Figure 66a upper pons crosssection

Dorn Spinal Therapy

Spine Healing Therapy

Get Instant Access

This level is presented mainly to allow an understanding of the transition of midbrain to pons. This particular section is taken at the uppermost pontine level, where the trochlear nerve, CN IV, exits (below the inferior collicu-lus, see Figure 7). This is the only cranial nerve that exits posteriorly; its fibers cross (decussate) before exiting (see Figure 48).

Anteriorly, the pontine nuclei are beginning to be found. Cortico-pontine fibers will be terminating in the pontine nuclei. From these cells, a new tract is formed that crosses and projects to the cerebellum forming the middle cerebellar peduncle. The cortico-spinal fibers become dispersed between these nuclei and course in bundles between them (see Figure 45 and Figure 48).

The ascending tracts include the medial lemniscus and anterolateral system (somatosensory from the body, see Figure 33, Figure 34, and Figure 40), the ascending trigeminal pathway (see Figure 35 and Figure 40) and the lateral lemniscus (auditory, see Figure 37). The fibers of the trigeminal system that have crossed in the pons (discriminative touch from the principal nucleus of V), and those of pain and temperature (from the descending nucleus of V) that crossed in the medulla join together in the upper pons with the medial lemniscus (see Figure 35, Figure 36, and Figure 40). The medial lemniscus is located midway between its more central position inferiorly, and the lateral position found in the midbrain (see Figure 40). In sections stained for myelin, it has a somewhat "comma-shaped" configuration. The auditory fibers are located dor-sally, just before terminating in the inferior colliculus in the lower midbrain (see Figure 38 and Figure 40). Centrally, the cerebral aqueduct is beginning to enlarge, becoming the fourth ventricle. The MLF is found in its typical location ventral to the fourth ventricle, next to the midline.

The nuclei of the reticular formation are located in the tegmentum (see Figure 42A and Figure 42B). The special nucleus at this level, the locus ceruleus, is located in the dorsal part of the tegmentum not too far from the edges of the fourth ventricle. The nucleus derives its name from its bluish color in fresh specimens, as seen in the photographic image in the previous illustration. As explained, the pigment is lost when the tissue is processed for histology. The locus ceruleus is usually considered part of the reticular formation (as discussed with Figure 42B) because of its widespread connections with virtually all parts of the brain. It is also unique because noradrenaline is its catecholamine neurotransmitter substance.

The superior cerebellar peduncle is found within the tegmentum of the pons. These fibers carry information from the cerebellum to the thalamus and the red nucleus. The fibers, which are the axons from the deep cerebellar nuclei, leave the cerebellum and course in the roof of the fourth ventricle (the superior medullary velum, see Figure 10 and Figure 40). They then enter the pontine region and move toward the midline, finally decussating in the lower midbrain (see Figure 57 and Figure 65B).

The uppermost part of the cerebellum is found at this level. One of the parts of the vermis, the midline portion of the cerebellum, the lingula, is identified. This particular lobule is a useful landmark in the study of the cerebellum and was identified when the anatomy of the cerebellum was explained (see Figure 54).

Additional Detail

Several very large neurons belonging to the mesencephalic nucleus of the trigeminal may be found near the edges of the fourth ventricle (see Figure 8B). This small cluster of cells may not be found in each and every cross-section of this particular region.

Decussation of CN IV

Mesencephalic nucleus of CN V

Lateral lemniscus

Anterolateral system

Medial lemniscus

Trochlear nerve (CN IV)

Decussation of CN IV

Trochlear Nerve Pathway

Mesencephalic nucleus of CN V

Lateral lemniscus

Anterolateral system

Medial lemniscus

Trochlear nerve (CN IV)

Superior cerebellar peduncle

Reticular formation

Cortico-spinal tract

Pontine nuclei

Middle cerebellar peduncle

Lingula of cerebellum

— 4th ventricle Locus ceruleus

Superior cerebellar peduncle

Reticular formation

Cortico-spinal tract

Pontine nuclei

Middle cerebellar peduncle

Lower Pons Cross Section

FIGURE 66A: Brainstem Histology — Upper Pons

Was this article helpful?

0 0
Peripheral Neuropathy Natural Treatment Options

Peripheral Neuropathy Natural Treatment Options

This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.

Get My Free Ebook


Post a comment