Unconditioned blink reflex. Conditioned protective (blinking) reflex. What is the arc of the reflex

The nervous activity of the human body is the transmission of impulses. One of the results of such transmissions are reflexes. In order for a certain reflex to be performed by the body, a connection must be established from receiving a signal to a response to a stimulus.

A reflex is a reaction of a part of the body to changes in the external or internal environment as a result of exposure to receptors. They can be located on the surface of the skin, generating exteroceptive reflexes, as well as on internal organs and vessels, which underlies the interrecessive or myostatic reflex.

Responses to stimuli by their nature are conditional and unconditional. The second includes reflexes, the arc of which has already been formed by the time of birth. In the first, it is created under the influence of external factors.

What is the reflex arc made of?

The arc itself represents the entire path of the nerve impulse from the moment a person contacts 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 the processes of nerve fibers of the centripetal type or neurons.
sensory fiber transmits excitation to the central nervous system. The structure of a sensitive neuron is such that its body is located outside the nervous system, they lay in a chain in nodes along the spine and at the base of the brain.
the switch from sensory to motor fibers occurs in the spinal cord. The brain is responsible for the formation of more complex reflexes.
motor fiber carries excitation to the reacting organ. This fiber is an element of the motor neuron.

The effector is actually the reacting organ itself, responding to irritation. The reflex reaction can be contractile, motor or excretory.

Polysynaptic arcs

Polysynaptic includes a three-neuron arc, in which a nerve center is located between the receptor and the effector. Such an arc is clearly illustrated by the withdrawal of the hand in response to pain.

Polysynaptic arcs have a special structure. Such a circuit necessarily passes through the brain. Depending on the localization of the neurons that process the signal, there are:

spinal;
bulbar;
mesencephalic;
cortical.

If the reflex is processed in the upper parts of the central nervous system, then the neurons of the lower sections also take part in its processing. Parts of the brainstem and spinal cord are also involved in the formation of high-level reflexes.

Whatever the reflex, if the continuity of the reflex arc is broken, then the reflex disappears. Most often, such a gap occurs as a result of injury or illness.

In complex reflexes, to respond to a stimulus, various organs are included in the links of the chain, which can change the behavior of the organism and its systems.

Also interesting is the structure of the arc of the blinking reflex. This reflex, due to its complexity, makes it possible to study such a movement of excitation along an arc, which is difficult to study in other cases. The reflex arc of this reflex begins with the activation of excitatory and inhibitory neurons simultaneously. Depending on the nature of the damage, different parts of the arc are activated. The trigeminal nerve can provoke the onset of the blinking reflex - a response to touch, auditory - a response to a sharp sound, visual - a response to a light drop or a visible danger.

The reflex has an early and a late component. The late component is responsible for the formation of the response delay. As an experiment, touch the skin of the eyelid with a finger. The eye closes with lightning speed. When you touch the skin again, the reaction is slower. After processing the received information by the brain, the acquired reflex is consciously inhibited. Thanks to such inhibition, for example, women very quickly learn to paint their eyelids, overcoming the natural desire of the eyelid to cover the cornea of the eye.

Other variants of polysynaptic arcs are also amenable to study, but they are often too complex and not very visual to study.

No matter how high science has reached, the blink and knee reflexes remain the basic reflexes for studying human reactions. The study and measurement of the speed of passage of an impulse in the trigeminal and facial nerves are the basis for assessing the state of the brain stem in various pathologies and pains.

monosynaptic reflex arc

An arc, which consists of only two neurons, which is quite enough for an impulse, is called monosynaptic. The classic example of a monosynaptic arc is the knee jerk. That is why a detailed diagram of the knee reflex arc is placed in all medical textbooks. A feature of the composition of such an arc is that it does not involve the brain. The knee jerk refers to the muscular unconditioned. In humans and other vertebrates, such muscular reflexes are responsible for survival.

It is not surprising that it is the knee jerk that is checked by a neurologist as one of the indicators of the state of the somatic nervous system. When a hammer strikes the tendon, the muscle is stretched, after the passage of irritation through the centripetal fiber to the spinal ganglion, the signal through the motor neuron into the centrifugal fiber. Skin receptors do not take part in this experiment, nevertheless, its result is very noticeable and the strength of the reaction is easy to differentiate.

