In the back we have muscles that affects the spine among others. It’s the superficial back muscles and the deep back muscles.
The superficial back muscles are fastened to the upper extremities. We have the trapezius, which together with, among others, the saw shaped muscle (serratus anterior), moves the shoulder blade in comparison to the chest. Trapezius starts from the neck bone and from the throats and breats vertebraes. It is fastened at the collar bone and the shoulder blade. Things it helps to do is to keep the shoulder blade still when the arm is moved, to rise the shoulder blade and to turn the shoulderblade as the arm is lifted over the head. Then there is also the broad back muscle, which together with, among others, the big chest muscle, moves the bone of the overarm in comparison to the shoulder blade. The broad back muscle starts from a broad area on the back, the area is, very simplified, from the end of the back to underneath the shoulderblades. It forms the shoulder harnesses and is fastened at the bone of the overarm. The muscle moves the arms up and down (think of skiing and when they only uses their arms).
The deep back muscles is situated underneath the superficial back muscles and they move the back and the chest. The erector spinae, or spinal extensors, is the biggest one of these muscles. It is situated on either sides of the spine and starts from the hip and processes over most of the spine. It is fastened at processes at the backs side of the ribs. Apart from erector spinae, there are also multiple small deep back muscles. Together the deep back muscles straightens the spine, turns it and bends it to the side. They also create nodding movements, turns the head and bends the head to the side.
Something to ponder about: What do you think happens if a muscle gets tense and kept in a tense state? How will that affect the spine, do you think? And if the spine is affected, which affect will that have on the rest of the body?