Vegetative ganglia: structure and function
The central nervous system of a person exercises control over the activity of his body and is divided into several departments. The brain sends and receives signals from the body and after processing it has information about the processes. The nervous system is divided into vegetative and somatic nervous systems.
Differences in the autonomic and somatic nervous system
The somatic nervous system is regulated by the human consciousness and can control the activity of the skeletal musculature. All components of a person's reaction to external factors are under the control of the cerebral hemispheres. It provides sensory and motor reactions of a person, controlling their excitation and inhibition.
The autonomic nervous system controls the peripheral activity of the body and is not controlled by consciousness. It is characterized by autonomy and generalized effects on the body in the total absence of consciousness. Efferent innervation of the internal organs allows it to control metabolic proc
The structure of the vegetative system
The work of the autonomic nervous system is controlled by the hypothalamus, which is located in the central nervous system. The autonomic nervous system has a metasegmental structure. Its centers are in the brain, spinal cord and cortex. Peripheral departments are formed by trunks, ganglia, plexuses.
In the autonomic nervous system distinguish:
- Sympathetic. Its center is located in the thoracolumbar section of the spinal cord. It is characterized by paravertebral and prevertebral ganglia of the VNS.
- Parasympathetic. Its centers are concentrated in the middle and oblong brain, the sacral region of the spinal cord. Nerve nodes are mostly intramural.
- Metasympathetic. It innervates the gastrointestinal tract, vessels, internal organs of the body.
Its structure includes:
- Nucleus of nerve centers located in the brain and spinal cord.
- Vegetative ganglia, which are located on the periphery.
- Nerve fibers.
Reflex arc of the autonomous nervous system
The reflex arc of the autonomic nervous system consists of three links: the
- is sensitive or afferent;
- interlaced or associative;
Their interaction is carried out without the participation of additional intercalary neurons, as in the reflex arc of the central nervous system.
The sensory link is located in the spinal ganglion. This ganglion has nerve cells formed by groups, and their control is carried out by the nuclei of the central brain, the large hemispheres and their structures.
The sensory link is represented in part by unipolar cells that have one bringing or carrying axon, and they belong to the spinal or cranial nodes. And also nodes of vagus nerves, having a structure similar to spinal cells. This link includes Dogel type II cells, which are components of vegetative ganglia.
The insertion link in the autonomic nervous system serves for transmission through the lower nervous centers, which are vegetative ganglia, and it is realized through the synapses. It is located in the lateral horns of the spinal cord. There is no direct connection from the afferent link to preganglionic neurons for their connection, there is a shortest path from the afferent neuron to the associative neuron and from it to the preganglionic neuron. Transmission of signals and nerve impulses from afferent neurons in different centers is carried out with a different number of intercalary neurons.
For example, in the arc of the spinal autonomous reflex between the sensory and effector link, there are three synapses, two of which are located in the spinal cord, and one in the autonomic knot in which the efferent neuron is located.
The efferent link is represented by effector neurons, which are located in vegetative nodes. Their axons form the demyelinated fibers, which in the composition with mixed nerve fibers innervate the internal organs.
Vegetative reflex arcs are located in the lateral horns.
Structure of the nodal node
Ganglion is a cluster of nerve cells that look like nodular extensions of about 10 mm in thickness. In its structure, the vegetative ganglion is covered from above with a connective tissue capsule, which forms a stroma of loose connective tissue within the organs. Multipolar neurons, which are built from a rounded nucleus and large nucleoli, consist of one efferent neuron and several divergent afferent neurons. These cells are of their type to the cells of the brain and are motor. They are surrounded by a loose shell - mantle glia, which creates a permanent environment for nervous tissue and ensures the full functioning of nerve cells.
The vegetative ganglion has a diffuse arrangement of nerve cells and a variety of processes, dendrites and axons.
The spinal ganglion has nerve cells that are arranged in groups, and their arrangement is orderly conditioned.
Vegetative nerve ganglia are divided into:
- Sensory neurons that are located close to the dorsal or central part of the brain. The unipolar neurons, of which this ganglion consists, represent a bearing or carrying out process. They serve for afferent transfer of impulses, and their neurons form a bifurcation when branching branches. These processes transmit information from the periphery to the central afferent neuron - it is a peripheral process, the central one - from the body of the neuron to the brain center.
- Motor, motor consists of efferent neurons, and depending on their position they are called paravertebral, prevertebral.
Paravertebral chains of ganglia are located along the vertebral column in sympathetic trunks, which run a long string from the base of the skull to the coccyx.
Prevertebral plexuses are closer to the internal organs, and their localization is concentrated in front of the aorta. They form the ventral plexus, which consists of the solar, lower and upper plexus plexuses. They are represented by motor adrenergic and inhibitory effects of cholinergic neurons. Also, the connection between the neurons is carried out by preganglionic and postganglionic neurons, which use mediators acetylcholine and noradrenaline.
Intramural nerve nodes have three types of neurons. Their description was made by the Russian scientist Dogel A.S., who, examining the histology of the neurons of the autonomic nervous system, isolated such neurons as long-axis efferent cells of the first type, equispentiated afferent cells of the second type and associative cells of the third type.
Afferent neurons perform a highly specialized function, and their role is to perceive stimuli. Such receptors are mechanoreceptors( reaction to tension or pressure), photoreceptors, thermoreceptors, chemoreceptors( responsible for reactions in the body, chemical bonds), nociceptors( the reaction of the body to pain stimuli is skin damage and others).
In sympathetic trunks, these receptors pass through the reflex arc to the central nervous system information that serves as a signal for damage or disturbances in the body, as well as normal operation.
Each ganglion has its own location, blood supply, and its functions are determined by these parameters. The spinal ganglion, which has innervation from the brain nuclei, provides a direct connection of processes in the body through the reflex arc. From these structural components of the spinal cord innervates the glands, smooth muscles of the muscles of internal organs. Signals coming through the reflex arc are slower than in the central nervous system, and they are completely regulated by the vegetative system, and it also has a trophic, vasomotor function.