The nervous activity of the human body involves the transformation of incoming signals. As a result of the transformations that have occurred, there will be responses to stimuli. In order to implement them, the body must have an established relationship from receiving an impulse to responding to a stimulus.
Almost all reflexes are closed within the brain and spinal cord. However, there are those in which the arc is closed outside the central nervous system in the autonomic ganglia or even within the boundaries of a specific internal organ (for example, the heart). Proper functioning of reflexes is the basis for the full flow of impulses, which determines the activity of the central nervous system.
General information
A reflex is a holistic response to a stimulus that is carried out by the central nervous system.
It manifests itself in controlled and uncontrolled movements, in the functioning of the body, in behavioral changes, emotions and susceptibility. The perception of a stimulus is carried out due to the activity of receptors. They are nerve fibers and structures that are susceptible to irritation. These receptors are capable of perceiving some of them - sound, light, temperature changes, pressure, etc. Based on these criteria, receptors are divided into corresponding varieties.
During the process of stimulation, excitation occurs inside the receptor. It begins to convert energy into impulses of electrical origin. The perceived data arrives as an electrical signal and is sent along the nerve endings of neurons before contacting the rest of the nerve fibers. The impulse is transmitted to interneurons, and then to motor neurons. It arrives in the same way as from receptive neurons.
Neural circuits enter the central nervous system, where they form the nerve center. The received data is processed, as a result of which a control command is formed. Next, it is sent to the working organ, where the impulse provokes muscle contraction.
Types of reflexes
A reflex involves the body’s response to changes in the external or internal environment due to the influence on receptors. They are located on the upper layer of the skin, forming exteroceptive reflexes inside the vessels.
The response to stimuli can be conditional or unconditional in origin.
The latter include reflexes, whose arc is formed even before birth. In conditional conditions, it is formed under the influence of various external provoking factors.
Classification
The arc is the path through which the impulse is directed to the working element. It consists of neural circuits. They themselves and their endings form the path through which the signal is transmitted during the implementation of any reflex. There is a certain classification that divides these formations into types.
Polysynaptic arcs
This variety includes a 3-neuron arc, within which the nerve center is located between the receptor and effector. Its manifestation will be withdrawal of the limb as a response to pain.
The polysynaptic arc has a specific structure. Such a chain certainly goes through the brain. Taking into account the location of the neural circuits that process the impulse, the following are distinguished:
- spinal;
- bulbar;
- mesencephalic;
- cortical.
When a reflex is perceived by the upper parts of the central nervous system, neural circuits in the lower parts are involved in its processing.
Regardless of the reflex, when the constancy of the arc is disrupted, it disappears. Often, such a rupture can occur due to injury or illness. In complex reflexes, other organs are included in the reaction process, which can cause a behavioral change within the body.
Arc of the blink reflex
This reaction of the body, due to its own complexity, makes it possible to study such a movement of excitation along an arc, which is extremely difficult to study in other situations. It begins with the activation of the processes of excitation and inhibition at the same time. Taking into account the nature of the lesion, different parts of the arc may become active. The trigeminal nerve is capable of causing the blink reflex - a reaction to touch, the auditory - a reaction to noise, the visual - a response to light amplitudes or a perceived threat.
The response is characterized by early and late components. The second is responsible for inhibiting the reaction. For example, touching the skin of the eyelids. The eye will close instantly. When the dermis is touched again, the reflex will be slower. When the received data is processed, a controlled slowdown of the resulting reflex is carried out. This slowdown, for example, teaches women to use eye cosmetics extremely quickly, overcoming the natural tendency of the eyelid to close the cornea. Other variations of such arcs are also being studied, but they often have an overly complex structure and are not very clear.
Monosynaptic
A formation consisting of 2 neural circuits sufficient to carry out a signal. A striking example of such a structure is the knee reflex. A characteristic feature will be the lack of connection to the reaction of parts of the brain. Such a reflex is considered unconditioned.
This reaction will be directly checked by a specialist as an indicator of the state of the somatosensory nervous system. In the process of hitting the knee with a hammer, the muscle begins to stretch. The stimulus will be sent through the afferent fiber to the spinal ganglion, and the impulse to the efferent fiber. In this experiment, skin receptors are not involved, but the result will be visible and the strength of the response can be easily differentiated.
The vegetative arc can be interrupted into sections, forming a connection, while within the animal system the direction that the signal is traversed will not be interrupted by anything.
Polysynaptic arcs
Polysynaptic is a three-neuron arc in which a nerve center is located between the receptor and the effector. This arc is clearly illustrated by withdrawing the hand in response to pain.
Polysynaptic arcs have a special structure. Such a circuit necessarily passes through the brain. Depending on the location of the neurons processing the signal, there are:
- spinal;
- bulbar;
- mesencephalic;
- cortical.
If the reflex is processed in the upper parts of the central nervous system, then neurons in the lower parts also take part in its processing. Parts of the brain stem and spinal cord are also involved in the formation of high-level reflexes.
Whatever the reflex, if the continuity of the reflex arc is disrupted, then the reflex disappears. Most often, such a rupture occurs as a result of injury or illness.
In complex reflexes to react to a stimulus, various organs are included in the links of the chain, which can change the behavior of the body and its systems.
Reflex Arc Levels
This formation is the anatomical structure of the reaction. It consists of a chain of nerve endings, which allows signals to be transmitted to the working organ.
The chain includes the following links:
- A receptor that perceives irritation (internal or external). It is responsible for the production of nerve signals.
