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CHAPTER 25 The Nervous System © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-2 Learning Outcomes 25.1 Explain the difference between the central nervous system and the peripheral nervous system. 25.2 Describe the functions of the nervous system. 25.3 Describe the structure of a neuron. 25.4 Describe the function of a nerve impulse and how a nerve impulse is created. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-3 Learning Outcomes (cont.) 25.5 Describe the structure and function of a synapse. 25.6 Describe the function of the blood-brain barrier. 25.7 Describe the structure and functions of meninges. 25.8 Describe the structure and functions of the spinal cord. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-4 Learning Outcomes (cont.) 25.9 Describe the location and function of cerebrospinal fluid. 25.10 Define reflex and list the parts of a reflex arc. 25.11 List the major divisions of the brain and give the general functions of each. 25.12 Explain the functions of the cranial and spinal nerves. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-5 Learning Outcomes (cont.) 25.13 Describe the differences between the somatic nervous system and autonomic nervous system. 25.14 Explain the two divisions of the autonomic nervous system. 25.15 Describe the causes, signs and symptoms, and treatments of various diseases and disorders of the nervous system. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-6 Introduction • Highly complex system of two parts – Central nervous system (CNS) – Peripheral nervous system (PNS) • Controls all other organ systems and is important for maintaining balance within those systems Disorders are numerous and often difficult to diagnose and treat © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-7 General Functions of the NS • CNS – Brain – Spinal cord • PNS – Peripheral nerves – Two sections • Somatic nervous system (SNS) – Skeletal or voluntary muscles • Autonomic nervous system (ANS) – Automatic functions © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-8 General Functions (cont.) • Three types of neurons – Afferent or sensory nerves • Sensory information from environment or inside body to CNS for interpretation – Efferent or motor nerves • Impulses from CNS to PNS to allow for movement or action – Interneurons • Interpretive neurons between afferent and efferent nerves in the CNS © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-9 Apply Your Knowledge Match the following: ANSWER: B Somatic nervous system ___ A. Motor nerves C Autonomic nervous system B. Governs skeletal or voluntary ___ muscles A Afferent nerves ___ C. Governs respiratory and GI systems E Efferent nerves ___ D. Go-betweens or interpreters D Interneurons ___ E. Sensory nerves © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-10 Neuron Structure • Functional cells of NS • Transmit electrochemical messages called nerve impulses to – Other neurons – Effectors (muscles or glands) © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-11 Neuron Structure (cont.) • Neurons lose their ability to divide – If destroyed, not replaced • Neuralgia – Support cells for neurons that can divide – Astrocytes – anchor blood vessels to nerves – Microglia – act as phagocytes – Oligodendrocytes – assist with production of myelin sheath © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-12 Neuron Structure (cont.) Neurons have a cell body and processes called nerve fibers that extend from the cell body. Dendrites – short Receive nerve impulses for the neuron Axons – long Send nerve impulses away from the cell body © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-13 Neuron Structure (cont.) • White matter – axons with myelin sheath Dendrites Schwann cells Axon – Schwann cells • Wrap around some axons • Cell membranes contain myelin • Myelin insulates axons and enables axons to send nerve impulses more quickly • Gray matter – axons without myelin sheath © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-14 Apply Your Knowledge True or False: ANSWER: ___ F Effectors are neurons. They are the muscles or glands. F Neurons can reproduce. ___ Neurons cannot reproduce. T Astrocytes anchor blood vessels to nerve cells. ___ T Microglia act as phagocytes. ___ F Oligodendrocytes are reproductive cells. ___ They take part in myelin production. T Repolarization is the return to the resting state. ___ GOOD JOB! © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-15 Nerve Impulse • Membrane potential – Neuron cell membrane at rest is in a polarized state • • Inside of cell membrane is negative Outside of cell membrane is positive due to more Na+ and K+ – As Na+ and K+ move into the cell, the membrane becomes depolarized • • Inside becomes more positive Action potential (nerve impulse) is created – Repolarization occurs when K+ and later Na+ move to the outside of the cell membrane • Return of the cell to polarized (resting) state © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-16 Nerve Impulse (cont.) • Impulse travels down axon to synaptic knob – Vesicles or small sacs in synaptic