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Ch. 3 S. 1
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Ch. 3 S. 1
The Nervous System
Obj: Explain how __________________ are transmitted by neurons, and describe the functions of the
______________________________ and the _________________ nervous system.
The Nervous System
The _________________ system regulates our internal functions. It is also involved in how we react
to the external world. Even learning and __________________ are made possible by the nervous
system. When we learn a new behavior or acquire new information, the nervous system registers
that experience and changes to accommodate its _________________.
Two main parts: the central nervous system and the peripheral nervous system.
• ___________________ nervous system – consists of the brain and the spinal cord.
• ____________________________ nervous system – made up of nerve cells that send messages
between the central nervous system and all the parts of the ____________.
Neurons
Nerve cells, called __________________, run through our entire bodies and __________________
with each other. Neurons send and receive messages from other structures in the body, such as
muscles and glands. These messages can affect events ranging from the sensation of a pinprick to
the first steps of a child, from the writing of a poem to the memory of a past event. Each of us has
more than 100 ___________________ neurons, most of which are found in the brain.
Components of a Neuron
Neurons are somewhat like _______________ in structure. Parts of neurons resemble the
_______________________, trunk, and _______________ of a tree. And, as in forests, many
nerve cells lie alongside one another like a thicket of trees. Unlike tress, however, neurons can
also lie end to end. Their “roots” are intertwined with the “branches” of neurons that lie below.
Every neuron consists of a cell body, dendrites, and an axon. The ______________________
produces energy that fuels the activity of the cell. Branching out from the cell body are think fibers
called _____________________. The dendrites receive information from other neurons and pass
the message through the cell body.
While the dendrites carry information to the cell body, the _______________ carries messages away.
A neuron has many dendrites but usually only one axon.
Axons vary greatly in _______________. Some are just a tiny fraction of an inch, while others stretch
to several feet. Because of the length of their axons, some neurons in your legs are several feet
long.
Many axons are covered with __________________, a white fatty substance that insulates and
protects the axon. This myelin sheath, or casing, also helps to speed up the transmission of the
message. At the end of the axon, smaller fibers branch out. These fibers are called
__________________________________.
The Communication Process
_______________________ are sent from the axon terminals of one neuron to the dendrites of other
neurons. In order for a message to be sent from one neuron to another neuron, it must cross the
_______________. The synapse is a junction between the axon terminals of one neuron and the
dendrites of another neuron. Messages travel in only one direction. Thus, messages are received
by the dendrites and _______________ through the cell body and the axon to the axon terminals.
From there, they cross synapses to the dendrites of other neurons. New synapses can develop
between neurons that were not previously connected, as when we learn something new.
The information that is sent and the place to which it goes depend on a number of factors. These
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factors include the ____________________ of the neuron in the body and the _______________
that produced the message. Sensory neurons are nerve cells that carry information received by the
senses to the central nervous system. ________________ neurons, on the other hand, are nerve
cells that carry information from the central nervous system to the muscles and the glands and
influence their functioning.
Occasionally, something happens to _______________ the message-sending process. For example,
a hard ______________ to the head from a car accident or a sports injury can cause a
________________________-an injury in which the soft tissue of the brain hits against the skull.
Sometimes, the person is affected for only a few seconds. Other times, the person may experience
effects for a much longer time.
Neurotransmitters: Chemical Messengers
Neurons send messages across synapses through the release of ______________________.
Neurotransmitters are chemicals that are stored in ____________ in the axon terminals. A neuron
______________, or sends its message, by releasing neurotransmitters-much like droplets of
water shooting out of a spray bottle. Neurons can fire hundreds of times every second.
There are several types of neurotransmitters. Each has its own structure and fits into a receptor site
on the next neuron, similar to the way in which a key fits into a lock. The message is converted into
an _____________________ impulse that travels the length of the neuron. The message is then
transmitted to the next neuron by neurotransmitters. The process continues until the message
arrives at its _____________________. This whole process takes only a _______________ of a
second.
Neurotransmitters are involved in _____________________ people do. Whenever a person waves a
hand, yawns, or thinks about a friend, neurotransmitters are involved. Some diseases and
psychological disorders may also be caused by the presence of too much or too little of various
neurotransmitters.
Researchers have identified _________________ of neurotransmitters and their functions. Examples:
noradrenaline-prepares the body for action; seratonin-emotional arousal and sleep; dopaminemotor behavior, but a deficiency plays a role in Parkinson’s and an excess may contribute to
_____________________________.
The Central Nervous System
Consists of the neurons of the spinal cord and the brain. The _____________________ extends from
the brain down the back. It is a column of nerves about as thick as a ______________, and it is
protected by the bones of the spine. It transmits messages between the brain and the muscles and
the ________________ throughout the body.
The spinal cord is also involved in spinal _____________________. A spinal reflex is a simple,
_______________________ response to something. For example, if a person touches a hot stove,
a message goes immediately from his or her hand to the spinal cord. A message to remove the
hand is then sent back to motor neurons in the hand. The ________________ of the hand is a
spinal reflex. (The person may also register pain in his or her brain. But the pain is not what causes
the reflex. In fact, the pain may not even be felt until after the hand has been removed.)
The Peripheral Nervous System
The ________________________ nervous system lies outside the central nervous system and is
responsible for transmitting ________________________ between the central nervous system and
all parts of the body. The two main _______________________ of the peripheral nervous system
are the somatic nervous system and the autonomic nervous system.
The Somatic Nervous System
The ____________________ nervous system transmits sensory messages to the central nervous
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system. It is activated by touch, pain, changes in temperature, and changes in body position. The
somatic nervous system enables us to experience the sensations of hot and cold and to feel pain
and pressure. For example, we can feel the softness a cat’s fur. The somatic system also
__________________ us that parts of the body have moved or changed positions. It sends
messages to the muscles and the glands and helps us maintain ___________________ and
balance.
The Autonomic Nervous System
The word autonomic means “occurring involuntarily,” or automatically. The __________________
nervous system regulates the body’s _______________ functions, such as heartbeat, breathing,
digestion, and blood pressure. We generally do not have to think about these activities-they occur
_________________________ and are essential for keeping us alive.
Psychologists are interested in the autonomic system because of its involvement in the experience of
_________________. The response of the autonomic nervous system is particularly important
when a person experiences something ____________________ in the environment.
This system has two ____________________: the sympathetic and the parasympathetic nervous
system. These systems generally have opposing functions.
 The ______________________ system is activated when a person is going into action. This is
the “fight or flight” response. It does this by ____________________ digestion, increasing the
heart and respiration rates, and _____________________ the blood pressure.
 The __________________________ system restores the body’s reserves of energy after an
action has occurred. Heart rate and blood pressure are normalized, breathing is slowed, and
digestion returns to normal.