35-2 The Nervous System

Pg. 897

Introduction

• 1. The Nervous system controls and manages functions in response to internal and external stimuli.

Introduction

• 2. Homeostasis occurs when organisms keep internal conditions constant despite changes in external conditions.

A. Neurons

• 1. Neurons are the cells that send messages through the body.

A. Neurons

• 2. The largest part of a neuron, containing the nucleus and most of the cytoplasm, is the cell body.

A. Neurons

• 3. Short and branched extensions that spread out from the cell body are called dendrites.

A. Neurons

• 4.The long fiber that carries a nerve impulse away from the cell body is called an axon.

A. Neurons • 5. Some axons are insulated by a membrane

called a myelin sheath.• 6. Axons that have a myelin sheath increase

the speed a nerve impulse can travel.

B. The Nerve Impulse

• 1. The resting potential of a neuron is the electrical charge of a neuron at rest.

B. The Nerve Impulse

• 2. A neuron at rest, has more positive charges on the outside of the cell and more negative charges in the cell.

B. The Nerve Impulse

• 3. When a neuron is stimulated by the environment or another neuron, an impulse (signal) travels through that neuron.

B. The Nerve Impulse

• 4. Protein channels along a neuron act as gateways for negative and positive charges.

B. The Nerve Impulse• 5. When the charges are

reversed from positive to negative, the neuron has an impulse in progress, or the action potential.

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C. The Synapse

• 1. The synapse is the space that separates the axon terminal of one neuron from the dendrites of the neighboring neuron.

C. The Synapse

• 2. Neurotransmitters are chemicals that travel along the synapse to transmit the impulse to the next neuron.