Anatomy of nervous system – classification, organs and functions

Anatomy of the nervous system – classification, organs, and functions

Anatomy of the nervous system – The human body is a multistage structure, each organ, and system of which is closely interconnected with each other and with the environment. And so that this connection is not interrupted for even a split second, the nervous system is provided – the most complex network that permeates the entire human body and is responsible for self-regulation and the ability to adequately respond to external and internal stimuli. Thanks to the well-coordinated work of the nervous system, a person can adapt to the factors of the external world: any, even insignificant, change in the environment makes nerve cells transmit hundreds of impulses at an incredibly high speed so that the body can instantly adapt to new conditions for itself. Internal self-regulation works similarly, in which the activity of cells is coordinated by current needs.

The functions of the nervous system affect the most important processes of life, without which the normal existence of the organism is unthinkable. These include:

  • regulation of the work of internal organs by external and internal impulses;
  • coordination of all units of the body, from the smallest cells to organ systems;
  • harmonious human interaction with the environment;
  • the basis of higher psychophysiological processes inherent in humans.

How does this complex mechanism work? What cells, tissues, and organs in the human nervous system represented, and what is each of its departments responsible for? A short excursion into the basics of the anatomy and physiology of the human body will help find answers to these questions.

Organization of the human nervous system – Anatomy of Nervous System

Nerve cells cover the entire body as a whole, forming an extensive network of fibers and endings. This system, on the one hand, unites every cell of the body, forcing it to work in one direction, and on the other hand, it integrates a particular person into the environment, balancing his needs with external factors. The nervous system ensures the normal processes of digestion, respiration, blood circulation, the formation of immunity, metabolism, etc. – in short, everything without which normal life is inconceivable.

Nervous System - Structure & Function of Nervous System (CNS & PNS)


In Anatomy, The efficiency of the nervous system depends on the correct formation of the reflex – the response of the body to irritation. Any impact, be it external changes or internal imbalance, triggers a chain of impulses that instantly affect the body, and he, in turn, forms a response. Thus, the human nervous system forms the unity of tissues, organs, and systems of the human body with each other and with the surrounding world.

The entire nervous system consists of millions of nerve cells – neurons, or neurocytes, each of which has a body and several processes.

The classification of neuron processes depends on what function it performs:

  • the axon sends a nerve impulse from the body of the neuron to another nerve cell, or the ultimate goal of the chain is a tissue or organ that must perform a certain action;
  • the dendrite receives the sent impulse and leads it to the body of the neuron.

Because each nerve cell is polarized, the chain of nerve impulses never changes direction, getting back on track. Thus, each nerve impulse is promoted, initiating the work of muscles, internal organs, and systems.

Varieties of nerve cells – Anatomy of Nervous System

Before considering the nervous system as a whole, it is necessary to understand what functional units it consists of. The National Assembly includes:

  1. Sensitive neurons. They are located in nerve nodes that receive information directly from receptors.
  2. Intercalary neurons are an intermediate link through which the received impulse is transmitted from sensory neurons further along the chain.
  3. Motor neurons. They act as initiators of a response to a stimulus, transmitting a signal from the brain to the muscles or glands, which normally should perform the function assigned to them.

Anatomy of nervous system - The nervous system is composed of organs, principally the brain, spinal cord, nerves, and ganglia.

It is according to this scheme that any response of the human body to an external or internal signal-stimulus is built, which acts as an impetus for a specific action. As a rule, the passage of a nerve impulse takes a few fractions of a second, but if this time is delayed or the chain is interrupted, this indicates the presence of pathology of the nervous system and requires serious diagnosis.


The structure and types of the nervous system: a structural classification & Anatomy

To simplify the structure of the nervous system, in medicine, several classifications are depending on the structure and functions. So, anatomically, the human nervous system can be divided into 2 broad groups:

  • central (CNS), formed by the brain and spinal cord;
  • peripheral (PNS), represented by nerve nodes, endings, and nerves directly.

The basis of this classification is extremely simple: the central nervous system is a kind of connecting link in which the received impulse is analyzed and the further regulation of the activity of organs and systems is carried out. And PNS serves to transport the incoming signal from the receptors to the central nervous system and the subsequent activator, but from the central nervous system to the cells and tissues that will perform a specific action.

central nervous system – Anatomy of Nervous System

The central nervous system is a key component of the nervous system because it is here that the main reflexes are formed. It consists of a spinal cord and a brain, each of which is reliably protected from external influences by bone structures. Such thoughtful protection is necessary, since each part of the central nervous system performs vital functions, without which it is impossible to maintain health.

