Peripheral nerves are a group of axons bundled together in the form of an electric cable. It conducts efferent (motor) signals from cells in the anterior horn of the spinal cord to a particular muscle or group of muscles, and afferent (sensory) signals from peripheral receptors via cells in the posterior root ganglia to the spinal cord. Humans have a total of 31 pairs of spinal nerves, which connect with all the skin and muscles of the limbs and trunk. Before supplying to the limbs, these nerves may form a particular arrangement called plexus (brachial plexus for the upper limb and lumbar plexus for the lower limb).