The peripheral nervous system (PNS) is the part of the nervous system that is outside the central nervous system (CNS). It consists of fibers (nerves), nerve ganglia and terminal organs. The function of the PNS is to connect the CNS with the other parts of the human body.
The nerves are divided into three types:
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Sensitive Nerves: it is the nerves that have the role of transmitting the nervous impulses of the receptor organ up to the CNS;
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Motor Nerves: carry the encoded impulse in the brain (CNS), to the effector organ;
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Mixed Nerves: It has the same role as the sensory and motor nerves at the same time.
The receptor organs are the organs of the senses (sight, hearing, smell, taste and tactile corpuscles) with nerve connections adapted to the transduction of the different types of stimuli captured in the external world (see list of receivers below). The effector organs are basically the smooth and striated glands and muscles. We can group the receptors in: chemoreceptors: they receive stimuli by means of substances that allow the sense of the smell and palate; Photoreceptors: luminous stimuli allow the vision: color images etc; Thermoreceptors: thermal stimuli, allows tact, and are located in different parts of the body; Mechanoreceptors: mechanical stimuli of pressure, allows to be auditory, tactile or even pain.
Unlike the central nervous system, the peripheral nervous system is not protected by the blood-brain barrier.
It is thanks to this system that the brain and the spinal cord receive and send the information allowing us to react to the different situations that originate in the external or internal environment.
The peripheral nervous system is organized into plexuses and functions can be divided into two different classes depending on the origin or termination of the nerve terminals that constitute it. If the nerves begin or end in the brain, we have the 'cranial nerve pairs', but if they start in the spinal cord, we are dealing with 'spinal nerves'. As for the functions can be distinguished the autonomic nervous system and the somatic / sensorial.