The vegetative reflex arc breaks into pieces, forming a synapse, while in the somatic system the path traversed by the impulse from the receptor to the acting skeletal muscle is not interrupted by anything.

Obtaining a blinking reflex and conditions that cause its inhibition:

When touched inner corner eyes - involuntary blinking of both eyes.

In Fig. 1, the reflex arc of this reflex.

The circle is the part of the medulla oblongata where the centers of the blinking reflex are located. The bodies of sensory neurons 2 lie outside the brain in the ganglion.

Irritation of receptors → the flow of nerve impulses directed by dendrite to body sensory neuron 2 and from it axon in medulla oblongata. There's excitement through synapses transmitted intercalary neurons 3. Information is processed by the brain, including the cortex. We after all felt a touch to a corner of an eye! → then the executive neuron 4 is excited, the excitation along the axon reaches the circular muscles of the eye 5 and causes blinking. Let's continue monitoring.

But, if you touch the inner corner of the eye several times - reflex slowed down.

When answering, it should be taken into account that along with direct connections, according to which the "orders" of the brain go to the organs, there are feedback carrying information from organs to the brain. Since our touches were not dangerous for the eye, after a while the reflex faded.

A completely different result would have been if a speck had got into the eye. Disturbing information would reach the brain and increase the response to irritation. In all likelihood, we would try to extract the mote.

By force of will it is possible slow down blink reflex:

To do this, touch with a clean finger to the inner corner of the eye and try not to blink. Many succeed. Impulses from the cortex, slowed down the nerve centers of the medulla oblongata - this central braking , discovered by a Russian physiologist Sechenov: « Higher Centers of the Brain able to regulate work Lower Centers: enhance or inhibit reflexes.

Spinal knee jerk: cross your legs. Relax the muscles in your outstretched leg. With the edge of your hand, hit the tendon of the quadriceps muscle of the thrown leg. The leg should bounce. Don't be surprised if the reflex doesn't happen. To get into the reflexogenic zone, you need to stretch the tendon. In all other cases, there will be no reflex.

Organism Levels:cellular, tissue, organ, system, organism.

Organ level form organs - independent anatomical formations that occupy a certain place in the body, have a certain structure and perform certain functions.

System level represented by groups (systems) of organs that perform common functions.

organism as a whole, uniting the work of all systems, constitutes the organismic level.

Behavioral level, which determines the adaptation of the organism to the natural, and in humans, to the social environment.

The nervous and endocrine regulatory systems unite all levels of the body, ensuring the coordinated work of all executive organs and their systems.

A reflex is a response of the body to irritation, carried out by excitation of the central nervous system and having an adaptive value.

This definition contains 5 signs of a reflex:

1) it is a response, not a spontaneous one,

2) irritation is necessary, without which the reflex does not occur,

3) the reflex is based on nervous excitation,

4) the participation of the central nervous system is necessary to turn sensory excitation into effector,

5) a reflex is needed to adapt (adapt) to changing environmental conditions.

Reflexes are divided into 2 large groups: unconditional and conditional.

Blink reflex - a protective reaction of the body to light, sound, touching the cornea or eyelashes, tapping in the glabella and other irritants. It also occurs with electrical stimulation of the supraorbital nerve (a branch of the trigeminal), which is used as a neurophysiological test.

The blinking reflex was described in 1896 and is reduced to a contraction of the circular muscle of the eye during mechanical stimulation of the superior ophthalmic nerve.
The center of this protective reflex, like many protective reflexes (sneezing, coughing, vomiting, tearing), is located in the medulla oblongata of the brain.

When you touch the inner corner of the eye, a blinking reflex occurs, after several touches it is inhibited. Touching the inner corner of the eye causes irritation of the receptors. They are excited, and nerve impulses from the receptors are transmitted along the sensitive neuron to the CIS.

From the CIS, nerve impulses arrive at the executive neuron. A synapse is formed at the point of contact between the axon of the executive neuron and the muscle cell. Bubbles with excitatory biologically active substances burst, the liquid pours into the synaptic cleft and affects the cell wall of the muscle cell, which is excited and contracts. There is a blinking reflex. After several touches, the blinking reflex disappears.

