What is the Difference Between CNS and ANS

The main difference between CNS and ANS is that CNS is one of the two main divisions of the nervous system, whereas ANS is one of the two divisions of the PNS.  The other division of the nervous system is the peripheral nervous system (PNS) while the other division of the PNS is the somatic nervous system. Furthermore, CNS is composed of the brain and the spinal cord, while ANS is composed of sympathetic, parasympathetic, and enteric nervous systems. 

CNS (central nervous system) and ANS (autonomic nervous system) are two divisions of the nervous system. Generally, they are responsible for regulating the functions of the body by responding to both internal and external stimuli. The main function of CNS is to receive sensory output from the PNS, process and send necessary information to the various parts of the body through the PNS while the main function of the ANS is to control involuntary functions of the body including the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal.  

Key Areas Covered 

1. What is CNS
     – Definition, Structure, Function
2. What is ANS
     – Definition, Structure, Function
3. What are the Similarities Between CNS and ANS
     – Outline of Common Features
4. What is the Difference Between CNS and ANS
     – Comparison of Key Differences

Key Terms 

ANS, Brain, CNS, Enteric, Nervous System, Parasympathetic, PNS, Spinal Cord, Sympathetic

What is CNS 

CNS (central nervous system) is one of the two main divisions of the nervous system of vertebrates. However, the second main division of the nervous system is the peripheral nervous system (PNS). The two main components of the CNS include the brain and the spinal cord. The brain occurs inside the cranial cavity or the skull while the spinal cord occurs inside the spinal canal or the vertebral column. Moreover, both brain and spinal cord are made up of gray and white matter. Generally, gray matter consists of neurons and unmyalinated fibers, while white matter consists of axons and oligodendrocytes. 

Figure 1: Organization of the Nervous System

Furthermore, cranial nerves start from the brain while spinal nerves start from the spinal cord. Both cranial and spinal nerves are continuous with the peripheral nervous system. Moreover, the main function of the brain includes recieval of the sensory inputs through the sensory neurons of the PNS, followed by the processing and sending information to the effector organs through the motor neurons of the PNS. Also, the brain is responsible for storing memories while generating thoughts and emotions. On the other hand, the main function of the spinal cord is to conduct nerve impulses in and out of the brain. It also controls reflex activities. 

What is ANS 

ANS (autonomic nervous system) is one of the two divisions of the motor neurons of the PNS. In contrast, the second motor neuron division of PNS is the somatic nervous system responsible for controlling the voluntary movements of the body. Furthermore, the main function of ANS is to control the involuntary movements of the body, influencing the functions of the internal organs. Primarily, these functions include controlling the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal.

Figure 2: ANS Functions

Moreover, the three components of the ANS include sympathetic, parasympathetic, and enteric nervous systems. The main function of the sympathetic nervous system is to prepare the body for “fight or flight” system. In contrast, the parasympathetic nervous system is the opposite of the sympathetic nervous system, preparing the body for the “rest and digest” system. Meanwhile, the enteric nervous system is the nervous system of the digestive system. It regulates the secretions of the gut, sensing both chemical and mechanical changes of the gut, and controlling peristalsis, which is the contraction and relaxation of muscles of the intestine. 

Similarities Between CNS and ANS 

• CNS and ANS are two divisions of the nervous system of vertebrates.  
• They are made up of neurons. That means; both the structural and the functional unit of them is the neuron.  
• Their main function is to regulate the functions of the body based on the internal and external stimuli.  
• Both can take part in the regulation of the involuntary functions of the body. 

Difference Between CNS and ANS 

Definition 

CNS (central nervous system) refers to the part of the nervous system, consisting of the brain and the spinal cord, while ANS (autonomic nervous system) refers to the part of the nervous system responsible for the coordination of involuntary functions of the body. 

Divisions 

Moreover, CNS is one of the two main divisions of the nervous system, while ANS is one of the two divisions of the PNS. 

Occurrence 

CNS occurs in the dorsal body cavity while ANS occurs in the periphery of the body. 

Components 

The two components of the CNS are the brain and the spinal cord, while the three components of the ANS are the sympathetic, parasympathetic, and enteric nervous systems. 

Function  

The main function of CNS is to receive sensory output from the PNS, process and send necessary information to the various parts of the body through the PNS while the main function of the ANS is to control involuntary functions of the body including the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal.  

Conclusion 

CNS is one of the two main divisions of the nervous system while the second being the PNS. The two main components of the CNS are the brain and the spinal cord. The main function of CNS is to receive sensory inputs and send processed information to the corresponding parts of the body through PNS. In contrast, ANS is one of the two divisions of the PNS. However, the main function of ANS is to control the involuntary functions of the body. Moreover, the three components of ANS include the sympathetic, parasympathetic, and enteric nervous system. Therefore, the main difference between CNS and ANS is their division and function. 

References:

1. “The Nervous System.” The Nervous System, Changing Works, Available Here.

Image Courtesy:

1. “1205 Somatic Autonomic Enteric StructuresN” By OpenStax (CC BY 4.0) via Commons Wikimedia   
2. “The Autonomic Nervous System” By Geo-Science-International – Own work (CC0) via Commons Wikimedia