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35-2 The Nervous System
1. What are the functions of the nervous system?
The nervous system controls and coordinates functions throughout the body and responds to internal and external stimuli.
2. What are impulses?
The electrical signal messages carried by the nervous system.
3. What are the cells that transmit these impulses called?
Neurons.
Photo Credit: AP/Wide World Photos.
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Neurons
4. How are neurons classified?
According to the direction in which an impulse travels.
5. What are the three types of neurons and their functions?
Sensory neurons carry impulses from the sense organs to the spinal cord and brain.
Motor neurons carry impulses from the brain and spinal cord to muscles and glands.
Interneurons connect sensory and motor neurons and carry impulses between them.
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Neurons
Structures of a Neuron
Nucleus
Dendrites
Axon terminals
Cell body
Myelin sheath
The nervous system controls and coordinates functions throughout the body. The basic units of the nervous system are neurons.
Axon
Nodes
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Neurons
6. What are characteristics of the different parts of
a neuron?
The largest part of a typical neuron is the cell body. It contains the nucleus and much of the cytoplasm.
Dendrites extend from the cell body and carry impulses from the environment toward the cell body.
The axon is the long fiber that carries impulses away from the cell body.
The axon ends in axon terminals.
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5. What are the three types of neurons?
The cells that transmit electrical signals called impulses are _____, or nerve cells.
What are the three types of neurons?
Match the following neuron parts and functions:
Largest part of a neuron a. dendrites
Extend from cell body b. axons
Long fibers that carry impulses c. cell body
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Neurons
7. What are the other parts of an neuron?
The axon is sometimes surrounded by an insulating membrane called the myelin sheath. There are gaps in the myelin sheath, called nodes, where the membrane is exposed.
8. How are nodes involved in an impulse?
Impulses jump from one node to the next.
Myelin sheath
Nodes
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Neurons
9. How are impulses transmitted from one neuron
to another?
The sodium-potassium pump is used to create an electric potential across the membrane of the neuron.
10. How is a nerve impulse transmitted?
An impulse begins when a neuron is stimulated by another neuron or by the environment.
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The Nerve Impulse
Sodium-Potassium Pump
The sodium-potassium pump in the neuron cell membrane uses the energy of ATP to pump sodium out of the cell and, at the same time, to pump potassium in. This ongoing process maintains resting potential.
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9. What are the gaps called in the myelin sheath?
What things jump from one node to the next?
The sodium-potassium pump is used to create a(n) _______ _______ across the membrane of the neuron.
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The Synapse
11. What happens at the end of the neuron?
The impulse reaches an axon terminal. Usually the neuron makes contact with another cell at this site. The neuron may pass the impulse along to the second cell.
12. What is the synapse?
The location at which a neuron can transfer an impulse to another cell.
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The Synapse
13. How is the impulse transmitted across the synapse?
Terminals contain vesicles filled with neurotransmitters.
14. What are they?
They are chemicals used by a neuron to transmit an impulse across a synapse to another cell.
When an impulse reaches the end of the axon of one neuron, neurotransmitters are released into the synaptic cleft. The neurotransmitters bind to receptors on the membrane of an adjacent dendrite.
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The Synapse
15. How are sodium ions involved?
They rush across the membrane, stimulating the next cell. If the stimulation exceeds the cell’s threshold, a new impulse begins.
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The location at which a neuron can transfer an impulse to another cell is called a ________.
Neurotransmitters are ________ used by a neuron to ______ ___ ______ across a synapse to another cell.
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35-2
Neurons that carry impulses from the brain and spinal cord to the muscles are
interneurons.
sensory neurons.
resting neurons.
motor neurons.
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35-2
The part of the neuron that carries impulses toward the cell body is the
axon.
myelin sheath.
dendrite.
nodes.
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35-2
The minimum level of a stimulus that is required to activate a neuron is called its
action potential.
resting potential.
threshold.
synapse.
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35-2
Chemicals that are used by a neuron to transmit impulses are called
neurotransmitters.
synapses.
axons.
inhibitors.
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35-2
An action potential begins when
sodium ions flow into the neuron.
potassium ions flow into the neuron.
sodium and potassium ions flow into the neuron.
sodium and potassium ions flow out of the neuron.
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