tailieunhanh - Ebook Handbook of general anatomy (4/E): Part 2

All the chapters have been extensively illustrated by simple colour diagrams. Each chapter begins with a quotation giving a subtle meaning to the topic. A new chapter on basic genetics has been added to make the book more meaningful. Chapter on radiology has been expanded and revised by extensive addition of radio-images. | 7 Nervous System Nervous system is the chief controlling and coordinating system of the body. It controls and regulates all activities of the body, whether voluntary or involuntary, and adjusts the individual (organism) to the given surroundings. This is based on the special properties of sensitivity, conductivity and responsiveness of the nervous system. The protoplasmic extensions of the nerve cells form the neural pathways called nerves. The nerves resemble the electricity wires. Like the electric current flowing through the wires, the impulses (sensory and motor) are conducted through the nerves. The sensory impulses are transmitted by the sensory (afferent) nerves from the periphery (skin, mucous membranes, muscles, tendons, joints, and special sense organs) to the central nervous system (CNS). The motor impulses are transmitted by the motor (efferent) nerves from the central nervous system to the periphery (muscles and glands) (Fig. ). Thus the CNS is kept continuously informed about the surroundings (environment) through various sensory impulses, both general and special. The CNS in turn brings about necessary adjustment of the body by issuing appropriate orders which are passed on as motor impulses to the muscles, vessels, viscera and glands. The adjustment of the organism to the given surroundings is the most important function of the nervous system, without which it will not be possible for the organism to survive. Parts of Nervous System The nervous system is broadly divided into central and peripheral parts 138 I Handbook of General Anatomy which are continuous with each other. Further subdivisions of each part are given below. A. Central nervous system (CNS) includes: 1. Brain or encephalon, which occupies cranial cavity, and contains the higher governing centres (Fig. ). 2. Spinal cord or spinal medulla, which occupies upper twothirds of the vertebral canal, and contains many reflex centres. Dorsal root ganglion Dorsal .