1. A patient suddenly developed weakness of his left arm; somatic sensations were not affected. Damage to which of the following brain regions is the most likely site of injury?

A. Ventral spinal cord white matter
B. Lateral spinal cord white matter
C. Ventral pons
D. Precentral gyrus

Comment: The patient has a highly selective lesion because the impairment is restricted to the left arm. White matter lesions in the brain stem and spinal cord are unlikely to produce a single limb motor impairment because axons from all body parts intermingle within very small regions. Among the choices, only the precentral gyrus has a clear somatotopic organization. Moreover, occlusion of a small cortical branch of the middle cerebral artery could selectively damage the arm area of primary motor cortex, in the precentral gyrus.
 

2. Complete the following analogy. Limb control is to trunk control, as

A. the lateral corticospinal tract is to the ventral corticospinal tract.
B. the reticulospinal tract is to the rubrospinal tract.
C. the motor cortex on the medial brain surface is to the motor cortex on the lateral brain surface.
D. the middle cerebral artery is to the basilar artery.

Comment: Both the medial and lateral motor cortex represent limb muscles. The territories supplied by the middle cerebral and basilar arteries also contain pathways or nuclei for both limb and trunk control.

3. Which of the following statements best describes why unilateral damage to the descending cortical pathway in the basis pedunculi results only in weakness/ paralysis of contralateral arm and leg muscles, but not trunk muscles?

A. Trunk muscles are not controlled by the corticospinal tract.
B. Trunk muscles are controlled by the rubrospinal tract.
C. Trunk muscles receive bilateral corticospinal tract control.
D. Trunk muscles are controlled by the corticobulbar tract, which was spared.

4. Which of the following statements does not describe a feature of the ventral corticospinal tract?

A. It descends primarily to the cervical spinal cord only.
B. It controls distal muscles only.
C. It descends in the ipsilateral ventral column.
D. It terminates bilaterally in the spinal cord.

5. The rubrospinal tract

A. is similar in function to the lateral corticospinal tract.
B. decussates in the spinal cord.
C. synapses only on motor neurons.
D. descends in the medial brain stem and spinal cord.

Comment: The rubrospinal tract is a lateral path and thus descends laterally in the spinal cord. As with other motor pathways, it synapses both on interneurons and motor neurons.

6. Which of the following statements best describes a key feature of the reticulospinal tracts?

A. They are components of the lateral descending pathways.
B. They descend to the cervical spinal cord only.
C. They originate from the medulla.
D. They regulate relatively automatic behaviors.

7. Occlusion of cortical branches of the anterior cerebral artery would disrupt control of which of the following muscle groups?

A. Foot
B. Arm
C. Neck
D. Face

Comment: In the motor cortex, the foot representation is supplied by the anterior cerebral artery.

8. The genu of the internal capsule contains which of the following fibers?

A. Corticospinal fibers from primary motor cortex.
B. Corticobulbar fibers from primary motor cortex.
C. Corticospinal and corticobulbar fibers from primary motor cortex.
D. Corticospinal and corticobulbar fibers from premotor cortical areas.

9. Occlusion of paramedian branches of the basilar artery will most likely infarct which of the following motor system components?

A. Pyramids
B. Rubrospinal tract
C. Corticospinal and corticobulbar tracts
D. Reticulospinal tract

10. The enlargement segments correspond to which of the following?

A. Thoracic segments
B. Segments innervating the limbs
C. Segments innervating the trunk
D. Segments with a greater number of medial motor neurons