Inhibition does not allow excitation to spread indefinitely. Receptors in muscle cells send signals to the nerve center. From the nerve center through the executive neuron, nerve impulses reach the synapse, the bubbles with inhibitory substances burst, the fluid pours into the synaptic cleft, and affects the cell membranes of muscle cells. The action of muscle cells is inhibited.

With the help of an effort of will, you can slow down the action of the blinking reflex. A nerve impulse arises in the nerve center. The nerve impulse reaches the synapse, in which bubbles with inhibitory biologically active substances burst. The fluid pours into the synaptic cleft and acts on the cell membranes of the muscle cells. There is inhibition of the blinking reflex.

When a mote enters the eye, the receptors of the membrane of the eye are irritated. They are excited, and nerve impulses from the receptors are transmitted through the sensitive neuron to the nerve center. From the nerve center, nerve impulses are sent to the executive neuron, which activates the circular muscles of the eye that close the eyelids. After removing the mote, the principle of "feedback" is triggered. A signal is sent to the nerve center. Information about the change in the situation is being processed. The nerve center sends nerve impulses that reach the synapse, the bubbles with inhibitory substances burst, the fluid pours into the synaptic cleft, and affects the cell membranes of muscle cells. The action of muscle cells stops. The blink reflex is inhibited.

The blinking reflex is a protective reaction of the body, which is carried out and controlled by the nervous system.

With a tension headache, an increase in reflex excitability occurs: reflexes begin to be caused by weaker stimuli (decrease in the threshold of sensitivity), at the same time, the response becomes more powerful and lasts longer. The pathogenesis (causes) of tension headache is associated with these phenomena, which are clearly visible when the blinking reflex is evoked: a pain reaction begins to occur as a result of exposure to even an inadequately weak stimulus.

The specificity of the vision of a newborn is a blinking reflex. Its essence lies in the fact that no matter how much you swing objects near the eyes, the baby does not blink, but he reacts to a bright and sudden beam of light. This is explained by the fact that at birth the child's visual analyzer is still at the very beginning of its development. The vision of the newborn is assessed at the level of sensation of light. That is, the baby is able to perceive only the light itself without perceiving the structure of the image.

Functions: 1.regulates the work bodies, ensuring their coordinated work;

2.provides accommodation organism to environmental conditions(and information comes through the senses).

Parts of the nervous system:

central part(CNS)- This is the spinal cord and brain;

peripheral- nerves and ganglions.

Departments of the Nervous System:

Somatic(from Greek soma - body) - controls the work of skeletal muscles (controlled by consciousness and will).

Vegetative / Autonomous- Regulates metabolism, the functioning of internal organs and the functioning of smooth muscles.

- its work does not depend on our desires (we cannot intentionally stop or increase the work of the heart, blush or turn pale (some people succeed, but after a long workout and in an indirect way). Intervene in the work of internal organs, regulated by the autonomic nervous system, stop illness, it is impossible to overcome alcoholism and drug addiction without medical assistance).

Rice. Nervous system:

1 - brain;

2 - spinal cord;

4 - nerve nodes.

Reflex is the simplest form of neural regulation.

There are reflexes in both the somatic and autonomic parts of the nervous system. .

The reflex is based chain of neurons or reflex arc.

5 links reflex arc Unconditioned / Innate reflex somatic department N.S. :

1. Receptor are nerve formations that perceive and transform irritation into nerve impulses→

2. Sensitive Neuron (their bodies are in nerve nodes) - perceives stimuli through receptors .

Nerve impulses arising from stimulation are transmitted by dendrite→into the body sensory neuron→ along the axon into the brain→

3. on the Interneurons - their processes do not extend beyond the central nervous system / CNS(brain and spinal cord) - processing of received information→

4. after, the signals are transmitted Executive / motor neurons, whose nerve impulses cause work →

5. body .

(Example: Blinking reflex, Patellar reflex, Salivation reflex, Hand withdrawal from a hot object).

5 Links of the Reflex Arc of the Blinking Reflex

Getting a blink flax reflex and condition defiant its inhibition :