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Lab 9 (ƒ 10) - Cranial Nerve Nuclei and Brain Stem Circulation

Cranial Nerve XI - Review (continued)

This is a section through the lower, “closed,” medulla near its junction with the spinal cord. Find the spinal trigeminal nucleus and tract. Fibers of the trigeminal (predominantly), facial, glossopharyngeal and vagus (V, VII, IX, and X, respectively) nerves travel in the spinal trigeminal tract and terminate within the spinal trigeminal nucleus. Note that this nucleus is continuous with the substantia gelatinosa (spinal cord). Recall that the sensations mediated by the spinal trigeminal nucleus are simple touch, pain and temperature from the face.

The spinal accessory nucleus (axons exit the brain in Cranial nerve XI) is a cell column extending from the anterior horn of the fifth (or sixth) cervical segment up into the medulla to the level of the pyramidal decussation. In the spinal cord, the spinal accessory nucleus occupies the lateral process of the anterior horn. At this level of the medulla, the nucleus is located within the lateral aspect of the remnants of the anterior horn. The spinal accessory nucleus neurons synapse directly with bilateral corticobulbar fibers for volitional control of head rotation. In the medulla, the corticobulbar fibers are located in the pyramids. The spinal accessory nucleus also receives inputs from the tectospinal tract and the lateral and medial vestibulospinal tracts. Recall the motor functions of the tectospinal tract (control of motor responses to visual and acoustic stimuli)

Blood Supply

At this level of the brain stem medial regions of the anterior medulla are supplied by branches of the anterior spinal artery. The major structures in the medial region include the pyramids, decussation of the pyramids, remnants of the anterior horn and the medial longitudinal fasciculus and tectospinal tract. The posterolateral regions of the medulla are supplied by branches of the posterior spinal arteries and include the fasciculi and nuclei gracilis and cuneatus. The mid-lateral regions of the medulla are supplied by branches of the vertebral artery and contain the spinal trigeminal nucleus and tract, the spinothalamic tracts, spinocerebellar tracts, rubrospinal tract, lateral vestibulospinal tract, medullary reticulospinal tract and the spinal accessory nucleus.