Chapter 1. Motor Control: Getting Things Moving

In this activity you will explore how the nervous system produces movement. In particular, you will consider the organization of neural areas related to movement, the hierarchical control of movement, and how neural firing rates in the motor cortex adjust to movements.

After completing this activity, you should be able to:

• Describe the different cortical areas involved in movement and their primary roles in movement.
• Describe neuronal firing rate adjustments for changes in force required for movement.
• Explain the connection between the descending motor tracks and location of movements (distal or proximal).
• Understand how other non-cortical neuronal circuits modulate movement.

This activity relates to the following principles of nervous system function:

• Principle 1: The Nervous System Produces Movement in a Perceptual World the Brain Constructs
• Principle 4: The CNS Functions on Multiple Levels
• Principle 6: Brain Systems Are Organized Hierarchically and in Parallel
• Principle 7: Sensory and Motor Divisions Permeate the Nervous System

Movement requires the use of multiple CNS areas, including the cerebrum, the brainstem, and the spinal cord. Multiple frontal lobe cortical areas are important for the initiation of appropriate movements and are primarily involved in different aspects of any movement.

Imagine that you are sitting in class, listening to a lecture, and you have decided to write down what your instructor has just said. The motor actions necessary to complete this voluntary task can be described in three simplified steps. Watch the video below and read the descriptions to see the connection between cortical areas and these simplified steps.

The first step in this movement is to decide to pick up the pencil and the paper to write a note. The prefrontal cortex (PFC) is important for planning appropriate movements including the decision to move. The second step in this voluntary task is to coordinate the placement of paper on the table and movement to pick up the pencil. The premotor cortex is important for the coordination of movements necessary to properly place the paper and pencil. The third step is producing the specific grasp needed to pick up the pencil. The motor cortex is critical for producing skilled movements like the grasp necessary to pick up the pencil.

The motor cortex, located in the frontal lobe, controls focal skilled movements, such as grasping an object. Researchers have learned about the role and importance of the motor cortex in these skilled movements by observing the neuronal firing patterns in the motor cortex before, during, and after a movement is made. Motor cortex neurons increase their firing rate prior to the actual movement and change firing rates depending on the amount of force required in the movement.

Using the pincer grip to pick up an object requires a focal skilled movement, and thus the motor cortex. Let’s examine the typical neural firing pattern in the motor cortex that we can expect when grasping various objects. Each line in the meter underneath the brain image represents an action potential produced in the neuron.

Let’s look more closely at how the motor cortex produces movement. Bundles of axons originating from the motor cortex divide in the brainstem into two corticospinal tracts—the lateral corticospinal tract and the anterior corticospinal tract. These axons carry neural information (action potentials) from the motor cortex to the brainstem and spinal cord so that movements can be executed.

Injury to the corticospinal tracts can result in paralysis to various parts of the body, depending on where the injury is located. Let’s investigate some possible injuries and their effects on movement. Select each of the three boxed regions of the figure to read a brief description.

Note: you must choose all areas before proceeding.

Congratulations! You have successfully completed the activity. In this activity, you reviewed the anatomical and functional roles of multiple cortical areas in the frontal lobe related to motor movement and examined how motor cortex neurons respond to changes in force required to perform motor tasks. You then explored the connection between regions of the descending corticospinal tracks and types of motor movement. Finally, you learned about the basal ganglia and how they can modulate activity in the motor cortex.

Your instructor may now have you take a short quiz about this activity. Good luck!