I suppose you could do it through serial connections. If you have a serial port (or a serial to USB adapter and driver) you can create and open a COM object in MatLab to communicate with the Arduino board (usually arduino terminals D0 and D1 are serial TX/RX).
The code would be something like:
arduinoCom = serial('COM3','BaudRate',9600 . . . );
sendData = 5;
You will have to look into using the correct terminators and do a bit of configuration with that. Let me know if this makes sense. Usually terminators are something like a linefeed / carriage return or an symbol (*, $, etc.)