Nervous System

neurons with black background

The nervous system is the body’s speedy electrochemical communication network. It consists of nerve cells within the peripheral and central nervous systems. 

Central Nervous System (CNS) 

The central nervous system includes the brain and spinal cord, which contain neural networks: brain neurons that cluster into work groups. The spinal cord acts as a two way information highway connecting sensory organs and the brain. Sensory information ascends up the spinal cord, while descending neural fibers send back motor control information to the muscles in the body. 

One of the most important functions of the central nervous system is reflexes, which are simple, automatic responses to a sensory stimulus. For instance, a pain reflex is demonstrated when one’s hand touches a flame. As the brain receives the stimulus, it responds by causing the hand to jerk away. Reflexes are composed of sensory and motor neurons that communicate between interneurons. 

There are many types of neurons, including sensory, motor, and interneurons. Sensory neurons carry incoming info from the sensory receptors to the brain and spinal cord. In contrast, motor neurons carry outgoing ingo from the brain and spinal cord to the muscles and glands. Finally, interneurons are located within the brain and spinal cord, communicate internally, and intervene between the sensory inputs and motor outputs. Nerves also play an important role in the nervous system as they form neural “cables” connecting the central nervous system with muscles, glands, and sense organs. 

Peripheral Nervous System (PNS)

The peripheral nervous system is amde up of the sensory and motor neurons that connect the CNS to the rest of the body. One part of the peripheral nervous system is the somatic nervous system, which is the division of the peripheral nervous system that controls the voluntary movement of skeletal muscles. 

Another branch of the peripheral nervous system is the autonomic nervous system, which controls the glands and the muscles of the internal organs. The autonomic nervous system controls self regulated actions, and is divided between the sympathetic nervous system and the parasympathetic nervous system. 

The sympathetic nervous system arouses the body, mobilizing energy in stressful situations. This includes accelerated heartbeat, increased blood pressure, perspiration, and dilated pupils. All of these responses occur automatically by the body in order to be prepared to face some kind of stressful, exciting, or fearful experience. 

In contrast, the parasympathetic nervous system calms the body in order to conserve its energy. For instance, the parasympathetic nervous system contrasts pupils, slows heartbeat, and decreases blood pressure. 

The sympathetic nervous system “turns off” bodily functions not necessary to survival at the moment of stress, such as digestion. Once the stres is alleviated the parasympathetic nervous system stimulates digestion, contracts the bladder, and continues other processes in the body. 

Overall, the nervous system is crucial to our survival as it controls our voluntary and automatic responses to the world around us. 


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