copyright 2003 by mosby, inc. all rights reserved. chapter 18 nervous system
TRANSCRIPT
Copyright 2003 by Mosby, Inc. All rights reserved.
CHAPTER 18
NERVOUS SYSTEM
Copyright 2003 by Mosby, Inc. All rights reserved.
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
Copyright 2003 by Mosby, Inc. All rights reserved.
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
Copyright 2003 by Mosby, Inc. All rights reserved.
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