Slide 1 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 8 The Nervous System

Slide 2 Mosby items and derived items © 2012 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 Central nervous system (CNS)brain and spinal cord Peripheral nervous system (PNS)all nerves Peripheral nervous system (PNS)all nerves Autonomic nervous system (ANS) Autonomic nervous system (ANS)

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Slide 4 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CELLS OF THE NERVOUS SYSTEM Neurons Neurons Consist of three main partsdendrites; cell body of neuron; axon (Figure 8-2) Consist of three main partsdendrites; cell body of neuron; axon (Figure 8-2) Dendritesbranching projections that conduct impulses to cell body of neuron Dendritesbranching projections that conduct impulses to cell body of neuron Axonelongated projection that conducts impulses away from cell body of neuron Axonelongated projection that conducts impulses away from cell body of neuron Neurons classified according to function Neurons classified according to function Sensory (afferent) neuronsconduct impulses to the spinal cord and brain Sensory (afferent) neuronsconduct impulses to the spinal cord and brain Motor (efferent) neuronsconduct impulses away from brain and spinal cord to muscles and glands Motor (efferent) neuronsconduct impulses away from brain and spinal cord to muscles and glands Interneuronsconduct impulses from sensory neurons to motor neurons or among a network of interneurons; also known as central or connecting neurons Interneuronsconduct impulses from sensory neurons to motor neurons or among a network of interneurons; also known as central or connecting neurons

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Slide 6 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CELLS OF THE NERVOUS SYSTEM (cont.) Glia (neuroglia) Glia (neuroglia) Support cells, bringing the cells of nervous tissue together structurally and functionally Support cells, bringing the cells of nervous tissue together structurally and functionally Three main types of glial cells of the CNS (Figure 8-3) Three main types of glial cells of the CNS (Figure 8-3) Astrocytesstar-shaped cells that anchor small blood vessels to neurons Astrocytesstar-shaped cells that anchor small blood vessels to neurons Microgliasmall cells that move in inflamed brain tissue carrying on phagocytosis Microgliasmall cells that move in inflamed brain tissue carrying on phagocytosis Oligodendrocytesform myelin sheaths on axons in the CNS Oligodendrocytesform myelin sheaths on axons in the CNS Schwann cells form myelin sheaths on axons of the PNS (Figure 8-2) Schwann cells form myelin sheaths on axons of the PNS (Figure 8-2)

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Slide 8 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. NERVES AND TRACTS (Figure 8-4) Nervebundle of peripheral axons Nervebundle of peripheral axons Tractbundle of central axons Tractbundle of central axons White mattertissue composed primarily of myelinated axons (nerves or tracts) White mattertissue composed primarily of myelinated axons (nerves or tracts) Gray mattertissue composed primarily of cell bodies and unmyelinated fibers Gray mattertissue composed primarily of cell bodies and unmyelinated fibers Nerve coveringsfibrous connective tissue Nerve coveringsfibrous connective tissue Endoneuriumsurrounds individual fibers within a nerve Endoneuriumsurrounds individual fibers within a nerve Perineuriumsurrounds a group (fascicle) of nerve fibers Perineuriumsurrounds a group (fascicle) of nerve fibers Epineuriumsurrounds the entire nervea Epineuriumsurrounds the entire nervea

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Slide 10 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. 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) 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 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) Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons (Figure 8-5)

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Slide 12 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. NERVE IMPULSES Definitionself-propagating wave of electrical disturbance that travels along the surface of a neuron membrane (also called action potential) Definitionself-propagating wave of electrical disturbance that travels along the surface of a neuron membrane (also called action potential) Mechanism Mechanism At rest, the neuron's membrane is slightly positive on the outsidepolarizedfrom a slight excess of Na + on the outside At rest, the neuron's membrane is slightly positive on the outsidepolarizedfrom a slight excess of Na + on the outside A stimulus triggers the opening of Na + channels in the plasma membrane of the neuron A stimulus triggers the opening of Na + channels in the plasma membrane of the neuron Inward movement of Na + depolarizes the membrane by making the inside more positive than the outside at the stimulated point; this depolarization is a nerve impulse (action potential) Inward movement of Na + depolarizes the membrane by making the inside more positive than the outside at the stimulated point; this depolarization is a nerve impulse (action potential) The stimulated section of membrane immediately repolarizes, but by that time, the depolarization has already triggered the next section of membrane to depolarize, thus propagating a wave of electrical disturbances (depolarizations) all the way down the membrane The stimulated section of membrane immediately repolarizes, but by that time, the depolarization has already triggered the next section of membrane to depolarize, thus propagating a wave of electrical disturbances (depolarizations) all the way down the membrane