Spinal cord – a part of the Anatomy of Nervous System

This structure is enclosed within the spinal column. She is responsible for the simplest reflexes and involuntary reactions of the body to a stimulus.

Spinal Cord of Nervous System

Besides, the neurons of the spinal cord coordinate the activity of muscle tissue, which regulates defense mechanisms. For example, having felt an extremely hot temperature, a person involuntarily pulls his palm, thereby protecting himself from a thermal burn. This is a typical spinal cord-controlled response.

Brain – a part of the Anatomy of Nervous System

The human brain consists of several sections, each of which performs several physiological and psychological functions:

  1. The medulla oblongata is responsible for the vital functions of the body – digestion, breathing, the movement of blood through the vessels, etc. Also, the nucleus of the vagus nerve is located here, which regulates autonomic balance and psycho-emotional response. If the nucleus of the vagus nerve sends active impulses, the person’s vitality decreases, he becomes apathetic, melancholic, and depressive. If the activity of the impulses emanating from the nucleus decreases, the psychological perception of the world changes to a more active and positive one.
  2. The cerebellum regulates the precision and coordination of movements.
  3. The midbrain is the main coordinator of muscle reflexes and tone. Also, neurons regulated by this part of the central nervous system contribute to the adaptation of the sense organs to external stimuli (for example, accommodation of the pupil at dusk).
  4. The diencephalon is formed by the thalamus and hypothalamus. The thalamus is the most important organ-analyzer of incoming information. In the hypothalamus, the emotional background and metabolic processes are regulated, there are centers responsible for the feeling of hunger, thirst, fatigue, thermoregulation, and sexual activity. Thanks to this, not only physiological processes are coordinated, but also many human habits, for example, the tendency to overeat, the perception of cold, etc.
  5. The cortex of the cerebral hemispheres. The cerebral cortex is a key link in mental functions, including consciousness, speech, perception of information, and its subsequent comprehension. The frontal lobe regulates motor activity, the parietal is responsible for bodily sensations, the temporal lobe controls hearing, speech, and other higher functions, and the occipital contains the centers of visual perception.


Peripheral nervous system – Anatomy of Nervous System

The PNS provides the relationship between organs, tissues, cells, and the central nervous system. Structurally, it is represented by the following morphofunctional units:

  1. Nerve fibers, which, depending on the functions performed, are motor, sensitive, and mixed. The motor nerves transmit information from the central nervous system to muscle fibers, the sensitive ones, on the contrary, help to perceive the information received with the help of the senses and transmit it to the central nervous system, and the mixed ones participate in both processes to one degree or another.
  2. Nerve endings, which are also motor and sensitive. Their function is no different from fiber structures with a single caveat – nerve endings begin or, conversely, end a chain of impulses from organs to the central nervous system and vice versa.
  3. Nerve nodes, or ganglia, are clusters of neurons outside the central nervous system. The spinal ganglia are responsible for the transmission of information received from the external environment, and the vegetative – data on the state and activity of internal organs and resources of the body.

Also, all peripheral nerves are classified according to their anatomical features. Based on this characteristic, 12 pairs of cranial nerves coordinate the activity of the head and neck, and 31 pairs of spinal nerves responsible for the trunk, upper and lower extremities, as well as internal organs located in the abdominal and chest cavities.

The cranial nerves originate from the brain. The basis of their activity is the perception of sensory impulses, as well as partial participation in respiratory, digestive, and cardiac activity. The function of each pair of cranial nerves is presented in more detail in the table.

