In the quote from Ramón y Cajal below, how well has his hypothesis been supporte
ID: 190102 • Letter: I
Question
In the quote from Ramón y Cajal below, how well has his hypothesis been supported by modern data? What kind of plasticity did Cajal overlook in his statement?
“… mental exercise promotes in the most involved areas a greater development of the protoplasmic extensions [i.e., dendrites] and [axon] collaterals. As a result, associations that have already been created between certain cell groups strengthen themselves, notably by multiplying the terminal twigs of the protoplasmic extensions [i.e., dendrites] and [axon] collaterals. In addition, entirely new intercellular connections may establish themselves thanks to the formation of new collaterals and the expansion of [dendrites].” – Ramon y Cajal, 1894
Explanation / Answer
Mental exercises strengthen the neuronal connections. A good number of examples support this hypothesis. As an organism grows, some specific neuronal connections become stronger based on the experience of the organism.
A child who once touched a flame, will avoid doing it in future. Some connections between groups of cortical neurons, make the child recollect the sequences that happened in the past - the flame, the terrific sensation he had in the finger and then withdrawal of his hand.
Research had been done on marine snail Aplysia californica to understand this neuronal plasticity. It has a siphon which draws water inside towards the gill. In a relaxed Aplysia, both the siphon and the gill visible. In presence of any harmful substance, the siphon as well as the gill, both are withdrawn. If the organism is touched more than once, the withdrawal reflex is sensitized which causes the organism to keep its gill in withdrawn state for a longer time than before.
Neuronal plasticity not only strengthens existing connections but it also make new axonal branches, axon terminals or spines in the dendrite. This kind of rewiring of the brain occurs during learning and memory or during brain damage.
Experiments on mice have shown that new axonal extensions are produced when they learn to blink their eye on hearing a particular sound.This sound was presented berfore a harmful stream of air is flown on their eye.
He overlooked synaptic plasticity.
According to Kajal's hypothesis, repeated firing of a neuron stimulates all the neurons with which it form synapses. But according to Hebbian rule regarding synaptic plasticity, connections strengthen between those neurons only which are active at the same time. In other words, "Neurons which fire together wire together ". If the pre-synaptic stimulation is accompanied by post- synaptic depolarization, then only synapses will be strengthened.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.