Chapter 7: Brain Mechanisms of Movement

Question 1

primary motor cortex 235

Answer 1

Neuroscientists have known that direct electrical
stimulation of the primary motor cortex—the precentral
gyrus of the frontal cortex, just anterior to the central sulcus —elicits movements.

Question 2

posterior parietal cortex 237

Answer 2

One of the first areas to become active in planning a movement is the posterior parietal cortex, which monitors the position of the body relative to the world.

Question 3

supplementary motor cortex 237

Answer 3

The prefrontal cortex and the supplementary motor cortex are also important for planning and organizing a rapid sequence of movements.

Question 4

antisaccade task 238

Answer 4

saccade is a voluntary eye movement from one target to another. Suppose you are staring straight ahead when something to one side or the other moves. You have a strong tendency to look toward the moving object. In the antisaccade task, you are supposed to
look the opposite direction. Most people agree that it is easier to look at the finger that moved than the other finger.

Question 5

mirror neurons 238

Answer 5

Mirror neurons, which are active both during preparation for a movement and while watching someone else perform the same or a similar movement.

Question 6

prefrontal cortex 238

Answer 6

The prefrontal cortex, which is also active during a delay before a movement, stores sensory information relevant to a movement. It is also important for considering the probable outcomes of possible movements. If you had damage to this area, many of your movements would be disorganized.

Question 7

premotor cortex 238

Answer 7

The premotor cortex is most active immediately before a movement. It receives information about the target to which the body is directing its movement, as well as information about the body’s current position and posture.

Question 8

corticospinal tracts 239

Answer 8

Paths from the cerebral cortex to the spinal cord are called the corticospinal tracts. We have two such tracts, the lateral and medial corticospinal tracts. Both tracts contribute in some way to nearly all movements, but a
movement may rely on one tract more than the other.

Question 9

lateral corticospinal tract 240

Answer 9

The lateral corticospinal tract is a pathway of axons
from the primary motor cortex, surrounding areas, and the red nucleus, a midbrain area that is primarily responsible for controlling the arm muscles. Axons of the lateral tract extend directly from the motor cortex to their target neurons in the spinal cord.

Question 10

red nucleus 240

Answer 10

A midbrain area that is primarily responsible for controlling the arm muscles.

Question 11

medial corticospinal tract 241

Answer 11

The medial corticospinal tract includes axons from many parts of the cerebral cortex, not just the primary motor cortex and its surrounding areas. The medial path also includes axons from the midbrain tectum, the reticular formation, and the vestibular nucleus, a brain area that receives input from the vestibular system. Axons of the medial tract go to both sides of the spinal cord, not just to the contralateral side. The medial tract controls mainly the muscles of the neck, shoulders, and trunk and therefore bilateral movements as walking, turning, bending, standing up, and sitting down.

Question 12

vestibular nucleus 241

Answer 12

A brain area that receives input from

the vestibular system.

Question 13

caudate nucleus 243

Answer 13

1

Question 14

cerebellar cortex 243

Answer 14

The cerebellum receives input from the spinal cord, from each of the sensory systems by way of the cranial nerve nuclei, and from the cerebral cortex.

The neurons are arranged in a precise geometrical
pattern, with multiple repetitions of the same units.
■ The Purkinje (pur-KIN-jee) cells are flat (twodimensional) cells in sequential planes, parallel to one another.
■ The parallel fibers are axons parallel to one another and perpendicular to the planes of the Purkinje cells.
■ Action potentials in parallel fibers excite one Purkinje cell after another. Each Purkinje cell then transmits an inhibitory message to cells in the nuclei of the cerebellum (clusters of cell bodies in the interior of the cerebellum) and the vestibular nuclei in the brainstem, which in turn send information to themidbrain and the thalamus.
Depending on which and how many parallel fibers are
active, they might stimulate only the first few Purkinje
cells or a long series of them. Because the parallel fibers’ messages reach different Purkinje cells one after another, the greater the number of excited Purkinje cells, the greater their collective duration of response. That is, if the parallel fibers stimulate only the first few Purkinje cells, the result is a brief message to the target cells; if they stimulate more Purkinje cells, the message lasts longer. The output of Purkinje cells controls the timing of a movement, including both its onset and offset.

Question 15

nuclei of the cerebellum 243

Answer 15

Nuclei of the cerebellum (clusters of cell bodies in the

interior of the cerebellum).

Question 16

parallel fibers 243

Answer 16

The parallel fibers are axons parallel to one another and perpendicular to the planes of the Purkinje cells.

Question 17

basal ganglia 243

Answer 17

The term basal ganglia applies collectively to a group of large subcortical structures in the forebrain. Various
authorities differ in which structures they include as part of the basal ganglia, but everyone includes at least the caudate nucleus, the putamen (pyuh-TAY-men), and the globus pallidus. The caudate nucleus and putamen together are known as the striatum or dorsal striatum.

Question 18

Purkinje cells 243

Answer 18

The Purkinje (pur-KIN-jee) cells are flat (twodimensional)
cells in sequential planes, parallel to one another.

Question 19

striatum or dorsal striatum 243

Answer 19

The striatum receives input from the cerebral cortex and substantia nigra and sends its output to the globus pallidus, which then sends output to the thalamus, which relays it to the frontal cortex. Two pathways, known as the direct and indirect pathways. The direct pathway from the striatum inhibits the globus pallidus, which inhibits part of the thalamus. By inhibiting an inhibitor, the net effect is excitation. Neuroscientists long believed that the direct pathway stimulates movements whereas the indirect pathway inhibits them. However, later evidence found that both pathways are active before a movement and neither is active
when the animal is at rest. Probably the direct pathway enhances the selected movement whereas the indirect pathway inhibits inappropriate competing movements. The indirect pathway is essential for learned performance.

Question 20

readiness potential 247

Answer 20

However, your motor cortex produces a kind of
activity called a readiness potential before any voluntary movement, and on the average, the readiness potential begins at least 500 ms before the movement. The key point is that the brain activity responsible for the movement apparently began before the person’s conscious decision! The results seem to indicate that your conscious decision does not cause your action.