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Chapter 14
Lecture Outline
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Nervous System
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Points to ponder • What are the three types of neurons?
• What are neuroglia?
• What is the structure of a neuron?
• What is the myelin sheath? Saltatory conduction? Schwann cell? Node of Ranvier?
• Explain the resting and action potential as they relate to a nerve impulse.
• How does the nerve impulse traverse the synapse?
• What are the two parts of the nervous system?
• What three things protect the CNS?
• What are the four parts of the brain and their functions?
• What is the reticular activating system and the limbic system?
• What are some higher mental functions of the brain?
• What are the two parts of the peripheral nervous system?
• How do abused drugs work?
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The nervous divisions
• Two divisions
– Central nervous system (CNS): Brain
and spinal cord
– Peripheral nervous system (PNS):
Nerves and ganglia (collections of cell
bodies)
14.1 Overview of the Nervous System
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The nervous divisions
14.1 Overview of the Nervous System
Figure 14.1 The two divisions of the nervous system.
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somatic motor
nerves: signals
to skeletal
muscles,
voluntary
autonomic motor
nerves: signals
to smooth
muscle, cardiac
muscle, glands,
involuntary
somatic sensory
nerves: signals
from skin,
muscles,
joints, special
senses
visceral sensory
nerves:
signals from
body organs
parasympathetic
division
“rest and digest”
sympathetic
division
“fight or flight”
sensory (afferent) nerves —
carry sensory information
into brain and spinal cord
motor (efferent) nerves —
carry motor information
from CNS to effectors
brain
cranial nerves
spinal nerves
spinal cord
Central Nervous System (CNS)
brain spinal cord
Peripheral Nervous System (PNS)
b. a.
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The nervous system
• The nervous system allows for
communication between cells through
sensory input, integration of data, and
motor output.
• Two cell types: neurons and neuroglia
14.1 Overview of the Nervous System
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Expanding on neurons
• Three types of neurons • Sensory – takes impulses from sensory
receptor to CNS
• Interneuron – receives information in the CNS and sends it to a motor neuron
• Motor – takes impulses from the CNS to an effector (i.e., gland or muscle fiber)
14.1 Overview of the Nervous System
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Expanding on neurons
• Neuron structure (Ch. 4 review) • Cell body – main cell where nucleus and
most organelles reside
• Dendrites – many short extensions that carry impulses to a cell body
• Axon (nerve fiber) – single, long extension that carries impulses away from the cell body
14.1 Overview of the Nervous System
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Types of neurons
Figure 14.2 The structure
of sensory neurons,
interneurons, and motor
neurons.
14.1 Overview of the Nervous System
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The myelin sheath • A lipid covering on long axons that acts to
increase the speed of nerve impulse conduction, insulation, and regeneration in the PNS
• Schwann cells – neuroglia that make up the myelin sheath in the PNS
• Nodes of Ranvier – gaps between myelination on the axons
• Saltatory conduction – conduction of the nerve impulse from node to node
14.1 Overview of the Nervous System
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Neuron structure
Figure 14.2 The structure
of sensory neurons,
interneurons, and motor
neurons.
14.1 Overview of the Nervous System
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The nerve impulse: Resting potential (RP)
• Resting potential – when the axon is not conducting a nerve impulse
• More positive ions outside than inside the membrane
• Negative charge of -70 mV inside the axon
• More Na+ outside than inside
• More K+ inside than outside
14.1 Overview of the Nervous System
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The nerve impulse: Resting potential (RP)
Figure 14.3a Generation of an action potential.
14.1 Overview of the Nervous System
+ + + + + + + + + +
+ + + + + + + + + +
K+
recording electrode
inside axon
reference electrode
outside axon
axonal membrane
inside axon
outside axon
Na+
gated Na+
channel
gated K+
channel
a. Resting potential: Na+ outside the axon, K+ and large
anions inside the axon. Separation of charges polarizes the cell and causes the resting potential.
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The nerve impulse: Action potential
• Action potential – rapid change in the axon membrane that allows a nerve impulse to occur
• Sodium gates open, letting Na+ in. • Depolarization occurs.
• Interior of axon loses negative charge (-55 mV, then +35 mV).
14.1 Overview of the Nervous System
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• Potassium gates open, letting K+ out. • Repolarization occurs.
• Interior of axon regains negative charge (-70 mV).
• Wave of depolarization/repolarization travels down the axon.
