Fig. 47.1 Pars centralis and pars peripherica
The nervous system is divided into the pars centralis (CNS) and pars peripherica (PNS). The CNS consists of the encephalon and medulla spinalis, which constitute a functional unit. The PNS consists of the nervi emerging from the brain (encephalon) and medulla spinalis (nn. craniales and nn. spinales, respectively).
Fig. 47.2 Substantiae grisea and alba matter in the CNS
Nerve cell bodies appear gray (grisea) in gross inspection, whereas nerve cell processes (axons) and their insulating myelin sheaths appear white (alba).
Fig. 47.4 Adult encephalon
See Fig. 47.7 for lobi cerebri. CN, n. cranialis.
Fig. 47.5 Cerebrum
Left lateral view. The cerebrum is part of the anterior subdivision of the embryonic forebrain (telencephalon)—the part of the adult forebrain that includes the hemispheria cerebri and associated structures. The surface anatomy of the cerebrum can be divided macroscopically into 4 lobes: lobi frontalis, parietalis, temporalis, and occipitalis. The surface contours of the cerebrum are defined by convolutions (gyri) and depressions (sulci).
Fig. 47.6 Insula
Lateral view of the retracted left hemispherium cerebri. Part of the cortex cerebri sinks below the surface during development forming the insula (or insular lobe). Those portions of the cortex cerebri that overlie this deeper cortical region are called opercula (“little lids”).
Fig. 47.7 Lobi in the hemispheria cerebri
The isocortex also may be functionally divided into association areas (lobi).
Fig. 47.8 Midsagittal section of the encephalon showing the facies medialis of the right hemispherium
The encephalon has been split along the fissura longitudinalis cerebri.
The diencephalon is the posterior subdivision of the prosencephalon—the part of the adult prosencephalon that includes the thalamus and associated structures.
Fig. 47.9 Diencephalon
Midsagittal section, medial view of the right hemispherium. The major components of the diencephalon are the thalamus, hypothalamus, and hypophysis (lobus posterior, neurohypophysis). The diencephalon is located below the corpus callosum, part of the cerebrum, and above the mesencephalon. The thalamus makes up four-fifths of the diencephalon but the only parts that can be seen externally are the hypothalamus (seen on the basal aspect of the encephalon) and portions of the epithalamus. In the adult brain the diencephalon is involved in endocrine functioning and autonomic coordination of the gl. pinealis, neurohypophysis, and hypothalamus. It also acts as a relay station for sensory information and somatic motor control via the thalamus.
Fig. 47.10 Arrangement of the diencephalon around the ventriculus tertius
Posterior view of an oblique transverse section through the telecephalon with the corpus callosum, fornix, and plexus choroideus removed. This figure clearly illustrates that the lateral wall of the ventriculus tertius forms the medial boundary of the diencephalon.
Fig. 47.11 The diencephalon and truncus encephali
Left lateral view. The hemispheria cerebri have been removed from around the thalamus. The cerebellum has also been removed. The parts of the diencephalon visible in this dissection are the thalamus, the corpus geniculatum laterale, and the tractus opticus. The latter two are components of the visual pathway. This dissection illustrates the role the diencephalon plays in linking the underlying truncus encephali to the overlying hemispheria cerebri.
Fig. 47.12 Location of the diencephalon in the adult encephalon
Basal view of the encephalon (truncus encephali has been sectioned at the level of the pons). The structures that can be identified in this view represent those parts of the diencephalon situated on the basal surface of the encephalon. This view also demonstrates how the tractus opticus winds around the pedunculi cerebri. The expansion of the telencephalon during development limits the number of structures of the diencephalon visible on the under surface of the encephalon. They are:
The stalk-like region of the encephalon connecting the hemi-spheria cerebri to the cerebellum and medulla spinalis consists of the diencephalon (thalamus and associated structures) and the truncus encephali—composed of the mesencephalon or midbrain, pons and medulla oblongata moving sequentially caudal. Fiber bundles pass through this region from the medulla spinalis on their way to and from the cerebrum; thick fiber bundles pass contralaterally from the cerebrum into the hemispheria cerebelli; and 10 of the 12 nn. craniales are associated with the truncus encephali.
Fig. 47.15 Pedunculi cerebellares
Tracts of afferent (sensory) or efferent (motor) axons enter or leave the cerebellum through pedunculi cerebellares. Afferent axons originate in the medulla spinalis, vestibular organs, oliva, and pons. Efferent axons originate in the nuclei cerebelli.
Fig. 47.16 Truncus encephali
The truncus encephali is the site of emergence and entry of the 10 pairs of true nn. craniales (CN III–XII). See p. 526 for an overview of the nn. craniales and their nuclei.
Fig. 47.17 Circulation of liquor cerebrospinalis (CSF)
The encephalon and medulla spinalis are suspended in CSF. Produced continually in the plexus choroideus, CSF occupies the spatium subarachnoideum and ventricles (ventriculi) of the encephalon and drains through granulationes arachnoideae into the sinus durae matris (primarily the sinus sagittalis superior) of the cavitas cranii. Smaller amounts drain along proximal portions of the nn. spinales into plexus venosi or lymphatic pathways.
