Chapter 33 Nervous System
Section 1: Structure of the Nervous System
Section 2: Organization of the Nervous System
Section 3: The Senses
Section 4: Effects of Drugs
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Chapter 33
Nervous System
33.1 Structure of the Nervous System
Neurons
 Neurons are specialized nerve cells that help
you gather information about your environment,
interpret the information, and react to it.
 Neurons consist of three main regions: the
dendrites, a cell body, and an axon.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
 Dendrites pass signals they receive on to the
cell body in electrical impulses.
 The axon passes those impulses on to the
other neurons or muscles.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
 There are three kinds of neurons: sensory
neurons, interneurons, and motor neurons.
 Sensory neurons
send impulses from
receptors in the skin
and sense organs to
the brain and spinal
cord.
 Interneurons carry impulses to motor organs.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
 Motor neurons carry impulses away from the
brain and spinal cord to a gland or muscles,
resulting in a secretion
or movement.
 The nerve impulse
completes a reflex
arc, or a nerve
pathway that
consists of a sensory neuron, an interneuron,
and a motor neuron.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
A Nerve Impulse
 Neurons at rest
do not conduct
impulses.
 Sodium ions (Na+)
collect on the outside
of the cell membrane.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
 Potassium ions (K+)
collect on the inside of
the cell membrane.
 Negatively charged
proteins actively
transport sodium ions
out of the cell and
potassium ions into the cell.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
An Action Potential
 A nerve impulse is also known as an action
potential.
 The minimum
stimulus to cause an
action potential to be
produced is called a
threshold.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
 When a stimulus reaches
threshold, channels open
in the plasma membrane.
 Sodium ions are rapidly
pumped through these
channels causing a
temporary change in the
electrical charges.
 More positive charges are
now inside the membrane.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
 The now positive charge
inside the membrane
causes other channels to
open and the potassium
is quickly pumped out of
the cell.
 The potassium restores
the positive charge
outside the cell.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
 This rapid positive to
negative to positive
charge reversal moves
along the axon like a
wave.
 The movement can be
seen by finding the
sodium-potassium
reversal pattern in the
three diagrams.
Chapter 33
Nervous System
33.1 Structure of the Nervous System
Speed of an Action Potential
 Nodes along the axon allow ions to pass
through the myelin layer to the plasma
membrane.
 The ions jump from node to node and
increase the speed of the impulse.
Visualizing
Action Potential
Chapter 33
Nervous System
33.1 Structure of the Nervous System
The Synapse
 The small gap between the axon of one
neuron and the dendrite of another neuron
is called a synapse.
 An action potential is carried across these
gaps by neurotransmitters.
Chapter 33
Nervous System
Chapter 33
Nervous System
33.2 Organization of the Nervous System
 The nervous system
consists of two major
divisions: the central
nervous system and
the peripheral nervous
system.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
The Central Nervous System
 The central nervous system (CNS) is made
up mostly of interneurons.
 Coordinates all of the body’s activities
 Relays messages, processes information,
and analyzes responses
Chapter 33
Nervous System
33.2 Organization of the Nervous System
The Brain
 The brain is
sometimes called
the control center
of the entire body.
 Divided into the
cerebrum, the
cerebellum, and
the brain stem.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
 The cerebrum is divided into two halves
called the left and right hemispheres.
 The functions of the brain include thought
processes (learning), memory, language,
speech, voluntary body movements, and
sensory perception.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
 The cerebellum controls balance, posture,
and coordination.
 The skeletal muscles are controlled to make
your motor skills coordinated and smooth.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
 The brain stem connects the brain and
spinal cord and is composed of the medulla
oblongata and the pons.
 The medulla oblongata helps control breathing
rate, heart rate, and blood pressure.
 The pons also aids in breathing.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
 The hypothalamus, located between the
brain stem and the cerebrum, is essential
for homeostasis.
 Regulates body temperature, thirst, appetite,
and water balance.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
The Spinal Cord
 Nerve column that
extends from the brain
to the lower back.