Slide 13 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. THE SYNAPSE Definitionthe place where impulses are transmitted from one neuron to another (the postsynaptic neuron) (Figure 8-7) Definitionthe place where impulses are transmitted from one neuron to another (the postsynaptic neuron) (Figure 8-7) Synapse made of three structuressynaptic knob, synaptic cleft, and plasma membrane Synapse made of three structuressynaptic knob, synaptic cleft, and plasma membrane Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse conduction by the membrane 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 neurotransmittersacetylcholine, catecholamines (norepinephrine, dopamine, and serotonin), endorphins, enkephalins, nitric oxide (NO), and other compounds Names of neurotransmittersacetylcholine, catecholamines (norepinephrine, dopamine, and serotonin), endorphins, enkephalins, nitric oxide (NO), and other compounds

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Slide 15 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM Divisions of the brain (Figure 8-9 and Table 8-1) Divisions of the brain (Figure 8-9 and Table 8-1) Brainstem Brainstem Consists of three parts of brain; named in ascending order: the medulla oblongata, pons, and midbrain Consists of three parts of brain; named in ascending order: the medulla oblongata, pons, and midbrain Structurewhite matter with bits of gray matter scattered through it Structurewhite matter with bits of gray matter scattered through it Functions Functions All three parts of brainstem conduct impulses to the higher parts of the brain All three parts of brainstem conduct impulses to the higher parts of the brain Sensory tracts in the brainstem conduct impulses to the higher parts of the brain 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 Motor tracts conduct from the higher parts of the brain to the spinal cord

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Slide 18 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM (cont.) Divisions of the brain (cont.) Divisions of the brain (cont.) Cerebellum Cerebellum Structure Structure Second largest part of the human brain Second largest part of the human brain Gray matter outer layer is thin but highly folded, forming a large surface area for processing information Gray matter outer layer is thin but highly folded, forming a large surface area for processing information Arbor vitaeinternal, treelike network of white matter tracts Arbor vitaeinternal, treelike network of white matter tracts Function Function Helps control muscle contractions to produce coordinated movements for maintaining balance, moving smoothly, and sustaining normal postures Helps control muscle contractions to produce coordinated movements for maintaining balance, moving smoothly, and sustaining normal postures Variety of additional coordinating effects, assisting the cerebrum and other regions of the brain Variety of additional coordinating effects, assisting the cerebrum and other regions of the brain

Slide 19 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM (cont.) Divisions of the brain (cont.) Divisions of the brain (cont.) Diencephalon Diencephalon Hypothalamus Hypothalamus Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter 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 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 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 Contains centers for controlling body temperature, appetite, wakefulness, and pleasure

Slide 20 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM (cont.) Divisions of the brain (cont.) Divisions of the brain (cont.) Diencephalon (cont.) Diencephalon (cont.) Thalamus Thalamus Dumbbell-shaped mass of gray matter extending toward each cerebral hemisphere Dumbbell-shaped mass of gray matter extending toward each cerebral hemisphere Relays sensory impulses to cerebral cortex sensory areas Relays sensory impulses to cerebral cortex sensory areas In some way produces the emotions of pleasantness or unpleasantness associated with sensations In some way produces the emotions of pleasantness or unpleasantness associated with sensations Pineal gland (pineal body) Pineal gland (pineal body) Small body resembling a pine nut behind the thalamus Small body resembling a pine nut behind the thalamus Adjusts output of time-keeping hormone melatonin in response to changing levels of external light (sunlight and moonlight) Adjusts output of time-keeping hormone melatonin in response to changing levels of external light (sunlight and moonlight)

Slide 21 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM (cont.) Divisions of the brain (cont.) Divisions of the brain (cont.) Cerebrum Cerebrum Largest part of the human brain Largest part of the human brain Outer layers of gray matter are the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons Outer layers of gray matter are 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 Interior of the cerebrum composed mainly of white matter Tractsnerve fibers arranged in bundles Tractsnerve fibers arranged in bundles Basal nucleiislands of gray matter regulate automatic movements and posture Basal nucleiislands of gray matter regulate automatic movements and posture Functions of the cerebrummental processes of all types including sensations, consciousness, memory, and voluntary control of movements Functions of the cerebrummental processes of all types including sensations, consciousness, memory, and voluntary control of movements

