The nervous system is classified as the central nervous system (CNS) and peripheral nervous system (PNS). The former includes the spinal cord, brain and nerve network. The latter comprises the whole network of nerves in the entire body. The PNS is divided in to somatic nervous system and autonomic nervous system. These two systems comprise the nerve network which does not include the spinal cord or the brain.
The somatic nervous system is in charge of allowing us to feel the external stimuli and for the voluntary movements of our body. The nerves in the five sense organs; ears, nose, eyes, skin and tongue are part of and regulated by the somatic nervous system. Some such voluntary movements are moving a finger or leg. Somatic nervous system controls the passage of signals from the peripheral nervous system to the different muscles in the body. This movement is regulated by the will of the individual and hence termed voluntary action. The input signals from the sensory nerves are transferred by these somatic nerves to the brain where they are interpreted. Typical examples include the taste we experience or the feel when we touch something.
The autonomic nervous system controls involuntary processes in our body like breathing, perspiration, heart rate and blinking. This system is again comprised of the parasympathetic and sympathetic nervous systems.
The functioning of the body involuntarily when it is in a state of rest is controlled by parasympathetic nervous system. Some examples are digestion, salivation and arousal for sex. The action termed as flight or fight is controlled by the sympathetic nervous system .These actions are performed by the body involuntarily when the body is alert or as a response to stress.
The somatic and autonomic nervous systems are comprised of two types of neurons which enable transmission of signal to and from our brain. The sensory neurons receive external stimuli and transfer them to the brain and spinal cord through afferent neurons. After interpretation in the brain, the response signal is transmitted to the targeted muscles through efferent or motor neurons.
Another part of the parasympathetic nervous system is the enteric system. This network of nerves is responsible for the control of all aspects related to digestion. All the systems comprising the digestive tract starting from the esophagus to the large intestine are part of the enteric system. Digestion is an involuntary process which is the reason for enteric system to be categorized as part of the autonomic nervous system.
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