Difference Between Somatic and Autonomic Nervous System

Main Difference – Somatic vs Autonomic Nervous System

Peripheral nervous system is the nervous system which is outside the brain and spinal cord. The main function of the PNS is to relay information between the central nervous system and the effector organs. Somatic and autonomic nervous system are the two parts of the peripheral nervous system (PNS).  The somatic nervous system is known as the voluntary nervous system and the autonomic nervous system is known as the involuntary nervous system. The main difference between somatic and autonomic nervous system is that somatic nervous system is involved in controlling voluntary muscular movements whereas the autonomic nervous system is involved in controlling involuntary muscular movements in the body

Key Areas Covered

1. What is Somatic Nervous System
      – Definition, Features, Types, Function
2. What is Autonomic Nervous System
      – Definition, Features, Types, Function
3. What are the Similarities Between Somatic and Peripheral Nervous System
      – Outline of Common Features
4. What is the Difference Between Somatic and Autonomic Nervous System
      – Comparison of Key Differences

Key terms: Afferent Neurons, Autonomic Nervous System (ANS), Cranial Nerves, Efferent Neurons, Involuntary Nervous System, Parasympathetic Nervous System, Reflex Arcs, Somatic Nervous System (SONS), Spinal nerves, Sympathetic Nervous System, Voluntary Nervous System

What is Somatic Nervous System

The somatic nervous system (SONS), also known as voluntary nervous system,  is a part of PNS and is involved in controlling the voluntary muscular movements of the body. It controls the skeletal muscles in the body according to the stimuli obtained from the sensory receptors of the body. On that account, the somatic nervous system is composed of both afferent and efferent nerves. The afferent neurons are responsible for carrying information from sensory receptors to the central nervous system. The efferent neurons are responsible for carrying information from the central nervous system to the effector organs. The afferent and efferent neurons are connected by interneurons at the central nervous system. The somatic nervous system is composed of two parts: cranial nerves and spinal nerves. The cranial nerves carry nerve impulses in and out of the brain. The spinal nerves carry nerve impulses in and out of the spinal cord. 

In addition to controlling voluntary muscular movements, the somatic nervous system is also involved in controlling involuntary muscular movements called reflex arcs. In reflex arcs, the skeletal muscles work without coordinating with the central nervous system. The nerve pathways of the reflex arcs are connected to the spinal cord. There are two types of reflex arcs: autonomic reflex arcs and somatic reflex arcs. The autonomic reflex arcs control the involuntary actions of organs while somatic reflex arcs control that of skeletal muscles. The knee reflex is shown in figure 1.

Figure 1: Knee Reflex

What is Autonomic Nervous System

The autonomic nervous system (ANS) is another part of PNS, controlling the involuntary muscular movements of the body. The autonomic nervous system controls the muscular movements of the heart and other smooth muscle movements in the stomach, intestine, liver, kidney, lungs, and blood vessels as well as the glands such as sweat, salivary, and digestive glands. Thus, the autonomic nervous system controls the blood pressure, heart beat, digestion, metabolism, body temperature, urination, and homeostasis. The innervation of the autonomic nervous system is shown in figure 2.

Figure 2: Innervation of the autonomic nervous system

The two components of the autonomic nervous system are sympathetic nervous system and parasympathetic nervous system. Sympathetic and parasympathetic nervous systems have opposite effects on the above-mentioned processes. The sympathetic nervous system prepares the body for fight-or-flight response under stressful conditions. Thus, the heart rate is increased, airways are dilated, and the energy-demanding processes such as digestion and urination are stopped. The parasympathetic nervous system maintains the body at rest. It decreases the blood pressure and heart rate while inducing the secretion, digestion, and urination.  

Similarities Between Somatic and Autonomic Nervous System

• Both somatic and autonomic nervous systems are two components of the peripheral nervous system.
• Both somatic and autonomic nervous systems are involved in controlling muscular movements of the body.

Difference Between Somatic and Autonomic Nervous System

Definition

Somatic Nervous System: The somatic nervous system is the part of the nervous system which controls the voluntary movements in the body

Autonomic Nervous System: The autonomic nervous system is the part of the nervous system which regulates the involuntary movements in the body.

Known as

Somatic Nervous System: This is also known as the voluntary nervous system.

Autonomic Nervous System: This is also known as the involuntary nervous system.

Innervation

Somatic Nervous System: This innervates the voluntary skeletal muscles.

Autonomic Nervous System: This innervates involuntary smooth muscles, cardiac muscles, and glands.

Stimuli

Somatic Nervous System: Smell, noise, taste, light, touch, pain, and temperature are the sensory stimuli detected by the somatic nervous system.

Autonomic Nervous System: The blood pressure, salinity, and pH are the sensory stimuli detected by the autonomic nervous system.

Excitatory/Inhibitory Response

Somatic Nervous System: The somatic nervous system always causes the excitatory response at the effector.

Autonomic Nervous System: The autonomic nervous system may cause either excitatory or inhibitory response at the effector.

Neurotransmitter

Somatic Nervous System: The somatic nervous system releases acetylcholine at the effector.

Autonomic Nervous System: The autonomic nervous system releases acetylcholine or norepinephrine at the effector.

Number of Neurons in the Efferent Path

Somatic Nervous System: The somatic nervous system is composed of a single neuron between the CNS and the effector organ.

Autonomic Nervous System: The autonomic nervous system is composed of two neurons with a single synapse between the CNS and the effector organ.

Structure of Nerve Fibers

Somatic Nervous System: This is composed of thick myelinated nerve fibers.

Autonomic Nervous System: This is composed of both thin and thick myelinated nerve fibers.

Branches

Somatic Nervous System: Spinal and cranial nerves are the two branches of the somatic nervous system.

Autonomic Nervous System: Sympathetic and parasympathetic nerves are the two branches of the autonomic nervous system.

Functions

Somatic Nervous System: Posture and movement are the functions of the somatic nervous system.

Autonomic Nervous System: Visceral functions such as secretion and control of metabolism are the functions of the autonomic nervous system.

Conclusion

Somatic and autonomic nervous systems are two components of the peripheral nervous system of the body. Both nervous systems are involved in controlling the functions of the body based on the internal and external stimuli. The somatic nervous system is composed of spinal and cranial nerves. The autonomic nervous system is composed of sympathetic and parasympathetic nervous systems. The somatic nervous system controls the voluntary muscular movements and the reflex arcs. The autonomic nervous system controls the involuntary movements of the body. Thus, the main difference between somatic and autonomic nervous systems is the type of movements controlled by each of them.

Reference:

1.” Somatic Nervous System: Definition, Function & Example.” Study.com. N.p., n.d. Web. Available here. 03 July 2017. 
2. Kendra Cherry. “What Is the Somatic Nervous System?” Verywell. N.p., n.d. Web. Available here. 03 July 2017. 
3. “Overview of the Autonomic Nervous System – Brain, Spinal Cord, and Nerve Disorders.” MSD Manual Consumer Version. N.p., n.d. Web. Available here. 04 July 2017.

Image Courtesy:

1. “Patellar-knee-reflex” By ChristinaT3 at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “1503 Connections of the Parasympathetic Nervous System” By OpenStax College – Anatomy & Physiology, Connexions Web site. June 19, 2013. (CC BY 3.0) via Commons Wikimedia