He peripheral nervous system Is a set of nerves and ganglia that control the motor and sensorial functions. It transmits information from the brain and spinal cord to the whole organism.
He Human nervous system it's divided in Central Nervous System And peripheral nervous system. The central nervous system includes brain and the spinal cord , While the peripheral nervous system is the one that is outside the nervous system. In fact,"peripheral"in anatomy has an opposite meaning to"central".
The peripheral nervous system comprises all the nerves that branch from the brain and spinal cord to other parts of the body. It includes the cranial nerves, the spinal nerves, the peripheral nerves and the neuromuscular junctions.
Nerves are cords of White matter Which branch into axons and / or dendrites. These transmit sensory and motor information from the brain to the periphery and in the opposite direction.
On the other hand, the ganglia are formed by groups of neurons; And are outside the Encephalon And spinal cord.
The main function of the peripheral nervous system is to connect the central nervous system with organs, limbs and skin.
This allows the brain and spinal cord to both receive and send information to other areas of the body. In this way, it allows us to react to environmental stimuli.
In the peripheral nervous system information is transmitted by bundles of nerve fibers or axons. In some cases these nerves are very small, however, in others they can reach a size that the human eye can grasp.
Parts of the peripheral nervous system
The peripheral nervous system is divided into two components, the somatic nervous system and The autonomic nervous system . Each one has very important functions:
Somatic nervous system
This system is responsible for sending and receiving sensory and motor information to the central nervous system. The somatic nervous system contains two Types of neurons : Sensory neurons and Motor neurons .
Sensory (or afferent) neurons transmit information from the nerves in the central nervous system.
While motor neurons (or efferent) carry information from the brain and spinal cord to the organs, muscle fibers, as well as to the glands in the periphery of the body. These neurons allow a physical response to the stimuli.
Autonomic nervous system
It is responsible for regulating the involuntary functions of the body. For example, heart rate, breathing and digestion. Thanks to autonomic nervous system , We can perform these functions without consciously thinking about their execution. This system is divided into sympathetic system and parasympathetic system.
The sympathetic system regulates the response to the stress produced by the hormones. These are the typical reactions of fight or flight. That is, it prepares us to face potential threats from our environment.
When this threat occurs, the body responds by accelerating the heart rate, increasing breathing, blood pressure, as well as sweat secretion and dilation of the pupils. These responses help us act quickly against threats.
In addition, it helps us to feel the cold or the heat, it dilates the bronchi and inhibits the intestinal motility and the production of urine.
On the other hand, the parasympathetic system is responsible for maintaining the functions of the body and for preserving the physical resources. It starts in the brainstem and regulates the internal organs.
Basically this system allows us to return to a normal or resting state, slowing the heart rate, breathing and blood flow.
Thus, pupils contract, increase saliva production, increase gastrointestinal movements, reduce blood pressure and heart rate, make us more resistant to infections, etc.
In short, it develops necessary tasks but does not need an immediate response as it does with the sympathetic nervous system.
Nerves of the peripheral nervous system
The peripheral nervous system consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves.
Cranial nerves
They originate in the brain, and are part of the head and neck. Its function can be sensitive, motor or mixed.
In this way, some of these pairs of nerves are exclusively sensory cells. For example, those that detect information about smell and vision.
Other pairs of nerves are exclusively motor cells, such as those found in the ocular muscles. There are also pairs of nerves that have both sensory and motor cells, for example, those involved in taste or swallowing.
The following are the cranial nerves and their functions:
I. Olfactory nerve: Is a sensory nerve that carries impulses of smell to the brain.
II. Optic nerve: Is responsible for sending the visual stimuli to the brain.
III. Oculomotor nerve: Transmits information to the outer eye muscles, which helps direct the position of the eyeball. They are also the constricting muscles of the iris and the ciliary musculature.
IV. Trochlear nerve: Is a motor nerve that carries impulses to the major oblique muscle of the eye.
V. Trigeminal nerve: Is a mixed nerve that produces general sensations of touch, temperature and pain. It has different branches.
In the ophthalmic branch it relates to the forehead, eye and upper nasal cavity. In the maxillary branch is associated with the sensation of the lower nasal cavity, the face, the upper teeth and the mucosa of the upper part of the mouth.
And in the mandibular branch, it is linked to the surfaces of the mandibles, lower teeth, and lower mucosa of the mouth. Just like the taste in the front of the tongue.
The trigeminal nerve in its motor function is related to the muscles of the jaws. In addition to functioning as a tensor of the eardrum, palate and digastric muscle (movement of the jaw).
SAW. Abducent nerve: It is also a mixed nerve, but mainly motor. It carries impulses to the outer rectus muscle of the eye.
VII. Facial Nerve: Is a mixed nerve and carries the taste sensations of the tongue. It also controls impulses in various muscles of the face. Like the tear, submandibular and sublingual glands.
