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Neurons are the excitable cells of the brain that function by communicating with other neurons and interneurons (via synapses), in neural circuits and larger brain networks. The two main neuronal classes in the cerebral cortex are excitatory projection neurons (around 70-80%) and inhibitory interneurons (around 20–30%). [2]
Pyramidal neurons, like other neurons, have numerous voltage-gated ion channels. In pyramidal cells, there is an abundance of Na +, Ca 2+, and K + channels in the dendrites, and some channels in the soma. [9] [10] Ion channels within pyramidal cell dendrites have different properties from the same ion channel type within the pyramidal cell soma.
Local interneurons have short axons and form circuits with nearby neurons to analyze small pieces of information. [5] Relay interneurons have long axons and connect circuits of neurons in one region of the brain with those in other regions. [5] However, interneurons are generally considered to operate mainly within local brain areas. [6] The ...
In lower vertebrates, mitral cells cannot be morphologically distinguished from tufted cells, and both are substantially morphologically different from the mammalian mitral cells. The cells often have multiple primary dendrites innervating different glomeruli and they are sometimes called simply projection neurons, to indicate that they are the ...
Each of these interneuron class can be further divided into diverse subpopulations of neurons with distinct neurotransmitter phenotype, axonal projection and function during locomotion. [38] For example, V2 interneurons are ipsilaterally projecting that can be further classified as excitatory V2a and inhibitory V2b.
Projection fibers consist of efferent and afferent fibers uniting the cortex with the lower parts of the brain and with the spinal cord. In human neuroanatomy, bundles of axons (nerve fibers) called nerve tracts , within the brain, can be categorized by their function into association tracts , projection tracts , and commissural tracts .
The medium spiny neurons are medium-sized projection neurons with extensively branched dendrites. The cell body is 15–18 μm and has five primary dendrites that become branched. At first the dendrites are without spines but at about the first branch point they become densely spined.
The majority of nerve axons are small (<4μm) in diameter. About 3% of nerve axons have a much larger diameter (16μm) and arise from Betz cells, mostly in the leg area of the primary motor cortex. These cells are notable because of their rapid conduction rate, over 70m/sec, the fastest conduction of any signals from the brain to the spinal ...