![]() ![]() This waiting period is known as the refractory period. After it fires, the neuron goes into a sleep mode temporarily, where its voltage cannot be increased no matter how many incoming synapses are excited. This firing is known as an action potential, and it is what is responsible for the neuron sending signals to other neurons. When the voltage of a neuron has increased beyond a certain level (due to repeated excitation through incoming synapses), the neuron “fires” a signal pulse down its axon and resets its voltage back to normal values. A synapse with neurotransmitters which decrease the voltage is called an inhibitory synapse. A synapse with neurotransmitters which increase the voltage of the receiving neuron is called an activating synapse. This neurotransmitter excites the dendrite which causes it to slightly increase or decrease the voltage inside neuron B. ![]() At the synapse, this electrical signal causes the axon to release a chemical, called a neurotransmitter, which crosses the synaptic junction to a dendrite of neuron B. Instead, neuron A will send an electrical signal down its axon to the tips of the axonal arborization, where the synapses are located. However, neurons are not actually electrically connected at the synapses. Neurons send electrical signals to one another. The connection between the axonal branch and the dendrite is known as a synapse. A neuron A connects to another neuron B by attaching an axonal branch to the dendrite of neuron B. ![]() Certain other cells, called Schwann cells wrap themselves around the axon, forming its myelin sheath. Neurons typically consist of three parts: the cell body or soma various dendrites which feed into the cell body and an axon which terminates with a branching called the axonal arborization, at the end of which are the axon terminals. The human brain consists of about 100 million neurons. 4 Neural Networks and Backpropagation Figure 19 A Neuron. ![]()
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