knob • Produce chemicals called neurotransmitters – Neurotransmitters are released by synaptic knob • Allow impulse transmission to postsynaptic structures – Dendrites – Cell bodies – Axons of other neurons © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-17 Nerve Impulse (cont.) • Functions of neurotransmitters – Cause muscles to contract or relax – Cause glands to secrete products – Activate or inhibit neurons © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-18 Apply Your Knowledge What is the function of neurotransmitters? ANSWER: Neurotransmitters cause muscles to contract or relax, cause glands to secret products, activate neurons to send nerve impulses, or inhibit neurons from sending them. Right! © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-19 Central Nervous System • • Includes the spinal cord and brain Blood-brain barrier – Protects layers of the membranes of the CNS – Formed by tight capillaries • • Prevents unwanted substances from entering the CNS tissues Inflammation can make more permeable © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-20 Central Nervous System (cont.) • Meninges –protect brain and spinal cord – Dura mater • Tough outer layer – Arachnoid mater • Middle layer (web-like) – Pia mater • • • Innermost and most delicate Directly on top of brain and spinal cord Holds blood vessels on the surface of these structures © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-21 Central Nervous System (cont.) – Epidural space • Above dura mater – Subdural space • Below dura mater – Subarachnoid space • • • Between arachnoid mater and pia mater Contains cerebrospinal fluid (CSF) Cushions CNS © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-22 Spinal Cord • Slender structure continuous with the brain • Descends into the vertebral canal and ends around the level of the first or second lumbar vertebra • 31 spinal segments: – – – – – 8 cervical segments 12 thoracic segments 5 lumbar segments 5 sacral segments 1 coccygeal segment © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-23 Spinal Cord (cont.) Cervical enlargement Motor neurons that control muscles of the arms Lumbar enlargement Motor neurons that control muscles of the legs © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-24 Spinal Cord (cont.) • Gray matter – Inner tissue with darker color – Contains neuron cell bodies and their dendrites – Divisions are called horns – Central canal runs down the entire length of the spinal cord through the center of the gray matter Spinal Cord/Nerve © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-25 Spinal Cord (cont.) • White matter – Outer tissue – Contains myelinated axons – Divisions are called columns (funiculi) • Columns contain groups of axons called nerve tracts Spinal Cord/Nerve © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-27 Spinal Cord (cont.) • One function of the spinal cord is to carry sensory information to and from the brain • Ascending tracts – Carry sensory information up to the brain • Descending tracts – Carry motor information down from the brain to muscles and glands © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-28 Spinal Cord (cont.) • Reflexes – Another function of the spinal cord is to participate in reflexes – Reflex – a predictable, automatic response to stimuli Receptor Sensory Neurons Interneurons Effectors Motor Neurons © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-29 Brain • Four sections –Cerebrum –Diencephalon –Brain stem –Cerebellum © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-30 Cerebrum • • Largest section Two cerebral hemispheres – Connected by a thick bundle of nerve fibers called the corpus callosum – Longitudinal fissure between hemispheres • • Sulci – grooves on surface Gyri or convolutions – bumps of brain matter between sulci Brain © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-31 Cerebrum (cont.) • Lobes – Frontal • Motor areas for voluntary body movements Parietal Frontal – Parietal • Somatosensory – interprets sensations – Temporal • Auditory – interprets sounds – Occipital Temporal Occipital • Interprets what a person sees © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-32 Cerebrum (cont.) • Cortex – Outer layer – gray matter • Contains about 75% of all neurons – Inner layer – white matter – Functions • Ventricles – Interconnected cavities within the brain – Filled with CSF • Interpret sensory information • Initiate body movements • Stores memories and creates emotions © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-33 Diencephalon • Between the cerebral hemispheres superior to the brain stem • Thalamus – Relay station for sensory information going to the cerebral cortex for interpretation • Hypothalamus – Maintains homeostasis by regulating vital activities Brain © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-34 Brain Stem • • Connects the cerebrum to the spinal cord Midbrain – – • Just beneath diencephalon Controls both visual and auditory reflexes Pons – – – • Medulla oblongata – Inferior portion of brain stem – Directly connected to spinal cord – Controls many vital activities, such as heart