Transcript The Nervous System

CHAPTER
25
The Nervous
System
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-2
Learning Outcomes
25.1 Explain the difference between the central
nervous system and the peripheral nervous
system.
25.2 Describe the functions of the nervous
system.
25.3 Describe the structure of a neuron.
25.4 Describe the function of a nerve impulse and
how a nerve impulse is created.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-3
Learning Outcomes (cont.)
25.5 Describe the structure and function of a
synapse.
25.6 Describe the function of the blood-brain
barrier.
25.7 Describe the structure and functions of
meninges.
25.8 Describe the structure and functions of the
spinal cord.
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25-4
Learning Outcomes (cont.)
25.9 Describe the location and function of
cerebrospinal fluid.
25.10 Define reflex and list the parts of a reflex arc.
25.11 List the major divisions of the brain and give
the general functions of each.
25.12 Explain the functions of the cranial and
spinal nerves.
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25-5
Learning Outcomes (cont.)
25.13 Describe the differences between the
somatic nervous system and autonomic
nervous system.
25.14 Explain the two divisions of the autonomic
nervous system.
25.15 Describe the causes, signs and symptoms,
and treatments of various diseases and
disorders of the nervous system.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-6
Introduction
•
Highly complex
system of two parts
– Central nervous
system (CNS)
– Peripheral nervous
system (PNS)
•
Controls all other
organ systems and is
important for
maintaining balance
within those systems
Disorders are numerous and often
difficult to diagnose and treat
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25-7
General Functions of the NS
• CNS
– Brain
– Spinal cord
• PNS
– Peripheral nerves
– Two sections
• Somatic nervous
system (SNS)
– Skeletal or
voluntary
muscles
• Autonomic
nervous system
(ANS)
– Automatic
functions
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25-8
General Functions (cont.)
• Three types of neurons
– Afferent or sensory nerves
• Sensory information from environment or inside
body to CNS for interpretation
– Efferent or motor nerves
• Impulses from CNS to PNS to allow for movement
or action
– Interneurons
• Interpretive neurons between afferent and efferent
nerves in the CNS
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-9
Apply Your Knowledge
Match the following:
ANSWER:
B Somatic nervous system
___
A. Motor nerves
C Autonomic nervous system B. Governs skeletal or voluntary
___
muscles
A Afferent nerves
___
C. Governs respiratory and GI systems
E Efferent nerves
___
D. Go-betweens or interpreters
D Interneurons
___
E. Sensory nerves
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25-10
Neuron Structure
•
Functional cells of
NS
•
Transmit
electrochemical
messages called
nerve impulses to
– Other neurons
– Effectors (muscles
or glands)
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25-11
Neuron Structure (cont.)
•
Neurons lose their ability to divide
– If destroyed, not replaced
•
Neuralgia
– Support cells for neurons that can divide
– Astrocytes – anchor blood vessels to nerves
– Microglia – act as phagocytes
– Oligodendrocytes – assist with production of
myelin sheath
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25-12
Neuron Structure (cont.)
Neurons have a cell
body and processes
called nerve fibers that
extend from the cell
body.