• Resting potential is restored by moving potassium inside and sodium outside.
14.1 Overview of the Nervous System
The nerve impulse: Action potential
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The nerve impulse: Stimulus causes
the axon to reach its threshold
Figure 14.3b Generation of
an action potential.
14.1 Overview of the Nervous System
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− −
+ +
− −
+ + + + + + + +
+ +
+ + + + + + + +
direction of signal
open
Na+
channel
b. Stimulus causes the axon to reach its threshold;
the axon potential increases from −70 to −55.
The action potential has begun.
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The nerve impulse: Action potential
Figure 14.3c Generation of an action potential.
14.1 Overview of the Nervous System
+ + + +
+ + + +
+ +
+ + + + + +
+ + + +
c. Depolarization continues as Na+ gates open
and Na+ moves inside the axon.
direction of signal
open
Na+
channel
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The synapse
• The synapse is a small gap between the sending neuron (presynaptic membrane) and the receiving neuron (postsynaptic membrane).
• Transmission is accomplished across this gap by a neurotransmitter (e.g., ACh, dopamine, or serotonin).
• Neurotransmitters are stored in synaptic vesicles in the axon terminals.
14.1 Overview of the Nervous System
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How does transmission across
the synapse occur?
• Nerve impulse reaches the axon terminal.
• Calcium ions enter the axon terminal and stimulate the synaptic vesicles to fuse with the presynaptic membrane.
• Neurotransmitters are released and diffuse across the synapse, where they bind with the postsynaptic membrane to inhibit or excite the neuron.
14.1 Overview of the Nervous System
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A synapse and how it functions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. After an action
potential arrives
at an axon
terminal (arrow),
Ca2+ enters,
and synaptic
vesicles fuse
with the plasma
membrane of
the sending
neuron.
2. Neuro-
transmitter
molecules
are released
and bind to
receptors
on the
membrane of
the receiving
neuron.
3. When an
excitatory
neuro-
transmitter
binds to a
receptor,
Na+ diffuses
into the
receiving
neuron, and
an action
potential
begins.
Sending neuron
axon of sending neuron
axon terminal
receiving neuron
Receiving neuron Synaptic cleft
arriving action potential
Ca2+
Synaptic vesicles enclose neuro- transmitter.
Synapse
Receiving neuron
neurotransmitter
neuro- transmitter
Receiving neuron
ion channel Na+
receptor
Figure 14.4 Signal transmission at
the synapse.
14.1 Overview of the Nervous System
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Synaptic integration
• Integration is the summation of the inhibitory
and excitatory signals received by a
postsynaptic neuron.
• This occurs because a neuron receives many
signals.
14.1 Overview of the Nervous System
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Synaptic integration
Figure 14.5 Integration of excitatory and inhibitory signals at the synapse.
14.1 Overview of the Nervous System
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The central nervous system • The CNS consists of the brain and spinal cord.
• Both are protected by
• Bones – skull and vertebral column
• Meninges – 3 protective membranes that wrap
around CNS
• Cerebral spinal fluid (CSF) – space between
meninges is filled with this fluid that cushions and
protects the CNS
14.2 The Central Nervous System
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The central nervous system • Both the brain and spinal cord are made up of two
types of nervous tissue.
• Gray matter – contains cell bodies and
nonmyelinated fibers
• White matter – contains myelinated axons
14.2 The Central Nervous System
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The CNS: Spinal cord
• It extends from the base of the brain and along the length of the vertebral canal formed by the vertebrae.
• The spinal cord functions to provide communication between the brain and most of the body.
• It is the center for reflex arcs.
• Gray matter in the center is a butterfly shape.
• White matter surrounds the gray matter.
14.2 The Central Nervous System
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What does the spinal cord look like? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
dorsal root
dorsal root
ventral root
ventral root
vertebra
spinal cord
white matter
central canal
gray matter
gray matter
white matter
gray matter
meninges
ventral
dorsal white matter
central canal
vertebra
b.
a.
c.
dorsal root
ganglion
spinal
nerve
dorsal root
ganglion
spinal
nerve
dorsal root
branches
dorsal root
ganglion
cut vertebrae
d. Dorsal view of spinal cord and dorsal roots of spinal nerves.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a: © Karl E. Deckart/Phototake; d: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer and Don Kincaid, dissections
Figure 14.7 The organization of white and gray matter in
the spinal cord and the spinal nerves.
