Sample NBDE Part I Question

Directions: Read the following question and select the best answer from the choices below.

Which of the following components of the extrapyramidal system primarily function to control skeletal muscle tone?

  1. Cerebellar nuclei
  2. Cerebral nuclei
  3. Red nucleus
  4. Superior colliculi
  5. Vestibular nuclei

Answer & Explanation:

The answer is C.

The axons of the pyramidal cells of the motor cortex descend to synapse on lower motor neurons in the brain stem and the spinal cord. Since there are no intervening synapses, the pyramidal system is able to provide rapid commands to the skeletal muscles and various other organs. There are several other centers that can issue somatic motor commands as a result of processing performed at the unconscious, involuntary level. These centers and their associated tracts comprise the extrapyramidal system. The red nucleus, located in the mesencephalon, is the component of the extrapyramidal system primarily in control of skeletal muscle tissue.

The cerebellar nuclei (choice A), located in the cerebellum, primarily controls coordination of movements and integration of sensory feedback.

The cerebral nuclei (choice B), also located deep in the cerebrum, primarily controls coordination and preparation of limb movements.

The superior colliculi (choice D), located in the mesencephalon, processes visual information and the vestibular nuclei (choice E), located in the pons and medulla oblongata, processes equilibrium sensations.