Which different nerve cells are there?
Nerve cells can be classified according to various criteria. Afferent cells send signals to the central nervous system (sensory), while efferent cells send signals to the periphery (motor). Particularly within the brain, a distinction can also be made between excitatory and inhibitory neurons, whereby inhibitory neurons usually have a short range and inhibit within a functional area (interneurons).
Neurons that (usually excitatory) reach cells in distant areas are called projection neurons. Based on the shape of the cell, a distinction can be made between bipolar, multipolar and pseudounipolar neurons, among others. Bipolar neurons have two extensions, while multipolar neurons have a multitude of extensions.
Of particular interest are pseudounipolar neurons, which have only one extension, but after a short time this extension branches out into two axons. These are the overwhelming majority of sensitive neurons, which mediate, among other things, the sense of touch.The nuclei of these neurons are located in ganglia next to the spinal cord, with one axon leading to the periphery and one axon to the brain. If these cells are excited at free ends in the skin, the information is passed on via a single cell to the brain. Nerve cells can also be distinguished according to the degree of their myelination (sheathing): motor fibers, for example, are highly myelinated and can therefore transmit signals very quickly. Neurons of the autonomic nervous system are weakly myelinated, as there is no need for delay-free transmission.
Summary
Neurons are nerve cells with all their extensions that are specialized in the formation and conduction of excitation. As such they form the smallest central functional element of the nervous system.
