1 - Lone Star College System

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Transcript 1 - Lone Star College System

Chapter 08
Lecture Outline
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8.1 Nervous System
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A. Functions
1.
2.
3.
Sensory input – sensory receptors
respond to external and internal stimuli
Integration – interpretation of sensory
input
Motor output – response by muscles,
glands, and organs
3
B. Divisions of the Nervous System
1.
Central nervous system (CNS)
a. Brain
b. Spinal cord
2. Peripheral nervous system (PNS) –
includes all the cranial and spinal nerves
a. Afferent (sensory) division – includes
somatic and visceral divisions
b. Efferent (motor) division – includes
somatic and autonomic divisions
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Organization of the Nervous System
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C. Nervous tissue
1.
Types of cells
a. Neurons (nerve cells) – transmit
impulses
b. Neuroglia – support and nourish
neurons
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2. Neuron (nerve cell) structure
a. Cell body – contains nucleus and other
organelles
b. Dendrites – receive signals from sensory
receptors or other neurons
c. Axon
1) Conducts nerve signals away from cell
body
2) Nerve – bundle of parallel axons in the
PNS
3) Tract – bundle of parallel axons in the
CNS
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Neuron structure, cont
d.
Axon may be covered by the myelin
sheath (lipid coating)
1) Formed by Schwann cells or
neurolemmocytes in PNS
2) Formed by oligodendrocytes in CNS
3) Provides insulation
4) Increases the speed of impulse
conduction
5) Nodes of Ranvier – gaps in the myelin
sheath
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Neuron Anatomy
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3. Types of neurons
a. Motor neurons
1) Take nerve impulses from the CNS to
muscles, organs, or glands
2) Multipolar – have many dendrites and a
single axon
b. Sensory neurons
1) Take nerve impulses from sensory
receptors to the CNS
2) Almost all are unipolar
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Types of neurons, cont
c.
Interneurons (association neurons)
1) All are in the CNS
2) Typically multipolar
3) Convey nerve impulses between various
parts of the CNS
4) Form complex pathways for thinking,
memory, and language
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D. Nerve signal conduction
1. Resting potential
a. Neuron possesses potential energy
b. The cell membrane is polarized
1) Positively charged outside the cell due
to sodium ions (Na+)
2) Negatively charged inside due to
potassium ions (K+) and large anions
c. The membrane is impermeable to Na+
but permeable to K+
d. The sodium/potassium pump moves
ions to maintain resting potential
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2. Action potential
a.
b.
c.
d.
e.
Process of conduction of nerve signals
Occurs in the axons
Begins with a stimulus
Voltage-gated channels in the cell
membrane open and sodium ions rush
into the cell (depolarization); the
membrane becomes negative outside and
positive inside
Sodium channels close and voltage-gated
potassium channels open to allow K+ to
move out; the Na+/K+ pump returns ions
to their proper place and the cell
repolarizes
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Resting potential and action potential in an
unmyelinated axon
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3. Conduction of action potentials (APs)
a.
b.
c.
d.
e.
As the axon depolarizes, Na+ will diffuse
into the next section, causing
depolarization
Continues down the axon, followed by
repolarization
It is an all-or-none event
Intensity of message determined by the
rate of action potentials
Refractory period
1) Axon cannot conduct an AP
2) Ensures one-way direction of an impulse
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Conduction of action potentials (APs), cont
f. In unmyelinated axons
1) Slow (~1 meter/second)
2) Each section of the axon must be
stimulated
g. In myelinated axons
1) Called saltatory conduction
2) An AP at one node of Ranvier can “jump”
over myelinated portion of axon to the
next node
3) Much faster (>100 meters/second)
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Conduction of an action potential
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E. Transmission across a synapse
1. Axon terminal – small swelling at tips of the
branched end of an axon
2. Synapse components
a. Region of close proximity between two
neurons
b. Presynaptic membrane – membrane of
the first neuron
c. Postsynaptic membrane – membrane of
the next neuron
d. Synaptic cleft – small gap between the
presynaptic and the postsynaptic neuron
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Transmission across a synapse, cont
3.
Neurotransmitters (NTs) – molecules
stored in the axon terminal that transmit a
nerve impulse across a synapse
4. Information transfer
a. Nerve impulse reaches axon terminal
b. Calcium channels are opened and Ca2+
enters the terminal
c. Causes synaptic vesicles to fuse with the
presynaptic membrane and release NT
by exocytosis into synaptic cleft
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Information transfer, cont
d.
e.
f.
g.
