Neurotropic Drugs
This chapter is dedicated to medicines affecting the functions of the nervous system of the body. A distinction is made between drugs that primarily affect the peripheral nervous system and those which primarily affect the CNS (the brain and spinal cord).
Drugs Affecting the Peripheral Nervous System
The peripheral nervous system includes afferent innervation (nerve fibers transmitting excitation from organs and body tissues to the CNS) and efferent innervation (nerve fibers transmitting excitation from the CNS to organs and tissues) (fig. 3.1).
Drugs Affecting Afferent Innervation
Afferent innervation is represented by sensory nerve endings (endings of sensory nerve fibers) and primary afferent nerve cells whose fibers enter the spinal cord through the posterior horns. Sensory nerve endings (sensory receptors) are located in the skin, tissues and organs, and are capable of perceiving stimuli in response to which they generate impulses which are transmitted via sensory nerve fibers to the CNS. Peripheral endings of primary afferent somatic and visceral fibers respond to thermal, mechanical and chemical stimuli. Excitation is transmitted via primary afferent fibers to posterior horns of the spinal cord (see
fig. 3.1).
Drugs Inhibiting Afferent Innervation
Drugs inhibiting afferent innervation can reduce the sensitivity of afferent nerve fiber endings and/or inhibit conduction of excitation via sensory nerve fibers (local anesthetic drugs). Besides, certain substances are used to limit exposure to irritating factors (including irritating substances) on sensory nerve endings (astringent, enveloping and adsorbing agents).
3.1. LOCAL ANESTHETIC DRUGS (LOCAL ANESTHETICS)
Local anesthetic drugs (from Greek aisthe-sа - sensation, and an - denial prefix) re-versibly block impulse generation and nerve