Chapter 11: Cranial Nerve Motor Nuclei and Brain Stem Motor Functions
Which statement below best describes the spatial relationship between cranial nerve motor and sensory nuclei in the medulla and pons?
A. Motor nuclei are ventral to sensory nuclei.
B. Motor nuclei are dorsal to sensory nuclei.
C. Motor nuclei are medial to sensory nuclei.
D. Motor nuclei are lateral to sensory nuclei.
Comment: Unlike the spinal cord, where the motor nuclei are located ventral to sensory nuclei, it is different in the caudal brain stem. This is because as the fourth ventricle develops, it displaces the sensory nuclei laterally. In the midbrain, the only cranial nerve sensory nucleus, the mesencephalic trigeminal nucleus, is located dorsal to the oculomotor nucleus, a dorsoventral organization like the spinal cord. Here in the midbrain, development of the narrow cerebral aqueduct does not displace the sensory nuclei.
Which of the following statements best describes the difference between the innervation of skeletal muscle and smooth muscle by central nervous system neurons?
A. Central nervous system neurons innervate skeletal muscle monosynaptically and innervate smooth muscle disynaptically, via a synapse in peripheral ganglia.
B. Central nervous system neurons innervate skeletal and smooth muscle monosynaptically.
C. Central nervous system neurons innervate skeletal muscle disynaptically, via a synapse in peripheral ganglia, and innervate smooth muscle monosynaptically.
D. Central nervous system neurons innervate skeletal and smooth muscle disynaptically, via a synapse in peripheral ganglia.
After an internal capsule stroke, a person can lose some cranial nerve motor functions. When this occurs the lost function typically is expressed only on the contralateral side. Which statement below best explains this contralateral pattern?
A. All corticobulbar projections are contralateral. Thus, a unilateral lesion will produce contralateral deficits affecting all cranial nerve motor nuclei.
B. All corticobulbar projections are bilateral, but the contralateral projections are the strongest. When these strong connections are eliminated after a unilateral lesion, contralateral deficits occur in all cranial nerve motor nuclei.
C. Some cranial nerve motor nuclei receive contralateral corticobulbar projections, whereas others receive a bilateral projection. Nevertheless, the contralateral projections are the strongest, and when they are eliminated after a unilateral lesion, contralateral deficits occur in all cranial nerve motor nuclei.
D. Cranial nerve motor nuclei that receive bilateral corticobulbar projections are protected from gross impairment after unilateral corticobulbar lesions, whereas ...