Click on Arrows to Move Object.

I have a Human1 Object and 4 directional Arrow Object (Up, Down, Left, Right)

I want to do the following in one script

OnMouseDown,
Check which directional Arrow was Clicked.

Move Human1 according to the directions.

Example code;

OnMouseDown(){

switch(gameobject)
{    
up:    
Human1 Moves up;    
break;   
down:    
Human1 Moves down; 
break;
Left:    
Human1 Moves Left  ;  
break;
Right:
Human1 Moves Right ;   
Break;
}//end switch  


}//end OnMouseClick

the problem with using OnMouseDown() on every arrow object will not make any of my object move.
Because it is checking only whether I click my left button mouse was clicked.

What I wanted was to check which arrow was being clicked.

I understand that there is another solution to use raycast to check on the position of my mouse.

Sadly I felt it was a little complicated to me, maybe some bright minds can try to guide me on how to get that done?