Peripheral nervous system

The peripheral nervous system (PNS) is of great interest in understanding how the human being is formed. This part of the nervous system is composed of a set of ganglia and nerves, being in charge of sensory and motor functions. These nerves are called peripheral because they are the ones outside the central nervous system (CNS).

Information from the PNS is transmitted, through branching nerves , through the brain and spinal cord to all other parts of the human body.

The peripheral nervous system is made up of the cranial nerves and the spinal nerves. The cranial (12 pairs of cranial nerves) are those that are related to the innervation of the head, while the spinal (31 pairs of spinal nerves) are those that start from the spinal cord and innervate the entire body. Both the cranial and spinal nerves are made up of nerve extensions , responsible for producing motor nerve impulses.

As we can see below, the peripheral nervous system has its own characteristics, being different from those of the central nervous system, and those of the plant nervous system.

The functions of the peripheral nervous system

The SNP is responsible in our body for sending the appropriate information to our brain , so that it encodes the signals and responds to what happens in our environment. The brain is therefore responsible for making the final decision about the messages it is receiving, about how to intervene with our muscles and organs.

The main function of the SNP, as it has been understood, is to connect the CNS with our skin, muscles, extremities and organs . Everything that is part of our periphery. Thanks to this we can react quickly to the stimuli present in our environment. Through the information that the SNP sends to the SNC in a matter of milliseconds.

It is thus understood that the neurons present in the peripheral nervous system are not as complex with those of the central nervous system. Because the decisions they make are based on the transmission of information , while those of the CNS are the ones that encode the information, make decisions and carry out the sensory and motor function; which allows us to walk, capture information, see images, ride a bicycle and interact with people.

Peripheral nervous system anatomy

Specifying how its autonomy is composed , we check all the associations that the SNP has. Because it runs throughout our body, it contains a large number of peripheral nerves that are in relation to the other nervous systems, as we will see below.

Autonomic nervous system (ANS)

This part of the SNP is in charge of bodily functions that are involuntary. They are vitally important functions such as: respiration, digestion, blood flow and heartbeat. These are the basics that are not under our voluntary control. In addition, these processes occur without being aware of them, since it is not necessary to think or decide what to do.

The autonomic nervous system is divided into the sympathetic nervous system and the parasympathetic nervous system:

Sympathetic nervous system

This system is what drives us to fight or flight . He is in charge of mobilizing and preparing us to respond to a dangerous situation. It is triggered by threats that can pose a danger to our survival.

It manifests itself in the body, since there is associated a body over-activation . It can be seen that there is an activation of this system that prepares us for the alert; When our pupils are dilated, sweating, heart rate and breathing increase. Depending on the perception we have about our resources, we will stay to face the danger or we will flee.

The parasympathetic nervous system

This system, unlike the sympathetic one, helps us conserve energy and physical resources that we have . It is responsible for maintaining normal body functions, such as heart rate, blood pressure or digestion. After an alert situation, this system is the one that regulates us to return to calm. When the parasympathetic system is activated, our muscles relax, leading us to well-being and rest.

Somatic nervous system

It is another part of the peripheral nervous system, responsible for motor and sensory information, leading it to the central nervous system. Therefore, as we have seen, it is responsible for sensory information and voluntary movements of our body, after a previous evaluation of our brain.

The somatic system is made up of the nerves of the sensory receptors of our body. For this work, he has different types of neurons:

Motor or efferent neurons

These neurons are the ones that send sensory information to the central nervous system. They collect information and direct it through the spinal cord to the brain.

Sensory or afferent neurons

These neurons do the opposite process, they emerge from the central nervous system going towards the muscle fibers of our entire body. . Through these neurons, we offer faster responses to stimuli from our environment.

Nerves of the peripheral nervous system

Actually, the nerves that are associated with the PNS are axons that contain neuronal cells . On the one hand we find the nerves or cranial nerves that are homologous to the spinal nerves at the level of the trunk.

Cranial nerves

Among the nerves or cranial nerves we find the following:

