Human nervous system - structure, functions, work

Structural units

To facilitate understanding of what the somatic system is, it is necessary to know the features of its structure. Thus, the basic unit is the motor neuron. The processes of many sensitive neurocytes end on his body. Therefore, information from hundreds of intermediate neurons accumulates in it. After all, they themselves are not able to activate - they wait for an impulse from the motor units.

Motor neurons are controlled by both the spinal cord and its central, intracranial part. This division has its advantages - many simple reflexes can be carried out at the level of the spine. For example, withdrawing your hand when touching a flame.

However, the somatic and autonomic systems are subordinate to the cerebral cortex - clarity of movements, their thoughtfulness. The peculiarity of the functioning is that the dorsal and ventral branches of the radicular nerve are used to form the impulse. This can be seen especially clearly in the sacral plexus - the knee reflex.

The spinal nerves themselves, thanks to motor neurons, provide innervation to almost all muscle organs. Meanwhile, in the frontal lobe there is a motor zone - the highest regulation of motor activity.

Characteristics of the reflex arc

The functioning of the nervous system is the continuous processing of information coming from outside and reaction to it. The somatic section in this chain is responsible for motor reflexes - in most cases, even without control from the brain.

Anatomically, the path of impulse transmission is described by a reflex arc. Among its links are several neurons that are interconnected by synapses. It is through them that the unidirectional movement of an information impulse occurs - in most cases through a chemical intermediary. It is also called a mediator.

Structures of the somatic arc:

sensory neuron - localized in the spinal ganglion or in the zone of sensory ganglia inside the brain;
intercalary, peripheral neuron - located in the nuclei of the dorsal horns of the spinal cord or the nuclei of the subcortical brainstem;
The motor neuron lies in the nuclei of the ventral horns of the spinal substance, as well as in the nuclei of the central brain stem.

The originating nerve impulse travels all the way from the sensory neuron to the muscle bundle, which innervates the motor neuron as part of the spinal fiber. For example, from the receptor on the skin of the finger, with which a person checks the heating of the stove, to the muscles of the same finger, if it is necessary to withdraw the hand to avoid a burn.

Structure of the somatic nervous system

The animal nervous system has a simple structure; it is controlled by neurons, on the work of which activities and functions are based:

sensory (spinal) neurons - deliver impulses to the central nervous system;
motor (cranial) neurons - deliver information from the brain to muscle tissue.

Neurons are located throughout the body from the center to important receptors and muscles. Their bodies are located in the central nervous system, and their axons extend to the skin, muscle tissue, and sensory organs. The muscles located on the left are under the control of the right hemisphere of the brain, and the muscles on the right are controlled by the left side. In addition to supplying nerves, it also influences interaction with muscles. The somatic nervous system includes reflex arcs designed to control unconscious actions and reflexes. With their help, the motor work of muscles is controlled without signals from the brain.

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Cranial nerves

The somatic nervous system includes 12 pairs of cranial nerves that carry information to and from the brain stem:

olfactory;
visual;
oculomotor;
block;
trigeminal;
diverting;
facial;
auditory;
glossopharyngeal;
wandering;
additional;
sublingual.

Almost all of them innervate the area of the head and neck, that is, the sensory organs, muscle tissue inside the skull, and include motor and secretory cells of the brain, where nuclear clusters of neurons are formed. Individual cranial nerves (for example, the optic nerve) are built only from sensory fibers. The vagus nerve innervates the heart, gastrointestinal tract, lungs and is responsible for their activity. The sensory fiber bodies are located near the brain, and the motor fiber bodies are located inside it.

Spinal nerves

Other structures with somatic innervation are the 31 pairs of spinal nerves with numerous branches to supply areas below the neck. Each spinal nerve is formed by the connection of the posterior and anterior (sensitive and motor) roots, the fusion of their fibers. The posterior ones supply the skin, muscles of the dorsal region, areas of the coccyx, sacrum, the anterior ones - the skin, muscle tissue of the arms, legs and the front part of the body.

Functions

Experts traditionally include the regulation of activity and body position in direct dependence on external stimulation as the functions of the somatic nervous system. A person “consciously” controls the parts of his body.

Since the motor neurons of the somatic nervous system innervate muscle structures on the periphery - limbs, internal organs, its functions will be as follows:

processing information that comes from the senses;
quick reactions to changing environmental conditions;
body orientation in space;
purposefulness of movements of all parts of the body.

Thanks to the motor neurons of the department, a person carries out conscious muscle movements - touching things, distinguishing tastes, assessing the position of his limbs in space and changing it as needed. At the same time, it regulates activity in the somatic nervous system, mainly its spinal part. Also called primitive. Despite the fact that in the process of evolution, people gained the ability to perform complex movements that obey the central structures of the cerebral cortex.

