Interneurons connect neurons to other neurons within the same region of the brain or spinal cord. Motor neurons receive signals from the brain and spinal cord to control everything from muscle contractions to glandular output.
Sensory neurons respond to stimuli such as touch, sound, or light that affect the cells of the sensory organs, and they send signals to the spinal cord or brain. Neurons are typically classified into three types based on their function. The ability to generate electric signals was a key innovation in the evolution of the nervous system. They eventually gained new gene modules which enabled cells to create post-synaptic scaffolds and ion channels that generate fast electrical signals. 800 million years ago, predecessors of neurons were the peptidergic secretory cells. The ability to generate electric signals first appeared in evolution 700 million years ago. Non-animals like plants and fungi do not have nerve cells. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. Neurons communicate with other cells via synapses - specialized connections that commonly use minute amounts of chemical neurotransmitters to pass the electric signal from the presynaptic neuron to the target cell through the synaptic gap.
Within a nervous system, a neuron, neurone, or nerve cell is an electrically excitable cell that fires electric signals called action potentials across a neural network.
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