The human back extend from the buttocks to the posterior portion of the neck and shoulders. It is opposite from the chest, and the vertebral column runs down the back. The pelvis at the bottom of the back and the shoulders at the top of the back give the back its breadth, and it narrows in between these two regions. There are three different muscle groups found in the back: the superficial group, the deep group, and the intermediate group.
Muscles found in the superficial group include: rhomboid major, rhomboid minor, levator scapulae, trapezius, latissimus dorsi.
Muscles found in the deep group include the spinotransversales, erector spinae (composed of the iliocostalis, longissimus and spinalis), the transversospinales, and the segmental muscles.
The serratus posterior inferior and the serratus posterior superior compose the intermediate group of muscles.
Let’s examine the muscles and muscle groups in greater detail.
Superficial Muscle Group
The trapezius or trapezoid muscles are two paired muscles that extend from the base of the thoracic vertebrae in the spine to the occipital bone and run out to the spine of the scapula. There are three parts to the trapezius. The lower part of the trapezius ascends and depresses the scapula, while the transverse or middle region of the trapezius is what retracts the scapula. Finally, the upper portion of the scapula is what supports the weight of the arm, as it pulls down on the shoulders and neck.
The latissimus dorsi muscle is located in the rear of the central portion of the abdomen, behind the arm. The trapezius partially covers this muscle near the midline portion of the back and spine. It’s a long flat muscle which stretches from the spine to the side of the body. The latissimus dorsi is responsible for the abduction and extension of the back, and it also allows for the internal rotation of the shoulder.
The rhomboid major functions to connect the spinal column or vertebrae to the scapula or shoulder bone. Its function is to pull the scapula towards the vertebral column and keep the scapula from moving away from the thoracic wall. It is directly below what the rhomboid minor.
The rhomboid minor muscle is a small skeletal muscle, and it can be found situated directly above the rhomboid major and just below the levator scapulae. Along with the rhomboid major, it functions it to keep the scapula pinned against the thoracic wall. The two muscles are capable of raising of the medial border of the scapula upwards and rotating it downwards along with the levator scapulae muscle.
The levator scapulae muscle is located near the neck, around the neck’s base and side. As the name of the muscle implies, the primary function of the levator scapulae is to raise the scapula, the shoulder bone. The muscle runs under the border of the scapula.
Intermediate muscle group
The two muscles which comprise intermediate muscle group are the serratus posterior inferior, and the serratus posterior superior. The serratus posterior inferior is located where the lumbar and thoracic regions join together. Specifically, this muscle blows out word from the T11 through L2 vertebrae., And insert through the lower border of the 9 to 12 ribs. The function of this muscle is to extend and rotate the trunk, pulling on of the lower portion of the ribs and moving them downwards and backwards. This movement also helps the lungs expel air by moving the ribs in accordance with the contraction of the lungs.
The serratus posterior Is a long thin quadrilateral muscle found at the rear upper portion of the thorax. It is located underneath the trapezius and rhomboid muscles. It borders the upper second through fifth ribs and much like the is serratus posterior inferior, it is responsible for elevating the ribs.
Deep Muscle Group
The deep muscle group can be subdivided into four smaller groups muscles. The four muscle groups that together make up the deep muscle group are the segmental muscles, the transversospinales, the erector spinae, and the spinotransversales.
The spinotransversales are made out of the splenius cervicis and the splenius capitis. The splenius cervicis is found at the base of the neck, and is comprised of a narrow band of tendon originating from the spinous processes belonging to the third through sixth vertebrae. Meanwhile, the splenius capitis is a much thicker, more broad muscle found on the back of the neck, which originates along the vertebrae in the neck and moves the base of the skull so that movements like shaking the head are possible.
The erector spinae’s spinalis portion is located near the spine and is a thick bundle of tendon and muscles. The spinalis cervicis, spinalis capitis, and spinalais dorsi are the three component parts of the spinalis. The spinalis dorsi is tightly blended with the longissimus dorsi. Three to four tendons from the lumbar region and the thoracic vertebrae comprise it.
The longissimus is the longest portion of the erector spinae, and it extends along the posterior of the cervical vertebrae. It can be divided into three different muscles: the longissimus cervicis, the longissimus capitis, and the longissimus thoracis. The final part of the erectus spinae is the iliocostalis, which arises out of the third through sixth the ribs, and runs into the fourth through sixth the cervical vertebrae.
The transversospinales is comprised of the rotatores, the multifidus, and the semispinalis. The rotatores are 11 different small muscles present in all spinal regions and are found beneath the multifidus. The multifidus muscles are located on either side of the vertebrae, and they run from the axis (the second cervical vertebrae) to the sacrum (the fused S1 and S5 vertebrae). They are right near the spine and help stabilize the joints in this area.
The levatores costarum muscles are 12 small muscles which, from the upper 11th thoracic vertebrae and the seventh cervical vertebrae, pass downwards and run into the outer portion of the ribs below the vertebrae. They help the lungs move and assist in the process of breathing. The interspinales muscles are pairs of muscles located on both sides of the interspinal ligament. There are six pairs found within the cervical region, a few pairs found within the thoracic region, and six pairs within the lumbar region. Finally, the intertransversarii are many small muscles located near the vertebrae, found inbetween the processes of the vertebrae. While these small muscles don’t contribute much movement than on their own, they stabilize the vertebrae and support the movement of other muscles in the region.
Organs Found In The Back
Beyond the muscles found in the back, there are also several organs found within the human back. The kidneys and lungs are located in the back, with the lungs found within the rear portion of the rib cage and the kidneys situated near muscles just below the cage.
The human lungs are found in the chest, within the thoracic cavity. The left lung is somewhat smaller than the right lung. The lungs are what bring oxygen into the body, supplying the blood with oxygen and by proxy supplying all the tissues of the body with oxygen. Humans have two lungs, one on each side of the body. In addition to filling the blood with oxygen, they also release build up carbon dioxide from the body. The muscles found near the lungs, in the back and otherwise, function to drive respiration by assisting in the movement of the lungs. The left lung is located near the heart, and for this reason it has a cardiac notch in it, a small recessed portion that allows the hearts to sit there.
The kidneys are two small, roughly bean-shaped organs found just below the rib cage. The function of the rib cage is to filter the blood it receives, processing the blood through absorption, secretion, filtration, and excretion. The byproduct of these processes is urine, and the kidneys are connected to the bladder via a tube called the ureter that carries this urine to the bladder.
The muscles, bones, ligaments, and tendons in the back can all be injured and cause back pain. Back pain is one of the most common kinds of pain for adults, and muscle strains are the most common type of back pain. Muscle or ligament strains can occur from repeated use of the muscles, or from improperly or awkwardly lifting heavy objects. Muscle pain usually resolves itself over the course of a couple of weeks with plenty of rest, though on occasion more intensive treatment may be required. Other common causes of back pain include various kinds of fractures, osteoarthritis, and disc herniation or degenerative disc diseases.