Somatic Nervous System

The somatic nervous system (SNS) controls voluntary movements and reflex arcs by transmitting sensory information to the central nervous system (CNS) and motor commands from the CNS to skeletal muscles. It consists of motor neurons that stimulate muscle contractions and sensory neurons that relay information from sensory organs. The SNS enables conscious control over bodily movements and responds to external stimuli. It plays an important role in activities such as walking, grasping, and reflex actions.

In this article, we will study the somatic nervous system, its components, functions, mechanism of action and disorders in detail.

The somatic nervous system (SNS) is a part of the peripheral nervous system responsible for voluntary control of body movements via skeletal muscles. It comprises motor neurons that transmit signals from the central nervous system (CNS) to muscles, initiating movement. Sensory neurons within the SNS relay information from sensory receptors (e.g., skin, eyes, ears) to the CNS, enabling perception and response to external stimuli. The SNS plays an important role in conscious activities such as walking, grabbing objects, and reflex actions. It facilitates communication between the CNS and the body’s external environment.

The somatic nervous system (SNS) is made up of nerves, neurons, and glial cells:

1. Nerves
   • Connect the brain and spinal cord to muscles and skin sensory receptors.
   • Transmit signals between the central nervous system (CNS) and the rest of the body.
   • Include cranial nerves originating from the brainstem and spinal nerves emerging from the spinal cord.
2. Neurons
   • Nerve cells that send and relay signals throughout the body.
   • Process and transmit information via electrical and chemical signals.
   • Include sensory neurons, motor neurons, and interneurons.
3. Glial Cells
   • Support cells that help develop and maintain neurons.
   • Provide structural support, insulation, and nourishment to neurons.
   • Include astrocytes, oligodendrocytes, and microglia in the CNS, and Schwann cells in the peripheral nervous system (PNS).

Also Read: Difference Between Sensory And Motor Neurons

The components of the somatic nervous system are:

Sensory Neurons

• Transmit sensory information from the body’s sensory receptors (such as those in the skin, muscles, joints, and organs) to the central nervous system (CNS), specifically the brain and spinal cord.
• These neurons detect stimuli such as touch, pressure, temperature, pain, and proprioception (awareness of body position and movement).

Motor Neurons

• Transmit signals from the CNS, particularly the brain and spinal cord, to skeletal muscles throughout the body.
• These neurons carry instructions for voluntary movements initiated by the brain, enabling actions such as walking, reaching, and speaking.

Neuromuscular Junctions

• Specialized synapses where motor neurons connect with skeletal muscle fibers.
• Neurotransmitters released at these junctions, such as acetylcholine, stimulate muscle contraction in response to motor neuron activation.

Sensory Receptors

• Specialized structures located throughout the body that detect various stimuli and convert them into electrical signals.
• Examples include mechanoreceptors (responding to mechanical pressure or touch), thermoreceptors (detecting temperature changes), nociceptors (sensing pain), and proprioceptors (monitoring body position and movement).

Spinal Cord

• Part of the central nervous system located within the vertebral column.
• Acts as a relay between the brain and peripheral nerves, processing sensory information and coordinating motor responses.
• Contains sensory and motor neurons, as well as interneurons that relay signals within the spinal cord.

Brainstem and Motor Cortex

• The brainstem, including structures such as the medulla oblongata and pons, regulates basic physiological functions and serves as a pathway for motor signals between the brain and spinal cord.
• The motor cortex in the brain’s cerebral cortex initiates and coordinates voluntary movements, sending motor commands to the spinal cord and peripheral nerves.

Cranial Nerves

• Twelve pairs of nerves originating from the brainstem and serving various sensory and motor functions.
• Some cranial nerves, such as the trigeminal nerve (V), facial nerve (VII), and glossopharyngeal nerve (IX), carry sensory information from the face, head, and neck to the brain, while others control muscles involved in chewing, facial expressions, and swallowing.

Also Read: Overview of Nervous System

The somatic nervous system (SNS) is a part of the peripheral nervous system responsible for voluntary control of body movements through skeletal muscles. It consists of afferent (sensory) nerves and efferent (motor) nerves. The main types within the somatic nervous system are:

1. Afferent (Sensory) Nerves

These nerves carry sensory information from the body to the central nervous system (CNS). They are responsible for transmitting information about external stimuli such as touch, pain, temperature, and body position.

• Exteroceptors: Receptors that respond to stimuli originating from outside the body, such as touch, pressure, pain, and temperature.
• Proprioceptors: Receptors that detect the position and movement of the body, located in muscles, tendons, and joints.

2. Efferent (Motor) Nerves

These nerves carry motor commands from the CNS to the muscles. They control voluntary muscle movements.

