Central and peripheral nervous system: structure and functions

Correct work of the nervous system on different fronts is extremely important for a person's full life. The human nervous system is considered the most complex structure of the body.

Modern ideas about the functions of the nervous system

A complex communication network, which in biological science is designated as a nervous system, is divided into central and peripheral, depending on the location of the nerve cells themselves. The first unites cells located inside the brain and spinal cord. But the nerve tissues that are located outside of them form the peripheral nervous system (PNS).

The central nervous system (CNS) implements key functions of processing and transferring information, interacting with the environment. The nervous system works according to the reflex principle. Reflex is the response of the body to a specific irritation. Nerve cells of the brain are directly involved in this process. Having received information from PNS neurons, they process it and direct the impulse to the executive body. By this principle, all voluntary and involuntary movements are carried out , the sense organs (cognitive functions) work, thinking and memory work, etc.

Cellular mechanisms

Regardless of the functions of the central and peripheral nervous system and the location of cells, neurons have some common characteristics with all cells of the body. So, each neuron consists of:

• Membrane, or cytoplasmic membrane;
• Cytoplasm, or the space between the membrane and the cell nucleus, which is filled with intracellular fluid;
• Mitochondria , which provide the neuron itself with the energy they receive from glucose and oxygen;
• Microtubules - fine structures that perform supporting functions and help the cell to retain its original form;
• Endoplasmic reticulum - internal networks, which the cell uses for self-maintenance.

Distinctive features of nerve cells

Nerve cells have specific elements that are responsible for their communication with other neurons.

Axons are the main processes of nerve cells, through which information is transmitted along the neural circuit. The more outgoing channels of information transfer form a neuron, the more branches there is in its axon.

Dendrites are other processes of the neuron. On them there are input synapses - specific points where contact with neurons occurs. Therefore, the incoming neural signal is called synoptic transmission.

Classification and properties of nerve cells

Nerve cells, or neurons, are divided into many groups and subgroups, depending on their specialization, functional, and place in the neural network.

The elements responsible for sensory perception of external stimuli (sight, hearing, tactile sensation, sense of smell, etc.) are called sensory. Neurons that are combined in a network to provide motor functions are called motor neurons. Also in the National Assembly there are mixed neurons that perform universal functions.

Depending on the location of the neuron in relation to the brain and the executive organ, the cells can be primary, secondary, etc.

Genetically, neurons are responsible for the synthesis of specific molecules by which they build synaptic connections with other tissues, but nerve cells do not have the ability to divide.

This is also the basis for the popular statement in the literature that "nerve cells are not being restored." Naturally, the neurons that can not be divided can not be restored. But they are able every second to create many new neural connections for performing complex functions.

Thus, the cells are programmed to constantly create more and more connections. This is how a complex network of neural communications develops. The creation of new connections in the brain leads to the development of intelligence, thinking. Muscular intelligence also develops in this way. The brain is irreversibly improved when learning all the new and new motor functions.

The development of emotional intelligence, physical and mental, occurs in the nervous system in a similar way. But if the emphasis is on something, the other functions do not develop so fast.

Brain

The adult brain weighs approximately 1.3-1.5 kg. Scientists found that until the age of 22, his weight gradually increases, and after 75 years begins to decrease.

In the brain of the average individual there are more than 100 trillion electrical connections, and this is several times greater than all the connections in all electrical devices in the world.

Researchers spend tens of years and tens of millions of dollars studying and trying to improve brain functions.

Divisions of the brain, their functional characteristics

Nevertheless, modern knowledge of the brain can be considered sufficient. Especially considering that the science of the functions of certain parts of the brain made possible the development of neurology, neurosurgery.

The brain is divided into such zones:

1. The forebrain. The forebrain is usually credited with "higher" mental functions. It includes:

• Frontal lobes, responsible for coordinating the functions of other areas;
• Temporal lobes responsible for hearing and speech;
• Parietal lobes regulate motion control and sensory perceptions.
• Occipital lobe in response to visual functions.

2. The middle brain includes:

• Thalamus, where the processing of almost all information entering the forebrain.
• The hypothalamus controls the information coming from the organs of the central and peripheral nervous system and the autonomic NA.

3. The hindbrain includes:

• Oblong brain, which is responsible for the regulation of biorhythms and attention.
• The brain stem gives rise to the nerve pathways through which the brain connects with the structures of the spinal cord, this is a kind of communication channel between the central and peripheral nervous system.
• The cerebellum, or small brain, makes the tenth part of mass of a brain. Above it are two large hemispheres. From the work of the cerebellum depends on the coordination of human movements, the ability to maintain balance in space.

