copyright ©2012 delmar, cengage learning. all rights reserved. chapter 24 the nervous system

Copyright ©2012 Delmar, Cengage Learning. All rights reserved.

Chapter 24

The Nervous System


The Two Main Divisions ofthe Nervous System

• Central nervous system (CNS)– Made up of the brain and spinal cord

• Peripheral nervous system (PNS)– Made up of all the nerves that connect the CNS to

every organ and area of the body


Nerve Cells (Neurons)


Two Types of Peripheral Nerves

• 12 pairs of cranial nerves – Connect the brain directly to the sensory organs

(eyes, ears, tongue, nose, and skin)• 31 pairs of spinal nerves that act as:

– Motor nerves to permit movement– Sensory nerves to perceive stimuli

Simple and Complex Reflex Actions

• Simple reflex actions– No interpretation or

decision is required; the nerve impulse travels only to the spinal cord and back

• Complex reflex actions– The impulse is relayed

through the spinal cord to the brain and the brain interprets the sensory impulse and sends it back down the spine



Synapses

• A synapse is a minute space between the axon of one neuron and the dendrite of another.

• These impulses release chemicals called neurotransmitters that either speed up or slow down the transmission.


The Effect of Various Substances on the Action of a Synapse

• Alcohol slows down reactions.• Stimulants speed up reactions.• Diseases can invade the body and neurotoxins

from the bacteria are released that can cause contraction or paralysis of muscle groups.


The Purpose of the Automatic Nervous System

• As part of the peripheral nervous system, these nerves are involuntary and unconsciously control breathing, heartbeat, and digestion.


The Action of the Two Divisions of the Autonomic Nervous System

• The sympathetic nervous system begins at the base of the brain and runs down the spinal cord.

• These nerves extend to all vital organs and blood vessels, the eyes, and the sweat glands.


The Action of the Two Divisions of the Autonomic Nervous System

• The parasympathetic nervous system contains the vagus nerve and the pelvic nerve, which are affected by emotions.

• The vagus nerve extends from the brain to the upper abdominal organs.

• The pelvic nerve branches into the lower abdominal and pelvic organs.


The Main Parts of the Brainand Their Functions



• Cerebrum– Controls sensory and motor activities and is

divided into lobes• Frontal lobe

– Located behind the forehead; related to emotion and personality

• Occipital lobe– Located at the far back of the cerebrum; related to

vision



• Temporal lobe– Located on the side of the cerebrum; associated

with hearing and smell• Parietal lobe

– Located between the frontal and occipital lobes; associated with movement in the hands, feet, and tongue as well as sensations of pain, heat, and cold



• Cerebellum– Found beneath the cerebrum; responsible for

smooth muscle movement and coordination• The medulla oblongata

– Adjoins the spinal cord; influences the function of the heart and lungs, stomach secretions, and opening of blood vessels



• Pons– Located just above the medulla; regulates breathing and

is responsible for chewing, tasting, and the secretion of saliva

• Midbrain– Located superior to the pons; control center for reflex

movements and pupil dilation of the eyes• Thalamus

– Located between the cerebrum and the midbrain; acts as a relay station for impulses going to and from the brain


The Hypothalamus• Located just below the thalamus• Responsible for:

– Controlling the autonomic nervous system– Controlling blood pressure– Maintaining body temperature– Stimulating hormones to conserve water and maintain water

balance– Assisting in appetite regulation– Increasing intestinal secretions and motility– Playing a role in emotions such as fear & pleasure– Maintaining state of wakefulness


The Coverings of the Brain andSpinal Cord and Their Purpose

• The meninges are the coverings on the brain and the spinal cord

• Made up of 3 layers:– Pia mater: inner layer contains nerve tissue– Arachnoid: middle layer made of delicate, lacelike

membranes– Dura mater: outer layer that protects CNS from

damage from contact with bony surfaces of the skull and spine


The Function of Cerebrospinal Fluid

• Cerebrospinal fluid (CSF) acts as a watery cushion or shock absorber to provide additional protection for the CNS.


Common Diagnostic Tests

• Arteriography– A catheter is inserted into an artery and then

threaded up to the carotid artery in the neck.– A dye is injected to detect aneurysms,

hemorrhage, arteriosclerosis, or to check for signs of a stroke.



