Neurocytes (neurons) are able to perceive, analyze irritation, come into a state of excitement, generate nerve impulses, transfer them to other neurons, or working organs. Number of neurons in nervous tissue a person reaches one trillion.

Neuron classifications

It is carried out according to three main groups of traits: morphological, functional and biochemical.

1. Morphological classification of neurons (by structural features). By the number of processes neurons are divided into unipolar(with one process), bipolar (with two branches ) , pseudo-unipolar(falsely unipolar), multipolar (have three or more processes). (Fig. 8-2). The latter in nervous system most.

Figure: 8-2. Types nerve cells.

1. Unipolar neuron.

2. Pseudo-unipolar neuron.

3. Bipolar neuron.

4. Multipolar neuron.

Neurofibrils are visible in the cytoplasm of neurons.

(According to Yu.A. Afanasyev and others).

Pseudo-unipolar neurons are called because, moving away from the body, the axon and dendrite first fit tightly to each other, giving the impression of one process, and only then they diverge in a T-shape (these include all receptor neurons of the spinal and cranial ganglia). Unipolar neurons are found only in embryogenesis. Bipolar neurons are bipolar cells of the retina, spiral and vestibular ganglia. By formup to 80 variants of neurons are described: stellate, pyramidal, pear-shaped, fusiform, arachnid, etc.

2. Functional (depending on the function performed and the place in reflex arc): receptor, effector, insertion and secretory. Receptor(sensitive, afferent) neurons with the help of dendrites perceive the effects of the external or internal environment, generate a nerve impulse and transmit it to other types of neurons. They are found only in the spinal ganglia and sensory nuclei of the cranial nerves. Effective (efferent) neurons, transmit excitation to the working organs (muscles or glands). They are located in the front horns spinal cord and vegetative nerve ganglia. Interlocking(associative) neurons are located between receptor and effector neurons; by their number the most, especially in the central nervous system. Secretory neurons(neurosecretory cells) is specialized neurons that resemble endocrine cells in function... They synthesize and secrete neurohormones into the bloodstream and are located in the hypothalamic region of the brain. They regulate the activity of the pituitary gland, and through it, and many peripheral endocrine glands.

3. Mediator(by chemical nature released mediator):

- cholinergic neurons (acetylcholine mediator);

- aminergic (mediators - biogenic amines, for example norepinephrine, serotonin, histamine);

- GABAergic (mediator - gamma-aminobutyric acid);

- aminoergic (mediators - amino acids such as glutamine, glycine, aspartate);

- peptidergic (mediators - peptides, for example, opioid peptides, substance P, cholecystokinin, etc.);

- purinergic (mediators - purine nucleotides, for example adenine), etc.

Internal structure of neurons

Nucleusthe neuron is usually large, round, with fine chromatin, 1-3 large nucleoli. This reflects the high intensity of transcription processes in the neuron nucleus.

Cell membrane neuron is able to generate and conduct electrical impulses... This is achieved by changing the local permeability of its ion channels for Na + and K +, changing the electrical potential and quickly moving it along the cytolemma (depolarization wave, nerve impulse).

All general-purpose organelles are well developed in the cytoplasm of neurons. Mitochondria are numerous and provide high energy requirements of the neuron associated with the significant activity of synthetic processes, the conduction of nerve impulses, the operation of ion pumps. They are characterized by fast wear and tear (Figure 8-3). Golgi complex very well developed. It is no coincidence that this organelle was first described and demonstrated in the course of cytology in neurons. With light microscopy, it is revealed in the form of rings, filaments, grains located around the nucleus (dictyosome). Numerous lysosomes provide constant intensive destruction of the worn components of the neuron cytoplasm (autophagy).

R
is. 8-3. Ultrastructural organization of the neuron body.

D. Dendrites. A. Axon.

1. Nucleus (the nucleolus is shown by the arrow).

2. Mitochondria.

3. Golgi complex.

4. Chromatophilic substance (areas of the granular cytoplasmic reticulum).

5. Lysosomes.

6. Axon mound.

7. Neurotubules, neurofilaments.

(According to V.L.Bykov).

For the normal functioning and renewal of neuron structures, the protein synthesizing apparatus must be well developed in them (Fig. 8-3). Granular cytoplasmic reticulum forms clusters in the cytoplasm of neurons, which are well stained with basic dyes and are visible under light microscopy in the form of lumps chromatophilic substance (basophilic, or tiger substance, Nissl's substance). The term "Nissl's substance" is preserved in honor of the scientist Franz Nissl, who first described it. Lumps of chromatophilic substance are located in neuronal perikaryons and dendrites, but never found in axons, where the protein synthesizing apparatus is poorly developed (Fig. 8-3). With prolonged irritation or damage to the neuron, these clusters of the granular cytoplasmic reticulum disintegrate into separate elements, which at the light-optical level is manifested by the disappearance of Nissl's substance ( chromatolysis, tigrolysis).