NT diffuses to postsynaptic membrane and
binds to its specific receptor
Ligand-regulated gates will open
Depending on the NT, the postsynaptic
membrane will be excited or inhibited
The NT will be removed from the synapse
so that further stimulation may occur
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Synaptic structure and function
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F. Graded potentials and synaptic integration
1. Graded potentials – each small signal from
a synapse
2. Excitatory neurotransmitters produce a
graded potential that promotes an AP;
opens Na+ gates inward
3. Inhibitory neurotransmitters produce a
graded potential that inhibits an AP; opens
K+ gates outward or Cl- gates inward
4. Integration involves summing up the
excitatory and inhibitory signals
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G. Neurotransmitter molecules
1. At least 75 have been identified
2. Two well-known neurotransmitters
a. Acetylcholine (ACh)
b. Norepinephrine (NE)
3. After a neurotransmitter has initiated a response it
is removed from the synaptic cleft
a. Enzymes may inactivate the neurotransmitter
b. The neurotransmitter may be reabsorbed by the
presynaptic membrane
c. Prevents continuous stimulation (or inhibition)
of postsynaptic membranes
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8.2 Central Nervous System
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A. Introduction
1.
2.
Gray matter – contains cell bodies and
unmyelinated fibers
White matter – contains myelinated axons
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B. Meninges and cerebrospinal fluid
1.
Meninges – protective membranes of the
CNS
a. Dura mater – outer menix composed of
two layers of tough, fibrous connective
tissue; dural venous sinuses – spaces
between the dura mater layers
containing venous blood
b. Arachnoid mater – middle menix
composed of spider-web-like connective
tissue
c. Pia mater – deepest menix that adheres
to the brain and spinal cord
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Meninges
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2. Cerebrospinal fluid (CSF)
a. Produced from blood by the choroid plexus
into the ventricles
b. Fills the following:
1) Subarachnoid space – space between
the arachnoid mater and the pia mater
2) Ventricles – hollow, interconnecting
cavities of the brain
3) Central canal – hollow, space of the
spinal cord
c. Reabsorbed back into dural venous sinuses
d. Blockages can occur that can cause
hydrocephalus
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Ventricles of the brain
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C. The spinal cord
1. Introduction
a. Extends from the foramen magnum to the first
lumbar vertebra
b. Protected by vertebral column
c. Occupies the vertebral canal
2. Spinal nerves – connect to the spinal cord through
nerve roots through intervertebral foramen
a. Posterior (dorsal) root – carries sensory fibers
into the spinal cord; posterior root ganglion
b. Anterior (ventral) root – carries motor fibers
out of the spinal cord
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3. Structure of the spinal cord
a. Central canal contains CSF
b. Centrally located gray matter
1) H-shaped
2) Contains portions of sensory and motor neurons
and interneurons
c. White matter – surrounds gray matter
1) Posterior white matter composed of ascending
tracts carrying sensory information to the brain
2) Anterior white matter composed of descending
tracts carrying motor information from the brain
3) Tracts generally cross from one side of the
spinal cord to the other
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Spinal Cord
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4. Functions of the spinal cord
a. Provides communication between the brain
and the peripheral nerves
b. Reflex arcs
1) Sensory receptors respond to a stimulus
2) Impulse travels over sensory neurons to
the spinal cord
3) Interneurons integrate data and relay a
response by way of motor neurons
4) Motor neurons cause effectors to respond
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A reflex arc
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D. The brain
1.
2.
3.
4.
5.
Cerebrum
Diencephalon
Cerebellum
Brain stem
Ventricles
a. Two lateral ventricles (cerebrum)
b. Third ventricle (diencephalon)
c. Fourth ventricle (brain stem and
cerebellum)
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The human brain
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E. The cerebrum
1. Introduction
a. Largest portion of the brain
b. Receives sensory input, carries out
integration, and initiates voluntary
motor responses
c. Coordinates the activities of the other
parts of the brain
d. Involved in higher thought processes
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2. Structure of the cerebrum
a.
The cerebral hemispheres
1) Longitudinal fissure divides the cerebrum
into left and right hemispheres
2) Connected internally by the corpus
callosum
3) Gyri (ridges) are separated by sulci
(shallow grooves)
b. Lobes
1) Frontal lobe
4) Occipital lobe
2) Parietal lobes
5) Insula
3) Temporal lobes
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The lobes of a cerebral hemisphere
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Structure of the cerebrum, cont
c.