Dendrites – short


Receive nerve impulses
for the neuron
Axons – long

Send nerve impulses
away from the cell body
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25-13
Neuron Structure (cont.)
• White matter – axons
with myelin sheath
Dendrites
Schwann
cells
Axon
– Schwann cells
• Wrap around some
axons
• Cell membranes
contain myelin
• Myelin insulates axons
and enables axons to
send nerve impulses
more quickly
• Gray matter – axons
without myelin sheath
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-14
Apply Your Knowledge
True or False:
ANSWER:
___
F Effectors are neurons.
They are the muscles or glands.
F Neurons can reproduce.
___
Neurons cannot reproduce.
T Astrocytes anchor blood vessels to nerve cells.
___
T Microglia act as phagocytes.
___
F Oligodendrocytes are reproductive cells.
___
They take part in
myelin production.
T Repolarization is the return to the resting state.
___
GOOD JOB!
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25-15
Nerve Impulse
•
Membrane potential
– Neuron cell membrane at rest is in a polarized state
•
•
Inside of cell membrane is negative
Outside of cell membrane is positive due to more Na+ and K+
– As Na+ and K+ move into the cell, the membrane
becomes depolarized
•
•
Inside becomes more positive
Action potential (nerve impulse) is created
– Repolarization occurs when K+ and later Na+ move to
the outside of the cell membrane
•
Return of the cell to polarized (resting) state
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25-16
Nerve Impulse (cont.)
•
Impulse travels down axon to synaptic
knob
– Vesicles or small sacs in synaptic knob
•
Produce chemicals called neurotransmitters
– Neurotransmitters are released by synaptic
knob
•
Allow impulse transmission to postsynaptic
structures
– Dendrites
– Cell bodies
– Axons of other neurons
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25-17
Nerve Impulse (cont.)
•
Functions of neurotransmitters
– Cause muscles to contract or relax
– Cause glands to secrete products
– Activate or inhibit neurons
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25-18
Apply Your Knowledge
What is the function of neurotransmitters?
ANSWER: Neurotransmitters cause muscles to
contract or relax, cause glands to secret products,
activate neurons to send nerve impulses, or inhibit
neurons from sending them.
Right!
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25-19
Central Nervous System
•
•
Includes the spinal cord and
brain
Blood-brain barrier
– Protects layers of the membranes
of the CNS
– Formed by tight capillaries
•
•
Prevents unwanted substances from
entering the CNS tissues
Inflammation can make more
permeable
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25-20
Central Nervous System (cont.)
•
Meninges –protect brain and spinal cord
– Dura mater
•
Tough outer layer
– Arachnoid mater
•
Middle layer (web-like)
– Pia mater
•
•
•
Innermost and most
delicate
Directly on top of brain
and spinal cord
Holds blood vessels on the
surface of these structures
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25-21
Central Nervous System (cont.)
– Epidural space
•
Above dura mater
– Subdural space
•
Below dura mater
– Subarachnoid space
•
•
•
Between arachnoid mater and pia mater
Contains cerebrospinal fluid (CSF)
Cushions CNS
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25-22
Spinal Cord
•
Slender structure continuous with
the brain
•
Descends into the vertebral canal
and ends around the level of the
first or second lumbar vertebra
•
31 spinal segments:
–
–
–
–
–
8 cervical segments
12 thoracic segments
5 lumbar segments
5 sacral segments
1 coccygeal segment
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25-23
Spinal Cord (cont.)

Cervical enlargement


Motor neurons that control
muscles of the arms
Lumbar enlargement

Motor neurons that control
muscles of the legs
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25-24
Spinal Cord (cont.)
•
Gray matter
– Inner tissue with darker color
– Contains neuron cell bodies and their
dendrites
– Divisions are called horns
– Central canal runs down the entire
length of the spinal cord through
the center of the gray matter
Spinal
Cord/Nerve
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25-25
Spinal Cord (cont.)
•
White matter
– Outer tissue
– Contains myelinated axons
– Divisions are called columns (funiculi)
•
Columns contain groups of axons called
nerve tracts
Spinal
Cord/Nerve
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25-27
Spinal Cord (cont.)
•
One function of the spinal cord is to carry
sensory information to and from the brain
•
Ascending tracts
– Carry sensory information up to the brain
•
Descending tracts
– Carry motor information down from the brain
to muscles and glands
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25-28
Spinal Cord (cont.)
•
Reflexes
– Another function of the spinal cord is to
participate in reflexes
– Reflex – a predictable, automatic response to
stimuli
Receptor
Sensory Neurons
Interneurons
Effectors
Motor Neurons
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25-29
Brain
• Four sections
–Cerebrum
–Diencephalon
–Brain stem
–Cerebellum
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25-30
Cerebrum
•
•
Largest section
Two cerebral hemispheres
– Connected by a thick bundle of nerve fibers
called the corpus callosum
– Longitudinal fissure between hemispheres
•
•
Sulci – grooves on surface
Gyri or convolutions – bumps of brain
matter between sulci
Brain
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25-31
Cerebrum (cont.)
• Lobes
– Frontal
• Motor areas for voluntary
body movements
Parietal
Frontal
– Parietal
• Somatosensory – interprets
sensations
– Temporal
• Auditory – interprets sounds
– Occipital
Temporal
Occipital
• Interprets what a person
sees
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25-32
Cerebrum (cont.)
• Cortex
– Outer layer – gray
matter
• Contains about 75%
of all neurons
– Inner layer – white
matter
– Functions
• Ventricles
– Interconnected
cavities within the
brain
– Filled with CSF
• Interpret sensory
information
• Initiate body
movements
• Stores memories and
creates emotions
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25-33
Diencephalon
• Between the cerebral hemispheres
superior to the brain stem
• Thalamus
– Relay station for sensory information going to
the cerebral cortex for interpretation
• Hypothalamus
– Maintains homeostasis by regulating vital
activities
Brain
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25-34
Brain Stem
•
•
Connects the cerebrum to
the spinal cord
Midbrain
–
–
•
Just beneath
diencephalon
Controls both visual
and auditory reflexes
Pons
–
–
–
• Medulla oblongata
– Inferior portion of brain
stem
– Directly connected to spinal
cord
– Controls many vital
activities, such as heart
rate, blood pressure, and
breathing
Rounded bulge on
underside of brain stem
Between midbrain and
medulla oblongata
Regulates respiration
Brain
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25-35
Cerebellum
•
Location
– Inferior to the occipital lobes of the
cerebrum
– Posterior to the pons and medulla
oblongata
•
Coordinates
– Complex skeletal muscle contractions that
are needed for body movements
– Fine movements
Brain
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25-37
Preventing Brain and Spinal Cord Injuries
•
Wear appropriate
protective gear for
sports
•
Avoid diving into
unknown waters
•
Always wear seat belts
•
Follow safety rules on
playgrounds