Cytoskeleton neurons are well developed, forms a three-dimensional network, represented by neurofilaments (6-10 nm thick) and neurotubules (20-30 nm in diameter). Neurofilaments and neurotubules are connected to each other by transverse bridges; when fixed, they stick together into bundles 0.5-0.3 μm thick, which are colored with silver salts. At the light-optical level, they are described under the name neurofibrill.They form a network in the perikarya of neurocytes, and lie parallel in the processes (Fig. 8-2). The cytoskeleton maintains the shape of the cells, and also provides a transport function - it is involved in the transport of substances from the perikaryon to the processes (axonal transport).

Inclusions in the cytoplasm of a neuron are represented by lipid drops, granules lipofuscin- "aging pigment" - a yellow-brown lipoprotein nature. They are residual bodies (telolysosomes) with products of undigested neuron structures. Apparently, lipofuscin can also accumulate at a young age, with intensive functioning and damage of neurons. In addition, there are pigment inclusions in the cytoplasm of the neurons of the substantia nigra and blue spot of the brain stem. melanin... Inclusions occur in many neurons in the brain glycogen.

Neurons are not capable of division, and with age their number gradually decreases due to natural death. When degenerative diseases (Alzheimer's disease, Huntington's disease, parkinsonism) the intensity of apoptosis increases and the number of neurons in certain parts of the nervous system decreases sharply.

The structure of the main divisions of neurons

Like other cells, neurons are composed of cytoplasm and nucleus. The neuron secretes perikaryonor the cell body (part of the cytoplasm around the nucleus), appendagesand nerve endings (terminal branches)... The sizes of perikarions vary from 4 µm in cerebellar granule cells to 130 µm in ganglionic neurons of the cerebral cortex. The processes can be up to 1 m long (for example, the processes of the neurons of the spinal cord and spinal nodes reach the tips of the fingers and toes (Fig. 8-1).

Figure: 8-1. General principles of neuron structure. 1. The body of the neuron. 2. Axon. 3. Dendrites. 4. Interception of Ranvier. 5. Nervous ending. (After Stevens, 1979).

The processes of neurons are divided into two types: axons (neurites)and dendrites.The axon in a nerve cell is always one, it removes the nerve impulse from the body of the neuron and transmits it to other neurons or cells of working organs (muscles, glands). There are one or more dendrites (from the Greek dendron - tree) in the nerve cell, they bring impulses to the body of the neuron. Dendrites increase the receptor, perceiving surface of the neuron thousands of times (Figure 8-1).

A neuron is an independent structural and functional unit, but with the help of its processes it interacts with other neurons, forming reflex arcs - the neural circuits that make up the nervous system.

In the human body, a nerve impulse is transmitted from one neuron to another, or to a working organ not directly, but through a chemical mediator - mediator.

In the nervous system of animals and humans, about a hundred different mediators have been found, and, accordingly, neurons of various mediator nature.

Axonal and dendritic transport

Axonal transport

Axonal transport (axotoc) is the movement of substances from the body of the neuron to the processes ( anterograde axotoc) and in the opposite direction ( retrogradeaxotok). Distinguish slow axonal flow of substances (1-5 mm per day) and quick (up to 1-5 m per day). Both transport systems are present in both axons and dendrites.

Axonal transport ensures the unity of the neuron. It creates a permanent connection between the body of the neuron (trophic center) and processes. The main synthetic processes take place in the perikaryon. The organelles necessary for this are concentrated here. In the shoots, synthetic processes are weak.

Anterograde fast system transports to the nerve endings proteins and organelles necessary for synaptic functions (mitochondria, membrane fragments, vesicles, enzyme proteins involved in the exchange of neurotransmitters, as well as precursors of neurotransmitters). Retrograde system returns to the perikaryon used and damaged membranes and proteins for degradation in lysosomes and renewal, brings information about the state of the periphery, nerve growth factors.

Slow transport Is an anterograde system that conducts proteins and other substances to renew the axoplasm of mature neurons and ensure the growth of processes during their development and regeneration.

Retrograde transport can play a role in pathology. Due to it, neurotropic viruses (herpes, rabies, poliomyelitis) can move from the periphery to the central nervous system.

It is assumed that the human CNS consists of approximately 10 "neurons. They vary in shape and size, but all neurons have some common structural features (fig. 1.1). The external structure of a neuron is the soma (body) and processes: axon and dendrites. The axon is a long process that conducts excitation from the cell body to other neurons or to peripheral organs. The axon departs from the soma at a location called the axonal hillock. For several tens of microns, the axon does not have a myelin sheath. This section of the axon, together with the axonal hillock, is called the initial segment.

Scheme 1. Departments of the nervous system

Further, the axon can be covered with a myelin sheath. The myelin sheath consists of a protein-lipid complex - myelin and is formed as a result of repeated wrapping of the axon by Schwann cells (a type of oligodendroglial cells).

Along the course of the myelin sheath there are nodal interceptions of Ranvier, corresponding to the boundaries between the Schwann cells. The myelin sheath performs an insulating, supporting, barrier and, apparently, trophic and transport functions. The speed of impulse conduction in myelinated (pulp) fibers is higher than in unmyelinated (non-fleshy) fibers, since the propagation of a nerve impulse in them occurs abruptly from interception to interception, where the extracellular fluid is in direct contact with the axon membrane. The evolutionary meaning of the myelin sheath is to save the metabolic energy of the neuron. Pulp fibers are part of sensitive and motor nervessupplying the sensory organs and skeletal muscles, belong mainly to the sympathetic division of the autonomic nervous system.

