Lesson Overview The Neuron

Objectives 31.1The Neuron

-Identify the functions of the nervous system.

-Describe the function of neurons.

-Describe how a nerve impulse is transmitted

Lesson Overview The Neuron

Functions of the Nervous System

The Nervous System is divided into the:

1. Central Nervous System

2. Peripheral Nervous System

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Functions of the Nervous System1. The central nervous

system, consists of the brain and spinal cord, processes the information and creates a response.

2. The peripheral nervous system, consists of nerves and supporting cells, collects information about the body’s external and internal environment.

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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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Types of Neurons

Neurons can be classified into three types:

1. Sensory neurons carry impulses from the sense organs to the spinal cord and brain.

2. Motor neurons carry impulses from the brain and the spinal cord to muscles and glands.

3. Interneurons process information from sensory neurons and then send commands to motor neurons.

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Structure of Neurons

The largest part of a typical neuron is its cell body, which contains the nucleus and much of the cytoplasm.

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Structure of Neurons

Spreading out from the cell body are short, branched extensions called dendrites, which RECEIVE information.

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Structure of Neurons

The long fiber that carries impulses AWAY from the cell body is the axon.

An axon ends at the axon terminal.

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The Resting Neuron

Neurons have a charge, or electrical potential, across their cell membranes.

The inside of a neuron has a voltage of –70 millivolts (mV) compared to the outside. This difference is known as the resting potential.

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A Nervous Impulse

A neuron remains in its resting state until it receives a stimulus large enough to start a nerve impulse.

Once this happens ion channels open and the electrical charge inside and outside the neuron reverse.

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Threshold

The minimum level of a stimulus that is required to cause an impulse in a neuron is called its threshold.

*Any stimulus that is weaker than the threshold will not produce an impulse.

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The Synapse

The point at which a neuron transfers an impulse to another cell is called a synapse.

The space that physically separates two neurons is called a synaptic cleft.

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Neurotransmitters

Neurotransmitters are chemicals that transmit an impulse across the synapse.

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True or False• Your nervous system receives information that a baseball is being

thrown in your direction. After the information is processed by your brain, your central nervous system directly stimulates the muscles in your hands to catch the ball. _________________________

• Spreading out from the cell body of a neuron are short, branched extensions called axons that gather information. _________________________

• Myelin sheaths can be damaged by strokes or nutritional deficiencies. If a neuron has a damaged myelin sheath, impulses move faster through the axon than they would in a healthy neuron. _________________________

• When a stimulus is weaker than the threshold of a neuron, it will not produce an impulse. _________________________

• A resting potential is produced when the inside of the cell temporarily becomes more positive than the outside of the cell._________________________

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Answers• Your nervous system receives information that a baseball is being

thrown in your direction. After the information is processed by your brain, your central nervous system directly stimulates the muscles in your hands to catch the ball. False, peripheral

• Spreading out from the cell body of a neuron are short, branched extensions called axons that gather information. False, dendrites

• Myelin sheaths can be damaged by strokes or nutritional deficiencies. If a neuron has a damaged myelin sheath, impulses move faster through the axon than they would in a healthy neuron. False, slower

• When a stimulus is weaker than the threshold of a neuron, it will not produce an impulse. True

• A resting potential is produced when the inside of the cell temporarily becomes more positive than the outside of the cell.

False, action potential