Children should be in
car seats appropriate
for age and weight

Know how to get help
quickly in emergencies

Follow traffic rules and
signs while walking,
biking, or driving
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-38
SUPER!
Apply Your Knowledge
Match the following:
___
H Meninges
A. Carry motor information from brain
___
D Ascending tracts
B. Stores memories and creates emotions
___
A Descending tracts C. Grooves on the surface of the cerebrum
___
B Cerebral cortex
D. Carry sensory information to the brain
___
F Hypothalamus
E. Predictable, automatic response to stimuli
___
C Sulci
F. Maintains homeostasis
___
G Cerebellum
G. Coordinates skeletal muscle contractions
___
E Reflexes
H. Protects the brain and spinal cord
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25-39
Peripheral Nervous System
• Nerves that branch off
the CNS
• Peripheral nerves
– Two types:
• Cranial nerves
• Spinal nerves
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25-40
Cranial Nerves
I.
Olfactory nerves
– Carry smell information to the brain for
interpretation
II. Optic nerves
– Carry visual information to the brain for
interpretation
III. Oculomotor nerves
– Found within the muscles that move the eyeball,
eyelid, and iris
IV. Trochlear nerves
– Act in the muscles that move the eyeball.
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25-41
Cranial Nerves (cont.)
V. Trigeminal nerves
– Carry sensory information from the surface
of the eye, the scalp, facial skin, the lining
of the gums, and the palate to the brain for
interpretation
– Also found within the muscles needed for
chewing
VI. Abducens nerves
– Act in the muscles that move the eyeball
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25-42
Cranial Nerves (cont.)
VII. Facial nerves
– Found in the muscles of facial
expression as well as in the salivary and
tear glands
– Also carry sensory information from the
tongue
VIII. Vestibulocochlear nerves
– Carry hearing and equilibrium
information from the inner ear to the
brain for interpretation
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25-43
Cranial Nerves (cont.)
IX.
Glossopharyngeal nerves
– Carry sensory information from the throat
and tongue to the brain for interpretation
– Also act in the muscles of the throat
X.
Vagus nerves
– Carry sensory information from the
thoracic and abdominal organs to the brain
for interpretation
– Also found within the muscles in the throat,
stomach, intestines, and heart
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25-44
Cranial Nerves (cont.)
XI. Accessory nerves
– Found within the muscles of the throat,
neck, back, and voice box
XII. Hypoglossal nerves
– Found within the muscles of the tongue
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25-45
Spinal Nerves
•
•
Peripheral nerves originating from the
spinal cord
31 pairs of spinal nerves
– 8 pairs of cervical nerves (C1 through C8)
– 12 pairs of thoracic nerves (T1 through
T12)
– 5 pairs of lumbar nerves (L1 through L5)
– 5 pairs of sacral nerves (S1 through S5)
– 1 pair of coccygeal nerves (C0)
Spinal
Nerves
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25-46
Spinal Nerves (cont.)
• Dermatome
– Skin segment innervated by spinal nerve
– C1 is not associated with a dermatome
• Ventral root
– Axons of motor neurons only
• Dorsal root
– Axons of sensory neurons only
– Dorsal root ganglion
• Contains cell bodies of sensory neurons
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25-47
Spinal Nerves (cont.)
• Main portions of spinal nerves fuse to form
nerve plexuses
– Cervical – supply skin and muscles of neck
• Phrenic nerve originates from this plexus and
controls the diaphragm
– Brachial – control muscles in the arms
– Lumbosacral – lower abdomen, external
genitalia, buttocks, thighs, legs, and feet
• Sciatic nerve originates from this plexus and
controls muscles of legs
Spinal
Nerves
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25-49
Somatic Nervous System
• Nerves that connect the CNS to skin and
skeletal muscle
• “Voluntary” nervous system
– Controls skeletal muscles, which are under voluntary
control
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25-50
Autonomic Nervous System
•
Nerves that connect the CNS to organs and
other structures
• “Involuntary” nervous system
• Motor neurons located in ganglia
– Neuron cell bodies outside the CNS
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25-51
Autonomic Nervous System (cont.)
• Sympathetic division
– “Fight or flight” – Prepares body for stressful
or emergency situations
– Neurons release neurotransmitter
norepinephrine
•
•
•
•
Increases heart and breathing rates
Slows down muscles of the stomach and intestines
Dilates pupils
Constricts blood vessels – increases blood
pressure
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-52
Autonomic Nervous System (cont.)
• Parasympathetic division
– Prepares body for rest and digesting
– Controls most of the body’s organs
– Releases acetylcholine