P / p No. Name Function
I Olfactory Responsible for the perception of various odors, transmitting nerve impulses from the olfactory organ to the corresponding center of the brain.
II Visual Regulates the perception of data obtained visually by delivering impulses from the retina.
III Oculomotor Coordinates the movement of the eyeballs.
IV Block Along with the oculomotor pair of nerves, it takes part in the coordinated mobility of the eyes.
V Trigeminal Responsible for sensory perception of the facial area, and also participates in the act of chewing food in the oral cavity.
VI Diverting Another nerve that regulates the movement of the eyeballs.
Vii Facial The nerve that coordinates facial contractions of the facial muscles. Also, this pair is responsible for taste perception, transmitting signals from the papillae of the tongue to the brain center.
VIII Vestibular cochlear This pair is responsible for the perception of sounds and the ability to maintain balance.
IX Glossopharyngeal It regulates the normal activity of the pharyngeal muscles and partially transmits taste sensations to the brain center.
X Wandering One of the most important cranial nerves, the functionality of which depends on the activity of internal organs located in the neck, chest, and abdominal walls. These include the pharynx, larynx, lungs, heart muscle, and organs of the digestive tract.
XI Dorsal Responsible for the contraction of muscle fibers in the cervical and shoulder regions.
XII Sublingual Coordinates the activity of the language and partially forms the speech skill.

The activity of the spinal nerves is classified much more simply – each specific pair or complex of pairs is responsible for the section of the body of the same name assigned to it:

  • cervical – 8 pairs,
  • breast – 12 pairs,
  • lumbar and sacral – 5 pairs, respectively,
  • coccygeal – 1 pair.

Each member of this group belongs to mixed nerves formed by two roots: sensory and motor. That is why the spinal nerves can both perceive an irritating effect, transmitting an impulse along a chain, and activate activity in response to a message from the central nervous system.

Cranial Nerves

Morphofunctional division of the nervous system – Anatomy of Nervous System

There is also a functional classification of parts of the nervous system, which includes:

  • The somatic nervous system, which regulates the functions of skeletal muscles. It is controlled by the cerebral cortex, therefore it is completely subordinated to the conscious decisions of a person.
  • The autonomic nervous system is responsible for the activity of internal organs. Its centers are located in the brain stem, and therefore it is not consciously regulated in any way.

Also, the vegetative system is further subdivided into 2 significant functional divisions:

  • Sympathetic. It is activated at energy consumption;
  • Parasympathetic. Responsible for the recovery period of the body.


Somatic nervous system – Anatomy of Nervous System

Somatics is a division of the nervous system that is responsible for the delivery of motor and sensory impulses from receptors to the organs of the central nervous system and vice versa. Most of the nerve fibers in the somatic system are concentrated in the skin, muscled frame, and organs responsible for sensory perception. It is the somatic nervous system that almost 100% coordinates the conscious part of the activity of the human body and the processing of information received from the receptors of the sense organs.

The main elements of somatics are 2 types of neurons:

  • sensory, or afferent. Regulate the delivery of information to the cells of the central nervous system;
  • motor, or efferent. They work in the opposite direction, transporting nerve impulses from the central nervous system to cells and tissues.

Both those and other neurons stretch from the central nervous system directly to the final target of the impulses, that is, to the muscle and receptor cells, and the body in most cases is located directly in the central part of the nervous system, and the processes reach the required localization.

In addition to conscious activity, the somatic also includes a part of reflexes that are controlled unconsciously. With the help of such reactions, the muscular system comes into an active state, without waiting for an impulse from the brain, which allows it to act instinctively. Such a process is possible if the pathways of the nerve fibers pass directly through the spinal cord. An example of such actions is twitching the hand when a high temperature is felt or a knee reflex when hitting a tendon with a hammer.

Autonomic nervous system – Anatomy of Nervous System

Vegetation, or the autonomic nervous system, is a department that coordinates the activity of mainly internal organs. Since the main life processes – respiration, metabolism, cardiac contractions, blood flow, etc. – are not subject to consciousness, autonomic nerve fibers react mainly to changes in the internal environment of the body, remaining indifferent to conscious impulses. Thanks to this, the body maintains optimal conditions for providing the energy resources necessary in a particular situation.


The features of autonomic nervous activity imply that the main fibers are concentrated not only in the organs of the central nervous system but also in other tissues of the human body. Numerous nodes are scattered throughout the body, forming the autonomic nervous system outside the central nervous system, between the brain centers and organs. Such a network can regulate the simplest functions, but more complex mechanisms remain under the direct control of the central nervous system.