 Protected by the
vertebrae
 Processes reflexes
Chapter 33
Nervous System
33.2 Organization of the Nervous System
The Peripheral Nervous System
 A nerve is a bundle of axons and may contain
sensory and motor neurons.
 The peripheral nervous system (PNS) contains
all the neurons that are not part of the central
nervous system.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
The Somatic Nervous System
 Nerves in the somatic nervous system relay
information from external sensory receptors to
the central nervous system, and motor nerves
relay information from the central nervous
system to skeletal muscles.
 Voluntary movements and reflexes are a part
of the somatic nervous system.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
The Autonomic Nervous System
 The autonomic nervous system carries
impulses from the central nervous system
to the heart and other internal organs.
 The body responds involuntarily, not under
conscious control.
Chapter 33
Nervous System
33.2 Organization of the Nervous System
 There are two branches of the autonomic
nervous system.
 The sympathetic nervous system is most
active in times of emergency or stress when
the heart rate and breathing rate increase.
 The parasympathetic nervous system is most
active when the body is relaxed.
Chapter 33
Nervous System
Chapter 33
Nervous System
33.3 The Senses
Taste and Smell
 Specialized neurons in your body enable you
to taste, smell, hear, see, and touch, and to
detect motion and temperature.
 Taste buds detect combinations of chemicals
that we identify as sweet, sour, salty, and
bitter.
Chapter 33
Nervous System
33.3 The Senses
 Receptors associated
with taste and smell
are located in the
mouth and nasal
cavity.
 Signals from these
receptors work
together to create
a combined effect in the brain.
Chapter 33
Nervous System
33.3 The Senses
Sight
 Light travels through the cornea and the pupil
to the lens.
 The lens focuses
the image on the
retina.
 Rods and cones in
the retina provide
light-sensitivity and information about color.
Chapter 33
Nervous System
33.3 The Senses
Hearing
 Sound waves enter the auditory canal and
cause a membrane,
called the tympanum,
at the end of the ear
canal to vibrate.
 These vibrations
cause the cochlea to generate nerve impulses
that are interpreted by the brain.
Chapter 33
Nervous System
33.3 The Senses
Balance
 The semicircular canals, located in the
inner ear, transmit information about body
position and balance to the brain.
Chapter 33
Nervous System
33.3 The Senses
Touch
 Many types of
sensory receptors
that respond to
temperature,
pressure, and pain
are found in the
epidermis and
dermis layers of
the skin.
Chapter 33
Nervous System
33.4 Effects of Drugs
How Drugs Work
 A drug is a substance, natural or artificial,
that alters the function of the body.
Chapter 33
Nervous System
Chapter 33
Nervous System
33.4 Effects of Drugs
 Some drugs affect the nervous system in the
following ways:
 can cause an increase in the amount of a
neurotransmitter that is released into a synapse
 can block a receptor site on a dendrite,
preventing a neurotransmitter from binding
 can prevent a neurotransmitter from leaving
a synapse
 can imitate a neurotransmitter
Chapter 33
Nervous System
33.4 Effects of Drugs
 Many drugs that affect the nervous system
influence the level of
a neurotransmitter
called dopamine.
 Normally, dopamine
is removed from a
synapse by being
reabsorbed by the neuron that released it.
Chapter 33
Nervous System
33.4 Effects of Drugs
Classes of Commonly Abused Drugs
 Stimulants
 Drugs that increase alertness and
physical activity
 Nicotine
 Caffeine
Chapter 33
Nervous System
33.4 Effects of Drugs
Depressants
 Drugs that tend to slow down the central
nervous system
 Alcohol
 Inhalants
 Illegal drugs
Chapter 33
Nervous System
33.4 Effects of Drugs
Tolerance and Addiction
 Tolerance occurs when a person needs more
and more of the same drug to get the same
effect.
 The psychological and/or physiological
dependence on a drug is addiction.
