 Dear students, in this module we shall discuss the methods of transmission of signals in the nervous system. The neuronal signals are transmitted in the nervous system in two forms. The first method is the graded, electrotonically conducted potentials and the second form is in the form of action potentials. Dear students, a signal is coded alternately in these two forms that is graded potentials and action potentials. The graded potentials are produced for short distance conduction at the sensory and post synaptic membranes, while action potentials are generated for long distance conduction along the axons. This coding also involves interconversion of electrical and chemical methods at synapses. We shall take an example in which a stimulus is received by a receptor organ at its sensory neuron as a result a signal is generated which is transmitted through the neuron into the other components of nervous system. When a stimulus is received at the receptor endings of sensory neuron, a depolarization that is a change in membrane potential occurs. This change happens in proportion to the strength of the stimulus. This potential change at the receptor side is known as receptor potential. This receptor potential is graded potential because it varies in a continuous fashion. Dear students, the time course and amplitude of a receptor potential are closely related to the time course and intensity of the stimulus. So the receptor potential is an electrical neuronal analog of the stimulus. After receiving the signal, the signal spreads away from the receptor side passively through electronic conduction to the cell body part of the neuron. However, this signal decays over a relatively shorter distance. The decay happens because of the resistance of cytoplasm faced in the cell body as well as due to the reason that this part of the neuron does not contain voltage gated ion channels. So action potentials cannot be propagated or produced in this part of the sensory neuron. For distant transmission, if this signal has to be transmitted for a long time, then there are not many graded potentials for it. For this reason, regenerative action potentials are produced, which are produced at the spike initiating zone, that is the axon-heloc. Axon-heloc contains voltage-gated ion channels and this is the reason that action potentials can be initiated here. These action potentials can conduct signals without decrement for long distances when the signal reaches the axon terminals. It is transformed from electrically encoded signals into chemical signals in the form of neurotransmitter molecules. This chemical signal is then transmitted across the synapse to the next neuron. When the neurotransmitter reaches the next neuron, that is the post-synaptic neuron, it causes potential change in the post-synaptic cell. The change in membrane potential happens when the chemical signal is converted back into the electrical signal. This membrane potential generated in the post-synaptic neuron is known as post-synaptic potential. The post-synaptic signal or post-synaptic potential produces a graded signal that reflects the properties of the original stimulus, which initiated this process, which the receptor had received on the site and which generated the potential, post-synaptic potential is a potential change, which is graded. This graded post-synaptic potential again brings the spike initiating zone of post-synaptic cell to threshold, thereby triggering an action potential in the post-synaptic cell. In this way, if we look at it, the signal initiated from one cell has been transferred to another cell and during that time, it has moved on to electrical and chemical, both forms and in addition to this, the graded and regenerative action potential has moved on to both patterns. In this way, these signals move from the peripheral nervous system to the central nervous system.