Concept Practice
Structure of a Motor Neuron

Chapter 1. Structure of a Motor Neuron

axon
part of a neuron specialized to send impulses to other neurons (or to muscles and glands)
axon terminals
branching fibers at the end of an axon that contain the neurotransmitters (also called synaptic terminals or terminal buttons)
cell body
part of a neuron that contains the genetic material (in the nucleus) and generates energy; also called the <i>soma</i>
central nervous system (CNS)
the spinal cord and the brain
dendrites
parts of a neuron specialized to receive messages from other neurons and conduct them toward the cell body
interneurons
neurons in the brain and spinal cord that link sensory and motor neurons
motor neurons
neurons that carry instructions from the central nervous system to the body's organs and tissue
myelin
fatty, insulating coating on some axons; speeds up the movement of the neural impulse
nervous system
the body's fast communication system, consisting of billions of neurons; divided into the peripheral and central nervous systems
neural impulse
an electrical signal that carries a message along an axon
neuron
a single nerve cell, forming the basic unit of the nervous system
neurotransmitters
chemical messengers released by the axon terminal into the synaptic gap between neurons
peripheral nervous system (PNS)
the sensory and motor neurons outside the brain and spinal cord
sensory neurons
neurons that carry information from the body's tissues and organs to the central nervous system
Structure of a Motor Neuron
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The figure includes an image of a cell with a cell body on the left side of the screen. Extending from the cell body is a tube, which is the axon. The axon is surrounded by small sections that look like rolls of insulation around the axon. At the end of the axon it branches into many smaller tubes, which end with axon terminals. The cell has many dendrites extending from the cell body as well, which look like branches.
Learning Objectives:

Identify the major parts of a motor neuron.

Describe the functions of the major parts of a motor neuron.

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The figure includes an image of various cells connected to each other via axons and dendrites. The axons are surrounded by small sections that look like rolls of insulation around the axon. At the end of each axon it branches into many smaller tubes, which end with axon terminals. Each cell has many dendrites extending from the cell body as well, which look like branches, which are connected to other cells.

1. Neurons are the building blocks of the nervous system. The human body contains an estimated 90 billion neurons, with most of them contained within the brain and spinal cord (the central nervous system).

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2. Within the peripheral nervous system, sensory neurons carry information toward the brain, and motor neurons carry control signals from the brain to the muscles and glands. Interneurons relay messages from one neuron to another within the central nervous system.

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3. All neurons have the same basic structure, shown here in a motor neuron. The bushy dendrite fibers receive information and conduct it toward the cell body, which generates a neural impulse.

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4. The axon passes the neural impulse from the cell body to the knoblike terminals at the axon's end, where it triggers the release of chemical messengers called neurotransmitters, which relay the information to the dendrites of other neurons.

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5. A neural impulse travels faster in axons that are encased in a fatty sheath called myelin.

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Practice 1: Functions of the Neuron Structures

Roll over each label to see a brief description.

Function of the selected neuron structure:

receive signals from other neurons

generates energy and contains genetic material

carries signals from cell body to other neurons

increases speed of neural impulses

contain neurotransmitters; form junctions with dendrites

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Practice 2: Myelin and Neural Messages

Play the animation to watch how myelin forms and speeds up neural transmission.

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      dnd_test

      Quiz 1

      Drag each label to the gray area connected to the appropriate structure. When all the labels have been placed, select the CHECK ANSWER button.

      The figure includes an image of a cell on the left side of the screen, which the various parts unlabeled. The following descriptions are for the labels from left to right on the cell. The first label points to the center of the cell itself. The second label points to the many branches extending from the cell body. The third label points to the tube extending from the cell. The fourth label points to the rolls of insulation around the tube. The fifth label is at the endings of the tube where they have branched into many smaller tubes.
      asset/activities/motor_neuron/images/practice_2.svg
      Select the NEXT button and move to Quiz 2.
      Perhaps you should go back to review the structures in a motor neuron.
      Myelin
      Dendrites
      Axon terminals
      Cell body
      Axon
      matching_test

      Quiz 2

      Match the terms for structures with their functions by dragging each colored circle to the appropriate gray area. When all the circles have been placed, select the CHECK ANSWER button.

      Select the NEXT button and move to the Conclusion.
      Perhaps you should go back to review the structures in a motor neuron.
      dendrite
      cell body
      axon
      myelin
      axon terminal
      increases the speed of neural impulses
      contains neurotransmitters; forms junctions with other neurons
      generates energy for the neuron and contains genetic material
      carries signals to other neurons
      receives signals from other neurons
      end_slide
      The figure includes an image of a cell with a cell body on the left side of the screen. Extending from the cell body is a tube, which is the axon. The axon is surrounded by small sections that look like rolls of insulation around the axon. At the end of the axon it branches into many smaller tubes, which end with axon terminals. The cell has many dendrites extending from the cell body as well, which look like branches.
      Congratulations!
      You have completed the activity Structure of a Motor Neuron.