Nervous system: central and peripheral, somatic. Neurons, nerves, nerve ganglia.

LESSON #13

The date of the:____________________

Lesson topic:

Nervous system: central and peripheral, somatic. Neurons, nerves, nerve ganglia.

Number of hours

: 1

Lesson type

: Mastering new knowledge and types of learning activities

Target setting

: Formation of ideas about the significance of the nervous system and the general principles of its organization

Concepts and personalities

: Nervous system: central, peripheral. Bark. Cores. Nerve fibers. Nerve nodes. Excitation. Braking. Neurons: sensory, executive, intercalary

Planned results (in accordance with the Federal State Educational Standard):

Subject: The ability to explain the importance of the nervous system for the human body, characterize the structure of the human nervous system, distinguish between central and peripheral

nervous system, classify neurons depending on the functions they perform, describe and compare the processes of excitation and inhibition

Meta-subject: Cognitive UUD: ability to reproduce information from memory, work

with various sources of information, compare and analyze information, draw conclusions based on comparisons.

Nervous system

According to anatomical principles, the human nervous system is divided into central and peripheral.

The central nervous system (CNS) is formed by the brain and spinal cord.

The peripheral nervous system includes 12 pairs of cranial nerves, 31 pairs of spinal nerves, nerve plexuses and ganglia located in all parts of the body.

According to the anatomical and functional principle, the nervous system

conditionally divided into somatic and vegetative. Each of them has a central (located in the central nervous system) and peripheral (located outside the central nervous system) parts.

The somatic nervous system regulates the work of skeletal muscles, connecting the body with the external environment (through the somatic nervous system, the human brain receives information about the external environment and its effect on the body (for example, temperature changes, pain, touch, etc.). With its help, a person can voluntarily (i.e., at will) control the activity of skeletal muscles.

The autonomic nervous system (ANS) regulates the functioning of internal organs, controls the activity of smooth and cardiac muscles, the functioning of glands, metabolic reactions, maintaining the constancy of the internal environment in the human body. A person himself cannot control the operation of this system (for example, one cannot stop the heart at will, speed up the digestion process, or delay sweating), that is, it works involuntarily.

Anatomically, it includes elements of both the central and peripheral nervous systems

The centers of the autonomic nervous system are located in the gray matter

middle, medulla oblongata and spinal cord.
The excitation transmitted to the working organ passes through two neurons: the bodies of the first neurons lie in the central nervous system, and the bodies of the second ones lie in the nerve nodes lying outside it. Excitation is carried out much more slowly along the autonomic nerves. The autonomic nervous system consists of two divisions
- sympathetic and parasympathetic.

Sympathetic department

begins in the central parts of the spinal cord, in which the bodies of the first neurons are located. Their processes end in the sympathetic nerve ganglia, which lie on the sides of the spine and form chains. Inside the nodes are the bodies of second neurons, the processes of which go to the working organs.

The parasympathetic department begins in the medulla oblongata and the sacral part of the spinal cord (the bodies of the first neurons are located in them). The processes of neurons are sent to parasympathetic nodes (concentration of bodies of second neurons), located near organs or directly in the tissues of the innervated organ.

The autonomic nervous system has two divisions: parasympathetic and sympathetic. As a rule, the nerves of these two departments have opposite effects on the internal organs.

Parasympathetic nerve impulses weaken cardiac activity, dilate blood vessels in the skin, lower blood pressure, and lower blood glucose levels.

The sympathetic nervous system accelerates and strengthens the work of the heart, increases blood pressure, constricts blood vessels in the skin, and inhibits the functioning of the digestive system.

The nervous system controls, coordinates and regulates the coordinated work of all organ systems, maintaining the constancy of the composition of its internal environment (thanks to this, the human body functions as a single whole). With the participation of the nervous system, the body communicates with the external environment.

Physical exercise.

Nervous tissue

The nervous system is formed by nervous tissue, which consists of nerve cells - neurons - and small satellite cells (glial cells), which are approximately 10 times more numerous than neurons.

Neurons provide the basic functions of the nervous system: transmission, processing and storage of information. Nerve impulses are electrical in nature and spread along the processes of neurons.

Satellite cells perform nutritional, supportive and protective functions, promoting the growth and development of nerve cells.

Neuron structure

A neuron is the basic structural and functional unit of the nervous system.

The structural and functional unit of the nervous system is the nerve cell - neuron

. Its main properties are excitability and conductivity.

A neuron consists of a body

and
shoots
.

Short, highly branched processes - dendrites

, along which nerve impulses travel
to the body
of the nerve cell. There may be one or several dendrites.

Each nerve cell has one long process called an axon

, along which impulses are sent
from the cell body
.
The length of the axon can reach several tens of centimeters. Combining into bundles, axons form nerves
.

