Slide 1 of 38 - Rhinelander School District body d. Contains neurons (nerve cells that carry the impulses) 35-2 The Nervous System Slide 5 of 38 Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall

Biology

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35-2 The Nervous System


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What are the functions of the nervous

system?


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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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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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Neurons

3. Structures of a Neuron

Axon

terminals

Myelin sheath

Cell body

Nodes Axon

Dendrites

Nucleus


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Neurons

a. cell body:

*largest part of neuron

* contains nucleus and cytoplasm.

Cell body


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Neurons

b. Dendrites:

* extend from the cell body

* carry impulses toward the cell body.

Dendrites


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Neurons

c. axon: long fiber that carries impulses away from

the cell body.

Axon

terminals

Axon


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Neurons

d. axon terminals: bulbs at end of axon

Axon

terminals

Axon


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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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Activity ----unmyelinated vs myelinated neurons.



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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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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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The Nerve Impulse

Sodium-Potassium Pump


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The Nerve Impulse

b. resting potential:

The electrical charge across the cell membrane of a

neuron at rest


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The Nerve Impulse

How is a nerve impulse transmitted?


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The Nerve Impulse

c. The Moving Impulse

1. An impulse begins when a neuron is

stimulated by another neuron or by the

environment.

Resources/Movies/vaaction.mov


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The Nerve Impulse

2. sodium channels open allowing Na+ ions to

flow inside the axon.


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The Nerve Impulse

(The inside of the membrane temporarily becomes

more positive than the outside)


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The Nerve Impulse

3. action potential: reversal of charges inside axon

*continues along axon


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The Nerve Impulse

4. As action potential passes, potassium

channels open (allowing K+ ions to flow

out restoring the negative potential inside the axon)


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The Nerve Impulse

5. Neuron returns to rest.


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The Nerve Impulse

D. Threshold:

*minimum level of a stimulus that is required to activate a neuron


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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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The Synapse

E. Synapse:

*location at which a neuron can

transfer an impulse to another cell


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The Synapse

A Synapse

Resources/Movies/vasynapt.mov


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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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The Synapse

(Terminals contain

vesicles filled with

neurotransmitters).

1. Neurotransmitters:

chemicals used by a

neuron to transmit an

impulse across a

synapse

Vesicle

Neurotransmitter


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The Synapse

(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.)

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.)

- or -

Continue to: Click to Launch:

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35-2

Resources/Movies/vasynapt.mov

Resources/Movies/vaaction.mov

Resources/ch35_sectn02_quiz.qtb

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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.

END OF SECTION

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Slide 1 of 38 - Rhinelander School District body d. Contains neurons (nerve cells that carry the impulses) 35-2 The Nervous System Slide 5 of 38 Copyright Pearson Prentice Hall