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Medium spiny neurons (MSNs), also known as spiny projection neurons (SPNs), are a special type of inhibitory GABAergic neuron representing approximately 90% of neurons within the human striatum, a basal ganglia structure. [1] Medium spiny neurons have two primary phenotypes (characteristic types): D1-type MSNs of the direct pathway and D2-type ...
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 .
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.
C fibers synapse to second-order projection neurons in the spinal cord at the upper laminae of the dorsal horn in the substantia gelatinosa. [5] The second-order projection neurons are of the wide dynamic range (WDR) type, which receive input from both nociceptive terminals as well as myelinated A-type fibers. [ 5 ]
The striatum (pl.: striata) or corpus striatum [5] is a cluster of interconnected nuclei that make up the largest structure of the subcortical basal ganglia. [6] The striatum is a critical component of the motor and reward systems; receives glutamatergic and dopaminergic inputs from different sources; and serves as the primary input to the rest of the basal ganglia.
The stratum oriens is the location between layers containing basal dendrites. [8] The stratum lucidum , stratum radiatum , and the stratum moleculare-lacunosum are layers of apical dendrites and are ordered from least distant to most distant from the soma of the neuron.
The spinal cord is a uniformly organized, cylindrical structure of white and gray matter that is separated into four regions: cervical (C), thoracic (T), lumbar (L), and sacral (S). Each area is made up of many segments. Motor and sensory nerve fibers to and from every area of the body are found in the spinal nerve.
A reconstruction of a pyramidal cell. Soma and dendrites are labeled in red, axon arbor in blue. (1) Soma, (2) Basal dendrite, (3) Apical dendrite, (4) Axon, (5) Collateral axon. One of the main structural features of the pyramidal neuron is the conic shaped soma, or cell body, after which the neuron is named.