Download Chapter 29 Nervous System

NERVOUS SYSTEM
CHAPTER 29
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WHAT WILL YOU LEARN?
• The nervous system consists of the brain, the spinal cord, and the nerves. The
nervous system receives information at a great rate, from both inside the body
and outside of it. It then processes this information and issues instructions to
other organ systems to carry out. “Command central” of the human body, the
nervous system, is the subject of this chapter.
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WHEN YOU ARE FINISHED WITH THIS CHAPTER, YOU WILL
BE ABLE TO:
• 1.
List and describe the structures that make up the two main divisions of
the nervous system.
• 2.
• 3.
• 4.
• 5.
Discuss the main functions of the nervous system.
Describe how aging affects the nervous system.
Discuss various disorders that affect the nervous system.
List common diagnostic procedures that are used to help detect nervous
system disorders.
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STRUCTURE OF THE NERVOUS SYSTEM
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THE NERVOUS SYSTEM HAS
TWO MAIN DIVISIONS:
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The central nervous system
The peripheral nervous system
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THE CENTRAL NERVOUS SYSTEM IS PROTECTED BY:
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• Connective tissue called meninges
• The bony skull (brain)
• Vertebrae (spinal cord)
• The three layers of the meninges:
• Pia mater
• Arachnoid mater
• Dura mater
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MENINGES
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Pia mater
• Thin delicate layer of tissue rich in blood vessels that is attached to the surface of the
brain and spinal cord
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Arachnoid mater
• Web-like middle layer
• Dura mater
• Thick, tough outer layer that is attached to the inside of the skull and the vertebrae
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CEREBRAL SPINAL FLUID
• Cerebral spinal fluid (CSF) is located between the pia mater and arachnoid
• CSF is the “shock absorber” that protects the brain and the spinal cord.
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THE BRAIN HAS FOUR PARTS:
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Cerebrum
Diencephalon
Brain stem
Cerebellum
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THE BRAIN
• The cerebrum:
• Controls the voluntary movement of muscles
• Gives meaning to information received from the eyes, ears, nose, taste buds, and sensory
receptors in the skin
• Allows us to speak, remember, think, and feel emotions
• The right and left hemispheres:
• Communicate with each other
• Are connected by a structure called the corpus callosum
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THE BRAIN
• The diencephalon
• The thalamus
• Sorts out the impulses that arrive via the spinal cord from other parts of the body
• Sends them to the correct part of the cerebrum
• The hypothalamus
• Controls body temperature, fluid balance, appetite, sleep cycles, and some of the
emotions
• Regulates the pituitary gland
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THE BRAIN
• The brain stem connects the spinal cord to the brain and has three parts:
• The midbrain
• The pons
• The medulla
• The cerebellum helps to coordinate the brain’s commands to the muscles, allowing for smooth
and orderly movement
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THE SPINAL CORD
•
The spinal cord is the main connection between the brain and the rest of the
body
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Pathways of nerve tissue in the spinal cord, called tracts, carry messages to
and from the brain
• Ascending tracts carry information from the peripheral nervous system to the brain
• Descending tracts carry information from the brain to the peripheral nervous system
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There are 31 pairs of nerves that branch from the tracts.
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NEURON
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A cell that can send
and receive information.
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Consists of:
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Dendrites – receives information
Cell body
Axon – sends information
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A nerve impulse enters the neuron at the dendrite, passes through the cell body and
travels down the axon and to the next dendrite in line
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Chemical neurotransmitters carry the nerve impulse across the gap or synapse
Some are wrapped in a protective covering called myelin.
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THE PERIPHERAL NERVOUS SYSTEM
• The nerves that form the peripheral nervous system are
• Sensory nerves
• Motor nerves
• Sensory nerves carry information
• From the internal organs and the outside world
• To the spinal cord and up into the brain
• Motor nerves carry commands
• From the brain down the spinal cord
• To the muscles and organs of the body
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FUNCTION OF THE NERVOUS SYSTEM
• To receive, process and respond to information.
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REGULATION AND INTERNAL ENVIRONMENT
• The nervous system regulates what is going on within the body and makes adjustments as
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necessary to keep things within the range of normal (homeostasis)
When the central nervous system detects an imbalance, a special part of the peripheral
nervous system, called the autonomic system, is activated
• The sympathetic nervous system starts actions or speeds things up
• The parasympathetic nervous system stops those actions or slows them back down
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INTERACTION WITH THE EXTERNAL ENVIRONMENT
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The nervous system allows us to interact with the world around us
Five special senses that provide the brain with information about the outside world:
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Touch
Taste
Smell
Sight
Hearing
The brain responds to this information
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THE EFFECTS OF AGING ON THE NERVOUS SYSTEM
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SLOWED CONDUCTION TIME
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Some elderly patients or residents are not as quick to react to things as they
used to be
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The amount of myelin surrounding the axons decreases, reducing the speed
of nerve conduction by approximately 10%
•
Neurotransmitter imbalances can interfere with the ability of a nerve impulse
to travel across a synapse, slowing conduction
•
This can result in an increased risk for falls.