VIII. Cochlear or auditory vestibular nerve: Is a very important nerve since it is responsible for transferring the auditory impulses to the brain. Although it also handles the feelings of balance. The cells involved are the ciliated organ of Corti and those of the vestibular apparatus.
IX. Glossopharyngeal nerve: Is mixed and carries the information of the skin of the external ear and of the mucous membranes of the pharyngeal region. As well as the middle ear, and the posterior third of the tongue. In its motor function, it is related to the striated muscle of the pharynx, which helps swallow.
X. Vague nerve: Is a mixed nerve that carries impulses from the pharynx, larynx, and other more internal organs to the brain. The motor fibers of this nerve transmit information to the intestine, heart, and respiratory structures. As well as the striated muscles of the palate, pharynx and larynx.
XI. Accessory nerve: Has a motor function. It is associated with the muscles of the thoracic and abdominal viscera, as well as with the muscles of the back (sternocleidomastoid and part of the trapezius).
XII. Halibut: Is primarily a motor nerve, and transmits impulses to the muscles of the tongue and throat.
Spinal or spinal nerves
They branch from the spinal cord to the rest of the body. As mentioned above, there are 31 pairs. They are distributed in 8 cervical (neck), 12 thoracic (chest), 5 lumbar (lower back), 5 sacral (sacral bone) and 1 coccygeal (coccyx).
Each spinal nerve joins the spinal cord through two roots: a dorsal (posterior) sensory root and a ventral (anterior) root.
The fibers of the sensory root transmit pulses of pain, temperature, touch and sense of position from the joints, tendons and surfaces of the body.
In addition, they send sensory information from the trunk and limbs through the spinal cord, reaching the central nervous system. Nerves carry information about the skin to specific regions of the body called Dermatomas .
The ventral roots are those that have motor fibers. They transmit information about the state of the joints and control the skeletal muscles.
Each pair of spinal nerve has the same name as the segment of the spinal cord to which it connects, plus its corresponding number. Thus, the cervical goes from C1 to C8, the dorsal from D1 to D12, the lumbar, from L1 to L5 and the coccyx, corresponding to the coccygeal nerve.
Ganglia of the peripheral nervous system
A ganglion is a group of cellular bodies of neurons in the periphery. They can be classified into sensory ganglia or autonomic ganglia, according to their primary functions.
The most common sensory ganglion is the dorsal root ganglion (posterior). Another type of sensory ganglion is the ganglion of the cranial nerve. The roots of the cranial nerves lie within the skull, while the nodes are outside the skull.
Other categories of ganglia are those of the autonomic nervous system, which is divided into sympathetic and parasympathetic systems.
The sympathetic chain lymph nodes form a row along the spine. They arise from the lateral horn of the lumbar spine and upper thoracic spine.
While the parasympathetic ganglia, they are next to the organs where they act. Although there are some parasympathetic lymph nodes in the head and neck.
Diseases of the peripheral nervous system
The peripheral nerves are an extensive and complicated network that constitutes a very fragile system. The nerves of this system can be damaged by pressure, syndromes or neurological problems. There are people who are born with affectations of this type while others are acquired.
In short, there is a great variety of pathologies that can affect the peripheral nervous system. Some of them are:
- Neuropathy: Is usually a consequence of another condition and there are many types. It involves damage to any nerve or nerves in the body. The symptoms it causes usually consist of tingling and numbness.
For example, one type is diabetic neuropathy. It seems that a high blood sugar can affect the nerves. This produces high heart rate, dizziness, muscle weakness, changes in vision, pain in the extremities, loss of sensitivity, among others.
Nerves can also occur because they consume high amounts of alcohol, resulting in alcoholic neuropathy.
- Brachial plexus injury: The brachial plexus is a set of nerves that send information from the spine to the shoulders, arms and hands. Most brachial plexus injuries occur due to trauma. This can be due to traffic accidents, wounds, tumors... among others.
There is also the so-called obstetric palsy of the brachial plexus that occurs in at least 1% of births. It is common when there is difficulty in removing the baby's shoulder at the time of birth.
In this way, the nerves of the brachial plexus are injured. This results in loss of movement around the shoulder and inability to bend the elbow.
- Carpal tunnel syndrome: It is a disorder characterized by a pressure on the nerves of the hand. This causes the palm of the hand, fingers and palmar side to lose sensitivity.
Usually occurs in people who use computers throughout the day, as carpenters, assembly line workers, musicians and mechanics.
- Compression of the ulnar nerve: The ulnar nerve runs from the shoulder to the fingers, and is very superficial. Pressing on it can cause damage, which can lead to loss of sensitivity. It is commonly reflected in tingling, burning, or numbness.
- Guillain Barre syndrome: In this disorder, the immune system fails by mistakenly attacking part of the peripheral nervous system. In this way there is inflammation in some nerves, pain, tingling, loss of coordination, and muscle weakness.
References
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