Figure: 1.1.

Spinal cord motor neuron. The functions of the individual structural elements neuron (by R. Eckert, D. Randall,

J. Augustine, 1991)

Short processes (dendrites) of the neuron branch out around the cell body. Their function is to perceive nerve impulses coming from other neurons, and then conduct excitation to the soma. The bodies of neurons (somas) in the central nervous system are concentrated in gray matter large hemispheres of the brain, in the subcortical nuclei, in the brainstem, in the cerebellum and in the spinal cord. Non-fleshy fibers innervate the muscles, they are also part of the autonomic nervous system. Myelinated fibers form white matter different departments spinal cord and brain. The shape and size of the bodies of neurons and their processes, even in the same parts of the central nervous system, can differ significantly. Thus, the diameter of the grain cells of the cerebral cortex does not exceed 4 microns, and the diameter of the giant pyramidal cells in the cerebral cortex or in the anterior horns of the spinal cord can vary from 50 to 100 microns or more.

The course, length and branching of the processes of nerve cells also vary greatly. Thus, the axons of most cells have branching only at the level of the initial segment (axon collateral) and at the end when approaching another cell or an innervated organ. For the most part, they do not branch, in contrast to dendrites, which branch very intensively and mainly closer to the cell body. The length of the axons of various cells can be measured both in microns (in the gray matter of the cerebral hemispheres) and in tens of centimeters (in the pathways of the spinal cord).

The morphological classification of neurons takes into account the number of processes in neurons and subdivides all neurons into the following types (Fig.1.2):

• unipolar neurons have one process; noted in humans during the early embryonic development, and in postnatal ontogenesis they are found only in the mesencephalic nucleus trigeminal nerveproviding proprioceptive sensitivity of the chewing muscles;
• bipolar neurons have two processes (axon and dendrite), usually extending from different poles of the cell. In humans, this type of neuron is usually found in the peripheral parts of the auditory, visual and olfactory sensory systems (bipolar cells of the spiral ganglion, retina). Bipolar cells are associated with a receptor by a dendrite, and an axon with a neuron of an overlying level. A variety of bipolar neurons are pseudo-unipolar neurons. The axon and dendrite of these cells extend from the soma in the form of a T-shaped outgrowth, which is further divided into two processes. One of them (dendrite) is directed to the receptors, and the second (axon) to the central nervous system. This type of cells is noted in the sensory spinal and cranial ganglia and provides the perception of temperature, proprioceptive, pain, tactile, baroreceptive and vibration sensitivity;
• multipolar neurons have one axon and more than two dendrites. They are widespread in the human nervous system.

According to their functions, the cells of the central nervous system are divided into afferent (sensitive), efferent (effector), intercalary (intermediate) neurons.

Figure: 1.2. Types of neurons, depending on the number of processes: 1 - unipolar; 2 - bipolar; 3 - multipolar;

4 - pseudo-unipolar

The soma of afferent neurons has a simple rounded shape with one process, which is divided into two fibers in a T-shape. One fiber goes to the periphery and forms there sensitive endings (in the skin, muscles, tendons), the second goes to the central nervous system (to the centers of the spinal cord or brain stem), where it branches into endings that end on other cells. The peripheral process is most likely a modified dendrite, and the process that is directed to the central nervous system is an axon. The soma of the sensory neuron is located outside the central nervous system in the spinal ganglia or in the ganglia of the cranial nerves. Sensitive neurons include some neurons in the central nervous system that receive impulses not directly from receptors, but through other neurons located below, an example is the neurons of the optic hillock.

The structure of efferent neurons is similar to the structure of afferent. However, through their axons, excitation is carried out to the periphery. Those of the efferent neurons that form motor nerve fibers that go to skeletal muscles are called motoneurons. Their bodies lie on average medulla oblongata, in the anterior horns of the spinal cord. Many efferent neurons transmit excitation not directly to the periphery, but through the cells located below. For example, efferent neurons of the cerebral hemispheres or the red nucleus of the midbrain, whose impulses go to the motor neurons of the spinal cord.

Insertion (intermediate) neurons are a special type of neurons. Their main difference from afferent and efferent neurons is that they are located inside the central nervous system and their processes do not leave its limits. These neurons do not establish direct communication with sensory or effector structures. They seem to be inserted between sensory and motor cells and unite them together, sometimes through very long chains of switching. The variety of their shapes and sizes is great, but on the whole their structure corresponds to the structure of afferent and efferent neurons. The differences are mainly determined by the shape of the soma, as well as the length and degree of branching of the processes. Some classifications include up to 10 or more types of intercalary neurons. According to these characteristics, pyramidal, stellate, basket-like, fusiform, polymorphic neurons, grain cells, etc. are distinguished.

Morphological polarization of neurons (dendrite - soma - axon) is associated with their functional polarization. It manifests itself in the fact that only the axon of the cell has structures on its branches designed to transfer activity to other cells. There are no such structures on the surface of the soma and dendrites. Therefore, in a system of neurons connected to each other, excitation is transmitted only in one direction through the processes of their neurons.

The axons of each neuron, approaching other nerve cells, branch, forming numerous endings on the dendrites of these cells, on their bodies and on the terminal branches - the germinals of the axons. On the body of a large pyramidal cell of the cerebral cortex, there can be up to a thousand nerve endings formed by the nerve processes of other neurons, and one nerve fiber can form up to 10 thousand such contacts on many nerve cells. Using the method of electron microscopy, the researchers studied in detail the areas of communication between nerve cells (intercellular contacts), which were called synapses (synaptic connections) by C. Sherrington in 1897.

CLASSIFICATION OF NEURONS

The classification of neurons is carried out according to three characteristics: morphological, functional and biochemical.

Morphologicalclassification neuronstakes into account the number of their processes and subdivides all neurons into three types (Figure 8.6): unipolar, bipolar and multipolar.

Figure: 8.6. Morphological classification of neurons. UN - unipolar neuron, BN - bipolar neuron, PUN - pseudo-unipolar neuron, MN - multipolar neuron, PC - perikarion, A - axon, D - dendrite.

1. Unipolar neurons have one process. According to most researchers, they are not found in the nervous system of humans and other mammals. Some authors still refer to such cells as amacrine neurons of the retina and interglomerular neurons of the olfactory bulb.

2. Bipolar neurons have two processes - an axon and a dendrite, usually extending from the opposite poles of the cell. They are rare in the human nervous system. These include bipolar cells of the retina, spiral and vestibular ganglia.

Pseudo-unipolar neurons - a kind of bipolar, in which both cell processes (axon and dendrite) depart from the cell body in the form of a single outgrowth, which then divides in a T-shape. These cells are found in the spinal and cranial ganglia.

3. Multipolar neurons have three or more processes: an axon and several dendrites. They are most common in the human nervous system. Up to 80 variants of these cells have been described: fusiform, stellate, pear-shaped, pyramidal, basket-like, etc. Golgi cells of type I (with a long axon) and Golgi cells of type II (with a short axon) are distinguished along the length of the axon.

Functional classification neurons separates them by the nature of their function (according to their place in the reflex arc) into three types: sensitive, motor and associative.

1. Sensitive (afferent) neurons generate nerve impulses under the influence of changes in the external or internal environment.

2. Motor (efferent) neurons transmit signals to working organs (skeletal muscles, glands, blood vessels).

3. Associative (interneurons) neurons (interneurons) carry out connections between neurons and quantitatively predominate over neurons of other types, accounting for about 99.98% of the the total these cells.

Biochemical classification neuronsis based on the chemical characteristics of neurotransmitters used by neurons in the synaptic transmission of nerve impulses. There are many different groups of neurons, in particular, cholinergic (mediator - acetylcholine), adrenergic (mediator - norepinephrine), serotonergic (mediator - serotoin), dopaminergic (mediator - dopamine), GABAergic (mediator - gamma-aminobutyric acid), GABA , purinergic (mediator - ATP and its derivatives), peptidergic (mediators - substance P, enkephalins, endorphins, vasoactive intestinal peptide, cholecystokinin, neurotensin, bombesin and other neuropeptides). In some neurons, terminals simultaneously contain two types of neurotransmitter.

The distribution of neurons using various neurotransmitters in the nervous system is uneven. Impaired production of some mediators in certain brain structures is associated with the pathogenesis of a number of neuropsychiatric diseases. Thus, the content of dopamine is reduced in parkinsonism and increased in schizophrenia, a decrease in norepinephrine and serotonin levels is typical for depressive states, and their increase is for the manic.

NEUROGLIA

Neuroglia - an extensive heterogeneous group of elements of the nervous tissue, providing the activity of neurons and performing nonspecific functions: support, trophic, demarcation, barrier, secretory and protective function... It is an auxiliary component of the nervous tissue.

A multipolar neuron contains:

1.one process axon

4.one branch dendrite

A bipolar neuron contains:

1.one process axon

2.two processes - axon and dendrite

3.several processes, one of which is an axon, the rest are dendrites

4.one branch dendrite

5. one process extending from the body, which then divides into two processes in a T-shape

A pseudo-unipolar neuron contains:

1.one process axon

2.two processes - axon and dendrite

3.several processes, one of which is an axon, the rest are dendrites

4.one branch dendrite

5. one process extending from the body, which then divides into two processes in a T-shape

A unipolar neuron contains:

1.one process axon

2.two processes - axon and dendrite

3.several processes, one of which is an axon, the rest are dendrites

4.one branch dendrite

5. one process extending from the body, which then divides into two processes in a T-shape

Neurons have a unipolar form:

1.sensory neurons

2.neuroblasts

4.neurons of the sense organs and spinal ganglia

Pseudo-unipolar neurons are found in:

1.the organs of the senses

3.spinal ganglia

4. sense organs and spinal ganglia

5.the vegetative ganglia

Bipolar neurons are found in:

1.the organs of the senses

2.spinal and autonomic ganglia

3. sense organs, spinal and autonomic ganglia

4. sense organs and autonomic ganglia

5.the vegetative ganglia

Secretory neurons include:

1.sensory neurons

2.neuroblasts

3.neurons of the spinal nodes

4.the neurons of the hypothalamus

5.neuroblasts and neurons of the sensory organs

Most neurons in the human body are:

1.pseudo-unipolar

2.unipolar

3.bipolar

4.secretory

5.multipolar

Which of the following neurons have the ability to synthesize neurohormones

1.sensory neurons

2.neurons of autonomic ganglia

3.neurons of the spinal nodes

4.the neurons of the hypothalamus

5.neurons of the spinal nodes and neurons of the sensory organs

Localization of the chromatophilic substance of the neuron:

1.perikarion

2.dendrites

4.perikaryon and dendrites

5.axon and dendrites

A chromatophilic substance is an accumulation of:

1.granular and agranular EPS

2.free ribosomes and agranular EPS

3.polis and Golgi complex

4.granular EPS, free ribosomes and polysome

5.Golgi complex and EPS

How many axons can be identified in each of the listed neurons:

1. each neuron has one axon

2.a multipolar neuron has several axons

3.the bipolar neuron has two axons

4.A pseudo-unipolar neuron has one or two axons

5.each neuron has two axons

What is the main function of neurons:

1.transport

2.participation in immune reactions

3.generation and conduction of a nerve impulse

4.homeostatic

5.protective

Which of the following neurons are not included in the morphological classification:

1.pseudo-unipolar

2.unipolar

3.bipolar

4.receptor

5.multipolar

Name the specific morphological features of the cytoplasm of neurons:

1.Lack of non-membrane organelles

2.weak development of EPS

3.large amount of pigment inclusions

4.presence of chromatophilic substance and neurofibrils

5. well developed Golgi apparatus, many lysosomes

Receptor neurons perform the function:

1.pulse perception

3.secretory

Effector neurons perform the function:

1.pulse perception

2. transmission of impulse to the tissue of working organs

3.secretory

4.Ensuring the existence and functioning of nerve cells

5.Making connections between neurons

Associative neurons perform the function:

1.pulse perception

2. transmission of impulse to the tissue of working organs

3.secretory

4.Ensuring the existence and functioning of nerve cells

5.Making connections between neurons

Macroglia develops from:

1.neuroblasts

2.mesenchyme

3.glioblasts of the neural tube

4.neural crest

5.cutaneous ectoderm

Microglia develop from:

1.neuroblasts

2.mesenchyme

3.glioblasts of the neural tube

4.neural crest

5.cutaneous ectoderm

Which neuroglial cells have phagocytic activity:

1.ependymocytes

2.astrocytes

3.oligodendrocytes

4.all types of macroglia

5.microglia

Ependymocyte function:

1.support and demarcation

Astrocyte function:

1.support and demarcation

2.secretion of cerebrospinal fluid

3.trophic, participation in the metabolism of neurons, the formation of myelin sheaths

4.Protection from infection and damage, removal of products of destruction of nerve tissue

5.generation and conduction of nerve impulses

Oligodendrocyte function:

1.support and demarcation

2.secretion of cerebrospinal fluid

3.trophic, participation in the metabolism of neurons, the formation of myelin sheaths

4.Protection from infection and damage, removal of products of destruction of nerve tissue

5.generation and conduction of nerve impulses

Microglial cell function:

1.support and demarcation

2.secretion of cerebrospinal fluid

3.trophic, participation in the metabolism of neurons, the formation of myelin sheaths

4.Protection from infection and damage, removal of products of destruction of nerve tissue

5.generation and conduction of nerve impulses

The neuroglia lining the ventricles of the brain and the spinal canal is represented by:

1.protoplasmic astrocytes

2.ependymocytes

3.fibrous astrocytes

4.microgliocytes

5.oligodendrocytes

Which of the following neurons are not included in the functional classification?

1.receptor

2.bipolar

3.insert

4.motor

5.receptor, insert

Cerebrospinal fluid is secreted by:

1.astrocytes

2.ependymocytes

3.oligodendrocytes

4.astrocytes and microgliocytes

5.microgliocytes

The function of isolating neurons from external influences is performed by:

1.astrocytes

2.ependymocytes

3.oligodendrocytes

4.astrocytes and microgliocytes

5.microgliocytes

What cells of the nervous tissue are glial macrophages?

1.astrocytes

2.ependymocytes

3.oligodendrocytes

4.astrocytes and ependymocytes

5.microgliocytes

Glyocytes of the ganglion are represented by cells:

1.astrocytes

2.ependymocytes

3.oligodendrocytes

4.astrocytes and microgliocytes

5.microgliocytes

What neuroglial cells originate from bone marrow promonocytes?

1.astrocytes

2.ependymocytes

3.oligodendrocytes

4.astrocytes and ependymocytes

5.microgliocytes

The following are involved in the formation of the nerve fiber sheaths:

1.astrocytes

2.ependymocytes

3.oligodendrocytes

4.astrocytes and microgliocytes

5.microgliocytes

When irritated, the cells lose their process shape and are rounded, forming granular balls. What kind of cells are they?

1.astrocytes

2.ependymocytes

3.oligodendrocytes

4.astrocytes and microgliocytes

5.microgliocytes

In the processes of degeneration and regeneration of nerve fibers, the main role belongs to:

1.ependymocytes

2.fibrous astrocytes

3.protoplasmic astrocytes

4.neurolemmocytes

5.microglia

Determine the type of synapse: the terminal branches of the axon of one neuron end on the body of another neuron:

1.axoaxonal

2.axosomatic

3.axodendritic

4.somatosomatic

5.dendrodendric

Determine the type of synapse: terminal branches of the axon of one neuron are in contact with the dendrite of another neuron:

1.axoaxonal

2.axosomatic

3.axodendritic

4.somatosomatic

5.dendrodendric

Determine the type of synapse: the terminal branches of the axon of one neuron end on the axon of another neuron:

1.axoaxonal

2.axosomatic

3.axodendritic

4.somatosomatic

5.dendrodendric

Neuroglial cells have a mesenchymal origin:

1.astrocytes

2.ependymocytes

3.oligodendrocytes

4.all macrogliocytes

Nerve tissue is a system of interconnected nerve cells and neuroglia that provide specific functions for sensing stimuli, arousal, generating an impulse and transmitting it. It is the basis of the structure of the organs of the nervous system, which ensures the regulation of all tissues and organs, their integration in the body and communication with the environment. Consists of nerve tissue and neuroglia.

Nerve cells (neurons, neurocytes) are the main structural components of nervous tissue that perform a specific function.

Neuroglia (neuroglia) ensures the existence and functioning of nerve cells, carrying out supporting, trophic, dividing, secretory and protective functions. Origin : Nerve tissue develops from the dorsal ectoderm. In an 18-day-old human embryo, the ectoderm forms a neural plate, the lateral edges of which form nerve ridges, and a neural groove forms between the ridges. The anterior end of the neural plate forms the brain. The lateral edges form the neural tube. The neural tube cavity is preserved in adults in the form of the system of the ventricles of the brain and the central canal of the spinal cord. Part of the cells of the neural plate forms the neural crest (ganglion plate). Subsequently, 4 concentric zones are differentiated in the neural tube: ventricular (ependymal), subventricular, intermediate (mantle) and marginal (marginal).

Classification of neurons by the number of processes:

Unipolar - have one process-axon (ex. Amocrine neurons of the retina)

Bipolar - have two processes - an axon and a dendrite, extending from opposite poles of the cell (ex. Bipolar neurons of the retina, spiral and vestibular ganglia) Among bipolar neurons, there are pseudo-unipolar ones - a process departs from the body, which then divides into dendrite and axon (ex. In the spinal) and cranial ganglia)

Multipolar - have three or more processes (one axon and several dendrites). Most common in human NS

Classification of neurons by function:

Sensitive (afferent) - generate nerve impulses under the influence of external or internal. Wednesday

Motor (efferent) - transmit signals to working organs

Insertion - carry out communication between neurons. In terms of number, they predominate over neurons of other types and make up about 99.9% of the total number of cells in the human NS

The structure of a multipolar neuron:

Their forms are varied. The axon and its collaterals end, branching into several branches-telodendrons, cat. End with terminal thickenings. A neuron consists of a cell body and processes that provide the conduction of nerve impulses - dendrites, which bring impulses to the body of the neuron, and an axon, which carries impulses from the body of the neuron. The body of the neuron contains the nucleus and the surrounding cytoplasm - the perikarion, cat. Contains synthetic. apparatus, and on the cytolemma of the neuron there are synapses that carry excitatory and inhibitory signals from other neurons.

The nucleus of the neuron is one, large, round, light, with 1 or 2-3 nucleoli. The cytoplasm is rich in organelles and is surrounded by a cytolemma, a cat. has the ability to conduct a nerve impulse due to the local current of Na ions into the cytoplasm and K ions from it through membrane ion channels. GREPS is well developed, forms complexes of parallel lying cisterns, in the form of basophilic lumps, called chromatophilic substance (or Nissl bodies, or tigroid substance)

AgrEPS is formed by a three-dimensional network of cisterns and tubules involved in the intracellular transport of substances.

The Golgi complex is well developed, located around the core.

Mitochondria and lysosomes are numerous.

The cytoskeleton of a neuron is well developed and is represented by neurotubules and neurofilaments. They form a three-dimensional network in the perikaryon, and in the processes are located parallel to each other.

The cell center is present, f-tion is the assembly of microtubules.

Dendrites branch strongly near the neuron body. Neurotubules and neurofilaments in dendrites are numerous, they provide dendritic transport, cat. is carried out from the cell body along the dendrites at a speed of about 3 mm / h.

The axon is long, from 1 mm to 1.5 meters, along which nerve impulses are transmitted to other neurons or cells of working organs. The axon departs from the axonal mound, onto the cat. a pulse is generated. The axon contains bundles of neurofilaments and neurotubules, cisterns AgrEPS, elements of the set. Golgi, mitochondria, membrane vesicles. Does not contain chromatophilic substance.

