MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 3. ANATOMICAL AND PHYSIOLOGICAL ASPECTS OF THE SELF-REGULATION OF BODY FUNCTIONS

AUTONOMIC PART OF THE PERIPHERAL NERVOUS SYSTEM

As mentioned above, the single Nervous System is conventionally divided into two parts: somatic (animal) and autonomic. The Autonomic (vegetative) nervous system consists of two parts: the sympathetic and the parasympathetic. It innervates all Organs and Tissues: glands, smooth Muscles of Blood Vessels and Internal Organs, Heart Muscle, Sensory Organs, as well as the Brain AND SPINAL cord (Fig. 3.51).

Most organs are innervated by both the sympathetic and parasympathetic Divisions of the Autonomic nervous system.

The parasympathetic division does not innervate striated muscles, smooth Muscles of the Uterus, most blood vessels, Ureters, Sweat Glands, Hair follicles of the Skin, Spleen, and Adrenal Glands.

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Fig. 3.51.

Diagram of the autonomic innervation of internal organs: a - Parasympathetic part; b - Sympathetic part

The autonomic nervous system does not have its own specific afferent sensory pathways. Sensory impulses from organs travel along sensory fibers that are shared by both the autonomic and somatic nervous systems. Higher control and Regulation of the Functions of the autonomic nervous system, much like the somatic system, are carried out by the Cerebral Cortex.

The somatic and autonomic nervous systems differ not only in function but also in Structure, specifically:

1. Somatic motor fibers emerge from the Spinal Cord segmentally, whereas autonomic fibers emerge only from specific centers: mesencephalic, bulbar (parasympathetic nuclei of the Cranial Nerves in the Rhomboid fossa), which are combined into the cranial division, and the thoracolumbar division.

The thoracolumbar division belongs to the sympathetic system, while the cranial and sacral divisions belong to the parasympathetic system.

2. Somatic nerve fibers have a well-defined myelin sheath, which is absent in autonomic fibers.

3. The Cell bodies of somatic Neurons are located in the anterior horns of the spinal cord, and their processes (axons) reach skeletal muscles without interruption. The nerve processes of autonomic neurons are interrupted in autonomic ganglia. Thus, there are preganglionic and postganglionic fibers here.

4. The simplest reflex arc of the somatic nervous system consists of two neurons, whereas that of the autonomic system consists of three neurons (featuring an interneuron); its efferent link consists of two neurons rather than one.