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MEMORY CHANGES
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Many older people experience a mild loss of memory for recent events, while
still having excellent long-term memory
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Dementia (a significant loss of mental capabilities) is a degenerative brain
disease, not a normal age-related change
•
Be sensitive to memory changes and forgetfulness.
• Respectfully redirect and restate information to orient your patients to person, place and
time.
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DISORDERS OF THE NERVOUS SYSTEM
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TRANSIENT ISCHEMIC ATTACK (TIA)
• Temporary (transient) episodes of dysfunction
• Caused by decreased blood flow (ischemia) to the brain
• Common symptoms may include:
• Dizziness
• Nausea
• Blurring or loss of vision
• Double vision
• Paralysis on one side of the body or face (with or without loss of sensation)
• The inability to speak or swallow
• The person usually recovers completely within 24 hours
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STROKE
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Also known as a “brain attack” or cerebrovascular accident (CVA )
Occurs when blood flow to a part of the brain is blocked, causing the tissue to die (infarction).
Signs of a stroke:
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Personality changes
Drooping of the eyelid or corner of the mouth
Slurring of speech
Paralysis
Severe headache
Loss of consciousness
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CAUSES OF STROKE
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Stroke is most often caused by a blood clot that blocks flow to part of the
brain, or cerebral hemorrhage
• Smoking
• Atherosclerosis
• Hypertension
• Diabetes
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EFFECTS OF STROKE
• Hemiplegia: paralysis on one side of the body
• Frequent repositioning is essential to prevent skin breakdown
• Aphasia: a general term for a group of disorders that affect the person’s ability to
communicate with others
• Expressive aphasia: inability to speak or form sounds into meaningful words
• Receptive aphasia: inability to understand the meaning of words
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PARKINSON'S DISEASE
• A neurotransmitter called dopamine is not produced in sufficient amounts
• The brain’s instructions regarding muscle movement never reach the muscle
• A progressive disease
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EFFECTS OF PARKINSON’S DISEASE
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It starts with a faint tremor that gets worse over a long period of time
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The person’s ability to chew and swallow is affected, and drooling may occur
The person may lose the ability to move the small muscles of the face (masklike facial expression)
The person may speak very slowly, in a voice that does not vary in tone
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EFFECTS OF PARKINSON’S DISEASE
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The muscles become weaker and rigid
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Perform personal care at the times when patients
are experiencing the greatest effect from their
Parkinson’s medication
The person may walk with a shuffling, leaning gait
It may be hard for the person to stop suddenly,
once he has begun walking
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EPILEPSY
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Characterized by chronic seizure activity
Grand mal seizures are characterized by generalized and violent contraction and relaxation of the body’s muscles
Petit mal (absence) seizures are mild and hardly noticeable
Causes of epilepsy
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Head injury
Brain infection
Stroke
Difficult birth, resulting in the infant not receiving enough oxygen
Often, the exact cause is never determined
People diagnosed with epilepsy may not be allowed to swim or drive.
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MULTIPLE SCLEROSIS (MS)
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An autoimmune disorder
The immune system attacks and destroys the myelin sheaths that protect the
nerves, resulting in faulty transmission of nerve impulses
Faulty transmission of motor neurons results in muscle weakness
The nerves in the hands, feet, and eyes are usually affected first
Muscle weakness, tingling sensations, twitching of the eyes, and visual
disturbances may be early signs
It is important to provide MS patients with range of motion (ROM) exercises
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Amyotrophic Lateral Sclerosis (ALS)
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Also known as ALS or Lou Gehrig’s disease
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ALS is a terminal illness
The nerves are destroyed, resulting in progressive muscle weakness
ALS usually strikes between the ages of 40 and 60 years.
People in the late stages of the disease experience difficulty breathing and
swallowing and are totally paralyzed, yet their minds remain sharp
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HEAD INJURIES AND SPINAL CORD INJURIES
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Head injuries
• Often result in physical disability, loss of mental function, or both
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Spinal cord injuries
• Quadriplegia: paralysis from the neck down
• Paraplegia: paralysis from the waist down
• The level of the spinal cord injury determines the character and extent of paralysis and
disabilities
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BRAIN DAMAGE
• Definition
• Causes of Brain Damage
• Near-drowning
• Drug overdose
• Choking
• Persistent vegetative state (PVS)
• Unable to respond to their environment
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DIAGNOSIS OF NEUROLOGIC DISORDERS
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TYPES OF DIAGNOSTIC TESTS
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Imaging Studies
• Radiography (“x-rays”)
• Computed tomography (CT)
• Magnetic resonance imaging (MRI)
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Used to help locate tumors of the brain, spinal cord, or surrounding bony
structures
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Useful for detecting fractures of the skull or vertebrae
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TYPES OF DIAGNOSTIC TESTS
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Electroencephalography (EEG)
• Records the electrical activity of the brain
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Used to pinpoint seizure activity within the brain
Used to monitor the person’s brain activity when there is a possibility that the
person is “brain dead”
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