Somatic nervous system

Main

The somatic nervous system (SNS) is a division of the peripheral nervous system that enables voluntary control of skeletal muscles and relays sensory information from the skin and other organs to the central nervous system (brain and spinal cord).

Elements of the somatic nervous system:

• Afferent (sensory) nerves: These nerves carry sensory information from receptors in the skin, muscles, and other organs to the central nervous system, allowing for the perception of touch, pain, temperature, and proprioception (body position and movement).

• Efferent (motor) nerves: These nerves transmit signals from the central nervous system to skeletal muscles, enabling voluntary movement and control of the body.

• Cranial nerves: There are 12 pairs of cranial nerves that originate from the brain stem. They are responsible for various functions, including facial movements, eye movements, hearing, taste, and smell.

• Spinal nerves: There are 31 pairs of spinal nerves that emerge from the spinal cord. They carry sensory information from the body to the spinal cord and motor commands from the spinal cord to the skeletal muscles.

Functions of the somatic nervous system:

• Voluntary muscle control: The SNS allows for conscious control of skeletal muscles, enabling movements such as walking, writing, and speaking.

• Sensory perception: The SNS relays sensory information from the skin and other organs to the central nervous system, allowing for the perception of touch, pain, temperature, and proprioception.

• Some reflexes: The SNS is involved in certain reflexes, such as the knee-jerk reflex, which are rapid, involuntary responses to specific stimuli.

• Interaction between the central nervous system and the external environment: The SNS serves as a bridge between the central nervous system and the external world, allowing for the integration of sensory information and the execution of appropriate motor responses.

The SNS facilitates the interaction between the central nervous system and the external environment, enabling functions such as voluntary muscle control, sensory perception, and some reflexes.

Terms

• Nervous system: The complex network of neurons and supporting cells that transmits signals between different parts of the body, consisting of the central nervous system (brain and spinal cord) and the peripheral nervous system (somatic and autonomic nervous systems).

• Peripheral nervous system: The part of the nervous system that lies outside the brain and spinal cord, consisting of the somatic nervous system (responsible for voluntary actions and sensory perception) and the autonomic nervous system (responsible for involuntary functions such as heart rate, digestion, and breathing).

Analogy

The somatic nervous system can be compared to a telephone network. The brain and spinal cord act as the central switchboard, while the afferent nerves are like the incoming lines, bringing information from the outside world. The efferent nerves are like the outgoing lines, carrying commands from the switchboard to the intended recipients (muscles). For example, when you decide to pick up a pen, your brain sends a signal through the efferent nerves to the muscles in your arm and hand, causing them to contract and grasp the pen.

Misconception

A common misconception is that all bodily functions are under conscious control. However, the somatic nervous system only controls voluntary movements and some reflexes, while the autonomic nervous system regulates involuntary functions such as heart rate, digestion, and breathing. For instance, people often believe they can consciously control their heart rate, but this is primarily regulated by the autonomic nervous system.

How to use it

1. Understanding the somatic nervous system can help you better control your voluntary movements. For example, when learning a new skill like playing the piano, focusing on the specific muscles involved and consciously directing your movements can improve your performance.

2. Knowledge of the SNS can also help you identify potential problems. If you experience numbness, tingling, or weakness in a specific area, it may indicate a problem with the sensory or motor nerves in that region, prompting you to seek medical attention.

3. Engaging in activities that challenge your somatic nervous system, such as learning a new dance or practicing a musical instrument, can help maintain and improve its function as you age, promoting better coordination and reducing the risk of age-related decline.

Facts

• The somatic nervous system contains approximately 43 segments of nerves, with 31 in the spinal cord and 12 in the brain stem.

• The longest nerve in the human body, the sciatic nerve, is part of the somatic nervous system and can be over 1 meter in length.

• The neurotransmitter acetylcholine has an excitatory effect in the somatic nervous system but an inhibitory effect in the autonomic nervous system.

• Some reflexes, like the knee-jerk reflex, are controlled by the somatic nervous system through a pathway called the reflex arc, which bypasses the brain for a faster response.

• Diseases affecting motor neurons, such as motor neuron disease (MND), can lead to neurodegeneration and muscle wasting due to somatic nervous system dysfunction.