• Glasgow coma scale– Tool used to determine the level of unconsciousness– Assesses eye movement, verbal response, and motor

response• Computerized axial tomography

– Series of x-rays of the layers of the brain; makes a three-dimensional picture

– Can identify tumors, bleeding, blood clots, disease, and edema



• Electroencephalography– A brain wave test that measures the brain’s

electrical signals, both normal and abnormal– Can detect abnormalities caused by epilepsy,

tumors, strokes, head injuries, or infections



• Electromyography– Uses electrical stimulation passed through small

needles inserted into the muscle to demonstrate the electrical activity of peripheral muscles

– Can diagnose disorders such as diabetic neuropathy and carpal tunnel syndrome



• Lumbar puncture– A spinal needle is inserted into a small space in the

lower back to remove small amounts of cerebrospinal fluid

– Can help diagnose bleeding or infection and can measure fluid pressure in the spine

• Myelography– After a lumbar puncture is performed, dye is instilled

to outline the structures of the spinal cord to detect abnormalities of the spinal cord



• Positron emission tomography– Uses agents, such as glucose or hormones; agents

are mixed with chemicals and injected into the blood; records images of where the material ends up in the body

– Can help diagnose epilepsy and Alzheimer’s disease• Skull x-rays

– X-ray images of the bony structure of the skull to identify tumors and fractures


Alzheimer’s Disease

• Progressive, degenerative disease that attacks the brain

• Results in impaired memory, thinking, and behavior, as well as memory loss

• 8th leading cause of death in the United States


Amyotrophic Lateral Sclerosis

• Lou Gehrig’s Disease • Fatal, progressive neurological disease that

causes degeneration of motor neurons in the brain and spinal cord

• Usually occurs between ages 40 and 70• Death occurs within 2 to 5 years of diagnosis


Bell’s Palsy

• Disease that affects the 7th cranial nerve of the face

• It occurs spontaneously and will usually subside spontaneously within 1 to 9 weeks.

• Causes weakness or paralysis on one side of the face


Cerebral Palsy

• Nonprogressive brain injury that occurs during fetal development, perinatally, or in early infancy; affects muscle and brain development

• Four forms of cerebral palsy include: – Spastic (50% to 75%)– Athetoid (15% to 20%)– Atonic (10%)– Mixed


Encephalitis

• Severe brain inflammation that causes edema and nerve cell destruction

• Onset of fever, headache, vomiting, and stiffness in the neck and back is sudden and acute


Epilepsy

• Seizure disorder that affects 1% to 2% of the population

• Generally associated with abnormal electrical impulses from the neurons

• Causes uncontrollable convulsions, loss of control of bodily functions, and unconsciousness


Essential Tremor

• Most common movement disorder of the nervous system

• Causes involuntary shaking of the hands and head, which is made worse by action or movement

• Often confused with Parkinson’s disease


Headache

• Often classified as vascular, muscle contractions (tension), or traction (inflammatory)

• Causes dull, persistent aching, and a feeling of a tight band around the head

• Can be caused by stress, fatigue, or environment


Migraine Headache

• Headache that causes severe throbbing pain• Beginning symptoms may include fatigue,

visual disturbances, or sensory symptoms• Triggers that may initiate migraines are

chocolate, red wine, and bright lights


Herpes Zoster

• Acute unilateral inflammation of the dorsal root ganglion

• Causes fluid-filled vesicle lesions on the skin and severe pain from the affected nerves

• The vesicles erupt in about 2 weeks• Episodes can last from 1 to 4 weeks.


Hydrocephalus

• Excess accumulation of cerebrospinal fluid within the ventricles of the brain

• Occurs most commonly in newborns• Increase in fluid compresses the brain tissue

against the skull and results in brain damage


Meningitis

• Inflammation of the meninges of the brain and spinal cord

• May be caused by a virus or bacteria• If untreated, mortality is 70% to 100% if it is

bacterial meningitis.


Multiple Sclerosis

• Demyelinating disorder of the nervous system that affects the central nervous system; usually first diagnosed between ages 20 and 40

• The disease attacks the myelin sheath of the nerves and destroys patches of tissue, which are replaced by scar tissue.


