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Not all animals have neurons; Trichoplax and sponges lack nerve cells altogether. Neurons may be packed to form structures such as the brain of vertebrates or the neural ganglions of insects. The number of neurons and their relative abundance in different parts of the brain is a determinant of neural function and, consequently, of behavior.
Micrograph showing a von Economo neuron of the cingulate. HE-LFB stain.. Von Economo neurons, also called spindle neurons, are a specific class of mammalian cortical neurons characterized by a large spindle-shaped soma (or body) gradually tapering into a single apical axon (the ramification that transmits signals) in one direction, with only a single dendrite (the ramification that receives ...
Brain mapping can show how an animal's brain changes throughout its lifetime. As of 2021, scientists mapped and compared the whole brains of eight C. elegans worms across their development on the neuronal level [68] [69] and the complete wiring of a single mammalian muscle from birth to adulthood. [38]
However, even sponges, unicellular animals, and non-animals such as slime molds have cell-to-cell signalling mechanisms that are precursors to those of neurons. [9] In radially symmetric animals such as the jellyfish and hydra, the nervous system consists of a nerve net , a diffuse network of isolated cells. [ 10 ]
The brains of all species are composed primarily of two broad classes of brain cells: neurons and glial cells. Glial cells (also known as glia or neuroglia ) come in several types, and perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development.
Each gap junction (sometimes called a nexus) contains numerous gap junction channels that cross the plasma membranes of both cells. [11] With a lumen diameter of about 1.2 to 2.0 nm, [2] [12] the pore of a gap junction channel is wide enough to allow ions and even medium-size molecules like signaling molecules to flow from one cell to the next, [2] [13] thereby connecting the two cells' cytoplasm.
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Brain cells make up the functional tissue of the brain. The rest of the brain tissue is the structural stroma that includes connective tissue such as the meninges, blood vessels, and ducts. The two main types of cells in the brain are neurons, also known as nerve cells, and glial cells, also known as neuroglia. [1]