Atlas of the Human Brainstem

Chapter 15 Atlas of the Human Brainstem^*

This series of five chapters on the functional anatomy of the brainstem concludes here, with a summary of the principal contents of the brainstem at each level (Figs. 15-1 to 15-3), a series of transverse sections of the brainstem (Figs. 15-4 to 15-9), and brief descriptions of structures that are indicated in these sections.

Figure 15-1 Three-dimensional reconstructions of the brainstem, with motor (left) and sensory (right) cranial nerve nuclei indicated. Dashed lines indicate the planes of the sections shown in Figures 15-4 to 15-9. Ab, abducens nucleus; Ac, accessory nucleus; Am, nucleus ambiguus; Co, cochlear nuclei; dV, dorsal motor nucleus of the vagus; EW, Edinger-Westphal nucleus; Fa, facial motor nucleus; Hy, hypoglossal nucleus; meT, mesencephalic nucleus of the trigeminal; msT, trigeminal main sensory nucleus; mT, trigeminal motor nucleus; Oc, oculomotor nucleus; Sal, salivary nuclei; Sol, nucleus of the solitary tract; spT, spinal trigeminal nucleus; Tr, trochlear nucleus; Ves, vestibular nuclei.

Figure 15-2 Schematic views of the transverse sections of the brainstem shown photographically in Figures 15-4 to 15-9, each enlarged to about three times its actual size. Major tracts and cranial nerve nuclei are indicated. DSCP, decussation of the superior cerebellar peduncles; IC, inferior colliculus; RN, red nucleus; SC, superior colliculus; SCP, superior cerebellar peduncle; SN, substantia nigra; other abbreviations as in Figure 15-1.

(Modified from Nolte J, Angevine JB Jr: The human brain in photographs and diagrams, ed 3, St. Louis, 2007, Mosby.)

Figure 15-3 Principal structures at different brainstem levels. Only the levels containing the major parts of structures are indicated. Many structures extend a short distance into adjacent levels (e.g., the nucleus of the solitary tract extends a bit into the caudal medulla and caudal pons). Raphe nuclei and other elements of the reticular formation are not indicated but are present at all brainstem levels. ALP, anterolateral pathway; CST, corticospinal tract; IC, inferior colliculus; ICP, inferior cerebellar peduncle; LCST, lateral corticospinal tract; MGN, medial geniculate nucleus; ML, medial lemniscus; MLF, medial longitudinal fasciculus; MVST, medial vestibulospinal tract; SCP, superior cerebellar peduncle.

Figure 15-4 Caudal medulla (close to the level of the obex).

1. Dorsal motor nucleus of the vagus. The caudal end of the nucleus of origin of most preganglionic parasympathetic neurons for thoracic and abdominal viscera.

2. Nucleus gracilis. Site of termination of fasciculus gracilis and the origin of the leg portion of the medial lemniscus.

3. Nucleus cuneatus. Site of termination of fasciculus cuneatus and the origin of the arm portion of the medial lemniscus.

4. Fasciculus cuneatus. Uncrossed primary afferents, carrying tactile and proprioceptive information from the arm.

5. Lateral cuneate nucleus. Arm equivalent of Clarke’s nucleus. Proprioceptive primary afferents travel through fasciculus cuneatus to reach the lateral cuneate nucleus, which then gives rise to uncrossed cuneocerebellar fibers that enter the cerebellum through the inferior cerebellar peduncle.

6. Spinal trigeminal nucleus (caudal nucleus). Site of termination of part of the spinal trigeminal tract, and the origin of part of the anterolateral pathway. At this level, the nucleus has the appearance of the spinal posterior horn, has a component similar to the substantia gelatinosa, and processes pain and temperature information.

7. Spinal trigeminal tract. Primary afferents from the ipsilateral side of the face, at this level conveying information about pain and temperature.

8. Posterior spinocerebellar tract. Uncrossed fibers from Clarke’s nucleus, carrying proprioceptive information from the leg that will reach the ipsilateral half of the cerebellar vermis and adjoining areas through the inferior cerebellar peduncle.

9. Anterolateral pathway. Mostly crossed fibers from the spinal posterior horns and intermediate gray, conveying pain and temperature information to the thalamus (spinothalamic tract), reticular formation, and midbrain.