The long processes of a nerve cell (axons) are covered with a myelin sheath.

.
Clusters of these processes, covered with myelin
(a white fat-like substance), in the central nervous system form the white matter of the brain and spinal cord.

The short processes (dendrites) and cell bodies of neurons do not have a myelin sheath, so they are gray in color. Their clusters form the gray matter of the brain.

Synapse

Neurons connect to each other in this way: the axon of one neuron joins the body, dendrites, or axon of another neuron. The point of contact between one neuron and another is called a synapse

. There are 1200–1800 synapses on the body of one neuron.

A synapse is the space between neighboring cells in which the chemical transmission of a nerve impulse from one neuron to another occurs.

Each synapse consists of three sections

membrane formed by the nerve ending ( presynaptic membrane

);

membranes of the cell body ( postsynaptic membrane

);

synaptic cleft

between these membranes

The presynaptic part of the synapse contains a biologically active substance ( transmitter

), which ensures the transmission of a nerve impulse from one neuron to another. Under the influence of a nerve impulse, the transmitter enters the synaptic cleft, acts on the postsynaptic membrane and causes excitation in the cell body of the next neuron. This is how excitation is transmitted from one neuron to another through a synapse.

The spread of excitation is associated with such a property of nervous tissue as conductivity

Types of neurons

Neurons vary in shape

Depending on the function performed, the following types of neurons are distinguished:

neurons, transmitting signals from the sensory organs to the central nervous system
(spinal cord and brain) are called
sensitive
. The bodies of such neurons are located outside the central nervous system, in nerve ganglia. A ganglion is a collection of nerve cell bodies outside the central nervous system.
Neurons, transmitting impulses from the spinal cord and brain to muscles and internal organs
called
motor
. They ensure the transmission of impulses from the central nervous system to the working organs.
Communication between sensory and motor neurons
carried out with the help of
interneurons
through synaptic contacts in the spinal cord and brain. Interneurons lie within the central nervous system (that is, the bodies and processes of these neurons do not extend beyond the brain).

A collection of neurons in the central nervous system is called the nucleus

(nuclei of the brain, spinal cord).

Nerves

The spinal cord and brain are connected to all organs by nerves

Nerves are sheathed structures consisting of bundles of nerve fibers formed mainly by neuronal axons and neuroglial cells.

Nerves provide communication between the central nervous system and organs, blood vessels and skin.

Nerves are distinguished:

sensitive

, ensuring the conduction of impulses from receptors to the central nervous system;

motor

, consisting of axons of motor neurons and ensuring the conduction of impulses from the central nervous system to the executive organs;

mixed

, capable of conducting impulses in both directions.

Nerve plexus is a collection of nerve fibers of various nerves that innervate the skin, skeletal muscles and internal organs.

One of the most famous nerve plexuses is the solar plexus.

located in the abdominal cavity.

6. Reflection.

Guys, let's discuss what you would praise yourself for today?

7. Homework:

Distinctive features

Each structural unit of the human nervous system has its own functional purposes. However, together they form a complex whole. However, in the somatic part of the nervous system, neurons are more stable, and the impulse reaches its target faster. After all, its speed can reach 100–120 m/s. This significantly increases the chances of people surviving in dramatically changed external conditions - for example, when attacked by a predator during a hunt.

It is in the somatic department that information processing will occur more slowly than in the autonomic nervous system. Since they are faced with different functional tasks - the first must respond to information from motor neurons and carry out a reaction to them. Whereas vegetatives is nutrition, respiration, and reproduction.

Another significant difference is that there is no division in the somatic department. Most often it is represented by standard reflex arcs. Whereas in the autonomic system it is customary to distinguish the sympathetic as well as the parasympathetic departments. This makes it easier to control different muscle groups on an unconscious level, which takes some of the load off the cerebral cortex.

In general, all departments of the system cannot exist without close interaction with each other. This is why a person gets the opportunity to survive even in the most difficult conditions.

The structure of the human nervous system, its functional division (Tables, Diagrams)

The nervous system is a set of special structures that unites and coordinates the activities of all organs and systems of the body in constant interaction with the external environment.

The meaning of the nervous system:

• Maintaining a constant composition of the internal environment of the body.

• Coordination of the work of bodies.

• Recognize the external environment to meet needs. Orientation in the external environment.

• Ensuring conscious regulation of behavior. Psyche - speech, thinking, social behavior.

Structure of the human nervous system diagram

The human nervous system is divided into the central nervous system (includes the brain and spinal cord) and the peripheral nervous system (includes nerve endings, nerves, nerve ganglia).

