chapt14_HumanBiology14e_lecture

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Chapter 14
Lecture Outline
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Nervous System
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Points to ponder
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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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14.1 Overview of the Nervous System
The nervous divisions
• Two divisions
– Central nervous system (CNS): Brain
and spinal cord
– Peripheral nervous system (PNS):
Nerves and ganglia (collections of cell
bodies)
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14.1 Overview of the Nervous System
The nervous divisions
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brain
Central Nervous System (CNS)
cranial nerves
brain
spinal cord
spinal cord
spinal nerves
Peripheral Nervous System (PNS)
sensory (afferent) nerves —
carry sensory information
into brain and spinal cord
somatic sensory
nerves: signals
from skin,
muscles,
joints, special
senses
a.
Figure 14.1 The two divisions of the nervous system.
visceral sensory
nerves:
signals from
body organs
motor (efferent) nerves —
carry motor information
from CNS to effectors
somatic motor
nerves: signals
to skeletal
muscles,
voluntary
autonomic motor
nerves: signals
to smooth
muscle, cardiac
muscle, glands,
involuntary
sympathetic
division
“fight or flight”
parasympathetic
division
“rest and digest”
b.
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14.1 Overview of the Nervous System
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
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14.1 Overview of the Nervous System
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)
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14.1 Overview of the Nervous System
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
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14.1 Overview of the Nervous System
Types of neurons
Figure 14.2 The structure
of sensory neurons,
interneurons, and motor
neurons.
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14.1 Overview of the Nervous System
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
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14.1 Overview of the Nervous System
Neuron structure
Figure 14.2 The structure
of sensory neurons,
interneurons, and motor
neurons.
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14.1 Overview of the Nervous System
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
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14.1 Overview of the Nervous System
The nerve impulse: Resting potential (RP)
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reference
electrode
outside axon
recording
electrode
inside axon
axonal
membrane
+

+

+
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+

+

+

+
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
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+
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+
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+
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+

+

+
inside axon
K+
Na+
gated K+
channel
outside axon
gated Na+
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.
Figure 14.3a Generation of an action potential.
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14.1 Overview of the Nervous System
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).
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14.1 Overview of the Nervous System
The nerve impulse: Action potential
• 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.
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14.1 Overview of the Nervous System
The nerve impulse: Stimulus causes
the axon to reach its threshold
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−
+
−
+
+
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+

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+

+

+
direction of signal
+
−
+
−

+

+

+

+

+
open
Na+
channel
Figure 14.3b Generation of
an action potential.
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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14.1 Overview of the Nervous System
The nerve impulse: Action potential
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

+

+
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+
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+
+
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+
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+
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+
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+
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+
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+
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+
direction of signal
+
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+

+

+


+

+

+
open
Na+
channel
c. Depolarization continues as Na+ gates open
and Na+ moves inside the axon.
Figure 14.3c Generation of an action potential.
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14.1 Overview of the Nervous System
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.
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14.1 Overview of the Nervous System
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.
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14.1 Overview of the Nervous System
A synapse and how it functions
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arriving action
potential
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.
Sending neuron
Ca2+
axon of
sending
neuron
axon
terminal
Synaptic vesicles
enclose neurotransmitter.
Synapse
receiving
neuron
Receiving neuron Synaptic
cleft
2. Neurotransmitter
molecules
are released
and bind to
receptors
on the
membrane of
the receiving
neuron.
Receiving neuron
neurotransmitter
neurotransmitter
receptor
Na+
Figure 14.4 Signal transmission at
the synapse.
Receiving
neuron
ion
channel
3. When an
excitatory
neurotransmitter
binds to a
receptor,
Na+ diffuses
into the
receiving
neuron, and
an action
potential
begins.
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14.1 Overview of the Nervous System
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.
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14.1 Overview of the Nervous System
Synaptic integration
Figure 14.5 Integration of excitatory and inhibitory signals at the synapse.
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14.2 The Central Nervous System
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
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14.2 The Central Nervous System
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
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14.2 The Central Nervous System
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.
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14.2 The Central Nervous System
What does the spinal cord look like?
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white matter
gray matter
central canal
a.
gray matter
white matter
spinal cord
vertebra
Figure 14.7 The organization of white and gray matter in
the spinal cord and the spinal nerves.
dorsal root
dorsal root
ganglion
spinal
nerve
vertebra
ventral root
b.
central canal
dorsal root
dorsal root
ganglion
dorsal
dorsal root
branches
gray matter
white matter
dorsal root
ganglion
ventral
spinal
nerve
ventral root
cut vertebrae
meninges
c.
d. Dorsal view of spinal cord and dorsal roots of spinal nerves.
a: © Karl E. Deckart/Phototake; d: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer and Don Kincaid, dissections
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14.2 The Central Nervous System
The CNS: Brain
Four major parts
1.
2.
3.
4.
Cerebrum
Diencephalon
Cerebellum
Brain stem
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14.2 The Central Nervous System
The CNS: Overview of the brain
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lateral
third
ventricle ventricle
pineal
gland
Cerebrum
skull
meninges
corpus
callosum
Diencephalon
thalamus
(surrounds the
third ventricle)
hypothalamus
pituitary gland
Brain stem
midbrain
pons
Cerebellum
fourth ventricle
medulla
oblongata
spinal cord
b. Cerebral hemispheres
a. Parts of brain
Figure 14.8 The human brain.
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14.2 The Central Nervous System
The brain: Cerebrum
• Cerebral hemispheres
• Cerebral cortex
• Primary motor and sensory areas of
the cortex
• Association areas
• Processing centers
• Central white matter
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14.2 The Central Nervous System
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
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14.2 The Central Nervous System
1. The brain: Cerebrum –
The cerebral lobes
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central sulcus
Frontal lobe
Parietal lobe
primary somatosensory area
primary motor area
premotor area
leg
motor speech
(Broca’s) area
trunk
somatosensory
association area
primary taste area
arm
prefrontal
area
hand
general interpretation area
face
anterior
ventral
tongue
posterior
dorsal
Occipital lobe
primary
olfactory
area
lateral sulcus
Temporal lobe
primary
visual area
visual
association
area
auditory association area
primary auditory area
sensory speech (Wernicke’s) area
Figure 14.9 The lobes of the cerebral hemispheres.
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14.2 The Central Nervous System
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
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14.2 The Central Nervous System
1. The brain: Cerebrum –
The cerebral cortex
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arm
trunk
forearm
thumb, fingers,
and hand
swallowing
hand, fingers,
and thumb
thigh
foot and
toes
a. Primary
motor area
longitudinal
fissure
leg
upper
face
leg
facial
expression
salivation
vocalization
mastication
arm neck trunk pelvis
forearm
thigh
pelvis
foot and
toes
lips
teeth and
gums
tongue and
pharynx
Figure 14.10 The primary motor and primary somatosensory areas of the brain.
genitals
b. Primary
somatosensory
area
longitudinal
fissure
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14.2 The Central Nervous System
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
34
14.2 The Central Nervous System
2. The brain: Diencephalon
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lateral
third
ventricle ventricle
pineal
gland
Cerebrum
skull
meninges
corpus
callosum
Diencephalon
thalamus
(surrounds the
third ventricle)
hypothalamus
pituitary gland
Brain stem
midbrain
pons
Cerebellum
fourth ventricle
medulla
oblongata
spinal cord
b. Cerebral hemispheres
a. Parts of brain
Figure 14.8 The human brain.
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14.2 The Central Nervous System
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)
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14.2 The Central Nervous System
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
37
14.2 The Central Nervous System
The reticular formation
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RAS radiates
to cerebral
cortex.
thalamus
reticular
formation
ascending sensory
tracts (touch, pain,
temperature)
Figure 14.11 The reticular formation of the brain.
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14.3 The Limbic System and Higher Mental Functions
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
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14.3 The Limbic System and Higher Mental Functions
The limbic system
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corpus
thalamus callosum
hypothalamus
olfactory bulb
olfactory tract
amygdala
Figure 14.12 The regions of the brain
associated with the limbic system.
hippocampus
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14.3 The Limbic System and Higher Mental Functions
Higher mental functions
• 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
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14.3 The Limbic System and Higher Mental Functions
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
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14.3 The Limbic System and Higher Mental Functions
What parts of the brain are
active in reading and speaking?
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primary auditory cortex
visual cortex
1. The word is seen in the
visual cortex.
Wernicke’s area
2. Information concerning the
word is interpreted in
Wernicke’s area.
primary motor cortex
Broca’s area
3. Information from Wernicke’s
area is transferred to 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.
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14.4 The Peripheral Nervous System
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
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14.4 The Peripheral Nervous System
The peripheral nervous system
Figure 14.14 The structure of a nerve.
45
14.4 The Peripheral Nervous System
The peripheral nervous system
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Cranial Nerves
I
from olfactory
receptors
II
from retina of
eyes
III
to eye muscles
IV
to eye muscles
V
from mouth and
to jaw muscles
VI
to eye muscles
VII from taste buds
and to facial
muscles and
glands
VIII from inner ear
IX
from pharynx
and to pharyngeal
muscles
XII to tongue
muscles
X from and to
internal organs
XI to neck and
back muscles
Figure 14.15 The cranial nerves.
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14.4 The Peripheral Nervous System
The PNS: Somatic division
• The somatic system serves the skin,
skeletal muscles and tendons.
• Automatic responses are called reflexes.
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14.4 The Peripheral Nervous System
The PNS: Somatic division
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pin
central canal
dorsal root ganglion
white matter
sensory
receptor
(in skin)
dendrites
Dorsal
gray matter
dorsal
horn
cell body of sensory
neuron
dendrite of sensory neuron
interneuron
dendrites
axon of motor neuron
cell body of
motor neuron
effector
(muscle)
ventral root
ventral horn
Ventral
Figure 14.16 The events in a spinal reflex.
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14.4 The Peripheral Nervous System
The PNS: Autonomic division
• The autonomic system regulates the
activity of involuntary muscles (cardiac and
smooth) and glands.
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14.4 The Peripheral Nervous System
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.
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14.4 The Peripheral Nervous System
The PNS: Autonomic division
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stimulates tears
constricts pupils
inhibits tears
dilates
pupils
Sympathetic Division
ganglion
Parasympathetic Division
inhibits salivation
stimulates
salivation
cranial
nerves
slows heart
speeds
heart
dilates air
passages
cervical
nerves
constricts
bronchioles
stimulates liver to
release glucose
stimulates gallbladder
to release bile
stimulates
adrenal
secretion
thoracic
nerves
vagus nerve
increases activity
of stomach and
pancreas
inhibits activity
of kidneys,
stomach, and
pancreas
increases
intestinal
activity
decreases
intestinal activity
lumbar
nerves
ganglion
inhibits
urination
Figure 14.17 The two
divisions of the
autonomic nervous
system.
causes
orgasmic
contractions
sympathetic ganglia
stimulates
urination
causes
erection
of genitals
sacral
nerves
Acetylcholine is neurotransmitter.
Norepinephrine is neurotransmitter.
51
14.5 Drug Therapy and Drug Abuse
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.
52
14.5 Drug Therapy and Drug Abuse
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.
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14.5 Drug Therapy and Drug Abuse
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.
54
14.5 Drug Therapy and Drug Abuse
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.
55
14.5 Drug Therapy and Drug Abuse
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.
56
14.5 Drug Therapy and Drug Abuse
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.
57
14.5 Drug Therapy and Drug Abuse
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.
58
14.5 Drug Therapy and Drug Abuse
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.
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