A recent conversation with a client:
Me: Try letting your shoulders turn with your head and see how that feels.
Client: Wait... is that an okay thing to do? I thought I needed to turn my head by itself for some reason...
Me: It's absolutely an okay thing to do.
Pop quiz: If you think about your neck and the rest of your spine, do you think of them as A) discrete sections of your body, or B) both as part of your spine?
Most people will answer A. It's very easy to think of your head and neck as separate from the rest of your spine and body, especially in a culture where our attention is so often in our head, not in our body.
Take a moment to look at a picture or a model of a spine though! They're the same structure! There are differences where your neck starts that give the vertebrae in your neck more mobility than the rest of your spine, but it's the same structure. That mobility is actually enhanced even more when there's cooperation and cohesion between your neck and the rest of your spine.
Try this: Hold your shoulders still and turn your head left and right. Notice how easily you can turn your head each direction, and notice the furthest spot on the wall you can easily see each direction. When you turn your head like this, you're treating your neck as separate from the rest of your spine.
Now try this: Turn your shoulders and let your head follow left and right. Notice what's different in your neck from the previous experiment, how easily you can turn your head, and the furthest spot you can see on the wall. When you turn your head like this, you're treating your neck as part of your spine. You could even try turning from your pelvis and be able to go even further.
Think of the way a chain twists. If you hold part of the chain still, only the links up to that point can twist. If every link can move, each individual link can move further. Your spine works the same way. If only cervical vertebrae get to move, you can only turn to the side as far as those vertebrae allow. If thoracic and even lumbar vertebrae get to move too, the mobility of each vertebrae adds up to you being able to turn to look behind yourself.
So, next time you're in the car and need to look out your blind spot or out the back window, take care of your neck. Treat your spine as a whole and turn from your body! Your neck will thank you.