Human Anatomy - M.M. Kurepina, A.P. Ozhigova, A.A. Nikitina 2010

Nervous system
Brain
Divisions of the brain

Based on origin, structural features, and functional significance, the Brain can be divided into three major regions: the Brainstem, the subcortical region, and the Cerebral Cortex. The brainstem consists of derivatives of the third and second vesicles of the three-vesicle stage of brain development, whereas the subcortical region and the cortex develop from the first vesicle (see 3.3.6). The latter two regions, while sharing a common origin, differ from each other in Structure and function.

The brainstem is represented by the Medulla Oblongata, Pons, Cerebellum, and Midbrain (Figs. 3.14, 3.15). In the brainstem, which develops above the anterior end of the notochord, signs of segmentation characteristic of the Spinal Cord are found. These are expressed in the sequential arrangement of the cranial nerve nuclei and The Emergence of their roots. Below the sulcus limitans, which continues here from the spinal cord, motor Neurons of the medulla oblongata, pons, and cerebral peduncles differentiate. Above them, in the region of the sulcus itself, the neurons of the Autonomic Nervous system of the medulla oblongata and midbrain are formed. The remaining structures of the brainstem develop from the alar plate.

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Fig. 3.14. The brain. Medial surface of the right hemisphere:

1 — body of fornix; 2 — hypothalamic sulcus; 3 — choroid plexus of the Third ventricle; 4 — Pineal Gland; 5 — corpora quadrigemina; 6 — splenium of corpus callosum; 7 — superior medullary velum; 8 — Fourth ventricle; 9 — vermis of cerebellum; 10 — cerebellum; 11 — choroid plexus of the fourth ventricle; 12 — medulla oblongata; 13 — cerebral aqueduct; 14 — cerebral peduncles; 15 — pons; 16 — thalamus; 17 — Oculomotor nerve; 18 — mammillary bodies; 19 — Pituitary Gland; 20 — infundibulum of Hypothalamus; 21 — optic chiasm; 22 — Optic nerve; 23 — interthalamic adhesion; 24 — anterior commissure; 25 — rostrum of corpus callosum; 26 — septum pellucidum; 27 — Column of fornix; 28 — body of corpus callosum

The subcortical region (the closest subcortex, according to I.P. Pavlov) consists of structures of the Diencephalon and Basal Ganglia of the hemispheres. Here, there are no longer any derivatives of the basal plate, which terminated along with the sulcus limitans in the midbrain. The subcortical region develops from the alar plate and is topographically located anterior to the rostral end of the notochord. There are no longer any signs of segmentation here; Nerve Cells group together in clusters called nuclei.

Fig. 3.15. The brain (inferior view):

1 — olfactory sulcus; 2 — olfactory bulb; 3 — olfactory tract; 4 — optic nerve; 5 — olfactory triangle; 6 — anterior perforated substance; 7 — optic tract; 8 — mammillary bodies; 9 — oculomotor nerve; 10 — Trochlear nerve; 11 — basilar sulcus; 12 — pons; 13 — Trigeminal nerve; 14 — Abducens nerve; 15 — Facial Nerve; 16 — intermediate nerve; 17 — Vestibulocochlear nerve; 18 — Glossopharyngeal nerve; 19 — Vagus nerve; 20 — Accessory nerve; 21 — olive; 22 — pyramid; 23 — medulla oblongata; 24 — decussation of pyramids; 25 — spinal cord; 26 — 1st spinal nerve; 27 — cerebellum; 28 — Hypoglossal nerve; 29 — cerebral peduncles; 30 — posterior perforated substance; 31 — tuber cinereum and 32 — infundibulum of hypothalamus; 33 — pituitary gland

The cerebral cortex also develops entirely from the alar plate. However, its cells do not group into nuclei, but are arranged in layers.

All three brain regions contain phylogenetically old and new structures; some of them develop, others undergo significant reorganization, and only a few undergo reduction. The phylogenetically youngest and most progressively developing part of the brain is the cerebral cortex. Its development drives the massive expansion of the cerebral hemispheres, which make up the bulk of the human brain (Fig. 3.14). The basal ganglia and the diencephalon (with few exceptions) are surrounded by the hemisphere substance; the brainstem structures are covered by the hemispheres from above and from the sides, and are visible only from the inferior aspect (Fig. 3.15). Both hemispheres are separated by a deep longitudinal cerebral fissure, at the bottom of which lies the corpus callosum, consisting of transverse fibers that connect the two hemispheres.