The nervous system functions to receive information from inside and outside the body, respond to stimuli, and maintain homeostasis. It is made up of neurons, which are cells that transmit electrochemical signals. There are three main types of neurons - sensory neurons detect stimuli, interneurons relay signals between neurons, and motor neurons activate glands and muscles. Nerve impulses travel along neurons when they are stimulated, moving from dendrites to the cell body and then down the axon to the axon tip via changes in electrical potential. At synapses, chemicals transmit impulses across gaps to the next neuron or structure.

1. Chapter 15 The Nervous System
What does it mean when someone
says that something makes them
nervous?

2. 15.1 Lecture
How the nervous system
works?

3. Section 1: How the Nervous System
Works
What are the functions of the nervous system?
What is the structure of a neuron and what kinds
of neurons are found in the body?
How do nerve impulses travel from one neuron
to another?
• 7.5.b• 7.5.b Students know organ systems function
because of the contributions of individual
organs, tissues, and cells. The failure of any
part can affect the entire system.

4. Functions of the Nervous System
• Includes the brain, spinal chord, and nerves that
run throughout the body.
– It also includes sense organs, such as the eyes and
ears.
• Communication network
• The nervous system receives information about
what is happening both inside and outside your
body.
• It also directs the way in which your body
responds to this information.
• In addition, your nervous system helps maintain
homeostasis.

5. Receiving Information
• Allows you to know what is going on around
you
• Checks conditions inside your body, for
example blood pressure

6. Responding to Information
• Stimulus = a change or signal in an organism’s
surroundings that causes the organism to
react.
• Response = an action or change in behavior
that occurs in reaction to a stimulus.
• Some responses are voluntary, some are
involuntary.

7. Maintaining Homeostasis
• Directs the body based on information it
receives.

8. WHAT IS A STIMULUS?
HINT: LOOK AT YOUR NOTES OR GO BACK TWO SLIDES
Reading Checkpoint

9. The Neuron
• Neurons = a cell that
carries information
through the nervous
system.
• Nerve impulse = a
message carried by a
neuron.

10. The Structure of a Neuron
• A neuron has a large cell body that
contains the nucleus, threadlike
extensions called dendrites, and an
axon.
• Dendrites = a threadlike extension
of a neuron that carries nerve
impulses toward the cell body.
• Axon = a threadlike extension of a
neuron that carries nerve impulses
away from the cell body.
• Nerve = a bundle of nerve fibers.

11. Kinds of Neurons
• Three kinds of neurons are found in the body –
sensory neurons, interneurons, and motor
neurons.
• Sensory neurons = a neuron that picks up stimuli
from the internal or external environment and
converts each stimulus into a nerve impulse.
• Interneurons = a neuron that carries nerve
impulses from one neuron to another.
• Motor neurons = a neuron that sends an
impulse to a muscle or gland, causing the muscle
or gland to react.

12. WHAT IS THE FUNCTION OF AN AXON?
HINT: LOOK AT YOUR NOTES OR GO BACK TWO SLIDES
Reading Checkpoint

13. How a Nerve Pulse Travels
• Billons of nerve impulses a day in the form of
chemical and electrical signals
1. begins at the dendrites
2. moves towards cell body
3. moves down axon to axon tip
• 120 meters per second!

14. The Synapse
• Then passes to another
structure:
– dendrite of another neuron
– muscle
– other organ
• Synapse = the junction
where one neuron can
transfer an impulse to
another structure.

15. How an Impulse is Transferred
• For a nerve impulse to be carried along at a
synapse, it must cross the gap between the
axon and the next structure.
• The axon tips release chemicals that carry the
impulse across the gap.