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Dorsal and ventral medium spiny neuron subtypes (i.e., direct D1-type and indirect D2-type) are identical phenotypes, but their output connections differ. [2] [3] Confocal microscopy Z projection of medium spiny neurons (MSNs) in the mouse striatum.
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.
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]
The location and severity of the spinal cord injury or disease determine the particular symptoms. In order to diagnose and treat spinal cord illnesses and to create prospective treatments for spinal cord injuries, it is essential to comprehend spinal neurons and their roles.
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]
Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body. Most spines have a bulbous head (the spine head), and a thin neck that connects the head of the spine to the shaft of the dendrite. The dendrites of a single neuron can contain hundreds to thousands of spines.
Location: Layer V of cortex in primary motor cortex: Shape: Multipolar pyramidal -- some of the longest axons in the body. Function: Excitatory projection neuron to spinal cord: Neurotransmitter: Glutamate: Presynaptic connections: Superficial cortical layers, premotor cortex: Postsynaptic connections: Ventral horn of the spinal cord ...