Figure 66 upper pons photographic view

This is a photographic image, enlarged, of the pontine region, with the cerebellum attached. The section is done at the level of the upper pons, as indicated in the upper images of the ventral view of the brainstem and in the midsagittal view.

The unique nucleus present at this level is the locus ceruleus, a small nucleus whose cells have pigment, much like those of the substantia nigra, pars compacta (see Figure 65). As with that nucleus, the pigment is lost during histological processing.

The ventral region has the distinctive appearance of the pontine nuclei, with the cortico-spinal and cortico-pontine fibers dispersed among them. The pontine tegmen-tum seems quite compressed. The space in the middle of the tissue section is the fourth ventricle, as it begins to widen. Behind the ventricle is a small area of white matter, called the superior medullary velum (see Figure 10 and Figure 41B). The thin folia of the cerebellum are easily recognized, with an inner strip of white matter bounded on either side by the thin gray matter of the cerebellar cortex.

The pons is to be represented by three sections:

• Figure 66A: The upper pons, at the level of the locus ceruleus.

• Figure 66B: The mid (middle) pons, at the level of the attachment of the trigeminal nerve. It includes the massive middle cerebellar peduncles.

• Figure 66C: The lower pons, just above the junction with the medulla. This lowermost level has the nuclei of cranial nerves VI, VII, and parts of both divisions of CN VIII.

Hippocampe CerveauPontocerebellar Fibers

Superior cerebellar peduncle

Locus ceruleus

Vestibulocochlear nerve (CN VIII)

4th ventricle

Superior medullary velum

Superior cerebellar peduncle

Locus ceruleus

Medial lemniscus

Pontine nuclei

Middle cerebellar peduncle

Ponto-cerebellar fibers

Vestibulocochlear nerve (CN VIII)

Cortico-spinal fibers

Ch = Cerebellar hemisphere

4th ventricle

FIGURE 66: Brainstem Histology — Pons (upper — photograph)

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