuli and focus on novel stimuli Caused by changes in the presynaptic axon terminal Inactivation of Ca2+ channels neurotransmitter release Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Invertebrate Learning and Memory Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.29 Aplysia Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Invertebrate Learning and Memory Sensitization Increase in the response to a gentle stimulus after exposure to a strong stimulus Caused by changes in the presynaptic axon terminal Involves a secondary circuit Serotonin released by facilitating interneuron Binds to receptors Activation of G-proteins Inactivation of K+ channels AP duration Ca2+ influx neurotransmitter release by sensory neuron Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Invertebrate Learning and Memory Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.30 Mechanism of Serotonin’s Effects Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.31 Memory in Mammals Hippocampus involved in long-term memory, but memories are “stored” in cerebrum Memories are “stored” by increasing the efficiency of the synapse between two neurons Long-term potentiation (LTP) – repetitive stimulation of hippocampal tissue leads to an increase in the response of the postsynaptic neuron Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Long-term Potentiation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 7.32 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Somatic Motor Pathways • “Voluntary nervous system” Control of skeletal muscles Usually under conscious control Cerebrum Some pathways are not under conscious control, for example, knee-jerk reflex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Somatic Motor Pathway Characteristics Control only one type of effector, skeletal muscle Cell bodies of motor neurons are located in the CNS Monosynaptic Axons are very long, and extend all the way to the muscle Axon splits into a cluster of axon terminals at the neuromuscular junction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Somatic Motor Pathway Characteristics Release the neurotransmitter acetylcholine Synaptic cleft between the motor neuron and the muscle is very narrow Effect on the muscle cell always excitatory For example, causes depolarization and contraction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings