![]() ![]() Here are some dimensions of simple dendritic spines as determined through serial electron microscopy.įiala J.C., Harris K. Electron microscopy must be used to determine the geometry of spines. This makes them difficult to study through light microscopy. Simple spines are very small, often less than 1 micron in diameter. Therefore, spines may play an important role in learning and memory. For these cells, more than 90% of their excitatory synapses occur on dendritic spines. These spines are frequent on the dendrites of the principal cells of most brain regions, notably on the pyramidal cells of cerebral cortex and the Purkinje cells of the cerebellar cortex. Each synaptic knob communicates with a dendrite or cell body of another neuron, the point of contact being a synapse. Axon terminals have knob-like swellings at the very end called synaptic knobs or end buttons. Perhaps the most common synaptic specialization of dendrites is that which Spanish anatomist Ramon y Cajal referred to as "espinas", since they resembled the thorns on a flower stem. Through synaptic gaps, a typical neuron may interconnect with thousands and tens of thousands of other neurons. Right: Reconstruction from serial electron microscopy. Spiny dendrites from hippocampal pyramidal neuron. Here are some examples of synaptic specializations of dendrites. These structures are often sites of synaptic contact and therefore can be referred to as synaptic specializations. Other neurons exhibit enlargements, protrusions, or other structural specializations along dendrites, or frequently, at the ends of dendrites. Here are some examples of patterns of dendritic arborization.ĭendrites of some neurons are smooth, tapered processes, such as in motor neurons of the spinal cord. The arbor formed by the dendrites of a neuron often has a characteristic shape as determined by the spatial domains into which the dendrites ramify. Thus, the dendrites of a neuron provide a surface for receiving synaptic inputs from other neurons. These synapses can occur on the cell bodies or the axons of other neurons, but most frequently they occur on dendrites. ![]() Axons typically make synapses with other neurons through specialized enlargements near their terminals. Neurons communicate through specialized junctions called synapses. Here are the dimensions of dendrites for a few types of neurons. In contrast, axons can extend to distant targets, more than a meter away in some instances.ĭendrites are rarely more than about a millimeter long and often much shorter. The dendrites branch and terminate in the vicinity of the cell body. A neuron typically has many dendrites and one axon. ![]()
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