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Name______________________________
Chapter 35
Class __________________
Date ______________
Nervous System
Summary
35–1 Human Body Systems
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The levels of organization in a multicellular
organism include cells, tissues, organs, and
organ systems. Cells are the basic units of
structure and function in living things. In
multicellular organisms, cells are specialized to perform certain functions. Tissues
are groups of similar cells that perform a
single function. There are four different
types of tissues. Epithelial tissue covers
body surfaces. Connective tissue supports
the body and connects its parts. Nervous
tissue carries messages throughout the
body. Muscle tissue enables the body to
move. An organ is a group of tissues that
work together to perform a complex function. An organ system is a group of organs
that perform related functions. Humans
have 11 organ systems.
Organ systems work together to maintain stable conditions in the body. The process of maintaining stable internal
conditions is called homeostasis. Homeostasis may involve feedback inhibition, or negative feedback. For example, the nervous
system senses when the body cools and signals the cells to produce more heat.
35–2 The Nervous System
The nervous system controls and coordinates
functions throughout the body and
responds to internal and external stimuli.
Messages carried by the nervous system are
electrical signals called impulses. Cells that
transmit impulses are called neurons. A
neuron has a cell body containing the nucleus. Short branches, called dendrites, carry
impulses toward the cell body. A long fiber,
called the axon, carries impulses away from
the cell body. A myelin sheath surrounds
parts of the axon in some neurons. Impulses
can jump over the myelin and travel faster.
A resting neuron is one that is not transmitting an impulse. Resting potential is the
difference in electrical charge across the cell
membrane of a resting neuron. An impulse
begins when a resting neuron is stimulated by
another neuron or by the environment. The
impulse is a sudden reversal of charge across
the cell membrane, called an action potential.
The lowest level of stimulus needed to activate a neuron is known as the threshold.
At the end of the axon is a synapse. A
synapse is the location at which a neuron
can transfer an impulse to another cell.
Chemicals called neurotransmitters transmit impulses across the synapse.
35–3 Divisions of the Nervous
System
The nervous system has two major divisions: the central nervous system and the
peripheral nervous system. The central nervous system is the control center of the
body. It relays messages, processes information, and analyzes information. The peripheral nervous system carries messages back
and forth between the environment and the
central nervous system.
The central nervous system consists of
the brain and spinal cord. Both are wrapped
in layers of tissue called meninges. Between
the meninges and nervous tissue is cerebrospinal fluid, which cushions and protects
nervous tissue.
The brain is divided into several regions.
The cerebrum controls voluntary actions.
The cerebellum controls actions of the muscles. The brain stem controls basic body
functions. The thalamus receives impulses
from the senses and sends them to the cerebrum. The hypothalamus connects the nervous and endocrine systems.
The spinal cord connects the brain and
rest of the body. Certain kinds of information, including some reflexes, are processed
directly in the spinal cord. A reflex is a
quick, automatic response to a stimulus.
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Sneezing is an example of a reflex. The
pathway an impulse travels in a reflex is
called the reflex arc.
The peripheral nervous system has two
divisions. The sensory division transmits
impulses from sensory neurons to the central nervous system. The motor division
transmits impulses from the central nervous
system to muscles and glands. The motor
division is further divided into somatic and
autonomic nervous systems. The somatic
nervous system controls voluntary actions.
The autonomic nervous system controls
involuntary actions.
35– 4 The Senses
The sense organs that detect taste are the
taste buds. Skin—the largest sense organ—
contains sensory receptors that respond to
temperature, touch, and pain.
35–5 Drugs and the Nervous
System
A drug is any substance, other than food,
that changes the structure or function of the
body. Several types of drugs can affect the
nervous system. Stimulants increase actions
controlled by the nervous system, such as
heart rate. Stimulants also increase the
release of neurotransmitters in the brain.
Depressants decrease actions, such as heart
rate, that are controlled by the brain.
Cocaine causes the sudden release in the
brain of a neurotransmitter called
dopamine. Opiates act like natural brain
chemicals called endorphins, which normally help overcome pain. Marijuana can
cause memory and concentration problems.
Alcohol is a depressant. It slows down
the central nervous system. Drinking alcohol during pregnancy may cause fetal alcohol syndrome (FAS). Babies born with FAS
have birth defects. People who are addicted
to alcohol have a disease called alcoholism.
Addiction is an uncontrollable dependence on a drug. Drug abuse is the intentional misuse of any drug for nonmedical
purposes. The best way to avoid the effects
of drugs is to avoid drugs.
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Sensory receptors are neurons that react to
stimuli in the environment and send
impulses to the central nervous system.
There are five types of sensory receptors.
Pain receptors respond to pain. Thermoreceptors respond to temperature.
Mechanoreceptors respond to pressure.
Chemoreceptors respond to chemicals.
Photoreceptors respond to light.
Light enters the eye through the pupil,
which is a small opening at the front of the
eye. Light then passes through the lens,
which focuses the light on the retina. Photoreceptors called rods and cones are located in the retina. Rods are sensitive to dim
light. Cones are sensitive to colors.
Sound vibrations enter the ear and create pressure waves in a fluid-filled structure
called the cochlea. Sensory receptors in the
cochlea send impulses to the brain. Three
tiny canals in the ear, called semicircular
canals, help the central nervous system
maintain balance.
Date ______________
Name______________________________
Chapter 35
Class __________________
Date ______________
Nervous System
Vocabulary Review
Completion Fill in the blanks in the table.
Tissue Type
Function
Epithelial
Connective
Nervous
Muscle
1.
2.
3.
4.
Covers body surfaces
Supports the body and connects its parts
Carries nerve impulses
Enables the body to move
True or False Determine whether each statement is true or false. If it is true, write true in the space
provided. If the statement is false, change the underlined word or words to make the statement true.
true
neurons
axon
threshold
true
6. Cells that transmit nerve impulses are known as meninges.
7. The long fiber that carries impulses away from the cell body of a nerve
cell is the dendrite.
8. The lowest level of stimulus needed to activate a neuron is called the
action potential.
9. The location at which a neuron can transfer an impulse to another cell is
referred to as a(an) synapse.
cerebrum
10. The part of the brain that controls voluntary actions is the brain stem.
thalamus
11. The part of the brain that receives impulses from the senses and sends
them to the cerebrum is the hypothalamus.
true
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5. The process by which organisms keep internal conditions relatively constant is called homeostasis.
12. Light enters the eye through a small opening called the pupil.
cones
13. Photoreceptors in the eye that are sensitive to colors are known as rods.
stimulants
14. Drugs called opiates increase actions controlled by the nervous system.
addiction
15. An uncontrollable dependence on a drug is known as drug abuse.
Answering Questions In the space provided, write an answer to each question.
16. List the levels of organization in a multicellular organism, from smallest to largest.
The levels of organization in a multicellular organism, from smallest to largest, are cells, tissues,
_____________________________________________________________________________
organs, and organ systems.
_____________________________________________________________________________
Resting potential is the difference in electrical charge across the cell
17. What is resting potential? ______________________________________________________
membrane of a resting neuron.
_____________________________________________________________________________
The function of the autonomic
18. What is the function of the autonomic nervous system? ____________________________
nervous system is to control involuntary actions.
_____________________________________________________________________________
Alcohol slows down the central
19. How does alcohol affect the central nervous system? ______________________________
nervous system.
_____________________________________________________________________________
Thermoreceptors react to temperature.
20. To which type of stimulus do thermoreceptors react? ______________________________