Somatic nervous system

This system is in charge of gathering and transmitting the information detected by the senses, and also of sending instructions that allow the voluntary movement of the muscles.

The Human Body Chapter 5: Peripheral Nervous System Peripheral Nervous System Spinal nerves Cranial nerves Autonomous nervous system Responses and reflexes Peripheral Nervous System Diseases What you must know Láminas bilingües para imprimir / Bilingual laminae to print

Imágenes Cross section of a sciatic nerve. There are 31 pairs of spinal nerves. Cranial nerves are born in the encephalon. LÁMINAS Peripheral nerves

The somatic nervous system (SNS) is made up of sensory neurons that carry information (for instance, pain) from the sensory receptors (of the senses: skin, eyes, etc.) -mainly located in the head, body surface and limbs- to the central nervous system (CNS). It is also made up of motor axons that conduct impulses to the skeletal muscles, in order to perform movements such as waving a hand or kicking a ball. It is important to mention that these last impulses (the motor ones) can be consciously controlled, therefore, this portion of the SNS has voluntary characteristics. Basically, SNS covers all the CNS and PNS structures responsible for conducting afferent information (sensory), conscious and unconscious, and information from the motor control to the skeletal muscle. Thus, the somatic nervous system has two canals: one as an entry, where the information is received (through somatic sensory or somatic afferent canals), which is related with temperature, pain, touch, pressure and space senses (sight, hearing, taste and smell) and also, the proprioception, which corresponds to the information gathered at the muscles and tendons. Along with all that received information, which is somatic, it also provides a voluntary somatic or effector (motor) response, corresponding to the contraction of the skeletal muscle.

Peripheral nerves

In order to carry out its functions, the somatic nervous system is integrated by the peripheral nerves, in charge of taking the information to and from the brain and spinal cord. The peripheral nerves are bundles of nerve fibers which have a diameter that fluctuates between 0.4 and 6 mm. The thicker fibers carry the messages that stimulate the muscles (motor nerve fibers) and those of tactile and position sensibility (sensory nerve fibers). The thinner fibers carry the sensibility of pain and temperature and control a few functions of the autonomous nervous system (heart rate, blood pressure, etc.). The PNS is made up of the cranial nerves (they come out of the cranium) and the spinal or rachidian nerves (they come out of the spinal cord). We will go into more depth about them next.

Sensory, motor and mixed

According to the category of the nerve impulse, there are three different kinds of nerve: sensory, motor and mixed.
- Sensory nerves (sensitive): They are the ones that carry the nerve impulse from the exterior or from the internal organs towards the CNS.
- Motor nerves: They carry the nerve impulse to the muscles (contraction) and glands and take the opposite route of the sensory nerves.
- Mixed nerves: They carry both afferent (sensory) and efferent (motor) nerve impulses.

PALABRAS CLAVE

• "Somatic nervous system"
• "Peripheral nerves"
• "Sensory nerves"
• "Motor nerves"
• "Mixed nerves"

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