- Peripheral nervous system: structure
- Peripheral Nervous System: Features
- Peripheral nervous system: types of receptors
- Peripheral Nervous System: Diseases
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The peripheral nervous system is essentially a part of the central nervous system, but this does not mean that its function is irrelevant. The basic elements of the peripheral nervous system are cranial nerves and spinal nerves, which are responsible for sending impulses from and to a specific "command center", which is the central nervous system. Exactly what functions does the peripheral nervous system perform and what diseases may affect it?
The peripheral nervous systemtogether with the central nervous system make up the nervous system. While the brain and spinal cord belong to the central nervous system, the nerves that emerge from these structures and other, other elements, belong to the peripheral nervous system.
Peripheral nervous system: structure
Within the peripheral nervous system, two main elements are distinguished: cranial nerves and spinal nerves. There are twelve pairs of cranial nerves, the ganglia of these nerves (i.e. the bodies of nerve cells from which nerve fibers - axons - are sent to further regions of the body) are located in different parts of the brain, but most of them are located in the brainstem. Among the twelve cranial nerves, the following are distinguished:
- olfactory nerve (I)
- optic (II) nerve
- oculomotor nerve (III)
- block (IV) nerve
- trigeminal nerve (V)
- nerve abduction (VI)
- facial nerve (VII)
- vestibulocochlear nerve (VIII)
- glossopharyngeal nerve (IX)
- vagus nerve (X)
- accessory nerve (XI)
- sublingual nerve (XII)
Most of the cranial nerves supply the head and neck area, with the exception of the vagus nerve, whose branches even innervate organs located in the abdominal cavity.
In addition to cranial nerves, spinal nerves are also included in the peripheral nervous system. As the name suggests, this type of nerve comes from the spinal cord and there are as many as 31 pairs of them in the human body. Among the spinal nerves, the following are distinguished:
- 8 pairs of cervical nerves (C1-C8)
- 5 pairs of lumbar nerves (L1-L5)
- 5 pairs of sacral nerves (S1-S5)
- 1 pair of coccygeal nerves (Co1)
As you can see, the distribution of spinal nerves is quite complicated, what's more - this onepart of the peripheral nervous system has an even more complex structure. Spinal nerves from individual segments of the spinal cord (apart from those originating in the thoracic segment) form nerve plexuses, in which nerve branches originating from separate areas of the spine are connected. Such structures include the cervical plexus, which is made up of the branches of the C1-C4 spinal nerves, and which gives rise to such nerves as, for example, the phrenic nerve, the great ear nerve, the minor occipital nerve or the transverse nerve of the neck.
Another nerve plexus, perhaps better known than the one discussed above, is the brachial plexus. This structure is made up of the C5-Th1 nerve fibers and is the source of many different nerves, such as the median nerve, ulnar nerve, and dermal-muscular nerve, as well as the radial, axillary, and dorsal scapula nerves.
Another important plexus forming part of the peripheral nervous system is the lumbosacral plexus, which is formed from the branches of the Th12-S5 spinal nerves. This part of the peripheral nervous system is the source of nerves such as the sciatic, femoral, and obturator nerves, as well as the vulva nerve, and the minor and major gluteal nerves.
Peripheral Nervous System: Features
The most important function of the peripheral nervous system is to transmit stimuli between the central nervous system and the peripheral nervous structures. Most generally, two types of nerve fibers can be distinguished in the peripheral nervous system. Afferent (centripetal, sensory) fibers are responsible for sending nerve impulses to the CNS from a variety of receptors scattered throughout the human body. The opposite role is played by efferent fibers (centrifugal, motor), which transmit impulses from the CNS to executive structures (e.g. to muscles that are about to make some movement).
Fibers of the peripheral nervous system can be divided not only according to the direction in which nerve stimuli flow in them (from or to the CNS), but also according to what information the fibers transmit. In the peripheral nervous system, it is possible to distinguish between its part belonging to the autonomic system and the part belonging to the somatic nervous system. The first of these - i.e. the fibers of the autonomic system - are responsible for the control of phenomena independent of our will, such as, for example, blood flow in the digestive tract or heart function. The somatic nervous system, in turn, controls the activities that we perform consciously, such as reaching for a cup of coffee or turning the pages of a book we are currently reading.peripheral nervous system, send the information they receive to the structures of the CNS. The reception of such information takes place thanks to a variety of receptors, about which it is worth mentioning a little more because there are relatively many of them in the peripheral nervous system.
Peripheral nervous system: types of receptors
The receptors of the peripheral nervous system can be divided into several different properties of these structures. The most important seems to be to distinguish between these receptors according to the types of stimuli they receive and their location.
In the first of these cases, we can mention mechanoreceptors (sensitive to pressure, vibration and touch), thermoreceptors (responsible for the reception of thermal sensations), photoreceptors (sensitive to light stimuli), as well as chemoreceptors (which receive chemical stimuli and are responsible for our perception of e.g. smell and taste) and nociceptors (which are sensitive to pain stimuli). As for the division of receptors of the peripheral nervous system according to their location, exteroreceptors (located on the surface of the body and responsible for the sensation of m e.g. pain, temperature and touch) and interoreceptors (present e.g. in internal organs and blood vessels, where they are responsible for receiving e.g. thermal or chemical impulses).
Peripheral Nervous System: Diseases
Basically, the peripheral nervous system can be considered the part of the nervous system that is more susceptible to disease - after all, the brain of the central nervous system is protected by the bones of the skull, while the spinal cord is protected by the spine. Structures belonging to the peripheral nervous system generally do not have such covers, and therefore they are much more exposed to various types of damage.
Nerves of the peripheral nervous system can be damaged, for example, as a result of some trauma - in a situation where a patient injures one, single nerve, it is called mononeuropathy. Having an accident is not the only condition that can lead to nerve damage - the cause of such a problem can also be the growth of a tumor mass near the nerve and the destruction of the nerve tissue associated with it.
Individuals with compression of individual nerve fibers can lead to the appearance of specific ailments in patients. Diseases of the peripheral nervous system of this type include e.g. carpal tunnel syndrome and Guyon's canal syndrome.
Damage to structures belonging to the peripheral nervous systemit can also occur as a result of various systemic diseases. A classic example of an entity that can lead to such a problem is diabetes mellitus (where diabetic neuropathy is common). Other conditions that can lead to dysfunction of the peripheral nervous system are, for example, amyloidosis and sarcoidosis. In humans, there can also be nerve damage associated with the toxic effects of various substances on the nervous system - alcohol can be used as a typical example of an agent that is consumed by humans and that can damage nerves (chronic abuse eventually leads to alcoholic neuropathy).About the authorBow. Tomasz NęckiA graduate of medicine at the Medical University of Poznań. An admirer of the Polish sea (most willingly strolling along its shores with headphones in his ears), cats and books. In working with patients, he focuses on always listening to them and spending as much time as they need.