14.2 The Central Nervous System
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The CNS: Brain
Four major parts
1. Cerebrum
2. Diencephalon
3. Cerebellum
4. Brain stem
14.2 The Central Nervous System
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The CNS: Overview of the brain 14.2 The Central Nervous System
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skull
meninges
pituitary gland
fourth ventricle
spinal cord
Cerebrum
Diencephalon
Cerebellum
hypothalamus
midbrain
pons
Brain stem
a. Parts of brain b. Cerebral hemispheres
lateral
ventricle
third
ventricle
pineal
gland
corpus
callosum
thalamus
(surrounds the
third ventricle)
medulla
oblongata
Figure 14.8 The human brain.
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The brain: Cerebrum
• Cerebral hemispheres
• Cerebral cortex
• Primary motor and sensory areas of
the cortex
• Association areas
• Processing centers
• Central white matter
14.2 The Central Nervous System
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1. The brain: Cerebrum –
The lobes • Cerebrum – largest portion of the brain
• Divided into four lobes
1. Frontal lobe: primary motor area and conscious thought
2. Temporal lobe: primary auditory, smell, and speech area
3. Parietal lobe: primary somatosensory and taste area
4. Occipital lobe : primary visual area
14.2 The Central Nervous System
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1. The brain: Cerebrum –
The cerebral lobes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Frontal lobe
Occipital lobe
Parietal lobe
auditory association area
primary auditory area
primary somatosensory area
primary taste area
general interpretation area
primary motor area
premotor area
lateral sulcus
central sulcus
trunk
arm
hand
face
tongue
leg
motor speech (Broca’s) area
prefrontal area
anterior ventral
primary
olfactory area
sensory speech (Wernicke’s) area
Temporal lobe
somatosensory
association area
posterior dorsal
primary visual area
visual association
area
Figure 14.9 The lobes of the cerebral hemispheres.
14.2 The Central Nervous System
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1. The brain: Cerebrum –
The cerebral cortex • Cerebral cortex – thin, outer layer of gray matter
• Primary motor area – voluntary control of skeletal muscle
• Primary somatosensory area – for sensory information from skeletal muscle and skin
• Association areas – integration occurs here
• Processing centers – perform higher level analytical functions including Wernicke’s and Broca’s areas, both involved in speech
14.2 The Central Nervous System
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1. The brain: Cerebrum –
The cerebral cortex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
salivation
vocalization
mastication longitudinal
fissure
facial
expression
swallowing
thumb, fingers,
and hand
forearm arm trunk
pelvis
thigh
leg
foot and
toes lips
upper
face
tongue and
pharynx
hand, fingers,
and thumb
forearm
arm neck trunk pelvis
thigh
leg
foot and
toes
genitals
teeth and
gums longitudinal
fissure b. Primary
somatosensory
area
a. Primary
motor area
Figure 14.10 The primary motor and primary somatosensory areas of the brain.
14.2 The Central Nervous System
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2. The brain: Diencephalon
• Includes the • Hypothalamus – helps maintain homeostasis
(hunger, sleep, thirst, body temperature, and water balance) and controls pituitary gland
• Thalamus – Two masses of gray matter that receive all sensory input except smell; involved in memory and emotions
• Pineal gland – secretes melatonin that controls our daily rhythms
14.2 The Central Nervous System
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2. The brain: Diencephalon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
skull
meninges
pituitary gland
fourth ventricle
spinal cord
Cerebrum
Diencephalon
Cerebellum
hypothalamus
midbrain
pons
Brain stem
a. Parts of brain b. Cerebral hemispheres
lateral
ventricle
third
ventricle
pineal
gland
corpus
callosum
thalamus
(surrounds the
third ventricle)
medulla
oblongata
Figure 14.8 The human brain.
14.2 The Central Nervous System
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3. The brain: Cerebellum
• Receives and integrates sensory input from the
eyes, ears, joints, and muscles about the current
position of the body
• Functions
• Maintains posture
• Coordinates voluntary movement
• Allows learning of new motor skills (i.e., playing
the piano or hitting a baseball)
14.2 The Central Nervous System
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4. The brain: The brain stem • Includes
• Midbrain – relay station between the cerebrum and spinal cord or cerebellum; reflex center
• Pons – a bridge between cerebellum and the CNS; regulates breathing rate; reflex center for head movements
• Medulla oblongata – contains reflex centers for regulating breathing, heartbeat, and blood pressure
• Reticular formation – major component of the reticular activating system (RAS) that regulates alertness
14.2 The Central Nervous System
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The reticular formation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
RAS radiates
to cerebral
cortex.
thalamus
reticular
formation
ascending sensory
tracts (touch, pain,
temperature)
Figure 14.11 The reticular formation of the brain.
