Alpha motor neurons originate in the basal plate, the ventral portion of the neural tube in the developing embryo. Sonic hedgehog (Shh) is secreted by the nearby notochord and other ventral structures (e.g., the floor plate), establishing a gradient of highly concentrated Shh in the basal plate and less concentrated Shh in the alar plate. Under the influence of Shh and other factors, some neurons of the basal plate differentiate into α-MNs.
Like other neurons, α-MNs send axonal projections to reach their target extrafusal muscle fibers via axon guidance, a process regulated in part by neurotrophic factors released by target muscle fibers. Neurotrophic factors also ensure that each muscle fiber is innervated by the appropriate number of α-MNs. As with most types of neurons in the nervous system, α-MNs are more numerous in early development than in adulthood. Muscle fibers secrete a limited amount of neurotrophic factors capable of sustaining only a fraction of the α-MNs that initially project to the muscle fiber. Those α-MNs that do not receive sufficient neurotrophic factors will undergo apoptosis, a form of programmed cell death.
Because they innervate many muscles, some clusters of α-MNs receive high concentrations of neurotrophic factors and survive this stage of neuronal pruning. This is true of the α-MNs innervating the upper and lower limbs: these α-MNs form large cell columns that contribute to the cervical and lumbar enlargements of the spinal cord. In addition to receiving neurotrophic factors from muscles, α-MNs also secrete a number of trophic factors to support the muscle fibers they innervate. Reduced levels of trophic factors contributes to the muscle atrophy that follows an α-MN lesion.
Read more about this topic: Alpha Motor Neuron
Other articles related to "development":
... was less willing to move forward on development, despite their enthusiasm for Hamm's script, which Batman co-creator Bob Kane greeted with positive feedback ...
... Over the years, Maldives has received economic assistance from multilateral development organizations, including the United Nations Development Programme, Asian ... European and Arab countries (such as Islamic Development Bank and the Kuwaiti Fund) also have contributed ...
... Kelley's first broadcast appearance as Doctor Leonard McCoy was in "The Man Trap" (1966) ... Despite his character's prominence, Kelley's contract granted him only a "featuring" credit it was not until the second season that he was given "starring" credit, at the urging of producer Robert Justman ...
... and gender disparities and with the United Nations Development Programme (UNDP), Maldives has implemented policies that directly address these issues ... In 2011, President Nasheed said, “The most important facility for a country’s development is its people… and since women are half of the population in any country, for a certainty their full ...
... The World Bank has already committed $17 million for education development in 2000-04, and plans to commit further $15 million for human development and distance learning during ... Over 2001-03, the ADB planned to support post-secondary education development in Maldives ...
Famous quotes containing the word development:
“Such condition of suspended judgment indeed, in its more genial development and under felicitous culture, is but the expectation, the receptivity, of the faithful scholar, determined not to foreclose what is still a questionthe philosophic temper, in short, for which a survival of query will be still the salt of truth, even in the most absolutely ascertained knowledge.”
—Walter Pater (18391894)
“I do seriously believe that if we can measure among the States the benefits resulting from the preservation of the Union, the rebellious States have the larger share. It destroyed an institution that was their destruction. It opened the way for a commercial life that, if they will only embrace it and face the light, means to them a development that shall rival the best attainments of the greatest of our States.”
—Benjamin Harrison (18331901)
“The young women, what can they not learn, what can they not achieve, with Columbia University annex thrown open to them? In this great outlook for womens broader intellectual development I see the great sunburst of the future.”
—M. E. W. Sherwood (18261903)