• Alpha Motor Neurons: Large neurons that innervate extrafusal muscle fibers, which are responsible for the contraction of muscles and the generation of force.
• Gamma Motor Neurons: Smaller neurons that innervate intrafusal muscle fibers, which are part of the muscle spindle and help regulate muscle tone and sensitivity to stretch.

3. Interneurons

These neurons are found within the CNS and connect sensory and motor pathways. They play an important role in reflexes and higher-order processing.

Also Read: What is a neural network

Difference between somatic nervous system and autonomic nervous system is given in the table below:

The mechanism of somatic nervous system are:

1. Sensory Input: Sensory receptors detect stimuli such as touch, pain, and temperature changes in the environment or within the body.
2. Transmission of Signals: Sensory neurons transmit signals from the receptors to the central nervous system (CNS), specifically the brain and spinal cord.
3. Processing in CNS: The CNS processes sensory information, integrating it with other sensory inputs and generating appropriate motor responses.
4. Motor Output: Motor neurons in the CNS send signals to skeletal muscles, initiating voluntary movements or reflex actions.
5. Neuromuscular Junction: At the neuromuscular junction, motor neurons release the neurotransmitter acetylcholine (ACh) to stimulate muscle contraction.
6. Muscle Contraction: ACh binds to receptors on muscle fibers, triggering a series of events that lead to muscle contraction and the execution of the desired movement.
7. Voluntary Control: The SNS allows for conscious control over skeletal muscles, enabling precise and coordinated movements in response to sensory stimuli or intentional actions.

Somatic Nervous System is the nervous system that helps to sense or helps to make communication with the environment. So, for that purpose, Somatic Nervous System has two functions:

• Sense the Environment: Somatic Nervous System helps to sense the Environment. It helps to take the inputs from the environment. Whatever the input form is. That might be a touch, smell, noise, etc. All the inputs will be received by the Somatic Nervous System. The backside of the human will take the touch inputs using the Somatic Nervous System. Then they move to the spinal cord. From the spinal cord, it moves to the brain.
• Movement Of Body Parts: The human body movement is controlled by the Somatic Nervous System. The brain provides the command. Those commands using the Somatic Nervous System move to the targeted area. There, they help to move the muscles. The muscles will help to move the body part. In this way, the Somatic Nervous System helps to move the human body.

Reflex Action

Reflex actions are those actions that occurred involuntarily. If there is any threat or any proper stimulation, then without any command or signal, muscles play a prompt action. This action is known as the Reflex Action. There are many reflex actions are present. Like suddenly bringing any element near to the eye, will promptly close the eye. This is the reflex action. Mainly Somatic Nervous System controls the reflex action.

It is the combined work of Motor Neurons & Sensory Neurons. The Sensory Neurons will sense the stimulus & then send the electrical signal to the CNS. CNS receives the signal & then decodes them to read the message. After reading the message, it sends a signal to the targeted cells to perform a certain action. This signal is transported with the help of the Motor Neurons. Two types of reflex mechanisms are present. In one case, there is another neuron in between the Sensory Neuron & Motor Neuron. This neuron is present inside the spinal cord. This is known as Polysynaptic. As there is more than one synaptic cleft or neuron joining in this path. Another is Monosynaptic. In this case, the Sensory & Motor neurons connect directly inside the spinal cord. There is only one synaptic cleft present in this case.

Somatic Nervous System is part of the Peripheral Nervous System. They are not part of the Central Nervous System. This means they don’t belong to the brain & spinal cord. But they are the most important for sensing the stimulus & performing certain tasks. Some common diseases are:

• Muscular Dystrophy: Genetic disorders characterized by progressive muscle weakness and degeneration due to defective genes that interfere with muscle protein production.
• Amyotrophic Lateral Sclerosis (ALS): Neurodegenerative disease affecting motor neurons in the brain and spinal cord, leading to muscle weakness, paralysis, and eventual respiratory failure.
• Myasthenia Gravis: Autoimmune disorder causing weakness and fatigue in voluntary muscles due to antibodies blocking acetylcholine receptors at the neuromuscular junction, impairing muscle contraction.
• Spinal Cord Injury: Traumatic damage to the spinal cord resulting from accidents or injuries, leading to paralysis, loss of sensation, and impaired motor function below the injury site.
• Multiple Sclerosis (MS): Autoimmune condition causing inflammation and damage to the myelin sheath covering nerve fibers in the CNS, disrupting communication between the brain and muscles, leading to weakness, numbness, and coordination problems.
• Peripheral Neuropathy: Damage or dysfunction of peripheral nerves, resulting in symptoms such as muscle weakness, numbness, tingling, and pain, often caused by diabetes, infections, or toxins.
• Cerebral Palsy: Neurodevelopmental disorder affecting movement and muscle coordination due to damage or abnormal development of the brain’s motor control centers, occurring before, during, or shortly after birth.

