Nervous System

All living organisms adapt to the situation they are put into. This adaptation is one of the key points in distinguishing a living being from a non-living being. One of the ways an organism adapts to the surrounding is by responding to the stimuli. The nervous system is the interface between the surroundings and the interaction of the organism. The nervous system performs coordination of actions and sensory information by giving and receiving information to and from the different parts of the body. The parts of the nervous system are the central and peripheral nervous systems. They help with proper step-by-step coordination between the different bodily responses and messages from the body parts to the brain and return. The central and peripheral nervous systems are made up of various small units of the signaling system called neurons. Neurons are further divided into sensory neurons, motor neurons, interneurons, etc. The brain communicates with and instructs the various parts of the body with the help of electrical signals. 

The Basics of Nervous System 

The nervous system is divided into the peripheral nervous and system central nervous system. The central nervous system is further divided into the brain and spinal cord. The peripheral nervous system encompasses the nerve cells outside the central nervous system. The central and peripheral nervous systems are protected by a hard internal skeleton like the skull and vertebral column to minimize any effect from trauma due to accidents. Any injury to the brain or spinal cord can lead to irreversible effects on the body; things like paralysis are common in case of a severe impact on the central nervous system. 

The peripheral nervous system consists of neurons transferring signals between the different parts of the body and the central nervous system. The neurons from the peripheral nervous system are not protected as the central nervous system is. The nervous tissue consists of neurons that help in carrying messages between the central nervous system and parts of the body. It also consists of glial cells that help providing nutrition, maintenance of homeostasis, and so on. The glial cells also help restore the protective myelin sheath, which is a fatty substance surrounding the neuronal axon in the event of wear and tear. 

The nervous cells or neurons are cells with all the functional properties similar to other cells from the body. However, they have different structural features. These structural properties differ between different types of nerve cells too. The neurons are further classified into unipolar, bipolar, pseudounipolar, and multipolar; this classification is based on the structure. They can be classified into sensory neurons, motor neurons, interneurons, and neurons in the brain; this classification is based on the location of the neuron and the function it serves. 

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Evolutionary Study of the Nervous System

All animals that are more complex than Porifera like sponges have a nervous system. In Porifera or other simpler animals, an elementary intercellular communication is discovered. This signaling mechanism is regarded as the primitive way of communication between the cells in the early embryonic stage too. In animals with radial symmetry like hydra and jellyfish, the nervous system is made up of a nerve net, which is a diffuse network of isolated cells. 

All animals with bilateral symmetry share a common structure of the nervous system, which originated over 550 million years ago in the Ediacaran period. This is regarded as evidence of the organic evolution of all lifeforms. The brain, as the most important part of the nervous system, too shows consistency in the evolutionary advancement of every class of the subphylum Vertebrata. Therefore, animals from the classes viz Pieces, Amphibia, Reptilia, and then Mammalia and Aves have more complex brains in ascending order. 

Brain

The brain is the most complex organ in a higher organism; particularly in vertebrates. Unlike invertebrates, the brain in vertebrates serves more complex functions in terms of movements and other bodily functions in response to the organism’s surroundings. The brain in human beings is divided into two hemispheres, and each hemisphere is divided into the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. These lobes are present on either side of the brain. Some classifications divide the anatomical parts of the brain into forebrain, midbrain, and hindbrain. 

Spinal Cord

The spinal cord is the secondary part of the central nervous system in vertebrates. It is enclosed within the structure of the body (vertebral column) covered by cerebrospinal fluid. It is the mediator between the brain and the peripheral nervous system.