14.2 The Central Nervous System
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The limbic system
• It joins primitive emotions (i.e., fear, pleasure) with higher functions such as reasoning.
• The limbic system can cause strong emotional reactions to situations but conscious thought can override and direct our behavior.
• Includes
• Amygdala – imparts emotional overtones
• Hippocampus – important to learning and memory
14.3 The Limbic System and Higher Mental Functions
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The limbic system Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
amygdala
hippocampus
olfactory bulb
olfactory tract
hypothalamus
corpus
callosum thalamus
Figure 14.12 The regions of the brain
associated with the limbic system.
14.3 The Limbic System and Higher Mental Functions
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• Learning – what happens when we recall and use past memories
• Memory – ability to hold a thought or to recall past events
• Short-term memory – retention of information for only a few minutes
14.3 The Limbic System and Higher Mental Functions
Higher mental functions
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Higher mental functions
• Long-term memory – retention of information for more than a few minutes and includes the following • Episodic memory – people and events
• Semantic memory – numbers and words
• Skill memory – performing skilled motor activities (i.e., riding a bike)
• Language – depends on semantic memory
14.3 The Limbic System and Higher Mental Functions
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What parts of the brain are
active in reading and speaking? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
primary auditory cortex
visual cortex
primary motor cortex
1. The word is seen in the
visual cortex.
2. Information concerning the
word is interpreted in
Wernicke’s area.
Wernicke’s area
3. Information from Wernicke’s
area is transferred to Broca’s
area.
Broca’s area
4. Information is transferred from
Broca’s area to the primary motor
area.
(all): © Marcus Raichle
Figure 14.13 The areas of the brain involved in reading.
14.3 The Limbic System and Higher Mental Functions
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The peripheral nervous system (PNS)
• It includes cranial nerves (12 pairs), spinal nerves (31 pairs), and ganglia outside the CNS.
- Spinal nerves conduct impulses to and from the spinal cord.
- Cranial nerves conduct impulses to and from the brain.
• The PNS is divided into two systems.
- Somatic division
- Autonomic division
14.4 The Peripheral Nervous System
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The peripheral nervous system
Figure 14.14 The structure of a nerve.
14.4 The Peripheral Nervous System
46 Figure 14.15 The cranial nerves.
14.4 The Peripheral Nervous System
The peripheral nervous system Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
I
II
III
IV
VI
VII
V
VIII
IX
X
XI
XII
Cranial Nerves
to eye muscles
to eye muscles
to eye muscles
from inner ear
from olfactory
receptors
from retina of
eyes
from mouth and
to jaw muscles
from taste buds
and to facial
muscles and
glands
from pharynx
and to pharyngeal
muscles
to tongue
muscles
from and to
internal organs
to neck and
back muscles
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The PNS: Somatic division
• The somatic system serves the skin,
skeletal muscles and tendons.
• Automatic responses are called reflexes.
14.4 The Peripheral Nervous System
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The PNS: Somatic division
Figure 14.16 The events in a spinal reflex.
14.4 The Peripheral Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
white matter
ventral root
axon of motor neuron
dendrite of sensory neuron
cell body of sensory neuron
pin
dorsal root ganglion
interneuron
Dorsal gray matter
central canal
ventral horn
sensory receptor (in skin)
effector (muscle)
cell body of motor neuron
Ventral
dorsal horn
dendrites
dendrites
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The PNS: Autonomic division
• The autonomic system regulates the
activity of involuntary muscles (cardiac and
smooth) and glands.
14.4 The Peripheral Nervous System
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The PNS: Autonomic division
• Two divisions 1. Sympathetic division: coordinates the body
for the “fight or flight” response by speeding up metabolism, heart rate, and breathing while slowing down and regulating other functions.
2. Parasympathetic division: counters the sympathetic system by bringing up a relaxed state by slowing down metabolism, heart rate, and breathing, and returning other functions to normal.
