Profesyonal Na Pagsulat

The nervous system comprises the central nervous system, consisting of the brain and spinal cord, and the peripheral nervous system, consisting of the cranial, spinal, and peripheral nerves, together with their motor and sensory endings.

Central nervous system

The central nervous system is composed of millions of nerve and glial cells, together with blood vessels and a little connective tissue. The nerve cells, or neurons, are

characterized by many processes and are specialized for reception and transmission of signals. The glial cells, termed neuroglia, are characterized by short processes that have special relationships to neurons, blood vessels, and connective tissue.

Brain

The brain is the enlarged, head end of the central nervous system; it occupies the cranium, or brain case. The term cerebrum (L., brain; adjective cerebral) generally means brain, but sometimes is used for the forebrain and midbrain only. Encephalon, of Greek origin, is found in such terms as encephalitis, which means inflammation of the brain.

The brain presents three main divisions: forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon) (fig. 3-1). The forebrain in turn has two subdivisions, telencephalon (endbrain) and diencephalon (interbrain). The hindbrain likewise has two subdivisions, the metencephalon (afterbrain) and the myelencephalon (marrowbrain). The bulk of the brain is formed by two cerebral hemispheres, which are derived from the telencephalon. The hemispheres are distinguished by convolutions, or gyri, which are separated by sulci. The diencephalon lies between the hemispheres. It forms the upper part of the brain stem, an unpaired stalk that descends from the base of the brain. The brain stem is formed by the diencephalon, midbrain, pons, and myelencephalon, or medulla oblongata. The last is continuous with the spinal cord at the foramen magnum. The cerebellum is a fissured mass of gray matter that occupies the posterior cranial...