Peripheral nervous system (autonomic and somatic): parts and functions.

Beyond the brain and spinal cord there are many neurons working for us to survive.

The peripheral nervous system is composed of nerves and ganglia that connect the central nervous system to the rest of the body and control voluntary movements, digestion or the fight-flight response.

In this article we will describe the peripheral nervous system and its two subdivisionsThe autonomic or vegetative nervous system and the somatic nervous system.

What is the peripheral nervous system?

The nervous system of animals, including humans, is concerned with the transmission of electrochemical impulses that enable a large number of biological processes to function. It is divided into two sets of connections: the central nervous system, composed of the brain and spinal cord, and the peripheral nervous system.

The term "peripheral" denotes the location of the components of this neural network in relation to the central nervous system. The neurons and fibers that make up the peripheral nervous system connect the brain and spinal cord to the rest of the body. connect the brain and spinal cord with the rest of the organism, making possible the exchange of electrochemical signals between the brain and spinal cord and the rest of the body.The neurons and fibers that make up the peripheral nervous system connect the brain and spinal cord with the rest of the body, making possible the exchange of electrochemical signals with the whole body.

The peripheral nervous system in turn consists of two subdivisions: the autonomic nervous system, which controls the internal organs, smooth musculature and physiological functions such as digestion, and the somatic nervous system, composed mainly of the cranial and spinal nerves.

Unlike the central nervous system, the peripheral nervous system is not protected by the skull. is not protected by the skull, the spinal column and the blood-brain barrier.. This makes it more vulnerable to different types of threats, such as traumatic injury or exposure to toxins.

The vegetative or autonomic nervous system

The autonomic, vegetative or involuntary nervous system is composed of sensory and motor fibers that connect the central nervous system with the smooth and cardiac musculature. connect the central nervous system with the smooth and cardiac musculature, as well as with the exocrine glands, which are found throughout the organism and perform idiosyncratic functions.as well as with the exocrine glands, which are found throughout the body and perform idiosyncratic functions.

Smooth muscles are located in the eyes, where they are associated with dilation and contraction of the pupil and accommodation of the lens, in the hair follicles of the skin, in the Blood vessels, in the walls of the digestive system and in the sphincters of the urinary and gall bladder.

Through the action of the autonomic nervous system occurs the control of the digestion, of the cardiac and respiratory frequency, of the urination, of the urinary and biliary sphincters.The autonomic nervous system controls digestion, heart rate, respiratory rate, urination, sexual response and the fight-flight reaction. This process, also known as "acute stress response", consists of a discharge of neurotransmitters with a protective function against threats.

Also dependent on the vegetative system are the autonomic or visceral reflexesThese are a series of automatic responses that appear as a consequence of certain types of stimulation. These include ocular, cardiovascular, glandular, urogenital and gastrointestinal reflexes, mainly peristalsis.

The sympathetic, parasympathetic and enteric branches

The subdivision of the autonomic nervous system into two branches is well known: the sympathetic and the parasympathetic, responsible for the maintenance of homeostasis or balance of the internal environment of the organism. However, there is a third branch that is often neglected: the enteric nervous system, responsible for the functioning of the intestinal tract..

Activation of the sympathetic nervous system is related to the fight-flight response: it increases energy consumption by the organism to enable functions such as the release of catecholamines, bronchodilation or mydriasis (pupillary dilation). The parasympathetic system controls sphincter relaxation, digestion and miosis.digestion or miosis (pupillary contraction).

These two branches of the autonomic nervous system always act together; however, different stimuli and physiological signals can cause them to become unbalanced so that the functions of one branch predominate over those of the other. For example, sexual arousal responses are associated with activation of the parasympathetic system.

The enteric nervous system is responsible for the innervation (both sensory and motor) of the gastrointestinal tract, pancreas and gallbladder, and thus for the control of the smooth musculature, blood vessels and mucous membranes. and mucous membranes located in these regions.

The somatic nervous system

The somatic nervous system is composed of nerves and ganglia with sensory and motor functions that allow the connection between the central nervous system and the rest of the body.

Nerves are bundles of nerve fibers, i.e. neuronal axons, and therefore specialize in the transmission of electrochemical impulses. Nerve ganglia are composed of the somas or cell bodies of the neurons of the peripheral nervous system, where the relay of signals between the various structures of the nervous system takes place.

This subdivision of the peripheral nervous system is related to the voluntary control of the contraction of skeletal musclesas well as that of the reflex arcs, which allow the execution of automatic responses by the motor neurons themselves, before the central nervous system receives the corresponding sensory afferents.

Cranial and spinal nerves

The 43 pairs of nerves in the human body constitute the somatic nervous system. Of these, 12 are located in the brainstem and 31 in the spinal cord, both in its dorsal root and its dorsal root.The former are called "spinal nerves" and the latter are called "spinal nerves". The former are called "cranial nerves" and the latter are called "spinal or spinal nerves".

The transmission of information between the brain and the peripheral nervous system occurs through the 12 cranial nerves: olfactory (I), optic (II), oculomotor (III), pathetic or trochlear (IV), trigeminal (V), abducens (VI), facial (VII), vestibulocochlear or auditory (VIII), glossopharyngeal (IX), vagus or pneumogastric (X), accessory (XI) and hypoglossal (XII).

Spinal nerves connect the spinal cord with the rest of the body. While the nerves that send afferent sensory information to the central nervous system are located in the dorsal or posterior root of the spinal cord, the somas of the motor or efferent motor neurons are located in the dorsal or posterior root of the spinal cord. motor or efferent neurons are located in its ventral horn..