Neurology is the study of neurons and their functions within the nervous system. Neurons are specially designed cells that transmit and receive messages enabling the body to perform tasks. Neurons consist of dendrites, cell body (or soma), and an axon. Dendrite comes from the latin word for tree as they branch out to make connections with other neurons. Dendrites create a graded potential when neurotransmitter substance opens chemically gated channels to receive incoming messages. If the signal is strong enough it will reach the neuron's threshold (in most cells it is about 70mv) and create an action potential by opening valtage gatted channels and the neuron is said to 'fire'. A neuron will either fire or it will not - this is the all-or-none law. If a neuron reaches threshold it will fire the same electrical energy every time. Normally a neuron has an overall negative charge. However when an action potential is created, sodium ions rush into the cell giving it a temporary positive charge. The electrical sign travels down the axon where it reaches the synapse. The synapse consists of the axon terminal of one neuron, the receptors on the dendrite or cell body of another neuron and the space between them (called the synaptic cleft). When the electrical signal reaches the axon terminal the energy is converted from electrical to chemical. A chemical neurotransmitter is released into the synapse where it will stimulate receptors on a postsynaptic neuron. Neurotransmitter fits into receptors like a lock and key - only specific neurotransmitter will stimulate a particular receptor. Examples of common neurotransmitter include dopamine, serotonin or acetylcholine.