$(window).keydown(function(e) {
    switch (e.keyCode) {
        case 37: case 38:  //key is left or up
            if (currImage <= 1) {break;} //if is the first one do nothing
            goToPrev(); // function which goes to previous image
            return false; //"return false" will avoid further events
        case 39: case 40: //key is left or down
            if (currImage >= maxImages) {break;} //if is the last one do nothing
            goToNext(); // function which goes to next image
            return false; //"return false" will avoid further events
    }
    return; //using "return" other attached events will execute
});