The encephalon includes:- The brain, weighing 20 to 28 g. It is compact, globular in the back, and has a truncated anterior stem. It measures 35 mm long, 37 mm wide, and 26 mm high. Its circumvolutions, or folds, are not very pronounced. The brain contains 80% water (9 to 11% protein and 6% fat). The hypothalamus, located in the median, central part of the brain, regulates the endocrine system;
- The cerebellum (involved in postural activity) and the brain stem (which regulates autonomic activity) in the hind section of the brain. Its surface is divided into wide lamellae. The cerebellum weighs 3 to 5 g;
- The whitish, cylindrical spinal cord inside the spine weighs 7 to 9 g. Emerging from each side of the spinal cord are the roots of the spinal nerves. Running inside are the sensory motor and associative paths.
The peripheral nervous system is the set of all nerve fibers grouped as follows:- Cranial nerves (twelve pairs: olfactory, optic, acoustic, vagus nerve, etc.);- Spinal nerves connected to the spinal cord (thirty-six to thirty-eight pairs, including eight cervical, thirteen dorsal, seven lumbar, three sacral, and five to seven coccygeal nerves).
It regulates the body's autonomic activities (organ function and the coordination of various organ functions), and it includes, in particular:- The sympathetic nervous system, with its nerves and ganglia. Sympathetic nerves run from plexus to plexus to the organs. The thoracic ganglia become aortic or pulmonary cardiac filaments. The sacral ganglia branch into hypogastric nerves running to the pelvic organs;- The parasympathetic nervous system. This system is the opposite of that above. It is formed of a cranial section and a pelvic section.
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