Introduction The nervous system is made up of cells. Various receptors and effectors in different parts connect these cells. The nervous system consists of two parts, including the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is divided into the brain and the spinal cord. The PNS consists of the nerves that link the CNS to receptors and effectors in the body. The nerves that emanate from the brain are referred to as cranial nerves while those that emanate from the spinal cord are referred to as spinal nerves. The nerve cell The nerve cells play a critical role in the body system. They consist of structural and functional units. They are charged with the responsibility of circulating impulses within the body. The human body has three types of neurons, including motor, sensory, and intermediate neurons. Each type has a specific function. Motor Neurons They transmit impulses from the CNS to the effectors. Its structure consists of a cell body whose cytoplasm and the nucleus are surrounded by a cell membrane. Dendrons emanate from the cell body forming dendrites, which look like filaments. Dendrites receive impulses from the neurons and transmit them to the cell body. At the opposite end of dendrites is the axon, which is also referred to as the nerve fiber. An axon transmits impulses from the body to a muscle or a gland. The myelin sheath covers the axon and is an electrical insulator as it enhances the speed at which the impulse moves along the axon. The sheath has the nodes of Ranvier that also perform similar duties. Sensory neurons They transmit impulses from receptors to the CNS. Most parts of the sensory neuron are located in a peripheral nerve, with a small portion of dendrites found in the CNS. Intermediate Neurons They link the sensory and motor neurons. This role gives them a different name. They are found in the brain and the spinal cord. They also do not have a myelin sheath. Their structures differ as they emanate from different parts of the CNS. The nerve impulse The impulse transmitted by a nerve fiber is electric in nature. A nerve cell has an electric gradient between the outer and the inner surface. The internal surface contains negative electrons and the external surface contains positive electrons. Upon stimulation, the inner membrane becomes positive and the outer membrane becomes negative. The membrane becomes depolarized. The change is short-lived since the environment keeps changing hence creating an action potential (Starr and McMillan 14). The movement of sodium and potassium ions in and out of the cell respectively controls this state. Potassium ions are found in plenty in the internal surface, as sodium ions are many in the external surface. Permeability of the cell membrane increases when the cell is stimulated causing the movement of ions across the cell. This causes polarization and depolarization, which in turn have tremendous effects to the functioning of the central nervous system. The changes consist of the action potential. The events on one part of a cell membrane stimulate the adjacent part whose permeability properties also change. This leads to the formation of another action potential. The result leads to t