Dendrite is Greek for “tree-like” and to explain what they do in the simplest terms possible, they receive electrochemical signals from other neurons and then pass these signal down to the soma or neural cell body. Dendrites play a critical role in determining the frequency of the action potential, which drives the electrical signal down axons of the body of the neuron towards the axon terminals. Dendrites are so essential that their architecture is a great indicator of the complexity of our neural connections. In fact, our brain function depends on strong synaptic connections, connections which are cultivated during infancy and early childhood.
Unfortunately, as with all things complex, sometimes something goes wrong in the developing process. Mental retardation occurs when there is a disruption in this early refinement of dendrites that results in cognitive impairment severe enough to disrupt adaptive behaviour. There is a wide array of genetic disorders and poor environmental conditions that can result in mental retardation. For example, Down Syndrome and PKU (both genetic disorders), accidents during pregnancy and childbirth, maternal infections with rubella, Fetal Alcohol Syndrome and environmental impoverishment. Poor environmental conditions in young children such as poor nutrition, isolation and neglect can even result in brain damage severe enough to cause damage to these sensitive dendrites.
Healthy dendrites have spines that look like small balloons that hang of the dendrite. In cases of mental retardation dendritic spines are very thin and long, resembling the dendritic spines of a fetus. This is clearly seen in the top most image, a) and c) are healthy dendrites. This clear difference reflects the failure of normal circuits in the brain’s development. Studies by Marin-Padilla and Purpura have discovered a correlation between extent of dendritic spine damage and degree of mental retardation.
Bear, Mark F., Barry W. Connors, and Michael Paradiso. “Neurons and Glia.”Neuroscience: Exploring the Brain. Baltimore, MD: Lippincott Williams & Wilkins, 2006. 43. Print.
Images courtesy of google images.