The key role of vegetation is to maintain relatively constant homeostasis by self-tuning the activity of internal organs, depending on the needs of the body. So, vegetative fibers optimize the secretion of hormones, the rate and intensity of blood supply to tissues, the intensity and frequency of respiration and heart rate, and other key mechanisms that must respond to changes in the external environment (for example, during intense physical activity, an increase in temperature or humidity, atmospheric pressure, etc., etc.). Thanks to these processes, compensatory and adaptive reactions are provided that maintain the body in optimal shape under any circumstances. Since the unconscious activity of internal organs can be regulated in two directions (activation and suppression),

Sympathetic nervous system – Anatomy of Nervous System

The sympathetic part of the vegetation is directly connected with the spinal substance located from the first thoracic to the third lumbar vertebra. It is here that the stimulation of the activity of internal organs is carried out, which is necessary during increased energy consumption – during physical exertion, stress, intense work, or emotional shock. Such mechanisms make it possible to support the body by providing it with the resources necessary to overcome adverse conditions.

Under the influence of sympathy, breathing, and pulsation of blood vessels become more frequent, due to which the tissues are better supplied with oxygen, energy is released from the cells faster. Thanks to this, a person can work more actively, coping with increased loads in conditions of disadvantage. However, these resources cannot be infinite: sooner or later, the amount of energy reserves decreases, and the body can no longer function “at increased speed” without respite. Then the parasympathetic department of vegetation is included in the work.

Parasympathetic nervous system – Anatomy of Nervous System

In Anatomy of Nervous System, The parasympathetic nervous system is localized in the midbrain and sacral spine. She, unlike sympathizers, is responsible for maintaining and accumulating energy depots, reducing physical activity, and good rest.

So, for example, parasympathetic slows down the heart rate during sleep or physical rest, when a person recovers spent strength, coping with fatigue. Additionally, during this time, peristaltic processes are activated, which have a positive effect on metabolism and, as a result, on the restoration of nutrient reserves. Thanks to such self-regulation, defense mechanisms are activated, which are especially important at a critical level of overwork or exhaustion – the human body simply refuses to continue working, requiring time for rest and recovery.


Features and differences of the sympathetic and parasympathetic nervous system

At first glance, it may seem that the sympathetic and parasympathetic divisions are antagonists, but in reality, this is not so. Both of these departments act in a coordinated manner and together, just in different directions: if the sympathetic activates the work, then the parasympathetic allows you to recover and rest. Thanks to this, the work of the internal organs always, to a greater or lesser extent, corresponds to a specific situation, and the body can adapt to any conditions. In fact, both of these systems form the basis of homeostasis, balancing the activity levels of the human body.

Most of the internal organs have both sympathetic and parasympathetic fibers, which have different effects on them. Moreover, the state of the organ at the current moment depends on which of the departments of the National Assembly prevails in the current circumstances. An illustrative example of the activity of these systems can be seen in the table below.

Organ Parasympathetic effects Sympathetic impact
Blood supply to the brain Narrowing of blood vessels, a decrease in the volume of incoming blood Expansion of blood vessels, activation of blood supply
Peripheral arteries and arterioles Narrowing of the lumen, increasing blood pressure and weakening blood flow Expansion of the diameter of arterial vessels and decrease in pressure
Heart rate The decrease in heart rate Increased heart rate
Digestive system Strengthening the motility of the gastrointestinal tract for the speedy absorption of nutrients The slowdown of peristalsis and, as a result, metabolism
Salivary glands Increased secretion The feeling of dry mouth
Adrenal glands Suppression of endocrine function Activation of hormone synthesis
Bronchi Narrowing of the lumen of the bronchi, heavier unproductive breathing Expansion of the bronchi, an increase in the volume of inhaled air, and the productivity of each respiratory movement
Visual analyzer Constriction of the pupils Dilated pupils
Bladder Reduction Relaxation
Sweat glands Reduced sweating Increased activity of sweat glands


Post Scriptum in Anatomy of Nervous System

Neurological problems associated with diseases of the human nervous system are among the most difficult in medical practice. Any damage to the nerve tissue leads to a partial or complete loss of control over the body, causing tremendous damage to the quality of life and reduces the functionality of a person. Only a complex and coordinated action of each neuron in all parts of the central and peripheral NS can maintain the body in an optimal state, ensure the correct operation of each organ, adequately fit into the surrounding realities and respond to external stimuli. Therefore, it is necessary to carefully monitor the health of your own nervous system, and at the slightest suspicion of a deviation, urgently take appropriate measures – this is one of those cases in which it is better to engage in prevention than to waste time.