Spinal cord

The average length of the adult human spinal cord is approximately 44 cm.

It originates from the brainstem and passes through the large occipital foramen in the skull. It ends at the level of the second lumbar vertebra. The end of the spinal cord is called the medulla cone. It ends in a cluster of lumbar and sacral nerves.

From the spinal cord, 31 pairs of spinal nerves branch. They help to connect the departments of the nervous system: central and peripheral. Through these processes, parts of the body and internal organs receive signals from the NS.

In the spinal cord, the primary processing of reflex information also occurs, thereby speeding up the process of responding to irritants in dangerous situations.

Liquor, or cerebral fluid, common to the spinal cord and brain, is formed in the vascular nodes of the brain's gaps from the blood plasma.

Normally, its circulation must be continuous. Liquor creates permanent internal cranial pressure, performs damping and protective functions. Analysis of the composition of the CSF is one of the simplest ways to diagnose serious diseases of the NS.

What causes lesions of the central nervous system of different origins

The lesions of the nervous system, depending on the period, are divided into:

1. Preperinatal - brain damage during intrauterine development.
2. Perinatal - when the lesion occurs during childbirth and in the first hours after birth.
3. Postnatal - when the lesion of the spinal cord or brain occurs after birth.

Depending on the nature, lesions of the central nervous system are divided into:

1. Traumatic (most obvious). It should be taken into account that the nervous system is of paramount importance for living organisms and from the point of view of evolution, therefore the spinal cord and brain are reliably protected by a number of membranes, cerebral fluid and bone tissue. However, in some cases this protection is not enough. Some injuries lead to damage to the central and peripheral nervous system. Traumatic lesions of the spinal cord lead to irreversible consequences. Most often these are paralysis, moreover degenerative (accompanied by the gradual dying off of neurons). The higher the damage, the larger the paresis (the decrease in muscle strength). The most common injuries are open and closed concussions of the brain.
2. Organic damage to the central nervous system often occurs during childbirth and leads to infantile cerebral palsy. They arise because of oxygen starvation (hypoxia). It is the result of prolonged labor or umbilical cord entanglement. Depending on the period of hypoxia, cerebral palsy can be of different degrees of severity: from mild to severe, which is accompanied by a complex atrophy of the central and peripheral nervous system. CNS lesions after a stroke are also defined as organic.
3. Genetically caused lesions of the central nervous system occur due to mutations in the gene chain. They are considered hereditary. The most common are Down's syndrome, Tourette's syndrome, autism (genetic-metabolic disorder), which manifest immediately after birth or in the first year of life. Diseases Kensington, Parkinson, Alzheimer's are considered degenerative and manifest in middle or old age.
4. Encephalopathy - most often occur as a consequence of damage to the brain tissue pathogens (herpetic encephalopathy, meningococcal, cytomegalovirus).

Structure of the peripheral nervous system

PNS form nerve cells located outside the brain and spinal canal. It consists of nerve nodes (cranial, spinal and vegetative). Also in the PNS there are 31 pairs of nerves and nerve endings.

In a functional sense, the PNS consists of somatic neurons that transmit motor impulses and contact the receptors of the sense organs, and the vegetative ones, which are responsible for the activity of internal organs. Peripheral neuronal structures contain motor, sensoric and vegetative fibers.

Inflammatory processes

Diseases of the central and peripheral nervous system are completely different in nature. If the CNS lesions most often have complex, global consequences, PNS diseases often manifest themselves as inflammatory processes in the zones of the nerve nodes. In medical practice, such inflammations are called neuralgia.

Neuralgia - it is a painful inflammation in the area of accumulation of nerve nodes, the irritation of which causes an acute reflex attack of pain. Neuralgia includes polyneuritis, radiculitis, inflammation of the trigeminal or lumbar nerve, plexitis, etc.

The role of the central and peripheral nervous system in the evolution of the human body

The nervous system is the only system of the human body that can be improved. The complex structure of the central and peripheral nervous system of man is caused genetically and evolutionarily. The brain has a unique property - neuroplasticity. This ability of CNS cells to take on the functions of neighboring dead cells, building new neural connections. This explains the medical phenomenon, when children with organic brain damage develop, learn walking, speech, etc., and people after a stroke eventually regain the ability to move normally. This is preceded by the construction of millions of new connections between the central and peripheral parts of the nervous system.

With the progress of various techniques for restoring patients after brain trauma, methods for human development are also being developed. They are based on the logical assumption that if both the central and peripheral nervous system can recover from injuries, healthy nerve cells are also able to develop their potential almost to infinity.