Axonal connectivity

The human brain is comprised of many millions of interconnected units, known individually as biological neurons. Each neuron consists of a cell to which is attached several dendrites (inputs) and a single axon (output). The axon connects to many other neurons via connection points called synapses. A synapse produces a chemical reaction in response to an input. The biological neuron fires if the sum of the synaptic reactions is sufficiently large. The brain is a complex network of sensory and motor neurons that provide a human being with the capacity to remember, think, learn and reason. 

Corpus caiiosum a brain structure consisting of axons connecting the two cerebral hemispheres. 

Tire anatomy of the brain is quite complex, and only a few terms will be defined here. Tire cerebrum, which is made up of two hemispheres, accounts for the largest part of the brain. Tire deeply folded outermost layer, the cerebral cortex, consists of gray matter, a mass of cell bodies, and fine unmyelinated nerve fibers. Beneath this lies a layer of white matter made up of myelin-covered axons connecting the cerebral cortex with other parts of the brain. Tire two cerebral hemispheres are connected by the corpus callosum, a band of 2 x 108 nerve fibers. Remarkably, these fibers can be completely severed with a relatively minimal disruption of the nervous system. In the past the corpus callosum was sometimes cut to control almost incessant epileptic seizures that could not be prevented by drugs. The "split-brain" patients suffered relatively little disability as long as both eyes functioned normally. Studies of these patients provided some insights into the differing functions of the two hemispheres of the cerebrum.395... 

Cowan WM, Gottlieb DI, Hendrickson AE, Price JL, Woolsey TA (1972) The autoradiographic demonstration of axonal connections in the central nervous system. Brain Res 37 21-51. 

Evidence for the maintenance of the topography of corticostriatal projections through the basal ganglia back through the thalamus to the cortex, eomes from studies in the primate by Strick and his colleagues (Holsapple et al. 1991 Hoover and Strick 1993 Schell and Strick 1984 Strick 1985). In one study in which they employed anterogradely transported trans-neuronally transferred viruses as axonal connectional markers which... 

Currently, several methods are available for the bulk isolation of purified plasma membrane fractions. Each of these plasma membrane isolation procedures involves three basic, successive steps tissue homogenization, subcellular fi-actionation, and assessment of the yield and/or purity of the isolated membrane fraction. During homogenization of brain tissue, nerve terminals are pinched off from their axonal connections and broken away from surrounding glial cell elements. Because nerve terminals are relatively resistant to mechanical stress, they can reseal to form synaptic bodies that are known as synaptosomes. Whittaker (4) and deRobertis (5) were the first to describe a method to purify these pinched-off nerve terminals. In their procedure, a crude... 

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