Nerves	accumulations of long processes of nerve cells outside the central nervous system, enclosed in a common connective tissue membrane and conducting nerve impulses.
Sensory nerves	formed by dendrites of sensory neurons.
Motor nerves	formed by the axons of motor neurons.
Mixed nerves	formed by both axons and dendrites.
Nerve nodes	accumulations of neuron cell bodies outside the central nervous system.
Receptor nerve endings	terminal formations of dendrites in organs; perceive irritations and convert them into nerve impulses.
Effector nerve endings	terminal formations of axons in working organs: muscles, glands.
Nerve impulse	an electrical signal propagating across cell membranes.
Gray matter	these are the bodies of neurons.
White matter	these are processes of neurons
Excitation	putting the cell into operation.
Braking	inhibition of cell function.

Functional division of the nervous system

Functionally, the nervous system is divided into Somatic (subordinate to the will of a person) and Autonomous (vegetative, which is not subject to the will of a person). The somatic nervous system regulates the functioning of skeletal muscles; its motor centers are located in the cerebral cortex. The autonomic or autonomic nervous system regulates the functioning of internal organs, glands, blood vessels and the heart. Its autonomic centers are located in the hypothalamus.

The autonomic system is in turn divided into the sympathetic and parasympathetic systems. The sympathetic system is activated during intense work that requires energy expenditure. The parasympathetic system helps restore energy reserves during sleep and rest.

_______________

A source of information:

Biology in tables and diagrams./ Edition 2, - St. Petersburg: 2004.

Rezanova E.A. Human biology. In tables and diagrams./ M.: 2008.

Role

It is difficult to overestimate the role of the somatic system in the full functioning of the human body. After all, it regulates a lot of conscious muscle contractions - from facial expressions to fine motor skills of the fingers.

Due to the fact that the somatic system does not respond in a timely manner to external irritating factors, a person gets the opportunity to control his body and keep it intact. In general, this structure, with the help of reflex arcs, regulates the work of every, even the smallest, skeletal muscle - through impulses from motor neurons.

You can imagine the role of the somatic system using the example of any extreme situation:

sense organs perceive and transmit information about changes in the external environment;
the corresponding neuron of the nerve fiber transmits the signal to the sensory neuron in the spinal ganglia;
the impulse travels through the entire chain of neurons to the motor neuron;
the required muscle group is activated.

It is the speed of reaction to the threat that directly determines the preservation of human bodies as units of living matter. The role of somatic regulation is not simply limited to processing the information received and reacting to it - the system is involved in the regulation of voluntary movements by the consciousness. For example, move your foot from a broken board slightly to the side to avoid falling, or move your body higher/lower and regain your balance.

What is he responsible for?

The functional division of the nervous system during the evolution of man as a biological unit gave him special advantages in the struggle for existence. So, if the somatic department began to specialize in the perception of information from the outside - temperature, the presence of danger, then the autonomous, or as it is also called, the vegetative department completely switched to managing internal organs.

A functional comparison of the parts of the nervous system allows us to see the complexity of their activities:

building a home, searching for food, hunting and fishing required coordination of the muscular frame of the human body - the somatic system began to be responsible for this;
establishment of the correct heart rate, depth of breathing, blood pressure on the wall of blood vessels, movement of the food bolus through the intestines and metabolic processes - the organization of the “internal economy” came under the control of the autonomous system.

However, both departments are subordinate to the brain - each at its own level. The regulatory role comes down to correcting possible failures so that the functioning of the body as a whole corresponds to the current situation. After all, despite the fact that people's goals are much more complex than those of animals, they ultimately come down to satisfying their needs.

So, having set a task for himself, a person thinks about the best ways to implement it. He subordinates his movements to her - moving the body in space, fine motor skills. At the same time, at an unconscious level, changes occur in the internal environment - pulse rate, breathing, release of hormones and neurotransmitters. All changes occur, both automatically and arbitrarily.

What can harm the nervous system?

Toxic substances
disrupt the electrochemical processes in the cells of the nervous system and lead to the death of neurons.
Heavy metals (for example, mercury and lead), various poisons (including tobacco and alcohol
), as well as some medications are especially dangerous for the nervous system.
Injuries occur when the limbs or spine are damaged. In the case of bone fractures, the nerves located close to them are crushed, pinched or even severed. This results in pain, numbness, loss of sensation or impaired motor function. A similar process can occur when posture is impaired
.
Due to the constant incorrect position of the vertebrae, the nerve roots of the spinal cord that exit into the foramina of the vertebrae are pinched or constantly irritated. These pinched nerves
can also occur in joint or muscle areas and cause numbness or pain. Another example of a pinched nerve is the so-called tunnel syndrome. In this disease, constant small movements of the hand lead to a pinched nerve in the tunnel formed by the bones of the wrist, through which the median and ulnar nerves pass. Some diseases, such as multiple sclerosis, also affect nerve function. During this disease, the sheath of nerve fibers is destroyed, causing conduction in them to be disrupted.