objective-c : @synchronized, how does it work?

i have two methods

-(void) a {
   @synchronized(self) {
      // critical section 1 
   }
}

-(void) b {
   @synchronized(self) {
      // critical section 2 
   }
}

now my question is if a thread is in critical section 1. will the critical section 2 be locked for other threads or other threads can access critical section 2.