Somatic nervous system: characteristics and functions

The essential function of the nervous system is communication. This occurs both with the environment that surrounds us and with the interior of our body. Based on its functions, the nervous system is divided into the Somatic Nervous System (SNS) and the Autonomous Nervous System (ANS).

The somatic nervous system is a complex system. It is the part of the nervous system that is responsible for carrying sensory information to the central nervous system. That is: the somatic nervous system is responsible for the body’s communication with the external environment. Meanwhile, the ANS is responsible for the communication of the organs with each other, which maintains homeostasis.

The SNS acts through skeletal muscles, regulating voluntary and reflex actions.. Through its receptors, this system captures the changes that occur. Thus, the motor fibers that are located in the somatic nervous system have some characteristics that differentiate them from the autonomic one:

First of all, there are no ganglia along its route. The neuronal bodies are located within the CNS. Furthermore, they run without interruption until they reach the effector (skeletal muscle). Furthermore, the conduction speed is much greater. The SNS may or may not stimulate the effector, but it does not inhibit it.

Sensory pathways of the somatic nervous system (SNS)

In order for us to perceive a sensation, the information must reach the cerebral cortex.. Thus, the pathway is the route that information takes through a set of neurons that link the peripheral nervous system with the central nervous system.

Thus, for a sensory stimulus to reach its destination, the central nervous system must go from the receptors to the CNS through the connection with three neurons. In the somatosensory cortex there is a representation proportional to the sensitivity of the different parts of the body (1). In this representation not all areas occupy the same size. Areas such as the fingertips or lips are the ones that occupy the most place in this representation.

There are different types of sensory pathways. According to the sensory modality they lead, they are divided into:

Way to fine touch. Discriminative or epicritic sensitivity.Path for diffuse touch. Gross or protopathic sensitivity.Route for pain and temperature. Thermoalgesic.Proprioceptive pathway. Body position.

Another way of naming them is according to the origin of the stimulus:

Exteroceptive pathways: They are those that carry information from the skin.Interoceptive pathways: they are those that conduct information from internal organs. Finally, proprioceptive pathways: They are those that carry information from the musculoskeletal system.

To transmit the sensation, nervous impulses travel through a relay of three neurons:

First, there are the first order neurons: are those that lead from the periphery of the body.Second order neurons: They are located in the posterior horn of the spinal cord or in the trunk. They are responsible for transmitting the nervous impulse from the trunk to the thalamus. That is where a synapse occurs with the third order neuron.Third order neurons: They are in the relay nuclei of the thalamus. Its function is to conduct the nervous impulse to the somesthetic areas (that is, somatic-sensitive) in the region located behind Rolando’s fissure in the parietal lobe.

Before reaching the cortex, where the sensation is interpreted, all sensory information is processed in the thalamus (except olfactory afferents). They are then integrated into the parietal cortex, where sensitivity is normally integrated.

motor pathways

When we reach out to grab somethingthis mental processing requires the contraction and relaxation of the muscles of both the arm and the hand.

The motor pathways take care of this: they conduct nerve impulses from the central nervous system to the skeletal muscles (somatic effectors). Thus, the neurons involved in this process are the motor neurons, which are located in the anterior horn of the spinal cord.

The motor tract system is divided into three fascicles, depending on the origin and termination of the nerves:

Corticogeniculate or corticonuclear. Its destination is the motor nuclei of the cranial nerves. That is, it is the pathway that controls the facial muscles.Juxtapyramidal. It originates in area 4 of the frontal gyrus. Its destination is the neurons of the reticular formation at the bulbar level.corticospinal or pyramidal bundle. It links the cortex with the neurons of the anterior horn of the spinal cord. Thus, it controls the muscles of the trunk, neck and extremities.

Thus, we can conclude that the somatic nervous system is a complex system. To produce movement, from the central nervous system, several connections are produced that allow the final action to be carried out. The same thing happens when someone touches us or we brush against an object: for our brain to find out, a multitude of neurons and areas are involved in the process.

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