rate, blood pressure, and breathing Rounded bulge on underside of brain stem Between midbrain and medulla oblongata Regulates respiration Brain © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-35 Cerebellum • Location – Inferior to the occipital lobes of the cerebrum – Posterior to the pons and medulla oblongata • Coordinates – Complex skeletal muscle contractions that are needed for body movements – Fine movements Brain © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-37 Preventing Brain and Spinal Cord Injuries • Wear appropriate protective gear for sports • Avoid diving into unknown waters • Always wear seat belts • Follow safety rules on playgrounds Children should be in car seats appropriate for age and weight Know how to get help quickly in emergencies Follow traffic rules and signs while walking, biking, or driving © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-38 SUPER! Apply Your Knowledge Match the following: ___ H Meninges A. Carry motor information from brain ___ D Ascending tracts B. Stores memories and creates emotions ___ A Descending tracts C. Grooves on the surface of the cerebrum ___ B Cerebral cortex D. Carry sensory information to the brain ___ F Hypothalamus E. Predictable, automatic response to stimuli ___ C Sulci F. Maintains homeostasis ___ G Cerebellum G. Coordinates skeletal muscle contractions ___ E Reflexes H. Protects the brain and spinal cord © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-39 Peripheral Nervous System • Nerves that branch off the CNS • Peripheral nerves – Two types: • Cranial nerves • Spinal nerves © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-40 Cranial Nerves I. Olfactory nerves – Carry smell information to the brain for interpretation II. Optic nerves – Carry visual information to the brain for interpretation III. Oculomotor nerves – Found within the muscles that move the eyeball, eyelid, and iris IV. Trochlear nerves – Act in the muscles that move the eyeball. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-41 Cranial Nerves (cont.) V. Trigeminal nerves – Carry sensory information from the surface of the eye, the scalp, facial skin, the lining of the gums, and the palate to the brain for interpretation – Also found within the muscles needed for chewing VI. Abducens nerves – Act in the muscles that move the eyeball © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-42 Cranial Nerves (cont.) VII. Facial nerves – Found in the muscles of facial expression as well as in the salivary and tear glands – Also carry sensory information from the tongue VIII. Vestibulocochlear nerves – Carry hearing and equilibrium information from the inner ear to the brain for interpretation © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-43 Cranial Nerves (cont.) IX. Glossopharyngeal nerves – Carry sensory information from the throat and tongue to the brain for interpretation – Also act in the muscles of the throat X. Vagus nerves – Carry sensory information from the thoracic and abdominal organs to the brain for interpretation – Also found within the muscles in the throat, stomach, intestines, and heart © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-44 Cranial Nerves (cont.) XI. Accessory nerves – Found within the muscles of the throat, neck, back, and voice box XII. Hypoglossal nerves – Found within the muscles of the tongue © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-45 Spinal Nerves • • Peripheral nerves originating from the spinal cord 31 pairs of spinal nerves – 8 pairs of cervical nerves (C1 through C8) – 12 pairs of thoracic nerves (T1 through T12) – 5 pairs of lumbar nerves (L1 through L5) – 5 pairs of sacral nerves (S1 through S5) – 1 pair of coccygeal nerves (C0) Spinal Nerves © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-46 Spinal Nerves (cont.) • Dermatome – Skin segment innervated by spinal nerve – C1 is not associated with a dermatome • Ventral root – Axons of motor neurons only • Dorsal root – Axons of sensory neurons only – Dorsal root ganglion • Contains cell bodies of sensory neurons © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-47 Spinal Nerves (cont.) • Main portions of spinal nerves fuse to form nerve plexuses – Cervical – supply skin and muscles of neck • Phrenic nerve originates from this plexus and controls the diaphragm – Brachial – control muscles in the arms – Lumbosacral – lower abdomen, external genitalia, buttocks, thighs, legs, and feet • Sciatic nerve originates from this plexus and controls muscles of legs Spinal Nerves © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-49 Somatic Nervous System • Nerves that connect the CNS to skin and skeletal muscle • “Voluntary” nervous system – Controls skeletal muscles, which are under voluntary control © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-50 Autonomic Nervous System • Nerves that connect the CNS to organs and other structures • “Involuntary” nervous system • Motor neurons located in ganglia – Neuron cell bodies outside the CNS © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-51 Autonomic Nervous System (cont.) • Sympathetic division – “Fight or flight” – Prepares body for stressful or emergency situations – Neurons release neurotransmitter norepinephrine • • • • Increases heart and breathing rates Slows down muscles of the stomach and intestines Dilates pupils Constricts blood vessels – increases blood pressure © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-52 Autonomic Nervous System (cont.) • Parasympathetic division – Prepares body for rest and digesting – Controls most of the body’s organs – Releases acetylcholine • Slows heart and breathing rates • Constricts pupils • Activates muscles of stomach and intestine – No communication with blood vessels • Sympathetic and parasympathetic divisions are antagonistic © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-53 Apply Your Knowledge What is the difference between the sympathetic and parasympathetic nervous systems? ANSWER: The sympathetic nervous system prepares the body for stress. It releases norepinephrine, causing an increase in heart and respiratory rate, slows down the GI system, and dilates pupils. The sympathetic system also controls constriction of blood vessels. The parasympathetic system prepares the body for resting and digesting. It releases acetylcholine, which slows heart and respiratory rates, constricts pupils, and stimulates the GI system. It has no effect on most blood vessels. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-54 Neurologic Testing • Typical neurologic examination – – – – State of consciousness Reflex activity Speech patterns Motor patterns © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-55 Diagnostic Procedures • Lumbar puncture • Magnetic resonance imaging (MRI) • • Positron emission tomography (PET) scan • Computerized tomography (CT) scan • Electroencephalogram (EEG) • X-ray Cerebral angiography © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-56 Cranial Nerve Tests • Olfactory nerves (Cranial nerve I) – Have patient smell various substances • Cranial nerves III, IV, and VI – Have patient track movement of finger • Cranial nerve V – Have patient clench teeth, feel jaw muscles © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-57 Cranial Nerve Tests (cont.) • Cranial nerve VII – Check patient’s facial expression • Cranial nerve XII – Have patient extend his tongue and move it from side to side © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-58 Reflex Testing • Areflexia – Absence of a reflex • Hyporeflexia – Decreased reflex • Hyperreflexia – Stronger-than-normal reflex © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-59 Reflex Testing (cont.) • Biceps reflex – Absence indicates spinal cord damage in the cervical region • Knee reflex – Absence may indicate damage to lumbar or femoral nerves • Abdominal reflexes – Used to evaluate damage to thoracic spinal nerves © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-60 Apply Your Knowledge Match the following: ANSWER: C State of consciousness ___ A Reflex activity ___ D Speech patterns ___ B Motor patterns ___ A. Determines the health of peripheral nerves B. Loss of balance, abnormal posture C. Stupor, delirium, vegetative D. Loss of ability to form words © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-61 Common Diseases and Disorders Disease/Disorder Description Alzheimer’s disease Progressive, degenerative disease of the brain Amyotrophic lateral sclerosis (ALS) Lou Gehrig’s disease Degeneration of neurons in the spinal cord and brain Bell’s palsy Weak or paralyzed facial muscles © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-62 Common Diseases and Disorders (cont.) Disease/Disorder Description Brain tumors and cancers Abnormal growths Can be primary or secondary tumors Most common – gliomas Epilepsy and seizures Occurs as a result of bursts of electrical signals that disrupt normal brain functioning Guillain-Barré Syndrome Body’s immune system attacks the PNS © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-63 Common Diseases and Disorders (cont.) Disease/Disorder Description Headaches Tension Migraines Cluster Episodic or chronic With aura/without aura Form of migraines; occurs in groups Meningitis Inflammation of meninges Multiple sclerosis (MS) Chronic disease of CNS Myelin is destroyed © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-64 Common Diseases and Disorders (cont.) Disease/Disorder Description Neuralgias Disorders causing nerve pain Parkinson’s disease Progressive and degenerative motor system disorder Sciatica Damage to sciatic nerve Stroke Brain cells die because of an inadequate blood flow; “brain attack” © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-65 Apply Your Knowledge True or false: ANSWER: Bravo! T Alzheimer’s disease is a progressive degenerative disease ___ of the brain. F Epilepsy is due to degenerative neurons in the spinal cord ___ and brain. Due to a burst of electrical signals that disrupt brain function. F Neuralgias are motor system disorders. ___ They are group of disorders referred to as nerve pain. T Stroke occurs when brain cells die because of inadequate ___ blood flow. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-66 In Summary 25.1 The central nervous system is composed of the brain and spinal cord. The peripheral nervous system consists of the peripheral nerves located throughout the body. The peripheral nervous system is further divided into two distinct systems: the somatic and autonomic nervous systems. 25.2 There are three separate types of neurons to carry out the functions of the nervous system. The afferent (sensory) nerves, the efferent (motor) nerves, and the interpretive interneurons that act as “interpreters” between the afferent and efferent nerves. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-67 In Summary (cont.) 25.3 All neurons are composed of a cell body, the shorter and more numerous dendrites that receive information for the cell body, and the longer axons that bring an impulse from the cell body to the dendrite of the next neuron. 25.4 The function of a nerve impulse is the sending of information either from the CNS to the PNS or vice versa. At rest, a neuron is said to be in a polarized state, and when it responds to stimuli, depolarization takes place. Repolarization occurs after the electrical current (impulse) has passed. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-68 In Summary (cont.) 25.5 A synapse is the space between the axon of one neuron and the dendrite of the next. At the end of each axon is the synaptic knob, which contains vesicles that produce neurotransmitters. These are released by the synaptic bulb to allow impulse transmission to continue to the next neuron. 25.6 The blood-brain barrier is a layer of tightly woven capillaries that protects the delicate tissues of the CNS. This barrier prevents certain substances, such as various waste products and drugs, from easily crossing this barrier and entering the brain tissues © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-69 In Summary (cont.) 25.7 The meninges, a triple-layered membrane protecting the brain and spinal cord, are composed of the following layers: The tough outer layer is the dura mater. The space between the cranium and the dura mater is called the epidural space. Below the dura mater is the subdural space. The middle layer is the arachnoid, and below it is the subarachnoid space, which contains cerebrospinal fluid (CSF). The innermost layer is the pia mater. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-70 In Summary (cont.) 25.8 The spinal cord is continuous with the brain and consists of 31 spinal segments: 8 cervical 5 sacral 12 thoracic 1 coccygeal 5 lumbar The basic function of the spinal cord is to carry sensory information from the body to the brain and motor information from the brain to the muscles and glands of the body. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-71 In Summary (cont.) 25.9 Cerebrospinal fluid (CSF) is located within the subarachnoid space of the brain and within the central canal of the spinal cord. It cushions the brain and spinal cord. 25.10 A reflex is a predictable automatic response to a stimulus. A typical reflex flows as follows: Sensory receptors send information (impulse) to the interneurons, which in turn send the information on to the effectors of the motor neurons, producing a response. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-72 In Summary (cont.) 25.11 The cerebrum is the largest part of the brain and is divided into two hemispheres subdivided into four lobes: frontal, parietal, temporal and occipital. The diencephalon contains the thalamus and hypothalamus. The brain stem consists of three parts: the midbrain, pons, and medulla oblongata. The cerebellum is the final area of the brain. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-73 In Summary (cont.) 25.12 Twelve cranial nerves carry sensory information: OlfactoryOptic Trochlear Facial Glossopharyngeal Oculomotor Trigeminal Vagus Accessory Abducens Vestibulocochlear Hypoglossal There are 31 pairs of spinal nerves, each except C1 innervating a dermatome. Refer to Figure 25.8 for a map of the spinal nerves. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-74 In Summary (cont.) 25.13 The somatic nervous system connects the CNS to the skin and skeletal muscle (voluntary functions). The autonomic nervous system connects the CNS to the internal organs (involuntary functions). 25.14 The autonomic nervous system is divided into the sympathetic system, which prepares the body for “fight or flight” (stressful) situations, and the parasympathetic system, which is the body’s everyday “resting” system for normal situations. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-75 In Summary (cont.) 25.15 There are many and varied diseases and disorders related to the nervous system. The signs, symptoms, and treatments of these diseases are as varied as the diseases themselves. Many of the more common diseases are included in the Pathophysiology section at the end of this chapter. © 2011 The McGraw-Hill Companies, Inc. All rights reserved. 25-76 End of Chapter 25 Activity of the nervous system improves the capacity for activity, just as exercising a muscle makes it stronger.” ~ Dr. Ralph Gerard © 2011 The McGraw-Hill Companies, Inc. All rights reserved.