Multiple Sclerosis

• The scar tissue distorts or interrupts the passage of the nerve impulse.

• This results in paralysis, double vision, loss of balance, weakness, speech and hearing difficulties, foot dragging, numbness, and a sensation of pins and needles.


Neuralgia

• Terms used to describe generalized nerve pain• Neuralgia causes severe pain along the course

of the involved nerve or nerves.• Can be the result of pressure, nutrition, toxins,

inflammation, or ganglial changes.


Paralysis

• Term used to describe temporary or permanent loss of voluntary function

• Spastic paralysis– Caused by upper motor neurons

• Flaccid– Caused by lower motor neurons

• Can be caused by trauma or by the destruction of nerve tissue


Hemiplegia

• Term used to describe one-sided paralysis that results from brain damage

• Damage to the left side of the brain will result in right-sided paralysis.

• Damage to the right side of the brain will result in left-sided paralysis.


Paraplegia

• Term used to describe the loss of motor or sensory function in the lower extremities

• Usually the result of trauma• Paralysis may be temporary or permanent,

spastic or flaccid


Quadriplegia

• Devastating permanent paralysis that affects all body systems, the arms, the legs, and all of the body below the level of the injury to the spinal cord


Parkinson’s Disease

• Progressive, crippling disease that affects 1 in every 100 people over the age of 60

• Parkinson’s disease affects more men than women

• Main symptoms are muscle rigidity and hand tremors with a masklike facial expression


Parkinson’s Disease

• Symptoms progress to include a peculiar gait, drooling, progressive tremors of the hands, and the head becomes bowed

• Body bends forward and steps become faster and faster; often results in falling


Reye’s Syndrome

• Acute childhood illness characterized by fatty infiltration of the liver and increased intracranial pressure

• Prognosis depends on the degree of CNS depression that results from the increased pressure

• This syndrome almost always follows within 1 to 3 days of an acute viral infection, such as an upper respiratory infection or chickenpox.

• A correlation exists with the use of aspirin in children and the flu and chickenpox.


Sciatica

• Term used to describe inflammation of the sciatic nerve of the leg

• It is usually a unilateral pain that begins gradually and runs down the back of the thighs

• Generally affects middle-age males


Spinal Cord Defects

• Spina bifida with meningocele– A sac protrudes from the opening that contains

the meninges and cerebrospinal fluid• Myelomeningocele

– In the sac that protrudes from the opening there is the meninges, CSF, and a portion of the spinal cord


Spinal Cord Defects

• Treatment and prognosis depend on the location and extent of the spinal cord defect.

• If CSF and meninges are involved, surgery is required to prevent further injury.


Subarachnoid Hemorrhage

• Term used to describe a collection of blood in the subarachnoid space usually caused be spontaneous rupture of a weakened blood vessel


Subdural Hematoma

• Term used to describe a collection of blood within the subdural space

• This is generally a slow process in which the gradual accumulation of blood causes progressive symptoms of seizures, motor disturbances, and progressive weakness.


Tourette Syndrome

• Neurological disorder that is characterized by “tics,” involuntary, rapid, sudden movements that occur repeatedly

• Onset is usually before the age of 21.• Some people may also vocalize unacceptable

words or echo things just heard.


Transient Ischemic Attacks

• Recurring strokelike events that last from a few seconds to a few hours and then disappear after 12 to 24 hours

• Considered to be a warning sign of an impending stroke

• Characterized by double vision, slurred speech, dizziness, and falling


Trigeminal Neuralgia

• Disorder of the fifth cranial nerve on one side of the face

• Produces episodes of excruciating pain on stimulation of a trigger zone

• Frequently follows exposure to heat or cold


Trigeminal Neuralgia

• Episodes may last from 1 to 15 minutes and recur from several times a day to a few times a year.

• Occurs mostly in people over age 40 and affects more women than men


Tumors

• When the tumors are malignant and located in the brain, almost all limit life from 6 months to 6 years following diagnosis

• More common in men than in women• Most prevalent between ages 40 and 60 in

adults and ages 2 and 12 in children• Symptoms vary with the size and location of

the tumor

copyright ©2012 delmar, cengage learning. all rights reserved. chapter 24 the nervous system

Documents