Slide 22 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM (cont.) Spinal cord (Figure 8-11) Spinal cord (Figure 8-11) Columns of white matter, composed of bundles of myelinated nerve fibers, form the outer portion of the H-shaped core of the spinal cord; bundles of axons called tracts Columns of white matter, composed of bundles of myelinated nerve fibers, form the outer portion of the H-shaped core of the spinal cord; bundles of axons called tracts Interior composed of gray matter made up mainly of neuron dendrites and cell bodies Interior composed of gray matter made up mainly of neuron dendrites and cell bodies Spinal cord tracts provide two-way conduction pathsascending and descending Spinal cord tracts provide two-way conduction pathsascending and descending Spinal cord functions as the primary center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain Spinal cord functions as the primary center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain

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Slide 24 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. CENTRAL NERVOUS SYSTEM (cont.) Coverings and fluid spaces of the brain and spinal cord Coverings and fluid spaces of the brain and spinal cord Coverings (Figure 8-13) Coverings (Figure 8-13) Cranial bones and vertebrae Cranial bones and vertebrae Cerebral and spinal meningesthe dura mater, the pia mater, and the arachnoid mater Cerebral and spinal meningesthe dura mater, the pia mater, and the arachnoid mater Fluid spaces Fluid spaces Subarachnoid spaces of meninges Subarachnoid spaces of meninges Central canal inside cord Central canal inside cord Ventricles in brain Ventricles in brain

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Slide 26 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. PERIPHERAL NERVOUS SYSTEM Cranial nerves (Figure 8-16 and Table 8-2) Cranial nerves (Figure 8-16 and Table 8-2) Twelve pairsattached to undersurface of the brain Twelve pairsattached to undersurface of the brain Connect brain with the neck and structures in the thorax and abdomen Connect brain with the neck and structures in the thorax and abdomen Spinal nerves Spinal nerves Thirty-one pairs contain dendrites of sensory neurons and axons of motor neurons Thirty-one pairs contain dendrites of sensory neurons and axons of motor neurons Conduct impulses necessary for sensations and voluntary movements Conduct impulses necessary for sensations and voluntary movements Dermatomeskin surface area supplied by a single cranial or spinal nerve Dermatomeskin surface area supplied by a single cranial or spinal nerve

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Slide 29 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM Functional anatomy Functional anatomy Autonomic nervous systemmotor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue; regulates the bodys automatic or involuntary functions (Figure 8-18) Autonomic nervous systemmotor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue; regulates the bodys automatic or involuntary functions (Figure 8-18) Autonomic neuronspreganglionic autonomic neurons conduct impulses from spinal cord or brainstem to an autonomic ganglion; postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue Autonomic neuronspreganglionic autonomic neurons conduct impulses from spinal cord or brainstem to an autonomic ganglion; postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue Autonomic or visceral effectorstissues to which autonomic neurons conduct impulses (i.e., cardiac and smooth muscle and glandular epithelial tissue) Autonomic or visceral effectorstissues to which autonomic neurons conduct impulses (i.e., cardiac and smooth muscle and glandular epithelial tissue) Composed of two divisionsthe sympathetic system and the parasympathetic system Composed of two divisionsthe sympathetic system and the parasympathetic system

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Slide 31 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM (cont.) Autonomic conduction paths 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) 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 In contrast, somatic motor neurons conduct all the way from the CNS to somatic effectors with no intervening synapses

Slide 32 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM (cont.) Sympathetic nervous system Sympathetic nervous system 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 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 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 A chain of sympathetic ganglia is in front of and at each side of the spinal column Functions of the sympathetic nervous system Functions of the sympathetic nervous system Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are triggered Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are triggered Group of changes induced by sympathetic control is called the fight-or-flight response Group of changes induced by sympathetic control is called the fight-or-flight response

Slide 33 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM (cont.) Parasympathetic nervous system Parasympathetic nervous system Structure 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 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 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 Each parasympathetic preganglionic neuron synapses with postganglionic neurons to only one effector Functiondominates control of many visceral effectors under normal, everyday conditions, counterbalances sympathetic function Functiondominates control of many visceral effectors under normal, everyday conditions, counterbalances sympathetic function

Slide 34 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. AUTONOMIC NERVOUS SYSTEM (cont.) Autonomic neurotransmitters Autonomic neurotransmitters Cholinergic fiberspreganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine Cholinergic fiberspreganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine Adrenergic fibersaxons of sympathetic postganglionic neurons release norepinephrine (noradrenaline) Adrenergic fibersaxons of sympathetic postganglionic neurons release norepinephrine (noradrenaline) Autonomic nervous system as a whole Autonomic nervous system as a whole Regulates the bodys automatic functions in ways that maintain or quickly restore homeostasis Regulates the bodys 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) 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)