Nodejs and the non-blocking nightmare

I am currently developing an API using node.js and MySQL. I am new to this non-blocking material and I have a question. I am using node and the MySQL module.

Let's say that we have such a function:

function doQuery(sql, callback) {
    connect(); //does the Client.connect()
    client.query(sql, function(err, results, fields) {
        if (err) {
            errorLog.trace(err, __filename);
            throw err;
        } else {
            logger.trace('DATABASE ACCESS: {query: ' + sql + '} result: OK', __filename);
        }
        client.end();

        callback(results);
    });
}

Everything works fine, callback handles returning values, but there something bothers me. My browser, until the answer returns, and I do not know if this is due to the fact that during this time the node is actually blocked or not.

So, how can I find out if an operation is really blocking my node process? I thought that when you pass a callback to a function, node automatically processes it and puts the execution of this callback in the event loop queue. But I'm not so sure about that.

Does all this make sense to you?