Insula
1) Deep to the lateral sulcus
2) Functions may include speech
processing, taste, and social emotions
d. Cerebral cortex
1) Outer layers of gray matter
2) Accounts for sensation, voluntary
movement, and consciousness
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3. Motor and sensory areas of the cortex
a. Primary motor area
1) In frontal lobe anterior to central sulcus
2) Each hemisphere controls voluntary commands
to skeletal muscle of the opposite side of the
body
3) Cortex area related to the size of the motor
units
b. Primary somatosensory area
1) Posterior to central sulcus in parietal lobes
2) Each hemisphere receives sensory information
from the skin and skeletal muscles on the
opposite side of the body
3) Cortex area related to the number of receptors
in an area
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Body areas of primary motor and
somatosensory areas of the cortex
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Motor and sensory areas of the cortex, cont
c. Primary taste area
1) Located in insula and parietal lobes
2) Taste sensations
d. Primary visual area
1) Located in the occipital lobe
2) Receives information from our eyes
e. Primary auditory area
1) Located in the temporal lobe
2) Receives information from our inner ears
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The lobes of a cerebral hemisphere
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4. Association areas
a. Where integration occurs
b. Where memories are stored
c. Next to the primary area for the activity
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5. Processing centers
a. Uses information from other association
areas for higher level analytical functions
b. Prefrontal area – reason and planning
actions
c. Premotor area – organizes motor functions
for skilled movements
d. Motor speech area (Broca’s area)
e. Wernicke’s area (general interpretive area)
– for written and spoken messages
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6. Central white matter
a. Tracts communicate information between
the different sensory, motor, and
association areas
b. Tracts communicate with other brain areas
c. Tracts communicate with the spinal cord
1) Descending tracts come from the primary
motor area
2) Ascending tracts go to the primary
somatosensory area
d. Corpus callosum joins the two cerebral
hemispheres
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7. Basal nuclei
a.
b.
c.
Masses of gray matter deep in the
cerebrum
Integrate motor commands
Huntington disease and Parkinson’s disease
– uncontrollable movements believed to be
from neurotransmitter imbalances in the
basal nuclei
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F. The diencephalon
1. Hypothalamus
a. Forms the floor of the third ventricle
b. Integrating center involved in
homeostasis
c. Regulates hunger, sleep, thirst, body
temperature, and water balance
d. Link between nervous and endocrine
systems
e. Produces hormones released by the
posterior pituitary gland
f. Secretes hormones that control the
anterior pituitary gland
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The diencephalon, cont
2.
Thalamus
a. Located in sides and roof of the third
ventricle
b. Functions as a sensory relay center for
all sensory input except smell
c. Involved in arousal of the cerebrum
d. Participates in memory and emotions
3.
Pineal gland regulates body’s daily
rhythms through the hormone melatonin
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The human brain
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G. Limbic system
1. Inferior to the cerebral cortex
2. Contains neural pathways that connect
portions of the cerebral cortex and the
temporal lobes with the thalamus and the
hypothalamus
3. Causes emotion
4. Involved in memory and learning
5. Hippocampus involved in processing shortterm memory to become long-term memory
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The Limbic System
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H. The cerebellum
1. Separated from brain stem by the fourth
ventricle
2. Two hemispheres composed primarily of
internal white matter in a tree-like pattern
3. Receives sensory input from the eyes, ears,
joints, and muscles
4. Receives motor output from the cerebral
cortex
5. Maintains posture and balance and ensures
smooth, coordinated voluntary movement
6. Assists in learning of new motor skills
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I. The brain stem
1. Midbrain
a. Relay station between cerebrum and the
spinal cord or cerebellum
b. Reflex centers for visual, auditory, and
tactile responses
2. Pons
a. Contains bundles of axons traveling
between the cerebellum and the rest of
the CNS
b. Helps regulate breathing rate with the
medulla oblongata
c. Reflex centers for head movements in
response to visual and auditory stimuli
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The brain stem, cont
3.
Medulla oblongata
a. Vital reflex centers for heart rate,
respiration, and blood pressure
b. Reflex centers for vomiting, coughing,
sneezing, hiccupping, and swallowing
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4. Reticular formation
a.
b.
c.
d.
e.
f.
Tracts and nuclei connected to many other
brain areas
Involved in maintaining muscle tone with
the cerebellum
Assists in regulating respiration, heart
rate, and blood pressure with the medulla
and pons
Helps rouse a sleeping person with the
thalamus
Processes sensory stimuli to keep us
mentally alert
Damage may result in coma
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The human brain
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8.3 Peripheral Nervous System
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A. Introduction
1.
