Breaking Down Back Anatomy
Understanding back anatomy is key to avoiding injury.
Bob Sallis, M.D., FASM
American College of Sports Medicine
- Understanding human anatomy is key to avoiding injury
- All of the parts of our body work in conjunction with each other; the back can be considered a function of the whole
- The back is able to withstand all of the pressure, shock and weight that it bears due to its remarkable inherent protective measures
- Humans are born with 33 bones in their spine
- About 10% of people are born with an extra vertebra in their lumbar region
- At birth, the discs that make up part of the spinal column are 80%-90% water
The human back is comprised of complex anatomical features that give us strength and power and house our most precious organs. The back is under constant stress and bears tremendous weight – even more so when we run, jump, or even walk. As athletes, the more we understand how the back works and how it relates to our activities, the better we will be at protecting it and letting it heal when we ask too much of it. Anatomy is not just for scientists anymore. Read on as we break down some back basics.
WHAT DOES THE BACK DO?
The back, the posterior part of the torso running from the neck down to the top of the buttocks, enables movement, provides structural support to the torso, and houses the nerves that transmit information to and from the brain. The muscles in the back power our limbs. One of the most special things about the human back is that it houses and protects the spinal cord. The spinal cord is the collection of nerves that transmits information between the brain and the rest of the body. The spinal cord allows you to sense and react to your environment, communicate with the various parts of you body, and to move.
COMPONENTS OF THE BACK
There’s a lot going on in your back – all the time. Your back provides structural support while at the same time allowing and powering movement throughout your body. The upper part of the back provides lots of structural support – it connects to your rib cage, which houses multiple organs, and moves less than your lower back, which provides the foundation for twisting and bending movements.
Bones & the Spinal Column
The adult spine is made up of 26 bones — 24 vertebrae, 1 sacrum, and 1 coccyx. Cushioning the bones are 23 intervertebral discs that sit between each vertebra to help support the body’s weight. Vertebrae are connected by a series of ligaments and muscles at two points on each surface. These connection points are called facet joints. Facets link each vertebra to the one above and below it and, together with the discs and spinal cord, form a working, moving unit. The hollow center of the spinal column is known as the vertebral canal, which houses the cluster of nerves that make up your spinal cord.
The vertebrae are divided into three major regions: cervical (upper/neck), thoracic (middle), and lumbar (lower). Most injuries occur in the lumbar region because that region experiences the most movement. Below the lumbar area of the spine are our sacrum and coccyx, two fascinating bones. Humans are actually born with 33 separate vertebrae, five of which fuse together to form the sacrum and four of which fuse together to form the coccyx. Fusion is not normally completed until our mid-twenties, though it occurs without our notice or knowledge during regular development.
Spinal Cord: Carrying Precious Cargo
Our spinal cord is precious indeed. When it is damaged, we can become disabled or even paralyzed. The nerves in the spinal cord run from our brain down to the lowest part of our spine and transmit feelings, sensations, and commands from our brain to our entire body. Without this cluster of nerves that runs through the vertebral canal, we cannot run, bike, sprint, jump or move at all. And because of those nerves transmitting messages to our brain as we run harder and faster, our brain sends out signals that we are loving (or hating) every second of it.
Protective Measures: Discs, Cartilage, and Freedom of Movement
To protect all of this precious anatomy, the spine has a great deal of support, flexibility, and cushioning, the most important components of which are the intervertebral discs, located between each vertebra like the creamy center of a cookie. Designed to serve as shock absorbers, discs are like watery, fibrous padding. Each disc has a softer center known as the nucleus pulposis. The nucleus pulposis is a gelatinous, jelly-like substance contained within a tougher outer ring, known as the annulus fibrosis. As your spine expands and compresses with movement, the discs are in place to absorb that compression. It’s no surprise, then, that when there is increased shock; you have an increased risk of injury.
Our backs also have a special type of cartilage, tougher than your average tissue. This cartilage is known as fibrocartilage, which is tough and thick and high in collagen. It’s really more like a tendon in makeup. Because it is so strong, tough, and elastic, fibrocartilage is located in places that need to absorb tremendous amounts of stress, such as between our intervertebral discs.
In order to prevent damages associated with bone-on-bone friction, each vertebral section has several layers of protection. First, the bone surfaces of the facet joints (the connection points of each vertebra) are covered with articular cartilage, another type of cartilage designed to reduce friction and shock and the most common type of cartilage in the human body. Next, each facet joint is lined by a membrane (the synovium) and enclosed in a fibrous sac called the joint capsule. Synovial fluid then surrounds the joint to provide a final layer of protection for the bones.
All of this – the discs, the facet joints, the cartilage, and the synovial fluid surrounding it – is designed to help vertebrae move smoothly, articulate with each other, and withstand force. It’s important to remember, though, that as we age, cartilage can lose its elasticity and the fluids can become thicker and drier – all the more reason to stay hydrated.
Muscles: Providing Support and Stability
You probably know that strong muscles help protect the bones and ligaments that they surround and your back is no exception. So many muscles, bones, and ligaments come together at the torso; it can be hard to keep them straight (shoulders, neck muscles, trapezius, etc.) – but there are a few that you should definitely remember: abdominals, the iliopsoas, and the erector spinae.
The most important muscles in your back are actually on your front. Your core muscles (hips, front abdominals, and obliques) help your back rotate and bear weight. For more information read physical therapist Jill Lohmann’s article on supporting and stabilizing the back.
The iliopsoas muscles connect to either side of the lumbar vertebrae supporting your spine and helping to keep you upright when you stand and flex your hips as you lift your leg or walk. A dysfunction or imbalance in this muscle will quickly lead to lower back pain because the iliopsoas actually traverses from the middle of the spine, across the front of the pelvis, to the hip – internally.
The erector spinae are the spine’s own set of muscles that it uses to extend itself. They are major muscle masses that when contracted allow your spine to move from side to side (laterally) or twist from front to back. The erector spinae change shape and thickness as they run vertically along the spine from the cervical spine (neck) down through the thoracic spine and rib cage, and down to the pelvis.
Ligaments and Tendons: Providing Stretch & Stability
Ligaments connect bones to each other – and the spine is made up of a lot of bones. Thankfully, the spine also has a strong longitudinal system of ligaments to provide stability and flexibility as those bones and joints move. Tendons are thick, fibrous bands of tissue that connect muscles to bones and the back has plenty of these too. Like ligaments they help provide strength and support to our joints as we move.
The back’s ligaments connect the vertebrae to each other and its tendons connect muscles to the vertebrae. Ligaments and tendons are particularly important because they not only provide added support and stability, but they also help keep the spine from moving too far in any one direction.
Given all that we ask our backs to do on a daily basis, it’s no surprise that so many of us will experience some sort of back pain at some point in our lives. With proper treatment, the majority of back injuries will heal within a couple of months and will not become chronic. This is due in part to the human body’s extraordinary ability to heal itself, as well as to the incredible system of checks and balances the spine has developed. Our backs have been masterfully designed to support every inch of our bodies, to allow us to move, bend, and twist in ways no other animal on the planet can, and to protect itself in the process.