- A sensory pathway that consists of neurons. Directly through them the impulse is sent to the brain nerve center.
- Nerve center with intercalary and motor neurons. The former direct the impulse to the latter, and they form teams.
- Centrifugal path. Through it the signal is sent to the working body.
- Executive agency.
A necessary condition for the reflex is the integral structure of each section of the arc. The loss of one (due to injury or other circumstances) is associated with the absence of the reflex itself.
Classification of reflexes
There are several classifications of reflexes that reflect their functions or indicate the level of perception.
Some of them can be cited. According to their biological significance, reflexes are distinguished:
- food;
- protective;
- sexual;
- indicative;
- reflexes that determine body position (posetonic);
- reflexes for movement.
Based on the location of the receptors that perceive the stimulus, we can distinguish:
- exteroceptors located on the skin and mucous membranes;
- interoreceptors located in internal organs and blood vessels;
- proprioceptors that perceive irritation of muscles, joints and tendons.
Knowing the three classifications presented, you can characterize any reflex: acquired or innate, what function it performs and how to cause it.
Properties of the system
The education in question has the following characteristics:
- Adequacy. The ability to respond to a special irritation that is formed for a given receptor in an evolutionary way (the reaction of the eyes to light changes).
- Multimodality. Ability to respond to irritation.
- Possibility of reacting with several signals to a stimulus. From some receptors frequent signals are sent, from 2 - rare, from 3 - in volleys. In view of this, the central nervous system is able to differentiate irritation (pain). The frequency of the signal depends on the strength of stimulation.
- The ability to convert energy into a signal.
- Sudden excitement. Self-excitation without the influence of stimuli. This can be provoked by increased tone of the fibers of the autonomic nervous system.
- Fluctuation. The ability to change the level of your own arousal. It varies depending on the state of the fibers of the vegetative nervous system.
- Device. Possibility of adaptation to prolonged exposure to irritation.
These characteristics are important in the functioning of the reflex arc, which in turn is the basis for the proper functioning of the central nervous system.
Implementation of a reflex arc
As a reaction to the stimulus, the nervous tissue is excited, and nervous processes occur that form or enhance the function of the organ. The basis of excitability will be a change in the content of anions and cations in the axon membrane.
In a 2-neuron arch, the cell dendrite has a significant length; it is directed to the periphery along with the receptive fibers of the nerve endings. It ends with a specific device for processing stimuli - a receptor. Excitability from it travels centripetally along the nerve ending to the ganglion. The neuron process becomes a component of the dorsal root.
This fiber enters the motor neuron of the anterior horn and, through a synapse, where the impulse is transmitted through a transmitter, contacts the body of the motor neuron. Its process becomes a component of the anterior root, through which the centrifugal impulse goes to the working organ. As a result, the muscle contracts.
Excitation is directed through nerve fibers, separately and does not spread to the other components of this process. This is prevented by the sheaths that cover these fibers.
Reflex arc concept, diagram, structure
The set of nerve pathways along which an impulse propagates. To perceive irritation, receptors are needed - the first link of the reflex arc. From the receptors, excitation is transmitted along afferent pathways, which always have an ascending direction to the brain.
Simple reflex arc
From the central nervous system, the impulse is sent down the descending efferent fibers. The latter end on the executive body, which closes the reflex arc. This forms a reflex ring.
The general diagram of the structure of the reflex arc can be presented in the following form.
Decryption of signatures:
- Muscle.
- Receptor.
- Interneuron.
- Sensory neuron.
- Motor neuron.
Taxiway braking value
Inhibition is the opposite process of excitation.
It ends the functioning of the second one, slows down or prevents its appearance. Excitation in one center of the nervous system can accompany inhibition in another: signals that enter the central nervous system can slow down various types of reflexes. Each of the processes is interconnected, which guarantees the coordinated functioning of the internal organs and the entire body. For example, in the process of human motor activity, alternating muscle contractions of flexors and extensors occur: during excitation of the flexion center, signals are sent to the muscles that are responsible for this process. At the same time, the extensor center slows down and does not send signals to the extensor muscles, eventually they will relax.
The interaction that determines excitatory and inhibitory processes, that is, self-regulation of the work of internal organs, occurs through direct connections between the central nervous system and the working organ.
The functioning of the body is a conditioned reflex reaction to irritation. A reflex is its reaction to stimuli, carried out with the help of the central nervous system. Its anatomical basis is the reflex arc. It is a sequential chain of nerve cells that provide a reaction, a response to receptor stimulation. To carry out a proper reaction of the body, there must be an established interaction between receiving an impulse and responding to a stimulus.
What does the reflex arc consist of?
The arc itself represents the entire path of a nerve impulse from the moment a person comes into contact with the stimulus to the manifestation of a response. The reflex arc contains different types of neurons: receptor, effector and intercalary.
The reflex arc of the human body works like this:
- receptors perceive irritation. Most often, such receptors are processes of centripetal-type nerve fibers or neurons.
- the sensitive fiber transmits excitation to the central nervous system. The structure of the sensitive neuron is such that its body is located outside the nervous system; they lie in a chain in the nodes along the spine and at the base of the brain.
- switching from sensory fiber to motor fiber occurs in the spinal cord. The brain is responsible for the formation of more complex reflexes.
- the motor fiber carries excitation to the reacting organ. This fiber is an element of a motor neuron.
The effector is actually the reacting organ itself, responding to irritation. The reflex reaction can be contractile, motor or excretory.
Scheme of the occurrence of a reflex arc
