Schematic drawing of the different synapsing modalities between neurons.ĭepending on the number of dendrites, neurons can be divided into: Therefore, synaptic endings can be: axosomatic, axodendritic, axospinous and axoaxonic.įigure N2. In the former case, synaptic endings are classified according to the neural region they connect with. Synaptic endings can connect with both neurons and effector organs. Each branch ends with a button-shaped swelling: the s ynaptic ending or bouton. They arises from the soma, in the axon hillock, and can repeatedly branch out. Generally, axons are much longer than dendrites. They can also present protrusions called spines. Such clusters are known as tigroid substance (Nissl bodies) and can be highlighted as basophilic granules with a light microscope. The nucleus is located inside the soma, together with the cytoplasmic organelles and several ribosomes associated with the rough endoplasmic reticulum to form clusters. The other neuronal component is the only cytoplasmic protrusion that transmits impulses: the axon (also known as neurite). Such processes are suitable to receive impulses and they are known as dendrites. The neuronĮach neuron consists of a cell body, called soma, which includes the nucleus and cytoplasm (perikaryon) from which one or more cytoplasmic processes leave. Equal numbers of neuronal and non-neuronal cells make the human brain an isometrically scaled-up primate brain. In an adult individual brain there are, on average, 86.1± 8.1 billion neurons and 84.6 ± 9.8 neuroglial cells (Azevedo FAC, Carvalho LRB, Grinberg LT, Farfel JM, Ferretti RE, Leite RE, Jacob Filho W, Lent R, Herculano-Houzel SJ. The neuron-neuroglial cells ratio is approximately 1:1. Other cell types, collectively known as neuroglia, or simply glia, aid them. It is excitable and has the ability to transmit impulses: it is called neuron. The functional unit of this tissue is a highly specialized cell with a precise structure. The nervous system is composed of nervous tissue, whose function is to receive, process and transmit impulses. The Nervous System includes the Central Nervous System (CNS), consisting of the brain and the spinal cord, and the Peripheral Nervous System (PNS), consisting of ganglia and cranial and spinal nerves.
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