• Par I. Olfactory: discrimination of smells and flavors.
• Par II. Optician: in charge of the visual representation in our hemispheres.
• Par III. Common ocular motor: it is the one that innervates the vast majority of the muscles of the eye. In charge of the vegetative innervation of the pupillary contraction. Injury to this nerve produces Ptosis, which is the drooping of the eyelid, and mydriasis , which is pupillary dilation.
• Par IV. Trochlear or pathetic: responsible for innervating the superior oblique muscle of the eye. His injury produces diplopia, which means double vision.
• Par VI. External ocular motor: it is the one that innervates the external rectus muscle. The movements that are made outside the eye.
• Par VII. Facial: regulates the movements of facial expression. It also has the sensation of taste in the anterior 2/3 of the tongue. His injury produces Bell’s palsy, which is the paralysis of one side of the face.
• For VIII. Vestibulocochlear: it is in which the responsibility of balance and spatial orientation falls, as well as auditory function.
• Par IX. Glossopharyngeal: it is where the sensitivity of the tongue occurs in the posterior third. It is involved in the parotid glands and blood pressure.
• Pair X. Vague or pneumogastric: represents the skin, ear, larynx, pharynx, esophagus, trachea, thoracic and abdominal viscera.
• Pair XI. Accessory or spinal: innervates the trapezius muscle and the sternocleidomastoid . An injury to this nerve on the right side weakens the left turn.
• Par XII. Hypoglossal: in charge of innervating the muscles of the tongue, making it convex and taking it out. It is involved in swallowing and speaking.

Spinal nerves

In the human body there are up to 31 pairs of spinal nerves. A spinal nerve arises from each segment of the cord. They are named in relation to the area from which they emerge.

• Cervical nerves (C1-C8) : there are 8 nerves that begin with the Atlas vertebra, and although there are 8 nerves, there are 7 cervical vertebrae.
• Thoracic nerves (T1-T12) : there are 12 that come out of the thoracic part of our spine that follow the cervical ones.
• Lumbar nerves (L1-L5) : they are 5 nerves that emerge from the lumbar area of ​​our spine, in the lower part of our back.
• Sacral nerves (S1-S5) : there are also 5 nerves that are located at the base of the spinal column.
• Coccygeal nerve : it is located in the coccyx or coccygeal bone.

This is how the 31 pairs of spinal nerves are structurally represented . Each of these nerves is linked to the spinal cord through two roots: the ventral motor root (efferent impulses) and the dorsal sensory root (afferent impulses). Those of the sensory root carry impulses to the spinal cord, generating sensations such as pain, temperature, tactile sense, body surface, joints, etc.

From the motor or spinal nerve, also known as spinal nerves, they are responsible for providing motor and sensory innervation to the whole body, in relation to its periphery.

Diseases related to the peripheral nervous system

There are certain diseases that are closely related to some abnormality of the structures of the peripheral nervous system. Specifically, there are up to more than 100 types of disorders or diseases that are associated with the peripheral nerves . We can find some that arise as a result of other diseases, such as neurological problems present in diabetics. Others after a viral infection, such as Guillain-Barre syndrome, etc.

We will see below some of the most common diseases that affect the nerves of the peripheral nervous system and their characteristics:

Ulnar nerve compression

This nerve is the one that runs throughout the entire arm . Being a nerve that is quite exposed on the surface, exerting a very prolonged pressure on it, it can cause significant damage. Symptoms of damage to this nerve include: tingling, loss of sensation in the hand, numbness of the arm and hand, among other associated symptoms.

Neuropathy

It is characterized above all because one or more nerves of the peripheral nervous system are affected, with serious implications.

Diabetic neuropathy

It is common in people with diabetes . Nerves are also susceptible to high blood sugar content, and can be damaged. Among the most frequent symptoms, the following can be highlighted: facial paralysis, vision changes, loss of the sensation of heat and cold, muscle weakness, numbness, among many others.

Carpal tunnel syndrome

It is a syndrome that affects the nerves that supply the hand, as they are damaged there is a loss of sensitivity in both the fingers and the palm of the hand.

Isaac syndrome

This disease that can appear between 15 and 60 years of age, is a neuromuscular disorder. It is caused by hyperexcitability and continued activation of peripheral nerve axons found in muscle nerves, whose function is to activate muscle fibers. Symptoms include progressive muscle stiffness, pain, and muscle weakness. And even breathing and speech can also be affected, if the laryngeal and pharyngeal muscles are involved.

Of note is the fact that some people are already born with peripheral nerve disorders . The symptoms, although they start gradually over time, end up getting worse. Among the most frequent symptoms are: muscle pain and weakness, sensitivity to touch, burning, tingling and numbness.

The treatment for these types of symptoms is to mitigate the pain and control the symptoms as much as possible so that they do not pose a great limitation for the sufferer.

In short, as we have highlighted about the peripheral nervous system. It must be borne in mind that it is formed by a branch of the nerve fibers that leave the spinal cord, and extend to any part of our body: neck, torso, legs, internal organs, arms and skeletal muscles.

Through its study it is possible to understand how a fundamental part of our organism and our body works. As we know, the brain sends messages to both the spinal cord and the nerves of the peripheral nervous system, which gives rise to the movement of the musculature, and even that the internal organs can perform their function. Although, as we have seen, they are controlled by the autonomic nervous system. In this way we understand how the different nervous systems participate in each other , giving rise to the machinery that we all know as the human body.