Have you ever thought how can you feel the various sensations, react to pain or a tickle, how can you instantly solve a simple mathematical problem, how can you cry when you are sad and laugh when you are happy? Well, the nervous system helps you experience all these sensations and emotions. It determines your emotional responses. Nerves detect the changes that take place in the internal and external environment. They collect information, transmit it to the brain and then transmit the message from the brain to the effector organs, so that the person can respond to the changes. The nervous system is responsible for your reactions during any situation. It generates and sends electrochemical impulses through nerves to all bodily organs. The effector organs like muscles contract or relax and the glands release or stop the release of hormones/enzymes as they receive the messages from the brain. The brain, spinal cord, retina, sensory neurons, ganglia, and the nerves are the organs of the nervous system. Central Nervous System (CNS) and Peripheral Nervous System (PNS) are the two main divisions of the human nervous system. The CNS consists of the brain, spinal cord and the retina. The PNS consists of sensory neurons, ganglia (clusters of neurons), and the nerves that collect and transfer information to and from the brain. The highly specialized nerve cells called neurons are capable of transmitting the information in chemical and electrical form from the brain to the body and vice versa. The dendrites, the cell body and the axon are the three important parts of a neuron. A neuron meets another neuron at a special junction called synapse, where certain chemicals (neurotransmitters) fill in the gap between the two neurons and help transmit the message. Apart from the neurons, the nervous system contains glial cells which provide support and nutrition to the system. These cells help maintain the health of the neurons and also aid in message transmission. The main organs of the nervous system, that is the brain and the spinal cord form the central nervous system. Brain The brain is one of the most important organs in the human body system. It is the center of all commands. It monitors all the conscious and unconscious processes of the body. The brain coordinates various organs of the body and controls all the voluntary movements in the body. The brain is the organ that helps you remember things, learn, understand, think, create, talk, hear, taste, etc. The brain is divided into three segments, that is, fore brain, mid brain and the hind brain. The fore brain consists of the cerebral hemispheres and olfactory lobes. The mid brain is the region that mostly contains optic lobes, and the hind brain is the region that includes the cerebellum and the medulla oblongata. The pituitary gland is present in the lower side of the fore brain. It is called the 'master gland' as it regulates the function of many other glands in the body. Spinal Cord The spinal cord is a bundle of nerves that run down the back from the brain in the spinal column. The spinal cord is about 40 cm in length and as wide as the thumb. The function of the spinal cord is to relay all the impulses, information and sensations from all around the body, internally and externally, to the brain. If the spinal cord gets affected due to an injury, it may sever some or most of the connections between the brain and other parts of the body, leading to paralysis in different parts of the body like the upper and lower limbs. The peripheral nervous system consists of the nerves that lie outside the brain and the spinal cord. These nerves carry impulses like sensations and information from the body to the spinal cord and from the spinal cord to the body. Thus, the peripheral nervous system connects the CNS to the muscles of the body. Nerves The 31 pairs of spinal nerves branch off and reach out to different parts of the body and perform different functions. The nerves of the cervical region supply information to the back of the head, neck, shoulders, arms, hands and the diaphragm. The nerves of the thoracic region supply information to the chest and some parts of the abdomen. The lumbar region nerves cover the lower back, parts of the thighs and the legs. The nerves of the sacral region provide information to the buttocks, most of the leg, feet, anal and genital area. Somatic and Autonomic Nervous System The PNS is further divided into the somatic nervous system and the autonomic nervous system. The somatic nervous system contains sensory (afferent) neurons that carry information from organs/muscles to the CNS, and motor (efferent) neurons that carry information from the brain and spinal cord to muscles of the body. Sensory neurons provide the brain all the information regarding the environment. The somatic nervous system plays an important role in transmitting the information and controlling voluntary movement. Sympathetic and Parasympathetic Nervous System The autonomic system regulates the involuntary body functions like respiration, heartbeat, blood flow and digestion. It is further subdivided into the sympathetic nervous system which regulates your flight-or-fight responses, and the parasympathetic system that helps regulate various normal functions of the body, for example, sexual arousal, salivation, lacrimation (shedding tears), urination, digestion, and defecation. Functions of the parasympathetic nerves include constriction of eye pupils, increase in secretion of saliva, increased digestion, decrease in heartbeat, etc. The sympathetic nerve functions involve dilation of eye pupils, sweating, production of goose bumps, decrease in digestion, etc. One of the important nerves, the vagus nerve is divided into sympathetic and parasympathetic nerves. The sensory system is also a part of the nervous system. Sensory systems for vision, hearing, somatic sensation (touch), taste and olfaction (smell) work with the help of the sensory receptors, neural pathways and certain parts in the brain that help process sensory information. When you feel cold or hot, it is the sensory neurons that are doing their work. The motor neurons are reactors, that help the body react to different environment. For example, the immediate pulling away of your hand when you touch a hot stove is a motor neuron reaction. The somatic motor neurons convey orders to the muscles. A subsystem of the peripheral nervous system is the enteric nervous system. Normally, it communicates with the CNS but studies show that it works autonomously too. It regulates the gastrointestinal system in the body. The nervous system is a complex and complicated network of nerves and neurons running throughout the body that send each and every minute detail of the surrounding and environment to the brain and bring back instant message to the concerned part. There are innumerable problems associated with the nervous system organs and functions. Damage to any part of the nervous system can result in many disorders like paralysis, memory loss, blindness, loss of motor skills or speaking ability, hearing loss, coma, etc.