There is axon transport - moving along the axon various substances and organelles. It is divided into 1) anterograde - from the body of the neuron to the axon. Sometimes it is slow (1-5mm / day) - it provides the transfer of enzymes and elements of the cytoskeleton and fast (100-500mm / day) - the transfer of various substances, cisterns of GREPS, mitochondria, vesicle membranes. 2) retrograde - from the axon to the body of the neuron. Substances move in AgrEPS tanks and membrane bubbles along microtubules.

Speed \u200b\u200b100 - 200 mm / day, promotes the removal of substances from the terminal area, the return of mitochondria, membrane vesicles.

Morpho-functional characteristics of the skin. Sources of development. Derivatives of the skin: hair, sweat glands, their structure, functions.

The skin forms the outer cover of the body, the area of \u200b\u200bwhich in an adult reaches 2.5 m 2. The skin consists of the epidermis (epithelial tissue) and the dermis (connective tissue base). The skin is connected to the underlying parts of the body by a layer of adipose tissue - subcutaneous tissue, or hypodermis. Epidermis. The epidermis is represented by stratified squamous keratinizing epithelium, in which renewal and specific differentiation of cells (keratinization) are constantly taking place.

On the palms and soles, the epidermis consists of many dozen layers of cells, which are combined into 5 main layers: basal, prickly, granular, shiny and horny. The rest of the skin has 4 layers (no shiny layer). They distinguish 5 types of cells: keratinocytes (epithelial cells), Langerhans cells (intraepidermal macrophages), lymphocytes, melanocytes, Merkel cells. Keratinocytes form the basis of these cells in the epidermis and in each of its layers. They are directly involved in the keratinization (keratinization) of the epidermis.

The skin itself, or dermis, is divided into two layers - papillary and reticular, which do not have a clear border between them.

Skin functions:

Protective - the skin protects tissues from mechanical, chemical and other influences. The stratum corneum of the epidermis prevents microorganisms from entering the skin. The skin takes part in ensuring the norms. water balance. The stratum corneum of the epidermis provides a barrier to evaporating fluid, prevents swelling and wrinkling of the skin.

Excretory - together with sweat, about 500 ml of water, various salts, lactic acid, nitrogen metabolism products are released through the skin per day.

Participation in thermoregulation - due to the presence of thermoreceptors, sweat glands and a dense network of shelters. vessels.

Skin is a blood depot. The vessels of the dermis, when they expand, can hold up to 1 liter of blood

Participation in the metabolism of vitamins - under the action of UV light, vit. D is synthesized in keratinocytes.

Participation in the metabolism of many hormones, poisons, carcinogens.

Participation in immune processes - antigens are recognized and eliminated in the skin; antigen-dependent proliferation and differentiation of T-lymphocytes, immunological surveillance of tumor cells (with the participation of cytokines).

It was an extensive receptor field that allows the central nervous system to receive information about changes in the skin itself and about the nature of the stimulus.

Sources of development ... The skin develops from two embryonic primordia. Its epithelial cover (epidermis) is formed from the skin ectoderm, and the underlying connective tissue layers - from dermatomes (derivatives of somites). In the first weeks of embryo development, the skin epithelium consists of only one layer of flat cells. Gradually, these cells are getting taller. At the end of the 2nd month, a second layer of cells appears above them, and at the 3rd month the epithelium becomes stratified. At the same time, keratinization processes begin in its outer layers (primarily on the palms and soles). At the 3rd month of the prenatal period, epithelial rudiments of hair, glands and nails are laid in the skin. During this period, fibers and a dense network of blood vessels begin to form in the connective tissue base of the skin. In the deep layers of this network, foci of hematopoiesis appear in places. Only in the 5th month of intrauterine development, the formation of blood elements in them stops and adipose tissue is formed in their place. Skin glands... There are three types of glands in human skin: milk, sweat and sebaceous. The sweat glands are divided into eccrine (merocrine) and apocrine. Sweat glands by their structure they are simple tubular. They consist of an excretory duct and an end section. The end sections are located in the deep parts of the reticular layer on the border with the subcutaneous tissue, and the excretory ducts of the eccrine glands open on the surface of the skin with sweat pore. The excretory ducts of many apocrine glands do not enter the epidermis and do not form sweat pores, but flow together with the excretory ducts of the sebaceous glands into the hair funnels.

The end sections of the eccrine sweat glands are lined with glandular epithelium, the cells of which are cubic or cylindrical. Among them, there are light and dark secretory cells. The end sections of the apocrine glands consist of secretory and myoepithelial cells. The transition of the end section to the excretory duct is made abruptly. The wall of the excretory duct consists of a bilayer cubic epithelium. Hair. There are three types of hair: long, bristly and vellus. Structure. Hair is an epithelial appendage of the skin. There are two parts in the hair: the shaft and the root. The hair shaft is located above the skin surface. The hair root is hidden in the thickness of the skin and reaches the subcutaneous tissue. The shaft of long and bristly hair consists of cortex, medulla and cuticle; vellus hair contains only cortical substance and cuticle. The hair root consists of epitheliocytes at different stages of the formation of the cortex, medulla and cuticle of the hair.

