A nerve consists of many bundles of nerve fibers, surrounded by connective tissue (endo- and epineurium). The thicker the myelin sheath, the faster and better signals can be conducted. According to the function of the fibers, there are different types of nerves: Motor nerves - sensory nerves - mixed nerves. They can also be classified according to their origin: Cranial nerves, that directly originate from the brain - Spinal nerves, that originate from the spinal cord. Nerve cells are responsible for conduction and processing of nerval impulses (excitations). The information is encoded as changes of the electric potential. By opening ion channels of the cell membrane, ions can flow in or out, which changes the charge of the cell. This change is conducted passively or via action potentials, and passed on to other nerves via synapses. A nerve is a bundle of thousands of nerve fibers. Afferent fibers run from receptors of sensory organs to the CNS, efferent fibers run from the CNS to effectors (muscles, glands). The path of conduction doesn`t have to include the CNS: Local reflex arcs can process information very quickly.