The symptoms of disorders affecting the Somatic Nervous System are:

1. Muscle Weakness: Difficulty in performing voluntary movements, lifting objects, or maintaining posture due to reduced muscle strength.
2. Fatigue: Persistent tiredness or exhaustion, especially during physical activity, resulting from muscle weakness or impaired neuromuscular function.
3. Numbness and Tingling: Sensations of numbness, tingling, or pins-and-needles in affected body regions, often indicating nerve damage or dysfunction.
4. Loss of Coordination: Difficulty in coordinating movements, maintaining balance, or performing precise motor tasks due to impaired neuromuscular control.
5. Muscle Spasms: Involuntary muscle contractions or spasms, causing sudden, uncontrolled movements, cramps, or stiffness.
6. Paralysis: Partial or complete loss of muscle function and sensation in affected body regions, typically resulting from severe nerve damage or spinal cord injury.
7. Difficulty Swallowing or Breathing: Impaired ability to swallow food or liquids, or difficulty breathing, which can occur in conditions affecting muscles involved in these functions, such as ALS or myasthenia gravis.
8. Pain: Chronic or acute pain in muscles, joints, or nerves, often accompanied by stiffness, tenderness, or shooting sensations, indicating underlying nerve damage or inflammation.
9. Gait Abnormalities: Altered walking pattern or gait, characterized by limping, dragging of the feet, or unsteady movements, commonly observed in conditions affecting motor control centers or peripheral nerves.

Treatments for Somatic Nervous System Disorders includes:

1. Physical Therapy: Exercises and techniques to improve muscle strength, flexibility, and coordination, often tailored to address specific movement impairments.
2. Medications: Drugs such as corticosteroids, immunosuppressants, or antispasmodics to manage symptoms like muscle weakness, spasms, or pain associated with somatic nervous system disorders.
3. Surgery: Surgical interventions to repair nerve damage, decompress nerves, or correct structural abnormalities contributing to symptoms, particularly in conditions like spinal cord injury or compression.
4. Assistive Devices: Use of mobility aids such as braces, orthotics, walkers, or wheelchairs to support mobility and improve independence in individuals with muscle weakness or paralysis.
5. Nerve Stimulation: Techniques like transcutaneous electrical nerve stimulation (TENS) or spinal cord stimulation to alleviate pain, improve muscle function, or modulate nerve activity in certain disorders.
6. Lifestyle Modifications: Adoption of healthy habits such as regular exercise, balanced nutrition, stress management, and adequate rest to support overall well-being and optimize treatment outcomes.
7. Symptom Management: Strategies to address specific symptoms like fatigue, numbness, or difficulty swallowing through symptom-targeted interventions such as energy conservation techniques or dietary modifications.
8. Psychological Support: Counseling, support groups, or therapy to address emotional and psychological challenges associated with somatic nervous system disorders, helping individuals cope with stress, anxiety, or depression.

In conclusion, the somatic nervous system plays a vital role in voluntary movement and sensory perception, facilitating communication between the central nervous system and skeletal muscles. Disorders affecting the somatic nervous system can lead to muscle weakness, coordination difficulties, and sensory impairments. Treatment approaches often involve a combination of physical therapy, medications, surgery, and lifestyle modifications aimed at managing symptoms and improving quality of life. Understanding the function and dysfunction of the somatic nervous system is essential for effective diagnosis, treatment, and support for individuals with related conditions.

Also Read:

• Autonomic Nervous System
• Diagram of Nervous System – Parts and Functions
• Animals Nervous System – Types, Neurons, Parts and Function

What is the Somatic Nervous System?

The somatic nervous system is responsible for voluntary control of skeletal muscles and the transmission of sensory information to the central nervous system.

What are the 31 Pairs of the Somatic Nervous System?

The somatic nervous system comprises 31 pairs of spinal nerves, including 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal nerves, each contributing to voluntary muscle control and sensory perception in specific regions of the body.

What is the Difference Between the Autonomic and Somatic Nervous Systems?

The autonomic nervous system controls involuntary bodily functions, while the somatic nervous system controls voluntary movements.

What is the Function of the Somatic Sensory System?

The somatic sensory system processes sensory information from the body’s external environment.

What is the Somatic Response System?

The somatic response system coordinates voluntary movements and reflex actions.

What is the Difference Between the Central Nervous System and the Autonomic Nervous System?

The central nervous system includes the brain and spinal cord, while the autonomic nervous system regulates involuntary functions like heart rate and digestion.