Noob question. Game is pausing using Update but not on FixedUpdate?

public class PauseMenu : MonoBehaviour {

 public bool isPaused;

 public string sceneName;

 public GameObject pauseMenuCanvas;

 void FixedUpdate ()
 {
     if (isPaused) 
     {
         pauseMenuCanvas.SetActive (true);
         Time.timeScale = 0f;
     }
     else 
     {
         pauseMenuCanvas.SetActive (false);
         Time.timeScale = 1f;
     }
 }

 public void Resume(AudioSource sources)
 {
     sources.Play ();
     isPaused = false;
 }

 public void MenuScreen(AudioSource sources)
 {
     sources.Play ();
     isPaused = false;
 }

 public void Quit(AudioSource sources)
 {
     sources.Play ();
     isPaused = false;
 }

 public void TriggerPause()
 {
     isPaused = !isPaused;
 }