Download THE NEURON

Lesson Overview
The Neuron
SEC 31.1
THE NEURON
Lesson Overview
The Neuron
THINK ABOUT IT
How do we know about the world outside our bodies?
When you reach for a ball at a ballgame, how does
your body make this happen? How do the sights,
sounds, and smells at the ballgame get into your
mind?
The answers to all these questions are found in the
nervous system.
Lesson Overview
The Neuron
Functions of the Nervous System
• collects information about the body’s internal
and external environment
• processes that information
• responds to it.
Lesson Overview
The Neuron
Parts of the Nervous System
Central nervous system
(CNS)
• consists of the brain and
spinal cord
• processes information and
creates a response
Lesson Overview
The Neuron
Parts of the Nervous System
Peripheral nervous system
(PNS)
• consists of nerves and
supporting cells
• collects information about
the body’s external and
internal environment
• creates a response in
glands or muscles
Lesson Overview
The Neuron
Neurons
The messages carried by the nervous system
are electrical signals called impulses.
Nervous system impulses are transmitted by
cells called neurons.
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The Neuron
Types of Neurons
Grouped according to the direction an impulse travels
1. Sensory neurons carry impulses from the sense organs, such
as the eyes and ears, to the CNS (spinal cord and brain).
2. Motor neurons carry impulses from the CNS (brain and the
spinal cord) to muscles and glands.
3. Interneurons process information from sensory neurons and
then send commands to other interneurons or motor neurons.
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The Neuron
Structure of Neurons
The largest part of a typical neuron is the cell body,
which contains the nucleus and much of the
cytoplasm.
Lesson Overview
The Neuron
Structure of Neurons
Spreading out from the cell body are short,
branched extensions called dendrites.
Lesson Overview
The Neuron
Structure of Neurons
Dendrites receive impulses from other
neurons and carry impulses to the cell body.
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The Neuron
Structure of Neurons
The long fiber that carries impulses away from
the cell body is the axon.
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The Neuron
Structure of Neurons
An axon ends in a series of small swellings
called axon terminals.
Lesson Overview
The Neuron
Structure of Neurons
Neurons may have dozens of dendrites, but
usually they have only one axon.
In most animals, axons and dendrites of
different neurons are grouped into bundles
called nerves.
Lesson Overview
The Neuron
Structure of Neurons
In some neurons, the axon is surrounded by an
insulating membrane called the myelin sheath.
Nodes are gaps in the myelin where the axon
membrane is exposed.
Lesson Overview
The Neuron
Structure of Neurons
As an impulse moves along the axon, it jumps
from one node to the next. This causes an
impulse to travel faster than it would without a
myelin sheath.
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The Neuron
The Nerve Impulse
An impulse begins when a neuron is stimulated
by another neuron or by the environment.
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The Neuron
The Resting Neuron
Neurons have a charge, or electrical potential,
across their cell membranes.
The inside of a neuron is negative compared
to the outside. This difference is known as the
resting potential.
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The Neuron
The Resting Neuron
The movement of sodium ions (Na+) and potassium
ions (K+) is responsible for the charge difference.
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The Neuron
The Moving Impulse
A neuron remains in its resting state until it receives a
stimulus large enough to start a nerve impulse.
The impulse travels quickly down the axon toward the
axon terminals.
Lesson Overview
The Neuron
The Moving Impulse
The impulse will cause the nerve cell to
become positively charged. This is called a
nerve impulse, or an action potential.
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The Neuron
The Moving Impulse
When the impulse passes, the neuron
becomes negatively charged and the resting
potential is restored.
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The Neuron
The Synapse
The point at which a neuron
transfers an impulse to
another cell is called a
synapse.
A space, called the synaptic
cleft, separates the axon
terminal from the next cell.
Lesson Overview
The Neuron
The Synapse
The axon terminal at a
synapse contains tiny
structures filled with chemicals
called neurotransmitters.
These chemicals travel across
a synapse to cause an
impulse in another cell.
Lesson Overview
The Neuron
The Synapse
Then neurotransmitters
are broken down or
recycled by the axon
terminal.