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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 interneurons found in the stratum lucidum are of two classes, spiny and aspiny. Spiny neurons are a "special type of inhibitory cell", characterized by spiny projections on the dendrites of the cell. The axons of these neurons in the hippocampus terminate primarily in the stratum lucidum and stratum radiatum of CA3.
The mesolimbic pathway and a specific set of the pathway's output neurons (e.g. D1-type medium spiny neurons within the nucleus accumbens) play a central role in the neurobiology of addiction. [20] [21] [22] Drug addiction is an illness caused by habitual substance use that induces chemical changes in the brain's circuitry. [23]
English: Complete neuron cell diagram. Neurons (also known as neurones and nerve cells) are electrically excitable cells in the nervous system that process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves.
The substantia nigra is located in the ventral midbrain of each hemisphere. It has two distinct parts, the pars compacta (SNc) and the pars reticulata (SNr). The pars compacta contains dopaminergic neurons from the A9 cell group that forms the nigrostriatal pathway that, by supplying dopamine to the striatum, relays information to the basal ganglia.
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 indirect pathway originates in the D2 subtype of the striatal medium spiny neuron, [2] which respond to the absence of continuous dopamine signal. The indirect pathway passes through the caudate , putamen , and globus pallidus , which are parts of the basal ganglia . [ 3 ]
Again, adjacent areas on the skin are represented by adjacent neurons in all aforementioned structures. This projection pattern has been termed somatotopy. One common diagram of the somatotopic map is the cortical homunculus. This illustration is a fairly accurate representation of how much cortical area represents each body part or region.