Chapter 33
Nervous System
Chapter Resource Menu
Chapter Diagnostic Questions
Formative Test Questions
Chapter Assessment Questions
Standardized Test Practice
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Animation
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Chapter 33
Nervous System
Chapter Diagnostic
Questions
Which is not one of the main parts of
a neuron?
A. axon
B. cell body
C. dendrites
D. nucleus
Chapter 33
Nervous System
Chapter Diagnostic
Questions
Another name for a nerve impulse
is _______.
A. synapse
B. threshold
C. reflex arc
D. action potential
Chapter 33
Nervous System
Chapter Diagnostic
Questions
What occurs when a motor neuron
synapses with a muscle cell?
A. muscle contracts
B. muscle relaxes
C. pain
D. numbness
Chapter 33
Nervous System
33.1 Formative
Questions
What type of neuron begins a reflex arc?
A. interneuron
B. motor neuron
C. sensory neuron
D. transmitter neuron
Chapter 33
Nervous System
33.1 Formative
Questions
What is another name for nerve impulse?
A. synapsis
B. threshold
C. action potential
D. neurotransmitter
Chapter 33
Nervous System
33.1 Formative
Questions
True or False
A stronger stimulus will cause a stronger
action potential.
Chapter 33
Nervous System
33.1 Formative
Questions
When a neuron is at
rest, what maintains
the high concentration
gradients of potassium
ions inside the cell and
sodium ions outside
the cell?
Chapter 33
Nervous System
33.1 Formative
Questions
A. diffusion
B. osmosis
C. active transport
D. ion channels
Chapter 33
Nervous System
33.2 Formative
Questions
Which is not part of the central nervous
system?
A. brain
B. spinal cord
C. interneurons
D. sensory neurons
Chapter 33
Nervous System
33.2 Formative
Questions
What does the cerebrum regulate?
A. breathing and heart rates
B. complex motor skills
C. sleep, aggression, and fear
D. voluntary body movements
Chapter 33
Nervous System
33.2 Formative
Questions
True or False
Some reflexes are processed only in the
spinal cord and do not need input from the
brain.
Chapter 33
Nervous System
33.2 Formative
Questions
What is a nerve?
A. a bundle of axons
B. a chain of neurons
C. a sensory synapse
D. a series of impulses
Chapter 33
Nervous System
33.2 Formative
Questions
What part of the nervous system is usually
under voluntary control?
A. autonomic nervous system
B. somatic nervous system
C. sympathetic nervous system
D. parasympathetic nervous system
Chapter 33
Nervous System
33.3 Formative
Questions
What are sensory receptors?
A. cells that create action potentials and
thresholds
B. localized areas of the central nervous
system
C. chemicals that cross a synapse between
two nerve cells
D. specialized neurons for detecting the
world around you
Chapter 33
Nervous System
33.3 Formative
Questions
Which part of the eye contains lightdetecting receptors?
Chapter 33
Nervous System
33.3 Formative
Questions
What is the function of the optic nerve?
A. It forms a visual image.
B. It controls the muscles of the iris.
C. It interprets light intensity and colors.
D. It sends action potentials to the brain.
Chapter 33
Nervous System
33.3 Formative
Questions
Where are sound vibrations converted
into nerve impulses?
Chapter 33
Nervous System
33.3 Formative
Questions
Where are the sensory receptors that
detect your body’s position and motion?
Chapter 33
Nervous System
33.4 Formative
Questions
Why is caffeine a drug?
A. It is a depressant.
B. It is an artificial substance.
C. It influences the nervous system.
D. It builds tolerance to its effects.
Chapter 33
Nervous System
33.4 Formative
Questions
Which neurotransmitter is influenced by
nicotine and amphetamines, and is involved
with most types of addiction?
A. adenosine
B. dopamine
C. epinephrine
D. serotonin
Chapter 33
Nervous System
33.4 Formative
Questions
Which is not a stimulant?
A. alcohol
B. caffeine
C. nicotine
D. methamphetamine
Chapter 33
Nervous System
33.4 Formative
Questions
What is the term for the body’s decreased
response to a drug?
A. addiction
B. dependence
C. tolerance
D. withdrawal
Chapter 33
Nervous System
33.4 Formative
Questions
When people who are addicted try to quit, why
is it difficult to resist going back to the drug?
A. Adenosine levels increase.
B. Dopamine levels decrease.
C. The central nervous system slows down.
D. Action potentials in neurons become
stronger.
Chapter 33
Nervous System
33.4 Formative
Questions
True or False
Physiological dependence on a drug is
stronger than psychological dependence.
Chapter 33
Nervous System
Chapter Assessment
Questions
Name the part of
the brain that is
responsible for
memory.
A. hypothalamus
B. medulla oblongata
C. cerebrum
D. cerebellum
Chapter 33
Nervous System
Chapter Assessment
Questions
Contrast the functions of the cerebellum
and the cerebrum.
Answer: The cerebellum controls balance,
coordination, and motor skills.
The cerebrum controls learning,
memory, speech, voluntary body
movements, and sensory
perception.
Chapter 33
Nervous System
Chapter Assessment
Questions
What part of the
brain is identified in
the image?
A. pons
B. cerebrum
C. hypothalamus
D. medulla oblongata
Chapter 33
Nervous System
Standardized Test
Practice
How do nerve impulses travel in a neuron?
A. dendrite
B. dendrite
C. dendrite
cell body
cell body
cell body
axon
axon
axon
Chapter 33
Nervous System
Standardized Test
Practice
What carries signals from the axon of one
neuron to the dendrite of another neuron?
A. interneurons
B. ion channels
C. neural nodes
D. neurotransmitters
Chapter 33
Nervous System
Standardized Test
Practice
Which word best describes the
hypothalamus?
A. processor
B. reflexor
C. regulator
D. transmitter
Chapter 33
Nervous System
Standardized Test
Practice
What part of the brain is highly developed
in animals that have finely tuned balance
and complex coordination?
A. cerebellum
B. medulla
C. thalamus
D. temporal lobe
Chapter 33
Nervous System
Standardized Test
Practice
How do the sympathetic and parasympathetic
nervous systems act together?
A. They send and receive neurotransmitters.
B. They send opposing signals to the same
organs.
C. They balance voluntary and involuntary
responses.
D. They receive the same impulses from
different receptors.
Chapter 33
Nervous System
Standardized Test
Practice
Why is this receptor
located closest to the
surface of the skin?
Chapter 33
Nervous System
Standardized Test
Practice
A. It detects cold.
B. It detects heat.
C. It detects heavy pressure.
D. It detects light touch.
Chapter 33
Nervous System
Standardized Test
Practice
What substances in the body are most
closely associated with a drug’s influence
on the nervous system?
A. endorphins
B. Na+ and K+ ions
C. neurotransmitters
D. proteins
Chapter 33
Nervous System
Standardized Test
Practice
Where in the nerve pathway do drugs
have their primary effect?
A. axons
B. dendrites
C. synapses
D. myelin sheaths
Chapter 33
Nervous System
Standardized Test
Practice
Which step is blocked by cocaine?
Chapter 33
Nervous System
Glencoe Biology Transparencies
Chapter 33
Nervous System
Image Bank
Chapter 33
Nervous System
Vocabulary
Section 1
neuron
node
dendrite
synapse
cell body
neurotransmitter
axon
reflex arc
action potential
threshold
Chapter 33
Nervous System
Vocabulary
Section 2
central nervous
system
peripheral nervous
system
cerebrum
medulla oblongata
pons
hypothalamus
somatic nervous
system
autonomic nervous
system
sympathetic
nervous system
parasympathetic
nervous system
Chapter 33
Nervous System
Vocabulary
Section 3
taste bud
lens
retina
rods
cochlea
semicircular canal
Chapter 33
Nervous System
Vocabulary
Section 4
drug
dopamine
stimulant
depressant
tolerance
addiction
Chapter 33
Nervous System
Animation
 Visualizing Action Potential
 Impulse Movement