14.4 The Peripheral Nervous System
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The PNS: Autonomic division Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ganglion
inhibits tears
inhibits salivation
stimulates tears
constricts pupils
slows heart
ganglion
sympathetic ganglia
vagus nerve
Sympathetic Division Parasympathetic Division
dilates
pupils
stimulates
salivation cranial
nerves
speeds
heart
cervical
nerves
dilates air
passages
stimulates liver to
release glucose
constricts
bronchioles
stimulates gallbladder
to release bile stimulates
adrenal
secretion increases activity
of stomach and
pancreas
increases
intestinal
activity
inhibits activity
of kidneys,
stomach, and
pancreas
decreases
intestinal activity
stimulates
urination
inhibits
urination sacral
nerves
causes
orgasmic
contractions causes
erection
of genitals
lumbar
nerves
thoracic
nerves
Acetylcholine is neurotransmitter. Norepinephrine is neurotransmitter.
Figure 14.17 The two
divisions of the
autonomic nervous
system.
14.4 The Peripheral Nervous System
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Drugs and drug abuse
• Both legal pharmaceuticals and illegal drugs of abuse have certain basic modes of action.
They: – promote the action of a neurotransmitter.
– interfere with or decrease the action of a neurotransmitter.
– replace or mimic a neurotransmitter or neuromodulator.
14.5 Drug Therapy and Drug Abuse
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Drugs and drug abuse
• Most drug abusers take drugs that affect dopamine and thus artificially affect this reward circuit to the point that they ignore basic physical needs in favor of the drug.
• Drug abusers tend to show a physiological and psychological effect.
• Once a person is physically dependent, they usually need more of the drug for the same effect because their body has become tolerant.
14.5 Drug Therapy and Drug Abuse
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Drug abuse: Alcohol
• Alcohol – a depressant directly absorbed from the stomach and small intestine
• Alcohol is the most socially accepted form of drug use.
• About 80% of college-aged people drink.
• Alcohol denatures proteins and causes damage to tissues such as the brain and liver; chronic consumption can damage the frontal lobe.
• High blood alcohol levels can lead to poor judgment, loss of coordination, or even coma and death.
14.5 Drug Therapy and Drug Abuse
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Drug abuse: Nicotine
• Nicotine – stimulant derived from tobacco plant
• Nicotine stimulates neurons to release dopamine that reinforces dependence on the drug.
• It adversely affects a developing embryo or fetus.
• Smoking increases heart rate and blood pressure.
• Nicotine causes psychological and physiological dependency.
14.5 Drug Therapy and Drug Abuse
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Drug abuse: Cocaine • Cocaine – stimulant derived from a shrub
• Cocaine causes a rush sensation that lasts from 5-30 minutes.
• A cocaine binge occurs when a user takes the drug at ever-higher doses, resulting in hyperactivity, little desire for food and sleep, and an increased sex drive.
• There is extreme physical dependence with this drug.
• “Crack” is the street name for cocaine that is processed to a free-base form for smoking.
14.5 Drug Therapy and Drug Abuse
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Drug abuse: Methamphetamine
• Powder form is called speed and crystal form is called meth or ice.
• It is a stimulant that reverses the effects of fatigue and is a mood elevator.
• High agitation is common after the rush and can lead to violent behavior.
• Methamphetamine causes psychological dependency and hallucinations.
• “Ecstasy” is the street name for a drug that has the same effects as meth without the hallucinations.
14.5 Drug Therapy and Drug Abuse
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Drug abuse: Heroin • Heroin – depressant from the sap of the opium poppy
plant
• It leads to a feeling of euphoria and no pain because it is delivered to the brain and converted into morphine.
• Side effects are nausea, vomiting, and depression of the respiratory and circulatory systems.
• Heroin use can lead to HIV, hepatitis, and other infections due to shared needles.
• Extreme dependency is common.
14.5 Drug Therapy and Drug Abuse
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Drug abuse: Marijuana • Marijuana – psychoactive drug derived from a hemp plant
called Cannabis
• It is most often smoked as a “joint.”
• Occasional users experience mild euphoria, alterations to vision and judgment, as well as impaired motor coordination with slurred speech.
• Heavy users may experience depression, anxiety, hallucinations, paranoia, and psychotic symptoms.
• Long term use may lead to brain damage.
• K2 (“Spice”) is a synthetic drug with higher potency than the active chemical in marijuana.
14.5 Drug Therapy and Drug Abuse