The hair root is located in the hair follicle, the wall of which consists of the inner and outer epithelial (root) sheaths. Together they make up the hair follicle. The follicle is surrounded by a connective tissue dermal sheath (hair follicle).

Arteries: classification, structure, function.

The classification is based on the ratio of the number of muscle cells and elastic fibers in the middle lining of the arteries:

a) elastic type arteries; b) muscular arteries; c) mixed type arteries.

Elastic, muscular and mixed arteries have general principle structures: 3 shells are distinguished in the wall - inner, middle and outer - adventitious. The inner shell consists of layers: 1. Endothelium on the basement membrane. 2. The subendothelial layer is a loose fibrous connective tissue with a high content of poorly differentiated cells. 3. Internal elastic membrane - a plexus of elastic fibers. The middle shell contains smooth muscle cells, fibroblasts, elastic and collagen fibers. At the border of the middle and outer adventitia membrane there is an external elastic membrane - a plexus of elastic fibers. The outer adventitia of the arteries is histologically represented by loose fibrous connective tissue with the vessels of the vessels and the nerves of the vessels. Features in the structure of the varieties of arteries are due to differences in the hemadynamic conditions of their functioning. Differences in structure mainly relate to the middle shell (different ratios of the constituent elements of the shell): 1. Elastic arteries - these include the aortic arch, pulmonary trunk, thoracic and abdominal aorta. Blood enters these vessels in jerks under high pressure and moves at high speed; there is a large pressure drop during the transition from systole to diastole. The main difference from other types of arteries is in the structure of the middle shell: elastic fibers predominate in the middle shell of the above components (myocytes, fibroblasts, collagen and elastic fibers). Elastic fibers are located not only in the form of individual fibers and plexuses, but form elastic fenestrated membranes (in adults, the number of elastic membranes reaches 50-70 words). Due to the increased elasticity, the wall of these arteries not only withstands high pressure, but also smoothes out large pressure drops (surges) during systole-diastole transitions. 2. Muscular arteries - these include all arteries of medium and small caliber. A feature of the hemodynamic conditions in these vessels is a drop in pressure and a decrease in blood flow velocity. Muscular arteries differ from other types of arteries by the predominance of myocytes in the middle membrane over other structural components; the inner and outer elastic membrane is clearly expressed. Myocytes in relation to the lumen of the vessel are oriented spirally and are found even in the outer shell of these arteries. Due to the powerful muscular component of the middle membrane, these arteries control the intensity of blood flow of individual organs, maintain the falling pressure and push blood further, therefore, muscular arteries are also called "peripheral heart". 3. Arteries mixed type - these include large arteries extending from the aorta (carotid and subclavian arteries). They occupy an intermediate position in structure and function. The main feature in the structure: in the middle membrane, myocytes and elastic fibers are represented approximately the same (1: 1), there is a small amount of collagen fibers and fibroblasts. 4 Human placenta: type. Maternal and fetal parts of the placenta, features of their structure.

The placenta (baby seat) of a person refers to type of discoidal hemochorial villous placentas. Provides a connection between the fetus and the mother's body. However, the placenta creates a barrier between the blood of the mother and the fetus. The placenta has two parts: embryonic, or fetaland maternal... The fetal part is represented by a branched chorion and an amniotic membrane adhered to it from the inside, and the maternal part is represented by a modified mucous membrane of the uterus, which is rejected during childbirth.

Development the placenta begins in the 3rd week, when vessels begin to grow into the secondary villi and tertiary villi form, and ends by the end of the 3rd month of pregnancy. At 6-8 weeks, connective tissue elements differentiate around the vessels. The main substance of the chorionic connective tissue contains a significant amount of hyaluronic and chondroitinsulfuric acids, which are associated with the regulation of placental permeability.

Mother and fetal blood never mix under normal conditions.

The hematochorionic barrier that separates both blood flows consists of the fetal vascular endothelium, the connective tissue surrounding the vessels, and the chorionic villi epithelium. The embryonic, or fetal, part the placenta by the end of 3 months is represented by a branching chorionic plate, consisting of fibrous connective tissue covered with cyto- and symplastotrophoblast. The branching villi of the chorion are well developed only from the side facing the myometrium. Here they pass through the entire thickness of the placenta and with their tops plunge into the basal part of the destroyed endometrium. The structural and functional unit of the formed placenta is cotyledon, formed by the stem villi. Mother part The placenta is represented by the basal plate and connective tissue septa separating the cotyledons from each other, as well as lacunae filled with maternal blood. At the points of contact of the stem villi with the decaying shell, peripheral trophoblast occurs. Chorionic villi destroy the layers of the main decaying shell closest to the fetus, blood gaps are formed in their place. The deep unresolved parts of the falling membrane together with the trophoblast form the basal plate.

Placenta formation ends at the end of the 3rd month of pregnancy. The placenta provides nutrition tissue respiration, growth, regulation of the rudiments of the fetal organs formed by this time, as well as its protection.

Placenta functions... The main functions of the placenta: 1) respiratory, 2) transport of nutrients, water, electrolytes and immunoglobulins, 3) excretory, 4) endocrine, 5) participation in the regulation of myometrium contraction.