The two types of mutations given in the question have different meanings. A missense mutation is a mutation that occurs where a codon is changed, and that results in a change in the amino acid it codes for (eg. changing AAA which codes for Lys, to AAC which codes for Asn).
A silent mutation occurs when a nucleotide is changed, but the overall expression of the amino acid does not change (eg. changing AAA to AAG, both codons code for Lys).
GTA mutating to GTG keeps the amino acid Valine. Both codons code for the same amino acid, so it is classified as a silent mutation.
Description of the nervous system Neurons send signals to other cells through thin fibers called axons, which cause chemicals known as neurotransmitters to be released at junctions called synapses
