Lecture 10. SPECIAL PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. PHYSIOLOGY OF SPINAL CORD

Plan

► General structure of the central nervous system (CNS).

► Structural and functional organization of the spinal cord:

• characteristics of neurons, nerve centers and pathways of the spinal cord;

• reflex function of the spinal cord;

• conducting function of the spinal cord.

General Structure of Central Nervous System

The CNS consists of the spinal cord and the brain. The brain is subdivided into the medulla oblongata, the pons Varolii, the mesencephalon (midbrain), the diencephalon, the cerebellum and the telencephalon (endbrain). The tel-encephalon contains large hemispheres covered with the cortex, the white matter and basal ganglia (Fig. 10.1).

Phylogenetically, the spinal cord is the most ancient formation in the CNS. It consists of several sections: cervical, thoracic, lumbar, sacral and coccygeal. All sections consist of segments. The cross section of each segment shows the gray matter (clusters of neurons), white matter (conducting pathways of the spinal cord), ventral and dorsal roots. Dorsal roots consist of nerve fibers of sensory (afferent) neurons, and ventral roots - of nerve fibers of effector (efferent) neurons. According to the law independently discovered by Charles Bells (1811) and Francois Magendie (1822), nerve fibers enter the spinal cord in dorsal roots (afferent fibers), and leave the spinal cord in ventral roots (efferent fibers). Later on it was shown that afferent fibers entering the spinal cord twice outnumber efferent fibers leaving the spinal cord. About 12 000 fibers enter the spinal cord whereas about 6000 fibers leave it.

Fig. 10.1. General Structure of the CNS

The spinal cord consists of 31 segments. Each dorsal root of the spinal cord is connected not only with its respective segment, but also with the upper and lower adjacent segments through a system of intersegmental connections. Each section of the spinal cord comprises a fixed number of segments: cervical section comprises 8 segments, thoracic - 12 segments, lumbar - 5, sacral - 5, coccygeal - 1-3 segments.