• Slows heart and breathing rates
• Constricts pupils
• Activates muscles of stomach and intestine
– No communication with blood vessels
• Sympathetic and parasympathetic
divisions are antagonistic
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-53
Apply Your Knowledge
What is the difference between the sympathetic
and parasympathetic nervous systems?
ANSWER: The sympathetic nervous system prepares the
body for stress. It releases norepinephrine, causing an
increase in heart and respiratory rate, slows down the GI
system, and dilates pupils. The sympathetic system also
controls constriction of blood vessels.
The parasympathetic system prepares the body for resting
and digesting. It releases acetylcholine, which slows heart
and respiratory rates, constricts pupils, and stimulates the
GI system. It has no effect on most blood vessels.
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25-54
Neurologic Testing
•
Typical neurologic examination
–
–
–
–
State of consciousness
Reflex activity
Speech patterns
Motor patterns
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25-55
Diagnostic Procedures
•
Lumbar puncture
•
Magnetic resonance
imaging (MRI)
•
•
Positron emission
tomography (PET)
scan
• Computerized
tomography (CT) scan
• Electroencephalogram
(EEG)
• X-ray
Cerebral angiography
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25-56
Cranial Nerve Tests
• Olfactory nerves (Cranial nerve I)
– Have patient smell various substances
• Cranial nerves III, IV, and VI
– Have patient track movement of finger
• Cranial nerve V
– Have patient clench teeth, feel jaw muscles
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25-57
Cranial Nerve Tests (cont.)
• Cranial nerve VII
– Check patient’s facial expression
• Cranial nerve XII
– Have patient extend his tongue and move it
from side to side
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25-58
Reflex Testing
• Areflexia
– Absence of a reflex
• Hyporeflexia
– Decreased reflex
• Hyperreflexia
– Stronger-than-normal reflex
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25-59
Reflex Testing (cont.)
•
Biceps reflex
– Absence indicates spinal cord damage in
the cervical region
•
Knee reflex
– Absence may indicate damage to lumbar or
femoral nerves
•
Abdominal reflexes
– Used to evaluate damage to thoracic spinal
nerves
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-60
Apply Your Knowledge
Match the following:
ANSWER:
C State of consciousness
___
A Reflex activity
___
D Speech patterns
___
B Motor patterns
___
A. Determines the health of
peripheral nerves
B. Loss of balance,
abnormal posture
C. Stupor, delirium,
vegetative
D. Loss of ability to form
words
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25-61
Common Diseases and Disorders
Disease/Disorder
Description
Alzheimer’s
disease
Progressive, degenerative disease of
the brain
Amyotrophic
lateral sclerosis
(ALS)
Lou Gehrig’s disease
Degeneration of neurons in the spinal
cord and brain
Bell’s palsy
Weak or paralyzed facial muscles
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25-62
Common Diseases and Disorders (cont.)
Disease/Disorder
Description
Brain tumors and
cancers
Abnormal growths
Can be primary or secondary tumors
Most common – gliomas
Epilepsy and
seizures
Occurs as a result of bursts of electrical
signals that disrupt normal brain
functioning
Guillain-Barré
Syndrome
Body’s immune system attacks the PNS
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25-63
Common Diseases and Disorders (cont.)
Disease/Disorder
Description
Headaches
Tension
Migraines
Cluster
Episodic or chronic
With aura/without aura
Form of migraines; occurs in groups
Meningitis
Inflammation of meninges
Multiple sclerosis
(MS)
Chronic disease of CNS
Myelin is destroyed
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-64
Common Diseases and Disorders (cont.)
Disease/Disorder
Description
Neuralgias
Disorders causing nerve pain
Parkinson’s
disease
Progressive and degenerative motor
system disorder
Sciatica
Damage to sciatic nerve
Stroke
Brain cells die because of an inadequate
blood flow; “brain attack”
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-65
Apply Your Knowledge
True or false:
ANSWER:
Bravo!
T Alzheimer’s disease is a progressive degenerative disease
___
of the brain.
F Epilepsy is due to degenerative neurons in the spinal cord
___
and brain. Due to a burst of electrical signals that disrupt brain function.
F Neuralgias are motor system disorders.
___
They are group of disorders referred to as nerve pain.
T Stroke occurs when brain cells die because of inadequate
___
blood flow.
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25-66
In Summary
25.1 The central nervous system is composed of the brain
and spinal cord. The peripheral nervous system
consists of the peripheral nerves located throughout
the body. The peripheral nervous system is further
divided into two distinct systems: the somatic and
autonomic nervous systems.
