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ANATOMY AND PHYSIOLOGY I SEMINAR 7 CHAPTER 8 THE NERVOUS SYSTEM RENITA K. HOLMES, MSN, RN KAPLAN UNIVERSITY THE NERVOUS SYSTEM The normal body must accomplish a gigantic and enormously complex job—keeping itself alive and healthy. Each one of its billions of cells performs some activity that is a part of this function. Control of the body’s billions of cells is accomplished in part by two body-wide communication systems: the nervous system and the endocrine system. Both systems transmit information from one part of the body to another, but they do it in different ways. Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 2 THE NERVOUS SYSTEM Nervous System Transmits information very rapidly by nerve impulses conducted from one body area to another. Endocrine System Transmits information more slowly by chemicals secreted by ductless glands into the bloodstream and circulated from the glands to other parts of the body. Slide 3 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. THE NERVOUS SYSTEM Nerve impulses and hormones communicate information to body structures, increasing or decreasing their activities as needed for healthy survival. Slide 4 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. THE NERVOUS SYSTEM The nervous system is a complex network of communication for the entire body. Chemical and electrical cell communication is rapid, specific, and almost immediate Following are the three nervous system integrated functions: 1. Sensory input is when and how information is gathered. 2. Integration is when the sensory input is deciphered. 3. Motor output is the response caused by this process. Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. ORGANS AND DIVISIONS OF THE NERVOUS SYSTEM (FIGURE 8-1) Central nervous system (CNS)—brain and spinal cord Peripheral nervous system (PNS)—all nerves Autonomic nervous system (ANS) Slide 6 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Divisions of the nervous system Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 7 CELLS OF THE NERVOUS SYSTEM Neurons Consist of three main parts Dendrites Cell body of neuron Axon Dendrites conduct impulses to cell body of neuron Axons conduct impulses away from cell body of neuron Slide 8 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. CELLS OF THE NERVOUS SYSTEM Neurons classified according to function Sensory (afferent) neurons: conduct impulses to the spinal cord and brain Motor (efferent) neurons: conduct impulses away from brain and spinal cord to muscles and glands Interneurons: conduct impulses from sensory neurons to motor neurons Slide 9 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. NEURON: DIAGRAM OF A TYPICAL NEURON SHOWING DENDRITES, A CELL BODY, AND AN AXON Slide 10 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. PHOTOMICROGRAPH OF A NEURON. Slide 11 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. CELLS OF THE NERVOUS SYSTEM Glia (neuroglia) Support cells, bringing the cells of nervous tissue together structurally and functionally Three main types of glial cells of the CNS (Figure 8-3) Astrocytes—star-shaped cells that anchor small blood vessels to neurons Microglia—small cells that move in inflamed brain tissue carrying on phagocytosis Oligodendrocytes—form myelin sheaths on axons in the CNS Schwann cells form myelin sheaths on axons of the PNS (Figure 8-2) Slide 12 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Glia: A: Astrocytes have extensions attached to blood vessels in the brain. B: Microglia within the central nervous system can enlarge and consume microbes by phagocytosis. C: Oligodendrocytes have extensions that form myelin sheaths around axons in the central nervous system. Slide 13 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. NERVES AND TRACTS Slide 14 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. NERVES AND TRACTS A nerve is a group of peripheral nerve fibers (axons) bundled together like the strands of a cable. Peripheral nerve fibers usually have a myelin sheath; because myelin is white, peripheral nerves often look white. Slide 15 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. NERVES AND TRACTS (FIGURE 8-4) Nerve—bundle of peripheral axons Tract—bundle of central axons White matter—tissue composed primarily of myelinated axons (nerves or tracts) Gray matter—tissue composed primarily of cell bodies and unmyelinated fibers Nerve coverings—fibrous connective tissue Endoneurium—surrounds individual fibers within a nerve Perineurium—surrounds a group (fascicle) of nerve fibers Epineurium—surrounds the entire nervea Slide 16 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. The nerve: Each nerve contains axons bundled into fascicles. A connective tissue called epineurium wraps the entire nerve. Perineurium surrounds each fascicle. Inset shows a scanning electron micrograph of a cross section of a nerve. Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 17 REFLEX ARCS Nerve impulses are conducted from receptors to effectors over neuron pathways or reflex arcs; conduction by a reflex arc results in a reflex (that is, contraction by a muscle or secretion by a gland) The simplest reflex arcs are two-neuron arcs— consisting of sensory neurons synapsing in the spinal cord with motor neurons Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons (Figure 8-5) Slide 18 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Patellar reflex. The neural pathway involved in the patellar (“knee-jerk”) reflex. Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 19 NERVE IMPULSES Definition—self-propagating wave of electrical disturbance that travels along the surface of a neuron membrane Mechanism A stimulus triggers the opening of Na+ channels in the plasma membrane of the neuron Inward movement of positive sodium ions leaves a slight excess of negative ions outside at a stimulated point; marks the beginning of a nerve impulse Slide 20 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. THE SYNAPSE Definition—chemical compounds released from axon terminals (of a presynaptic neuron) into a synaptic cleft Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse conduction by the membrane Names of neurotransmitters—acetylcholine, catecholamines (norepinephrine, dopamine, and serotonin), and other compounds Slide 21 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Components of a synapse. Diagram shows synaptic knob or axon terminal of presynaptic neuron, the plasma membrane of a postsynaptic neuron, and a synaptic cleft. On the arrival of an action potential at a synaptic knob, neurotransmitter molecules are released from vesicles in the knob into the synaptic cleft. The combining of neurotransmitter and receptor molecules in the plasma membrane of the postsynaptic neuron opens ion channels and thereby initiates impulse conduction in the postsynaptic neuron. Slide 22 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM Divisions of the brain (Figure 8-9 and Table 8-1) Brainstem Consists of three parts of brain; named in ascending order: the medulla oblongata, pons, and midbrain Structure—white matter with bits of gray matter scattered through it Function—gray matter in the brainstem functions as reflex centers (e.g., for heartbeat, respirations, and blood vessel diameter) Sensory tracts in the brainstem conduct impulses to the higher parts of the brain Motor tracts conduct from the higher parts of the brain to the spinal cord Slide 23 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 24 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Central Nervous System Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM Divisions of the brain (cont.) Diencephalon Structure and function of the hypothalamus Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter Acts as the major center for controlling the ANS; therefore, it helps control the functioning of most internal organs Controls hormone secretion by anterior and posterior pituitary glands; therefore, it indirectly helps control hormone secretion by most other endocrine glands Contains centers for controlling body temperature, appetite, wakefulness, and pleasure Structure and function of the thalamus Dumbbell-shaped mass of gray matter in each cerebral hemisphere Relays sensory impulses to cerebral cortex sensory areas In some way produces the emotions of pleasantness or unpleasantness associated with sensations Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 26 CENTRAL NERVOUS SYSTEM Divisions of the brain (cont.) Cerebellum Second largest part of the human brain Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain normal postures Cerebrum Largest part of the human brain Outer layer of gray matter is the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons Interior of the cerebrum composed mainly of white matter (that is, nerve fibers arranged in bundles called tracts) Functions of the cerebrum—mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements Slide 27 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM Spinal cord (Figure 8-11) Outer part is composed of white matter made up of many bundles of axons called tracts; interior composed of gray matter made up mainly of neuron dendrites and cell bodies Functions as the center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain Slide 28 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Spinal cord and spinal nerves. Inset is a dissection of the cervical segment of the spinal cord showing emerging cervical nerves. The spinal cord is viewed from behind (posterior aspect). Slide 29 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM Coverings and fluid spaces of the brain and spinal cord Coverings Cranial bones and vertebrae Cerebral and spinal meninges—the dura mater, the pia mater, and the arachnoid mater (Figure 8-13) Fluid spaces—subarachnoid spaces of meninges, central canal inside cord, and ventricles in brain (Figure 8-14) Slide 30 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Spinal cord The meninges, spinal nerves, and sympathetic trunk are visible. Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 31 Fluid spaces of the brain A: The ventricles highlighted within the brain in a left lateral view. B: The ventricles as seen from above. Slide 32 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. PERIPHERAL NERVOUS SYSTEM Cranial nerves (Figure 8-16 and Table 8-2) Twelve pairs—attached to undersurface of the brain Connect brain with the neck and structures in the thorax and abdomen Spinal nerves Structure—contain dendrites of sensory neurons and axons of motor neurons Functions—conduct impulses necessary for sensations and voluntary movements Slide 33 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Cranial nerves. View of the undersurface of the brain shows attachments of the cranial nerves. Slide 34 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Autonomic nervous system—motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue; regulates the body’s automatic or involuntary functions (Figure 8-18) Autonomic neurons—preganglionic autonomic neurons conduct from spinal cord or brainstem to an autonomic ganglion; postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue Slide 35 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Innervation of the major target organs by the autonomic nervous system. The sympathetic pathways are highlighted with orange, and the parasympathetic pathways are highlighted with green. Slide 36 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Autonomic or visceral effectors—tissues to which autonomic neurons conduct impulses (that is, cardiac and smooth muscle and glandular epithelial tissue) Composed of two divisions—the sympathetic system and the parasympathetic system Slide 38 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Autonomic Nervous System Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Autonomic conduction paths Consist of two-neuron relays (that is, preganglionic neurons from the central nervous system to autonomic ganglia, synapses, postganglionic neurons from ganglia to visceral effectors) In contrast, somatic motor neurons conduct all the way from the CNS to somatic effectors with no intervening synapses Slide 40 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Sympathetic nervous system Structure Dendrites and cell bodies of sympathetic preganglionic neurons are located in the gray matter of the thoracic and upper lumbar segments of the spinal cord Axons leave the spinal cord in the anterior roots of spinal nerves, extend to sympathetic or collateral ganglia, and synapse with several postganglionic neurons whose axons extend to spinal or autonomic nerves to terminate in visceral effectors A chain of sympathetic ganglia is in front of and at each side of the spinal column Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 41 AUTONOMIC NERVOUS SYSTEM Sympathetic nervous system Functions Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and strong emotions (anger, fear, hate, or anxiety) Group of changes induced by sympathetic control is called the fight-or-flight response Slide 42 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Parasympathetic nervous system Structure Parasympathetic preganglionic neurons have dendrites and cell bodies in the gray matter of the brainstem and the sacral segments of the spinal cord Parasympathetic preganglionic neurons terminate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors Each parasympathetic preganglionic neuron synapses with postganglionic neurons to only one effector Slide 43 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Parasympathetic nervous system Function—dominates control of many visceral effectors under normal, everyday conditions Slide 44 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Autonomic neurotransmitters Cholinergic fibers—preganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine Adrenergic fibers—axons of sympathetic postganglionic neurons release norepinephrine (noradrenaline) Slide 45 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Autonomic nervous system as a whole Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis Many visceral effectors are doubly innervated (that is, they receive fibers from parasympathetic and sympathetic divisions and are influenced in opposite ways by the two divisions) Slide 46 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM QUESTIONS? Slide 47 Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc.