Copyright 2003 by Mosby, Inc. All rights reserved. CHAPTER 18 NERVOUS SYSTEM.

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CHAPTER 18

NERVOUS SYSTEM

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

Figure 18-1 Divisions of the Nervous System

Table 18-1 Functions of the Peripheral Nervous

System

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

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

Figure 18-4 Neuron

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

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

• 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

Assessment Techniques

• Electroencephalography (EEG) • Lumbar puncture • Myelography • Nerve conduction velocity • Computed tomography (CT) • Positron emission tomography (PET) • Magnetic resonance imaging (MRI)

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

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

• 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

• 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

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

• 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

• 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

• 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

• Trigeminal neuralgia – A sudden intense, unpredictable pain on

one side of the face caused by pressure on or deterioration of the trigeminal facial nerve

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

Copyright 2003 by Mosby, Inc. All rights reserved. CHAPTER 18 NERVOUS SYSTEM.

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