The somatic nervous system (SNS) is a part of the peripheral nervous system, which controls voluntary skeletal muscle movements and gathers sensory information from the environment. It is responsible for our ability to react to the things going on around us and to make conscious decisions about our actions. The SNS consists of neurons that connect the brain and spinal cord to the skeletal muscles and sensory organs. The following article will explore the functions of the somatic nervous system in greater detail.
Structure:
The somatic nervous system is composed of motor neurons and sensory neurons. Motor neurons are located in the spinal cord and carry signals to the skeletal muscles. Sensory neurons carry information from the skin, muscles, and joints to the spinal cord, which then transmits it to the brain. The motor neurons are divided into two subtypes called alpha and gamma motor neurons. Alpha motor neurons connect to extrafusal fibers in skeletal muscles and control their contraction. Gamma motor neurons, on the other hand, connect to intrafusal fibers in skeletal muscles and regulate their sensitivity to sensory information.
Function:
The somatic nervous system is responsible for voluntary movements and reflexes. We consciously control the movements of skeletal muscles via motor neurons, which send signals from the spinal cord or brainstem to the muscles. Voluntary movements include activities such as walking, talking, and writing. The somatic nervous system also coordinates reflex actions that are necessary for survival, such as pulling away from a hot object or a sudden noise. These reflexes are triggered by sensory neurons that detect changes in the environment and send the information to the spinal cord or brainstem. The spinal cord then sends out motor neurons, which cause the body to react in a specific way.
Disorders:
Damage to the somatic nervous system can result in various disorders. Some of the common ones include:
Myasthenia Gravis
It is an autoimmune disorder that affects the function of the neuromuscular junction, where nerve impulses meet muscle fibers. The symptoms may include drooping eyelids, impaired speech, and difficulty swallowing. Treatment usually involves medication or surgery.
Multiple Sclerosis
It is a chronic autoimmune disease that causes damage to the outer membrane of nerve cells in the brain and spinal cord. The symptoms may include blurred vision, muscle weakness, and difficulty coordinating movements. Treatment usually involves medication or physical therapy.
Amyotrophic Lateral Sclerosis (ALS)
It is a progressive neurodegenerative disease that affects motor neurons in the brain and spinal cord. The symptoms may include muscle weakness, difficulty breathing, and difficulty speaking. There is currently no cure for ALS, but there are treatments available that can help manage symptoms.
Role in Movement:
The somatic nervous system plays a crucial role in skeletal muscle movement. It works in close association with the musculoskeletal system to coordinate voluntary movements. When a person decides to move a specific muscle, the brain sends a signal via the somatic nervous system to the alpha motor neurons in the spinal cord. The alpha motor neurons then send a signal to the specific muscle fibers, causing them to contract. This contraction results in movement.
Muscle Tone:
Muscle tone is the natural tension that is always present in muscles, even when they are at rest. The somatic nervous system is responsible for regulating muscle tone. The gamma motor neurons regulate the sensitivity of muscle spindles that respond to changes in muscle length. This regulation helps maintain the optimal level of muscle tone required for voluntary movement and reflexes.
Muscle Spindles:
Muscle spindles are specialized sensory receptors that are located within the skeletal muscles. These receptors detect changes in muscle length and send the information to the spinal cord via sensory neurons. The spinal cord then sends signals to the alpha motor neurons, which cause the muscles to contract or relax, depending on the situation. By detecting changes in muscle length, muscle spindles help maintain proper posture and balance.
Role in Reflexes:
The somatic nervous system is also responsible for coordinating reflex actions. Reflexes are rapid and automatic responses to a particular stimulus that help protect the body from harm. Reflexes are commonly classified into two types: spinal reflexes and cranial reflexes.
Spinal Reflexes:
Spinal reflexes are reflexes that are mediated by the spinal cord. They are of two types: monosynaptic and polysynaptic. The monosynaptic reflex involves a single synapse between sensory and motor neurons, while the polysynaptic reflex involves multiple synapses.
Cranial Reflexes:
Cranial reflexes are reflexes that are mediated by the brainstem. They are controlled by a network of neurons that are responsible for controlling reflexes related to the head and neck, such as blinking, chewing, and swallowing.
Conclusion:
The somatic nervous system is an essential component of our nervous system, responsible for controlling voluntary movements and reflexes. It plays a crucial role in the control of skeletal muscles, muscle tone, and reflex actions. Disorders of the somatic nervous system can result in various conditions, such as Myasthenia Gravis, Multiple Sclerosis, and ALS.
Frequently Asked Questions:
- What is the somatic nervous system responsible for?
- What is the difference between the sympathetic and somatic nervous systems?
- What are some common disorders of the somatic nervous system?
- What are muscle spindles?
The somatic nervous system is responsible for voluntary movements and reflexes. We consciously control the movements of skeletal muscles via motor neurons, which send signals from the spinal cord or brainstem to the muscles.
The sympathetic nervous system is responsible for the body’s response to stress or danger. It prepares the body for fight or flight. The somatic nervous system, on the other hand, controls conscious movements and reflexes.
Some common disorders of the somatic nervous system are Myasthenia Gravis, Multiple Sclerosis, and ALS.
Muscle spindles are specialized sensory receptors that are located within the skeletal muscles. These receptors detect changes in muscle length and send the information to the spinal cord via sensory neurons.
References:
- Bordoni, B., & Zanier, E. (2013). Clinical and symptomatological reflections: the fascial system. Journal of Multidisciplinary Healthcare, 6, 145–153.
- Gittoes, M. J., & Kearney, R. (2012). The clinical anatomy of the lesser occipital nerve: implications for surgical and anaesthetic management of occipital neuralgia. Clinical Anatomy, 25(6), 692–697.