Here is your answer! I hope you like it and please let me know if you need further clarification on either of the answers. They are both longer than 250 words, but I included some information at the cellular level, which I wasn't sure if you wanted or not. My source was a general biology textbook.
1. The three major functions of the nervous system are sensory input, integration, and motor output. There are several divisions of the nervous system that are specialized in order to carry out one of the three major functions. At the cellular level, the nervous system is made up of neurons and supporting cells called glia (which include cells such as Schwann cells and oligodendrocytes). Neurons conduct the impulses throughout the nervous system, from one location of the body to another. Neurons have processes such as dendrites, which convey signals from the process' tip to the rest of the neuron, and axons, which convey signals from the neuron to the tip of the process. In addition, axons are insulated by a myelin sheath, which is created by the supporting cells. Sensory neurons communicate to the body about the external and internal environment, such as feeling pain. Motor neurons convey impulses from the central nervous system to the rest of the body and illicit actions, such as moving a muscle.
At the tissue level, there are clusters of nerve bodies arranged in ganglia outside of the CNS, and in the brain are called nuclei. The nervous system is divided into two main systems, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and the spinal cord, while the PNS includes the rest of the body. The CNS is made up of bundles, which is just multiple neurons with myelinated sheaths that give the bundled appearance. The PNS has paired cranial and spinal nerves and associated ganglia (as mentioned above). The spinal nerves originate in the spinal cord and are able to convey information with the rest of the body. As mentioned above, the PNS includes sensory and motor divisions. In addition, the motor division is divided into the somatic system, which responds to external stimuli, and the autonomic system, which is involuntary and regulates the internal environment of the organism.
2. The spinal cord is part of the CNS and is attached to the base of the brain and runs through the vertebral column (spine). The function of the spinal cord is to integrate responses from stimuli and to convey information to and from the brain to or from the rest of the body. The spinal cord has white and gray matter, which is due to the location of different cell types. The white matter mostly contains the bundles, or tracts, of myelinated axons of neurons and is located towards the outside of the spinal cord. The tracts are separated based on function and whether or not they are associated with sensory or motor action. For example, motor tracts are descending in the spinal cord and from the center towards the outside of the spinal cord the tracts are associated from the arms to the feet. Sensory tracts are ascending in the spinal cord and are arranged in a similar manner to the motor tracts. In addition, the tracts are arranged in mirror images corresponding to the right or left side of the body, with mostly motor tracts located ventrally and sensory tracts located dorsally. Therefore, sensory or motor information on the right side of the body will be conveyed through the sensory or motor tract on the same side of the spinal cord. The gray matter mostly contains neuron cell bodies, dendrites and unmyelinated neurons and is typically located near the center of the spinal cord. In the very center of the spinal cord is the central canal, which is filled with cerebrospinal fluid that is continuous with the ventricles in the brain. This fluid conveys the nutrients, hormones, and white blood cells across the blood-brain barrier to the brain, and is also a shock absorber.
Campbell, N. A., Reece, J. B., Mitchell, L. G. (1999). Biology. 5th Edition. Benjamin Cummings. Menlo Park, CA.