Neurotransmitter

A chemical released from a nerve ending that transmits impulses from one neuron (nerve cell) to another neuron, or to a muscle cell. When a nerve impulse reaches a nerve ending, neurotransmitters are released from synaptic vesicles and cross a tiny gap (synapse) to reach the target cell. Here, they cause channels in the target cell to open, letting through charged particles that stimulate an impulse in the cell. Alternatively, neurotransmitters may inhibit nerve impulses. Scores of different chemicals fulfil this function in different parts of the nervous system. Many neurotransmitters act as both neurotransmitters and hormones, being released into the bloodstream to act on distant target cells. One of the most important neurotransmitters is acetylcholine, which causes skeletal muscles to contract when it is released by neurons connected to the muscles. Acetylcholine is also released by neurons that control the sweat glands and the heartbeat, and transmits messages between neurons in the brain and spinal cord. Another chemical, noradrenaline (norepinephrine), aids the nervous control of heartbeat, blood flow, and the body’s response to stress. Dopamine plays an important role in parts of the brain that control movement. Serotonin is one of the main neurotransmitters found in parts of the brain concerned with conscious processes. Another group of neurotransmitters is called the neuropeptides. This group includes the endorphins, which are used by the brain to control sensitivity to pain.