25.2 There are three separate types of neurons to carry
out the functions of the nervous system. The afferent
(sensory) nerves, the efferent (motor) nerves, and the
interpretive interneurons that act as “interpreters”
between the afferent and efferent nerves.
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25-67
In Summary (cont.)
25.3 All neurons are composed of a cell body, the shorter and more
numerous dendrites that receive information for the cell body,
and the longer axons that bring an impulse from the cell body to
the dendrite of the next neuron.
25.4 The function of a nerve impulse is the sending of information
either from the CNS to the PNS or vice versa.
At rest, a neuron is said to be in a polarized state, and when it
responds to stimuli, depolarization takes place.
Repolarization occurs after the electrical current (impulse) has
passed.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
25-68
In Summary (cont.)
25.5 A synapse is the space between the axon of one
neuron and the dendrite of the next. At the end of
each axon is the synaptic knob, which contains
vesicles that produce neurotransmitters. These are
released by the synaptic bulb to allow impulse
transmission to continue to the next neuron.
25.6 The blood-brain barrier is a layer of tightly woven
capillaries that protects the delicate tissues of the
CNS. This barrier prevents certain substances, such
as various waste products and drugs, from easily
crossing this barrier and entering the brain tissues
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25-69
In Summary (cont.)
25.7 The meninges, a triple-layered membrane protecting
the brain and spinal cord, are composed of the
following layers:
The tough outer layer is the dura mater.
The space between the cranium and the dura mater is
called the epidural space.
Below the dura mater is the subdural space.
The middle layer is the arachnoid, and below it is the
subarachnoid space, which contains cerebrospinal
fluid (CSF).
The innermost layer is the pia mater.
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25-70
In Summary (cont.)
25.8 The spinal cord is continuous with the brain and
consists of 31 spinal segments:
8 cervical
5 sacral
12 thoracic
1 coccygeal
5 lumbar
The basic function of the spinal cord is to carry
sensory information from the body to the brain and
motor information from the brain to the muscles and
glands of the body.
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25-71
In Summary (cont.)
25.9 Cerebrospinal fluid (CSF) is located within the
subarachnoid space of the brain and within the
central canal of the spinal cord. It cushions the brain
and spinal cord.
25.10 A reflex is a predictable automatic response to a
stimulus. A typical reflex flows as follows: Sensory
receptors send information (impulse) to the
interneurons, which in turn send the information on to
the effectors of the motor neurons, producing a
response.
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25-72
In Summary (cont.)
25.11 The cerebrum is the largest part of the brain and is
divided into two hemispheres subdivided into four
lobes: frontal, parietal, temporal and occipital.
The diencephalon contains the thalamus and
hypothalamus.
The brain stem consists of three parts: the midbrain,
pons, and medulla oblongata.
The cerebellum is the final area of the brain.
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25-73
In Summary (cont.)
25.12 Twelve cranial nerves carry sensory information:
OlfactoryOptic
Trochlear
Facial
Glossopharyngeal
Oculomotor
Trigeminal
Vagus
Accessory
Abducens
Vestibulocochlear
Hypoglossal
There are 31 pairs of spinal nerves, each except C1
innervating a dermatome. Refer to Figure 25.8 for a
map of the spinal nerves.
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25-74
In Summary (cont.)
25.13 The somatic nervous system connects the CNS to
the skin and skeletal muscle (voluntary functions).
The autonomic nervous system connects the CNS to
the internal organs (involuntary functions).
25.14 The autonomic nervous system is divided into the
sympathetic system, which prepares the body for
“fight or flight” (stressful) situations, and the
parasympathetic system, which is the body’s
everyday “resting” system for normal situations.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
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In Summary (cont.)
25.15 There are many and varied diseases and disorders
related to the nervous system. The signs, symptoms,
and treatments of these diseases are as varied as
the diseases themselves. Many of the more common
diseases are included in the Pathophysiology section
at the end of this chapter.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
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End of Chapter 25
Activity of the nervous system
improves the capacity for
activity, just as exercising a
muscle makes it stronger.”
~ Dr. Ralph Gerard
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.