Examples seen in vertebrate include pruning of axon terminals in the neuromuscular junction in the peripheral nervous system and the pruning of climbing fiber inputs to the cerebellum in the central nervous system. This means synapses that are frequently used have strong connections while the rarely used synapses are eliminated. The selection of the pruned terminal arbors follow the "use it or lose it" principle seen in synaptic plasticity. Certain terminal arbors are pruned by competition. Axons extend short axon terminal arbors toward neurons within a target area. The pruning that is associated with learning is known as small-scale axon terminal arbor pruning. Furthermore, it has been stipulated that the mechanism not only works in regard to development and reparation, but also as a means of continually maintaining more efficient brain function by removing neurons by their synaptic efficiency. ĭespite the fact it has several connotations with regulation of cognitive childhood development, pruning is thought to be a process of removing neurons which may have become damaged or degraded in order to further improve the "networking" capacity of a particular area of the brain. It is believed that the purpose of synaptic pruning is to remove unnecessary neuronal structures from the brain as the human brain develops, the need to understand more complex structures becomes much more pertinent, and simpler associations formed at childhood are thought to be replaced by complex structures.
In contrast, the neuron does not die in pruning, but requires the retraction of axons from synaptic connections that are not functionally appropriate.
In apoptosis, the neuron is killed and all connections associated with the neuron are also eliminated. Apoptosis and pruning are the two main methods of severing the undesired connections. Regressive events refine the abundance of connections, seen in neurogenesis, to create a specific and mature circuitry. Neurons send long axon branches to appropriate and inappropriate target areas, and the inappropriate connections are eventually pruned away. This variation of pruning is known as large-scaled stereotyped axon pruning. Therefore, the neurons in the visual cortex prune the synapses with neurons in the spinal cord, and the motor cortex severs connections with the superior colliculus. The neurons in each cortex are selectively pruned, leaving connections that are made with the functionally appropriate processing centers. Variations Regulatory pruning Īt birth, the neurons in the visual and motor cortices have connections to the superior colliculus, spinal cord, and pons. Pruning is influenced by environmental factors and is widely thought to represent learning. After adolescence, the volume of the synaptic connections decreases again due to synaptic pruning. Two factors contribute to this growth: the growth of synaptic connections between neurons and the myelination of nerve fibers the total number of neurons, however, remains the same. The infant brain will increase in size by a factor of up to 5 by adulthood, reaching a final size of approximately 86 (± 8) billion neurons. It was traditionally considered to be complete by the time of sexual maturation, but this was discounted by MRI studies. During pruning, both the axon and dendrite decay and die off. Pruning starts near the time of birth and continues into the late-20s. Synaptic pruning, a phase in the development of the nervous system, is the process of synapse elimination that occurs between early childhood and the onset of puberty in many mammals, including humans.
0 kommentar(er)
