The nervous system has main two parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS contains the brain and spinal cord, while the PNS has the outer nerves and is further divided into the somatic nervous system and autonomic nervous system. The autonomic nervous system also has three parts: sympathetic nervous system, parasympathetic nervous system and enteric nervous system. The brain is the center of the CNS and is integral in the three basic functions of the nervous system: receiving sensory input, processing it and responding to the stimulus, according to Maricopa Community Colleges.
Neurons
The basis of the nervous system in the brain is the neuron. The University of Washington states that the human brain contains about 100 billion nerve cells. Each neuron is made up of three basic parts: dendrite, cell body and axon. Dendrites receive the electrical signal, which sends the information throughout the brain. The cell body, also called the soma, is the center of the neuron and contains the nucleus, which has the genetic material of the cell. The axon is the pathway of the neuron and is where the electrical signal travels; the axon is covered with myelin sheath, made up of oligodendrocytes, that protects the signals. When the electrical signal reaches the end of the axon, it is transmitted via the terminal button to another neuron's dendrites.
Brain Hemispheres and Lobes
The brain is divided into the right and left hemispheres. Each hemisphere has four lobes--frontal, temporal, parietal and occipital--however, each hemisphere has specialized functions. For example, the left hemisphere contains the language regions of the brain, while the right hemisphere deals with visual imagery. Below the occipital lobe is the cerebellum, which is the coordination center. The different lobes of the brain are responsible for integrating the information gathered from the sensory input. For example, if the sensory nerve in your peripheral nervous system detects pain from a hot surface, the information is sent to the somatosensory cortex to identify the pain, according to Mayo Clinic, and then that information is sent back through the motor nerve to move your hand away from the hot surface.
Brain Stem and Spinal Cord
The bottom-most part of the brain, the brain stem is responsible for essential functions of the body, such as breathing and heart rate. The brain stem is also the connection between the brain and the spinal cord, which is the other part of the central nervous system. The University of Washington states that the spinal cord has five parts with multiple segments: eight cervical segments, 12 thoracic, five lumbar, five sacral and one coccygeal. The spinal cord also is a relay between the CNS and the PNS. It sends the sensory information into the brain and the motor information out to the rest of the body.
