Transcript 35-2 The Nervous System

Biology
Slide
1 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
Slide
2 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
35-2 The Nervous System
The nervous system
•
controls/coordinates functions in the
body
•
responds to internal & external stimuli.
Slide
3 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
Neurons
Neurons
Messages carried by the nervous system are
electrical signals called impulses.
The cells that transmit these impulses are called
neurons.
Slide
4 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
Neurons
Neurons are classified according to where the an
impulse travels.
• 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.
Slide
5 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
Neurons
Structures of a Neuron
Nucleus
Dendrites
Axon
terminals
Cell body
Myelin sheath
Axon
Nodes
Slide
6 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
Neurons
The largest part of a typical neuron is the cell body.
It contains the nucleus and much of the cytoplasm.
Cell body
Slide
7 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
Neurons
Dendrites carry impulses from the environment
toward the cell body.
Dendrites
Slide
8 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
Neurons
Axon - long fiber that carries impulses away from the
cell body.
The axon ends in axon terminals.
Axon
terminals
Axon
Copyright Pearson Prentice Hall
Slide
9 of 38
35-2 The Nervous System
Neurons
Axon is surrounded by an insulating membrane myelin sheath.
Nodes - gaps in the myelin sheath.
Impulses jump from one node to the next.
Myelin sheath
Nodes
Slide
10 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
How is a nerve impulse transmitted?
Slide
11 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
The Moving Impulse
An impulse begins when a neuron is
stimulated by another neuron or by the
environment.
Slide
12 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
Slide
13 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
Slide
14 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
Slide
15 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
Slide
16 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
Threshold
A stimulus must be of adequate strength to cause
a neuron to transmit an impulse.
The minimum level of a stimulus that is required to
activate a neuron is called the threshold.
A stimulus that is weaker than the threshold
produces no impulse.
Slide
17 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Synapse
The Synapse
At the end of the neuron, the impulse reaches an
axon terminal.
The neuron makes contact with another cell at this
site.
The neuron may pass the impulse along to the
second cell.
The location at which a neuron can transfer an
impulse to another cell is called a synapse.
Slide
18 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Synapse
A Synapse
Slide
19 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Synapse
The synaptic cleft
separates the axon
terminal from the
dendrites of the next
cell.
Synaptic cleft
Copyright Pearson Prentice Hall
Slide
20 of 38
35-2 The Nervous System
Terminals contain
vesicles filled with
neurotransmitters.
The Synapse
Vesicle
Neurotransmitters
are chemicals used by
a neuron to transmit
an impulse across a
synapse to another
cell.
Neurotransmitter
Slide
21 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
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.
Copyright Pearson Prentice Hall
The Synapse
Receptor
Slide
22 of 38
35-2 The Nervous System
The Synapse
The next cell is simulated.
If the stimulation exceeds the cell’s threshold, a new
impulse begins.
Slide
23 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Synapse
Moments 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.
Slide
24 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
DIVISIONS OF THE
NERVOUS SYSTEM
Slide
25 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Central Nervous System
The Central Nervous System
• The central nervous system relays messages,
processes information, and analyzes
information.
Slide
26 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Peripheral Nervous System
The Peripheral Nervous System
• The peripheral nervous system is all of the
nerves and associated cells that are not part of
the brain and the spinal cord.
• The peripheral nervous system includes cranial
nerves, spinal nerves, and ganglia.
• Ganglia are collections of nerve cell bodies.
Slide
27 of 38
Copyright Pearson Prentice Hall
35-2
Click to Launch:
Continue to:
- or -
Slide
28 of 38
Copyright Pearson Prentice Hall
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.
Slide
29 of 38
Copyright Pearson Prentice Hall
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.
Slide
30 of 38
Copyright Pearson Prentice Hall
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.
Slide
31 of 38
Copyright Pearson Prentice Hall
35-2
Chemicals that are used by a neuron to transmit
impulses are called
a. neurotransmitters.
b. synapses.
c. axons.
d. inhibitors.
Slide
32 of 38
Copyright Pearson Prentice Hall
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.
Slide
33 of 38
Copyright Pearson Prentice Hall
END OF SECTION
35-2 The Nervous System
The Nerve Impulse
The Nerve Impulse
The Resting Neuron
When resting, the outside of the neuron has a net
positive charge.
The inside of the neuron has a net negative
charge.
The cell membrane is electrically charged because
there is a difference in electrical charge between
its outer and inner surfaces.
Slide
35 of 38
Copyright Pearson Prentice Hall
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.
Slide
36 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
Sodium-Potassium Pump
Slide
37 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
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.
The electrical charge across the cell membrane of a
neuron at rest is known as the resting potential.
Slide
38 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
The inside of the membrane temporarily becomes
more positive than the outside.
Slide
39 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
This is called a nerve impulse, or an action
potential.
Slide
40 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
As the action potential passes, K+ ions flow out
restoring the negative potential inside the axon.
Slide
41 of 38
Copyright Pearson Prentice Hall
35-2 The Nervous System
The Nerve Impulse
The impulse continues to move along the axon.
An impulse at any point of the membrane causes an
impulse at the next point along the membrane.
Slide
42 of 38
Copyright Pearson Prentice Hall