copyright 2003 by mosby, inc. all rights reserved. chapter 18 nervous system
TRANSCRIPT
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CHAPTER 18
NERVOUS SYSTEM
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Structure and Function
• The nervous system is divided into two major structures – Central nervous system (CNS)– Peripheral nervous system (PNS)
• The function of the nervous system is:– To sense, interpret, and respond to
internal and external environmental changes in order to maintain a steady state in the body’s homeostasis
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Figure 18-1 Divisions of the Nervous System
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Table 18-1 Functions of the Peripheral Nervous
System
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The Autonomic Nervous System • Sympathetic system
– The sympathetic nerves are stimulated in situations that require action like the fight-or-flight reaction
• Parasympathetic system– The parasympathetic nervous system
functions in response to normal everyday situations
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Neurons
• A bundle of fibers that carries impulses
• Three main types of neurons – Afferent– Efferent– Interneuron
• Each carries messages, or impulses, to and from the body’s organs
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Figure 18-4 Neuron
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Neuroglia
• Special nervous tissue cells that act as “glue” to support, bind, repair, and protect neurons
• Five major types– Astrocyte cells– Oligodendroglia– Microglia – Ependymal cells – Neuroglia
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Synapse
• Space between two neurons • Impulses from one neuron are
transmitted across the synapse to another neuron by a chemical called a neurotransmitter
• Two most common neurotransmitters– Acetylcholine – Norepinephrine
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Brain
• Largest structure of the nervous system and one of the largest organs of the body
• The brain is covered by three layers of membranes called meninges – Dura mater– Arachnoid– Pia mater
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Assessment Techniques
• Electroencephalography (EEG) • Lumbar puncture • Myelography • Nerve conduction velocity • Computed tomography (CT) • Positron emission tomography (PET) • Magnetic resonance imaging (MRI)
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Disorders of the Nervous System • Alzheimer’s
– A form of senile dementia
• Cerebrovascular accident– Commonly called a stroke or CVA, is caused
by loss of oxygen to an area of the brain when a clot blocks a vessel or when a vessel breaks
• Down syndrome – A genetic disorder caused by the presence of
an extra chromosome
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Disorders of the Nervous System (continued)
• Encephalitis – An inflammation of the brain caused by a
virus, bacteria, or chemical agent
• Guillain-Barré syndrome – Also called infectious polyneuritis; it may
appear shortly after a viral immunization or infection
• Headache– The muscles around the occipital area of the
brain constrict the blood flow to the area
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Disorders of the Nervous System (continued)
• Migraine headaches – Vascular headaches of unknown cause; the
pain results from the narrowing of blood vessels in the brain
• Sinus headaches – From the swelling of the membranes that line
the sinus cavities
• Head injury – Occurs when the brain impacts with the skull
as a result of a blow or rapid movement
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Disorders of the Nervous System (continued)
• Huntington’s chorea – A degenerative neural disorder that affects
brain tissues
• Hydrocephalus – Occurs when more cerebrospinal fluid is
produced than absorbed into the circulatory system; the excess fluid increases intracranial pressure and may enlarge the head
• Intracranial tumors – Usually involve neuroglia, blood vessels, or
membranes rather than neurons
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Disorders of the Nervous System (continued)• Meningitis
– A serious inflammation of the meninges caused by a bacterium, virus, or fungus
• Meningocele – A birth defect that occurs when the membranes
covering the brain or spinal cord protrude through a congenital defect in the skull or spinal column
• Multiple sclerosis – From a defect in electrical transmission of the
neurons caused by degeneration of the myelin sheath
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Disorders of the Nervous System (continued)
• Neural tube defect – Defect in the formation of the skull and
spinal column
• Neurofibromatosis – Caused by a defect in an autosomal
dominant gene
• Parkinson’s disease – Results from degeneration of certain brain
cells
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Disorders of the Nervous System (continued)
• Poliomyelitis – Caused by a virus that spreads from the nose
and throat to neural tissue
• Sciatica – Cause is usually a rupture of an intervertebral
disk and osteoarthritis, producing pressure on the nerve or other nerve injury
• Seizure – Results from injury, infection, or epilepsy
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Disorders of the Nervous System (continued)
• Spina bifida– A birth defect involving a malformed spinal
column resulting from neural tube defects
• Spinal cord injuries – Trauma occurring in the cervical and lumbar
area of the spinal column
• Transient ischemic attack (TIA) – Caused by a decrease in blood to an area of
the brain resulting from a small clot that temporarily lodges in a vessel
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Disorders of the Nervous System (continued)
• Trigeminal neuralgia – A sudden intense, unpredictable pain on
one side of the face caused by pressure on or deterioration of the trigeminal facial nerve
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Issues and Innovations
• Memory research– Three components of memory: sensory memory, short-term memory, and long-term memory– Memories are retained differently and in different parts of the brain
• Parkinson’s correction– Causes three functional changes: slowness of
movement, tremor, and rigidity– Transplant of adrenal gland cells to stimulate
growth of dopamine– Fetal tissue research