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The Nervous System   

                       Everyday your nervous system receives                  

                    millions of messages. The system receives

                    and then responds to stimuli inside and

outside of your body. (A stimulus is anything that causes a response.)  When you see, hear, smell, taste, or touch you receive messages and

your nervous system interprets them and allows a response.

  

   How does your nervous system accomplish this? How are messages received and transmitted throughout your body and how are the messages interpreted? How do you respond?

 

Learning Objectives

By the end of this lesson, students should be able to:

  • Describe the structure of a neuron and how an impulse moves from one neuron to the next.

  • Explain the difference between the central nervous system and the peripheral nervous system.

  • Describe the structure of the brain and identify the different sections and what they control.

  • Compare and contrast three types of neurons.

 

Vocabulary

axon—a long nerve fiber that carries an impulse from the cell body of one neuron to the dendrites of the next neuron.

 

central nervous system—the part of the nervous system consisting of the brain and spinal cord.

 

cerebrospinal fluid— fluid between the meninges that acts like a shock absorber to protect the brain against injuries.

 

cerebellum—the part of the brain that controls balance and voluntary muscle action.

 

cerebrum—the largest part of the human brain that controls thinking and awareness.

 

dendrites—branches of a neuron that receive stimuli.

 

impulse—a message or signal that travels the length of a neuron.

 

interneuron— the type of neuron that connects sensory neurons and motor neurons and interprets the impulse; interneurons are found only in the brain and spinal cord.

 

medulla—the part of the brain at the base of the skull that controls involuntary muscle action.

meninges—the layers of tissue that protect the brain.

 

motor neuron—the type of neuron that carries impulses from the brain and spinal cord to muscles or glands that allow a response.

 

myelin sheath— a layer of protein and fatty substances covering the axon of a nerve cell that allows the impulse to transmit quickly along nerve cells.

neuron—a nerve cell.

 

peripheral nervous system—the part of the nervous system that includes all neurons except those in the brain and spinal cord.

 

sensory neuron— the type of neuron that carries messages from sense organs to the central nervous system.

 

stimulus—anything that causes a response

 

synapse—the small space between neurons.

 

   Your nervous system has two main parts:

1) The central nervous system, made up of the brain and the spinal cord.

2) The peripheral nervous system, made up of all the nerves of the body other than the nerves in the brain and spinal cord.

   A nerve cell, or neuron, is the functional unit of your nervous system. It passes messages (impulses) from one neuron to another throughout the body at about 120 meters per second!

 

 

 

 

 

 

 

 

Image: Structure of a nerve cell. https://commons.wikimedia.org/wiki/File:Neuron.svg

 

Impulses move from neuron to neuron in a set direction:

   1) Dendrites receive the message (impulse).

   2) The impulse passes through the cell body.

   3)  It moves through and over the axon which is covered by a layer of protein and fatty substances called the myelin sheath. This sheath allows the impulse to transmit quickly along nerve cells.

   4) The impulse causes a chemical to be released at the end of the axon (axon terminal) into a space between neurons called the synapse.

   5) The synapse ends next to dendrites of the next neuron and the impulse is passed on.

 

Fast Fact: Not all organisms have a myelin sheath. Most vertebrates (animals having a backbone) have a myelin sheath and nodes on axons that allow impulses to jump from node to node instead of traveling through the entire axon. This allows for faster response. The more quickly an organism can respond, the better adapted it is to its environment.  

   

Types of Neurons

   There are three kinds of neurons depending on what they do and where they are:

1) sensory neurons—carry messages from sense organs to the central nervous system. Sensory neurons are in the eyes, ears, nose, mouth and skin.

 

Each of these organs contain cells called receptors that react to stimuli. You can smell because receptors in your nose send messages to your brain that allow you to interpret the smell.

 

2) motor neurons—carry impulses from the brain and spinal cord to muscles or glands that allow a response.

3) interneurons—connect the sensory neurons and motor neurons and interpret the impulse. Interneurons are found only in the brain and spinal cord.

 

The Central Nervous System—the Brain and Spinal Cord

   The brain is the major control center of all body functions. Both the brain and spinal cord are protected by three layers of tissue called the meninges. Between the layers is a space filled with cerebrospinal fluid. This fluid acts like a shock absorber to protect the brain against injuries.

 

The brain is divided into three major parts:

1) The cerebrum is the largest part of the brain and is divided into two large sections called hemispheres. The cerebrum is the site for intelligence, learning, judgment, all voluntary muscle control, memory, and personality.

The outer layer of the cerebrum is further divided into lobes: the frontal, temporal, parietal, and occipital lobes. Each section or lobe of the cerebrum controls different senses and abilities.

● frontal lobe - concentration, planning, problem solving

● parietal lobe - understanding speech, using words

● temporal lobe - interpretation of sensory stimuli, memory of visual and auditory patterns

● occipital lobe - visual interpretations, combining visual images with recognition

 

 

 

 

 

 

 

 

 

 

2) The cerebellum is the second largest part of your brain. It interprets sensory information from the limbs, coordinates complex muscle movements and helps maintain posture.
 

3) The brainstem extends from the cerebrum and connects the brain to the spinal cord. It is made up of the midbrain, the pons and the medulla. The brainstem controls heartbeat, breathing, blood pressure and involuntary muscle movements.

 

The Peripheral Nervous System

   The peripheral nervous system consists of all the nerves except for the brain and spinal cord. It is made up of 12 pairs of cranial nerves from the brain and 31 pairs of spinal nerves that branch out from the spinal cord to the limbs and trunk. Different bundles of neurons in your peripheral nervous system control your voluntary muscles (the muscles you chose to move) and your autonomic functions, such as your heartbeat, breathing, and digestion.

 

Check Your Understanding:

1. Name the three types of neurons and state their function.

2. Draw and label the structure of a typical nerve cell.

 

3. Describe the sequence of events that allow you to sense when you are burning your finger on a hot pan and that allow you to pull back from pan.

 

4. Label the cerebellum and the four lobes of the cerebrum on the following diagram.

 

 

 

 

 

 

 

 

 

 

 

 

 

5. State the function of the following parts of the brain:

a) cerebrum—

b) frontal lobe—

c) temporal lobe—

d) occipital lobe—

e) parietal lobe—

f) cerebellum—

g) medulla—

 

 

 

© Wheeling University, 2023. All rights reserved.

 

 

image of a human brain
diagram of a nerve cell from dendrite to axon terminal
diagram of the lobes of the human brain
nervous-lobes of the brain-unlabeled.jpg
NDH logo.jpg
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