The reflex arc is the path that the nervous impulse passes to the working organ from the receptors and back. It consists of two halves. Being a complex structural-functional complex, the reflex arc is a closed ring.
The leading half consists of a peripheral sensory neuron. Its cell lies in the spinal or intervertebral ganglion. From it departs the process dividing into two branches. One part of it in the peripheral nerve goes to the periphery and ends in any part of the skin, deep tissues or mucous membrane terminal device. The second branch enters, included in the posterior root, in the spinal cord.
Sensing neurons in it can do different ways. Some, turning up and not interrupting, go to the medulla oblongata. Others end in gray matter. At the same time, from each sensory neuron in the substance of the spinal cord, collaterals or branches branch off in different directions. Some of them are directed through the gray matter to the motor cells in the anterior horn and end with branches. The central motor neuron also ends. The similarity of contacts is not an accident. This is due to the fact that the reflex arc in the sensory half plays a role similar to the pyramidal path.
The outflow consists of a peripheral motor neuron. Its cell lies in the region of the anterior horns of gray matter in the spinal cord. From here the outgrowth to the muscle first through the spine( anterior motive), then through the peripheral nerve.
The scheme of the reflex arc of the knee reflex includes the excitation formed in the tendon endings of the neurons as a result of external action( hammer impact).On the femoral nerve irritation enters the spinal cord. From it excitation is transmitted to the motor cells of gray matter, and then to the muscle. Due to its reduction, the leg is straightened in the knee joint.
Both halves, of which the reflex arc consists, contact each other.
Despite the fact that the reflex activity seems independent and autonomous relative to the brain, this is not entirely true. The pyramidal path also covers the anterolar cage with terminal branches. Thus, in some way stretching to the reflex arc, he contacts with it.
In relation to its activity, the function of the central neuron is inhibitory. In particular, this concerns the tendon reflexes.
Due to the fact that the muscles are under the influence of sensory drives, which includes a reflex arc, then, from a theoretical point of view, in each of them, it is possible to provoke a motor reflex. In addition to the elementary, there are likely and there are more complex abbreviations, in which whole muscular groups participate.
Thus, there must be a very significant amount of theoretically feasible motor reflexes. However, as practice shows, there are much less of them. Perhaps this is due to significant inhibition( in some cases before destruction) of reflexes by a pyramidal route.
The components of the reflex arc are:
- a receptor that perceives environmental irritation and turns it into a nerve impulse;
is an afferent path from the primary information processing area to the central nervous system;
- the center of "response"( a set of neurons in which information is processed and a reflex is formed);
is an efferent pathway to the periphery of the central nervous system;
- working organ( iron or muscle);
Depending on the complexity, the closed motion of the nerve impulse can be simple. In this case, the composition of the reflex arc includes two neurons( motor and sensory).A complex system is called a polysynaptic arc. It consists of three or more neurons.