The Somatic Nervous System (SNS), anatomy and function

The Somatic Nervous System (SNS), anatomy and function

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The somatic nervous system (SNS) is part of the peripheral nervous system (SNP), which is responsible for transmitting motor and sensory information both back and forth to the central nervous system (CNS).

The SNS is made up of nerves that connect to the skin, sensory organs and all skeletal muscles with the CNS. He is responsible for almost all voluntary muscle movements, as well as for the processing of sensory information that comes through external stimuli that include hearing, touch and sight. It transmits nerve impulses between the central nervous system, which is the brain and spinal cord, and skeletal muscles, skin and sensory organs.

Parts of the somatic nervous system

The term "somatic nervous system" derives from the Greek word soma, which means "body", which somehow describes its function, since this system transmits information to and from the SNC to the rest of the body.

The somatic system is made up of two different types of neurons, which are also called nerve cells:

  • Sensory neurons, also known as afferent neurons, which are responsible for bringing information from the nerves to the central nervous system.
  • Motor neurons, also known as efferent neurons, which are responsible for bringing information from the brain and spinal cord to muscle fibers throughout the body.

A neuron has a body and an axon; The body of the neuron is located in the central nervous system and the axon is embedded in skeletal muscles, sensory organs or skin.

The neurons that make up the somatic nervous system project outward from the central nervous system and connect directly to the muscles of the body, and carry signals from the muscles and sensory organs to the central nervous system.

The somatic nervous system adapts to the peripheral nervous system. Within the peripheral nervous system there are 12 pairs of cranial nerves and 31 pairs of spinal nerves, which as we have said, are formed by sensory neurons and motor neurons. Some pairs of nerves only have sensory cells, others only have motor cells and others have sensory and motor cells. Motor nerve cells are somatic or autonomic, although the latter are not part of the SNS.

SNS function

The main function of the somatic nervous system is connect the central nervous system to organs, muscles and skin. This allows us to perform complex movements and behaviors. Somatic neurons carry messages from the external areas of the body that are directly related to the senses. The information captured by the sensory systems is transmitted to the central nervous system. The CNS then sends signals through the nervous networks of the somatic system to the muscles and organs.

the process is the following: sensory / afferent neurons carry impulses to the central nervous system and the brain. After being processed by the central nervous system, motor or efferent neurons take the signal back to the muscles and sensory organs.

In addition to controlling voluntary muscle movements, the SNS also carries out involuntary movements known as reflex acts. During a reflex action muscles move involuntarily without brain intervention. This happens when a nerve pathway connects directly with the spinal cord. Some examples of reflex acts are removing the hand when we accidentally touch a hot pan or an involuntary jolt of the knee when the doctor hits the knee.

In reflex acts there is no conscious thought. Here the sensory nerves carry signals to the spinal cord, which usually connect with interneurons in the spine, and then quickly transmit the signals from the motor neurons to the muscles that trigger the reflex. The reflex arcs that go to the organs are called autonomous reflex acts, while those that affect the muscles are called somatic reflex acts.


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