Axons are extended regions of the neuron cell membrane. It starts from a portion of the cell body, known as the axon hillock. From there, the axon extends towards the target cell to what is known as the terminal. Along the cell membrane of the axon will be ion channels and ATP-driven pumps that will regulate ion concentrations within the axon. These ion concentrations will establish the resting membrane potential, which is the electrochemical charge of the membrane when the neuron is at rest. The function of the axon is to transmit information to different neurons, muscles and glands. In certain sensory neurons (pseudounipolar neurons), such as those for touch and warmth, the electrical impulse travels along an axon from the periphery to the cell body, and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction causes many inherited and acquired neurological disorders which can affect both the peripheral and central neurons. The neuron sends electrical impulses from its cell body through the axon to target cells. Each nerve cell has one axon. An axon can be over 20 cm (a foot) in length, which for the human body is remarkably long. Axons make contact with other cells—usually other neurons but sometimes muscle or gland cells—at junctions called synapses. At a synapse, the membrane of the axon closely adjoins the membrane of the target cell, and special molecular structures serve to transmit electrical or electrochemical signals across the gap. Some synaptic junctions appear partway along an axon as it extends—these are called en passant (“in passing”) synapses. Other synapses appear as terminals at the ends of axonal branches. A single axon, with all its branches taken together, can innervate multiple parts of the brain and generate thousands of synaptic terminals.