10. Location of nucleus ambiguus. Lower motor neurons for laryngeal and pharyngeal muscles and preganglionic parasympathetic neurons for the heart.

11. Anterior spinocerebellar tract. Crossed fibers from lumbosacral spinal gray matter, carrying proprioceptive and other information from the leg. This tract stays in approximately the same position until the rostral pons, where it moves over the surface of the superior cerebellar peduncle (see Fig. 15-7) and turns posteriorly into the cerebellum.

12. Inferior olivary nucleus (medial accessory nucleus). The inferior olivary complex gives rise to climbing fibers that end in the contralateral half of the cerebellum (see Chapter 20). Those from the accessory nuclei project mainly to the vermis and flocculus, those from the principal inferior olivary nucleus to the cerebellar hemisphere.

13. Pyramid. Corticospinal fibers from the ipsilateral precentral gyrus and adjacent areas of cerebral cortex.

14. Raphe nuclei. Widely projecting serotonergic neurons that collectively blanket the central nervous system (CNS). Those in caudal brainstem levels such as this project mainly to the spinal cord.

15. Medial lemniscus, the principal ascending pathway for tactile and proprioceptive information. Originates in the contralateral posterior column nuclei and terminates in the thalamus (ventral posterolateral nucleus [VPL]).

16. Medial longitudinal fasciculus (MLF). At this level, the fibers of the medial vestibulospinal tract.

17. Hypoglossal nucleus. Lower motor neurons for the ipsilateral half of the tongue.

18. Hypoglossal nerve fibers, on their way to the muscles of the ipsilateral half of the tongue.

19. Internal arcuate fibers, crossing from nuclei gracilis and cuneatus to form the medial lemniscus, the principal ascending pathway for tactile and proprioceptive information.

20. Fibers of the vagus nerve, on their way to muscles of the ipsilateral half of the larynx and pharynx. These caudal filaments of the vagus were formerly considered separately as the cranial part of the accessory nerve, but they all actually join the vagus directly.

21. Solitary tract and its nucleus. Primary afferents conveying visceral information from cranial nerves VII, IX, and X (and some chemosensory information from the trigeminal nerve) travel through the solitary tract to reach the surrounding nucleus of the solitary tract. Only information from viscera reaches this caudal level.

22. Central canal. Merges rostrally with the fourth ventricle and caudally with the central canal of the spinal cord.

Figure 15-5 Rostral medulla.

1. Fourth ventricle.

2. Medial longitudinal fasciculus (MLF). At this level, the fibers of the medial vestibulospinal tract.

3. Hypoglossal nucleus. Lower motor neurons for the ipsilateral half of the tongue.

4. Dorsal motor nucleus of the vagus. Most of the preganglionic parasympathetic neurons for thoracic and abdominal viscera.

5. Nucleus of the solitary tract. Site of termination of the visceral primary afferents in the solitary tract.

6. Solitary tract. Primary afferents conveying visceral information from cranial nerves VII, IX, and X (and some chemosensory information from the trigeminal nerve) to the surrounding nucleus of the solitary tract.

7. Nucleus cuneatus. Site of termination of fasciculus cuneatus and the origin of the arm portion of the medial lemniscus.

8. Lateral cuneate nucleus. Arm equivalent of Clarke’s nucleus. Proprioceptive primary afferents travel through fasciculus cuneatus to reach the lateral cuneate nucleus, which then gives rise to uncrossed cuneocerebellar fibers that enter the cerebellum through the inferior cerebellar peduncle.

9. Inferior cerebellar peduncle. By the time it enters the cerebellum, it contains crossed olivocerebellar fibers, the uncrossed posterior spinocerebellar tract, vestibulocerebellar fibers, trigeminocerebellar fibers, and other cerebellar afferents.

10. Posterior spinocerebellar tract entering the inferior cerebellar peduncle. Uncrossed fibers from Clarke’s nucleus, carrying proprioceptive information from the leg to the ipsilateral half of the cerebellar vermis.

11. Location of nucleus ambiguus. Lower motor neurons for laryngeal and pharyngeal muscles and preganglionic parasympathetic neurons for the heart.

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Jul 31, 2016 | Posted by admin in NEUROLOGY | Comments Off

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