The reflex arc is the path that the nerve impulse passes to the working organ from the receptors and vice versa. It consists of two halves. Being a complex structural and functional complex, the reflex arc is a closed ring.
Its leading half consists of a peripheral sensory neuron. Its cell lies in the spinal or intervertebral ganglion. A process divides into two branches leaves from it. One part of it in the composition of the peripheral nerve goes to the periphery and ends on some part of the skin, deep tissues or mucous membrane with the end apparatus. The second branch is included, which is part of the posterior root, in the spinal cord.
The sensing neurons in it can do various paths. Some, turning up and not interrupting, go to the medulla oblongata. Others end in gray matter. In this case, from each sensing neuron in the substance of the spinal cord depart in opposite directions of the collateral or branch. Some of them are directed through gray matter to motor cells in the anterior horn and end in branching. The central motor neuron also ends. The likeness of contacts is not an accident. This is due to the fact that the reflex arc in the sensing half plays a role similar to the pyramidal path.
The outlet part 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 process to the muscle leaves first through the root (anterior motor), then through the peripheral nerve.
The scheme of the reflex arc of the knee reflex includes excitation formed in the tendon ends of neurons as a result of external exposure (hammer blow). On the femoral nerve, irritation enters the spinal cord. From it, excitation is transmitted to the motor cells of the 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 are in contact with each other.
Although reflex activity seems to be independent and autonomous with respect to the brain, this is not entirely true. The pyramidal pathway also encompasses the anteropod cell with terminal branches. Thus, in some way, reaching out to the reflex arc, he makes contact with it.
In relation to its activity, the function of the central neuron is inhibitory. In particular, this applies to tendon reflexes.
Due to the fact that the muscles are influenced by 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 elementary, more complex contractions are likely and exist, in which whole muscular groups participate.
Thus, there should be a very significant number of theoretically feasible motor reflexes. However, as practice shows, they are much smaller. Perhaps this is due to significant inhibition (in some cases, before the destruction) of reflexes in a pyramidal way.
The components of a reflex arc are:
- a receptor that perceives irritation from the environment and turns it into a nerve impulse;
- afferent path, running from the area of primary information processing to the central nervous system;
- the center of the “response” (a set of neurons in which information is processed and a reflex is formed);
- the efferent pathway to the periphery of the central nervous system;
- working body (gland or muscle);
- Feedback.
Depending on complexity, the closed movement of a nerve impulse can be simple. In this case, the composition of the reflex arc includes two neurons (motor and sensory). The complex system is called the polysynaptic arch. It consists of three or more neurons.