HUMAN BIOLOGY

258 Chapter 13

disorders of the nervous system

Like PD, alzheimer’s disease involves the progres-

sive degeneration of brain neurons. At the same time,

there is an abnormal buildup of amyloid protein, leading

to the loss of memory and intellectual functions. Alzheim-

er’s disease is associated with advancing age, and we con-

sider it again in our discussion of aging in Chapter 17.

infections and cancer inflame

or destroy brain tissue

Meningitis is an often fatal disease caused by a bacterial

or viral infection. Symptoms—headache, a stiff neck,

vomiting—develop when the meninges in the central

nervous system become inflamed. encephalitis is inflam-

mation of the brain. It is usually caused by a viral infec-

tion, such as by the West Nile virus or a herpes virus.

Encephalitis can be extremely dangerous. Early symptoms

include fever, confusion, and seizures.

In cancer, cells divide much more often than normal.

Neurons generally do not divide, so cancer does not develop

in them. Glial cells do divide, however, and glial cancers,

called gliomas, can have extremely destructive effects in

the nervous system. An aggressive form called glioblastoma

multiforme usually strikes males and kills within a year of

the diagnosis (Figure 13.24D). Most cases of spinal cancer

are metastases, meaning that the cancer has spread to the

spine from a primary cancer elsewhere in the body.

Some people are concerned that the radio waves emit-

ted by cell phones could cause tumors. Although to date

research hasn’t shown increased brain tumor incidence

related to cell phone use, studies have shown increased

metabolic activity in cells near the phone. Some health

officials recommend using a headset to keep the radiation-

emitting part of the phone farther from the brain.

In young adults, the most common nervous system

disease is multiple sclerosis (MS). It is an autoimmune

disease that may be triggered by a viral infection in suscep-

tible people. MS involves progressive destruction of myelin

sheaths of neurons in the central nervous system. The

symptoms develop over time and include muscle weakness

or stiffness, extreme fatigue, and slurred speech. A dis-

order called Guillain-Barre syndrome produces similar

symptoms in the peripheral nervous system. It is caused

by a viral or bacterial infection and usually is temporary.

physical injury is a common cause

of nervous system damage

A blow to the head or neck can cause a concussion, one of

the most common brain injuries. Blurred vision and a brief

loss of consciousness result when the blow temporarily

upsets the electrical activity of brain neurons.

Damage to the spinal cord can lead to lost sensation and

muscle weakness or paralysis below the site of the injury.

Immediate treatment is crucial to limit swelling. Although

cord injuries usually have severe consequences, intensive

therapy during the first year after an injury can improve

the patient’s long-term prognosis. Using nerve growth fac-

tors or stem cells to repair spinal cord injuries is a major

area of medical research.

Brain injury, birth trauma, or other assaults can cause

various forms of epilepsy, or seizure disorders. Sometimes

the trigger is an inherited predisposition. A seizure results

when the brain’s normal electrical activity suddenly becomes

chaotic. Worldwide, thousands of people develop recurrent

seizures either as children or later in life. All but the most

difficult cases usually respond well to drug therapy.

In some disorders, brain neurons break down

Parkinson’s disease, or PD (Figure 13.24A–C), is a degen-

erative brain disorder. In PD, neurons in parts of the

thalamus (see Section 13.7) begin to die. Those neurons

make neurotransmitters (dopamine and norepinephrine)

required for normal muscle function, so PD symptoms

include muscle tremors and balance problems, among oth-

ers. Multiple factors contribute to the development of PD.

A head injury or exposure to pesticides in drinking water

may increase the risk. There is no cure, but surgery and

treatments that help replace absent neurotransmitters may

relieve some symptoms.

Figure 13.24 Many battle brain disease. a Parkinson’s disease affects former heavyweight champion Muhammad Ali, actor Michael J.

Fox, and about 500,000 others in the United States. PET scans from a healthy person B and an affected person c. The red area in D is a

glioblastoma multiforme tumor in a patient’s brain.

a

Left: AP Images/Kenneth Lambert; Center: © From Neuro Via Clinical Research Program, Minneapolis Medical Center; Right:

Gregory G. Dimijian, M.D./Science Source

13.11

B c D

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).