| MadSci Network: Neuroscience |
Apologies for the delay; I have been away these past two weeks. Aging in the Brain: While cerebral atrophy proves common by the age of 60, the degree is not invariable. Many factors appear to influence the degree. In general, by the age of 50 years, the brain loses roughly 2-3% of weight per decade over the following four decades. These statistics are based on post mortem studies of weight and volume. It seems the weight remains generally constant throughout the middle age. Now it appears reasonable that the atrophy described results from changes in the number or size of neurons. However, a great deal of variability exists between individuals. Examination of the cells—neurons and glia—demonstrate a number of changes which are not constant. For example intact neurons can loss dendritic processes—the processes by which neurons receive information. Neurons also generally contain increased amounts of lipofuscin. More astrocytes exist in the white matter of the brain—the region that contains the long axon processes of the neurons whose bodies reside in the cortex. Despite the high variability, some general trends exist: Significant Loss and/or Shrinkage: Cerebral cortex Hippocampus and amygdala Cerebellar purkinje cells Basal Ganglia and Nucleus Basalis Substantia nigra Locus ceruleus Inferior Olive Ventral horn cells—motor cells of spinal cord. Minimal Loss and/or Shinkage: Deep cerebellar nuclei Basal Ganglia and Nucleus Basalis Locus ceruleus Inferior Olive Cranial Nerves IV and VI Motor Nucleus of VII Ventral Cochlear Nucleus Dorsal Raphe Mamillary Bodies Note that some occupy both categories. As a further example of the variability, different aging diseases more prevalent with age will affect different population.s Parkinson’s affects the substantia nigra while chronic alcoholism can affect the mamillary bodies. While it is generally agreed that the hippocampus loses pyramidal cells with age, disagreement exists over the amount and which areas suffer the loss. Reference: Graham, David. "Ageing and the Brain," in Neurosurgery: The Scientific Basis of Clinical Practice. 3rd ed., Vol. 1 , Crockard, A, Hayward, R, and Hoff, J. Blackwell Science, 2000.
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