2.
3.
Lies outside of CNS
Composed of nerves and ganglia
Connective tissue components –
endoneurium, perineurium, epineurium
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4. Subdivisions of the PNS
a.
Afferent (sensory)
1) Somatic sensory serves the skin,
skeletal muscles, joints, and tendons;
also special senses
2) Visceral sensory serves the internal
organs
b. Efferent (motor)
1) Somatic motor system carries
commands from CNS to the skeletal
muscles
2) Autonomic motor system regulates
cardiac and smooth muscle and glands
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B. Cranial nerves
1.
2.
3.
4.
5.
6.
Twelve named pairs
Sensory nerves contain only sensory
fibers (nerves I, II, and VIII)
Motor nerves contain only motor fibers
(nerves III, IV, VI, XI, and XII)
Mixed nerves contain both sensory and
motor fibers (nerves V, VII, IX, and X)
Mostly involved with the head, neck, and
facial regions of the body
The vagus nerve (cranial nerve X) has
sensory and motor branches to the face
and most of the internal organs
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Cranial Nerves
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Cranial Nerves
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C. Spinal nerves
1.
2.
31 pairs
Designated according to their location in
relation to the vertebrae
3. Spinal nerves are mixed nerves
a. Sensory fibers enter at the posterior
root
b. Motor fibers exit at the anterior root
c. The cell body of a sensory neuron is in a
posterior-root ganglion
d. The cell body of a motor neuron is in the
anterior gray matter of the cord
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Spinal Nerves
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Spinal Nerves
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D. Somatic motor nervous system and
reflexes
1.
Includes voluntary actions that originate
in the motor cortex
2. Reflexes are automatic involuntary
responses to changes inside and outside
the body
a. Cranial reflexes involve the brain
b. Spinal reflex involves only the spinal
cord
3. Imbalances in reflexes can be used to
determine if the nervous system is
reacting properly, can help avoid injury,
and help maintain balance
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Reflex arc showing spinal reflex
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E. Autonomic Nervous System (ANS)
1.
Two divisions of ANS that:
a. Function automatically and involuntarily
b. Innervate all internal organs with fibers
from either or both divisions
c. Utilize two motor neurons (preganglionic
neuron and postganglionic neuron) and
one ganglion for each impulse
2. Visceral reflexes are important to the
maintenance of homeostasis
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3. Sympathetic division of ANS
a. Called the “Fight or Flight” division that
prepares the body for emergency situations
b. Preganglionic fibers arise from the thoraciclumbar portion of the spinal cord
c. Preganglionic fibers are short and
postganglionic fibers are long
d. The ganglia are near the spinal cord
e. Neurotransmitter released by the
postganglionic neuron is primarily
norepinephrine (NE)
f. Examples of functions - accelerates
heartbeat and dilates the bronchi; inhibits
the digestive tract
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4. Parasympathetic division of ANS
a. Called the “Rest and Digest” division that
controls normal body activities
b. Includes several cranial nerves and
preganglionic fibers that arise from the
sacral portion of the spinal cord
(craniosacral portion of ANS)
c. Preganglionic fiber is long and
postganglionic fiber is short
d. Ganglia are near or in the effectors
e. Acetylcholine (Ach) is the neurotransmitter
f. Examples of functions - promotes digestion
of food, slows heart rate, and decreases the
strength of cardiac contraction
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Comparison of ANS Divisions
Sympathetic division neurons and ganglion
Parasympathetic division neurons and ganglion
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ANS structure and function
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Autonomic Motor Pathways
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8.4 Effects of Aging
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Effects of Aging
A.
B.
C.
D.
E.
Brain mass decreases, particularly from
the cerebral cortex
Learning, memory, and reasoning decline
Neurotransmitter production decreases
Although structural changes occur, mental
impairment is not an automatic
consequence of getting older
Neurological disorders are more likely to
occur – Alzheimer disease, Parkinson’s
disease
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Effects of Aging, cont
F.
To help maintain good mental health:
1. Maintain cardiovascular system health
2. Do activities to stay mentally alert
3. Avoid depression
4. Exercise
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8.5 Homeostasis
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Homeostasis of the nervous system
A.
B.
C.
D.
Detects, interprets, and responds to
changes in the internal and external
environment
With the endocrine system, it coordinates
and regulates the functioning of other
systems
The hypothalamus and medulla oblongata
control vital functions
Controls body movements
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Human Systems Work Together
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