There is an error in the supposition: that these two regions are the only or largest concentrations of Muslims. They are neither. The largest number of Muslims are in South Asia: Pakistan, India, and Bangladesh. The country with the highest Muslim population count is Indonesia. However, between those two, the Middle East has a larger population of Muslims than Central Asia.
Islam is the major religion in north Africa and southwest Asia.
The Tigris River is in Southwest Asia, but is not in Central Asia.
Judaism, Christianity, and Islam were all founded in southwest Asia, more specifically the Middle East.
There are actually three branches of Islam that are dominant in at least one country in Southwest Asia. In order of popularity: Sunni Islam, Shiite Islam, Ibadi Islam.
Islam
Yes. Islam accounts for over 80% of the population in Southwest Asia and North Africa.
Islam.
Kazakhstan is the largest country in central and southwest Asia.
In Asia & Africa.
South east Asia and China
Hinduism, Buddhism, and Islam
southwest Asia