Summary
Nerve signals take the form of electrical signals, and are known as impulses. A neuron carries impulses in only one direction. This animation illustrates the propagation of the nerve signal through a single neuron, and its transmission from one neuron to another.Click on
to play the movie. Click on the magnifying glass to see some characteristics of the signal.
Learning goals
- To illustrate how nerve impulses travel in neurons, and from one neuron to another.
Learn more
Our 10 billion nerve cells transfer information using nerve signals, or impulses. The dendrites carry the signals toward the cell body. Then it can travel along a single axon attached to this cell body for long distances. At the synapses, the impulses can jump from one neuron to another, always in the same direction.The transmission of nerve signals is carried out by our ten billion neurons, which are themselves made up of a cell body from which extend dendrites and a single axon, the “cable” that carries the nerve message.The dendrites carry the signals toward the cell body. Then it can travel along a single axon attached to this cell body for long distances. The connections between neurons occur at the synapse that lies between the axon of one and a dendrite of the other.
The propagation of the nerve signal begins at the base of the cell body, and moves along the axon in the form of an electric impulse (the Action Potential). At the synapse, the message is transmitted from the pre-synaptic neuron to the post-synaptic neuron by chemical messengers known as neurotransmitters. These messengers permit the transmission of messages between neurons.
If electrodes are used to measure the nerve impulse at different points along the postsynaptic neuron, a series of identical action potentials is observed. The impulse conserves all of its properties (amplitude, frequency) during its progression through the axon. The postsynaptic potential depends on the neuron’s ability to integrate incoming signals, which are associated with variations in the concentration of ionic solutions. In effect, a single neuron receives information from its many neighbors by way of thousands of synapses – some excitatory and some inhibitory. The initiation of the Action Potential in such a neuron depends on its ability to integrate these multiple sources of excitation and inhibition. Excitatory and inhibitory synapses have opposite effects on the membrane potential of the postsynaptic neuron.
Once the incoming information is gathered, the neuron’s cell body sums up the nerve impulses coming from dendrites and from the cell body itself.
- If the threshold potential is reached, an action potential is created and neurotransmitters are released at the end of presynaptic neuron, and these carry the message to the postsynaptic neuron.
- If the threshold potential (-55mV) is not reached, the nerve message is not transmitted by the axon.
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