Biology
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35-2 The Nervous System
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35-2 The Nervous System
35-2 The Nervous System
What are the functions of the nervous
system?
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35-2 The Nervous System
35-2 The Nervous System
1. Nervous system:
a. controls and coordinates functions
throughout the body
b. responds to internal and external stimuli.
c. Carry impulses (electrical signals)
throughout body
d. Contains neurons (nerve cells that carry
the impulses)
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35-2 The Nervous System
Neurons
2. 3 Types of Neurons:
a. Sensory neurons:
carry impulses from the sense organs to the
spinal cord and brain.
b. Motor neurons:
carry impulses from the brain and spinal cord to
muscles and glands.
c. Interneurons:
connect sensory and motor neurons and carry
impulses between them.
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35-2 The Nervous System
Neurons
3. Structures of a Neuron
Nucleus
Dendrites
Axon
terminals
Cell body
Myelin sheath
Axon
Nodes
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35-2 The Nervous System
Neurons
a. cell body:
*largest part of neuron
* contains nucleus and cytoplasm.
Cell body
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35-2 The Nervous System
Neurons
b. Dendrites:
* extend from the cell body
* carry impulses toward the cell body.
Dendrites
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35-2 The Nervous System
Neurons
c. axon: long fiber that carries impulses away from
the cell body.
Axon
terminals
Axon
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35-2 The Nervous System
Neurons
d. axon terminals: bulbs at end of axon
Axon
terminals
Axon
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35-2 The Nervous System
Neurons
e. myelin sheath:
*an insulating membrane
*allows impulses to skip from node to node
f. Nodes:
*gaps in the myelin sheath.
Myelin sheath
Nodes
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35-2 The Nervous System
Activity ----unmyelinated vs myelinated neurons.
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35-2 The Nervous System
The Nerve Impulse
4. The Nerve Impulse (pg 899)
a. Resting Neuron
•outside of the neuron has a + charge.
• inside of the neuron has a - charge.
(The cell membrane is electrically charged
because there is a difference in electrical charge
between its outer and inner surfaces.)
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35-2 The Nervous System
The Nerve Impulse
(The sodium-potassium pump in the nerve cell
membrane pumps sodium (Na+) ions out of the cell
and potassium (K+) ions into the cell by means of
active transport.
As a result, the inside of the cell contains more K+
ions and fewer Na+ ions than the outside.
More K+ ions leak across the membrane than Na+
ions. This produces a negative charge on the inside
and a positive charge on the outside. )
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35-2 The Nervous System
The Nerve Impulse
Sodium-Potassium Pump
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35-2 The Nervous System
The Nerve Impulse
b. resting potential:
The electrical charge across the cell membrane of a
neuron at rest
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35-2 The Nervous System
The Nerve Impulse
How is a nerve impulse transmitted?
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35-2 The Nervous System
The Nerve Impulse
c. The Moving Impulse
1. An impulse begins when a neuron is
stimulated by another neuron or by the
environment.
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35-2 The Nervous System
The Nerve Impulse
2. sodium channels open allowing Na+ ions to
flow inside the axon.
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35-2 The Nervous System
The Nerve Impulse
(The inside of the membrane temporarily becomes
more positive than the outside)
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35-2 The Nervous System
The Nerve Impulse
3. action potential: reversal of charges inside axon
*continues along axon
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35-2 The Nervous System
out
The Nerve Impulse
4. As action potential passes, potassium
channels open (allowing K+ ions to flow
restoring the negative potential inside the axon)
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The Nerve Impulse
5. Neuron returns to rest.
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35-2 The Nervous System
The Nerve Impulse
D. Threshold:
*minimum level of a stimulus that is
required to activate a neuron
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35-2 The Nervous System
The Nerve Impulse
(A stimulus must be of adequate strength to cause
a neuron to transmit an impulse.
A stimulus that is stronger than the threshold
produces an impulse.
A stimulus that is weaker than the threshold
produces no impulse.)
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35-2 The Nervous System
The Synapse
E. Synapse:
*location at which a neuron can
transfer an impulse to another cell
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The Synapse
A Synapse
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The Synapse
(The synaptic cleft
separates the axon
terminal from the
dendrites of the
adjacent cell. )
Synaptic cleft
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35-2 The Nervous System
(Terminals contain
vesicles filled with
neurotransmitters).
The Synapse
Vesicle
1. Neurotransmitters:
chemicals used by a
neuron to transmit an
impulse across a
synapse
Neurotransmitter
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(As an impulse
reaches a terminal,
vesicles send
neurotransmitters
into the synaptic
cleft.
These diffuse across
the cleft and attach
to membrane
receptors on the
next cell.)
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The Synapse
Receptor
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The Synapse
(Sodium ions then rush across the membrane,
stimulating the next cell.)
2. If the stimulation exceeds the cell’s threshold, a
new impulse begins.
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The Synapse
(after binding to receptors, neurotransmitters are
released from the cell surface.
The neurotransmitters may then be broken down by
enzymes, or taken up and recycled by the axon
terminal.)
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35-2
Click to Launch:
Continue to:
- or -
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35-2
Neurons that carry impulses from the brain and
spinal cord to the muscles are
a. interneurons.
b. sensory neurons.
c. resting neurons.
d. motor neurons.
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35-2
The part of the neuron that carries impulses
toward the cell body is the
a. axon.
b. myelin sheath.
c. dendrite.
d. nodes.
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35-2
The minimum level of a stimulus that is required
to activate a neuron is called its
a. action potential.
b. resting potential.
c. threshold.
d. synapse.
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35-2
Chemicals that are used by a neuron to transmit
impulses are called
a. neurotransmitters.
b. synapses.
c. axons.
d. inhibitors.
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35-2
An action potential begins when
a. sodium ions flow into the neuron.
b. potassium ions flow into the neuron.
c. sodium and potassium ions flow into the
neuron.
d. sodium and potassium ions flow out of the
neuron.
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END OF SECTION