Flashcards in Spine Anatomy Deck (42):
The Back and Beyond
Bones are four times stronger than concrete. The minerals calcium and phosphorus make bones (and teeth) hard and strong. Eating foods that contain these minerals, such as yogurt and spinach, helps keep your bones healthy.
Bones are living, breathing structures. They don't exactly inhale and exhale, but bones do make red (and white) blood cells. Red cells deliver oxygen, whereas the white ones rush like battlefront nurses to fight germs and diseases. If bones weren't alive, a broken bone would remain broken forever. Instead, they remarkably repair themselves(often with a little help from our medical friends). This natural ability for self-repair is the same for a broken finger as it is for a fractured backbone.
More Bones at Birth
Bones come in many shapes and sizes, each designed for a particular function. The bones of the spine, called vertebrae, are like cylindrical building blocks. They stack on top of each other like small cans separated by little cushions called discs. The spinal column (also known as the vertebral column) is held together mainly by discs and facet joints with support from ligaments and muscles.
The place where two bones come together is a called a joint. In the spine, the joint formed at meeting of two vertebrae is called a facet joint. Like joints anywhere in the body, they can swell and pinch nerves. Many people focus on the discs as a source of back pain although the facet joints are often to blame.
This is your neck, which contains seven vertebrae(C1–C7). The last, C7 is the bone that generally sticks out the most. You can easily feel it at the base of your neck, especially when you bend your head forward. Go ahead, see if you can find it.
The cervical vertebrae's main job
The cervical vertebrae's main job is to support your head. This is no small feat given that the head can weigh as much as 11 pounds! That's why how you hold your head matters so much. For many computer workers, a small but constant forward jut of the head is not uncommon. The result can transmit forces deep into the neck and shoulders. Stress to your neck muscles can lead to joint misalignment, which can pinch nerves. The result? Ouch! A sore neck with pain possibly radiating down into your arms.
Think about how many directions you can move your head
Think about how many directions you can move your head. There's up, down, side to side, forward and back, and around. It can tilt like a bobble head. Thank the cervical vertebrae—in particular, the pivoting action of C1—for all those marvelous movements. And that's a good thing most of the time. On the downside, the highly flexible neck makes it especially vulnerable to injury—such as whiplash when your head is thrust forward due to impact from a rear-end auto crash.
This is your rib-cage/midback area and it has 12 vertebrae (T1–T12). Unlike your other vertebrae, these attach to your ribs. The thoracic spine can move forward relatively easily, though it's much more limited bending backward. This part of your back is not typically a huge problem when it comes to back pain(most problems occur in the lower back). The midback can, however, be overly curved in some individuals, a condition called kyphosis. It often results from bad posture—think of slouching teenagers. But it can also be caused by disease. Either way, the excessive curve makes a person appear hunchbacked.
There can be some discomfort with kyphosis caused by disease, but postural kyphosis doesn't generally cause much pain. However, excessively rounding your thoracic spine may also lead to the head being positioned forward, which, as we mentioned earlier, causes problems in your neck. The forward slumping also shortens the muscles in front of your torso and overstretches some back muscles. This can lead to discomfort when you try to sit up straight. The good news is that you can correct this with good posture and proper exercise.
Meet your lower back
the part that causes pain for the vast majority of people. But before you curse the day you were born with it, know that those five lumbar vertebrae (L1–L5) have a mighty big job to do: they support most of the weight of your body. As you can see in the illustration, being the largest of the vertebrae, they're highly qualified for the job. These bones are indeed made for walking, running, sitting, and lifting. All these activities, of course, have a potential injury risk—which you can reduce by keeping your back and abdominal muscles strong and maintaining proper flexibility throughout your back and body. Good muscle conditioning lends support to your lower back (and other parts of the spine), and with proper stretching, you can keep the area flexible as well.
Lumbar Lordosis or "Swayback"
An excessive curve in the lower back is called lordosis, also known as swayback. This curve puts way too much pressure on your lumbar vertebrae. Lordosis can be caused by disease, a movement of the spine such as bending the back, or bad posture. Think of the final pose of gymnasts when they dismount from the parallel bars. The chest is thrust forward, shoulders back, and the lower back arches. This is what extreme lordosis in the lower back can look like. Of course, gymnasts do it on purpose. Although it's not a disease when they perform these contortions, they can end up with back problems because of it.
For the rest of us mortals, simply sitting incorrectly can cause too much pressure on the lumbar spine. That's why knowing how your vertebrae should be aligned and taking appropriate steps to make that happen can go a long way toward relieving back issues.
Sacrum and Coccyx
You might think that spinal fusion is something only surgeons do, but nature actually does this too and if you're over 30 years old, it's already happened to you. Your sacrum (from the Medieval Latin os sacrum, meaning holy bone), the flat triangular bone situated between your hips, is actually five fused vertebrae. This fusion isn't complete until you're about 25 or 30. This part is the lowest and last curve in your spine. The curve, called the lumbosacral curve, helps support body weight.
Below the sacrum is the tail end of your spine, called the coccyx or tailbone. Again, several fused vertebrae (generally 3–5) form the coccyx. Injury to this area can lead to coccydynia, which is a real pain in the you-know-what.
Coccydynia is a painful condition involving swelling around your tailbone. When the ligaments and tendons in this area become inflamed, it hurts to sit. You can also get this pain from a fracture of the coccyx, which can happen if you fall and land on your tailbone.
Like other joints in the body, facet joints are subject to repetitive stress injuries and degenerative diseases such as osteoarthritis. Also, the joint capsule can rupture and form cysts that pinch nerves, but most of the time, they just flare up.
Cartilage is basically smooth, rubbery tissue. Your nose is composed of it, as are your ears. Cartilage caps the ends of bones, providing cushion and slipperiness, enabling bones to move easily. When cartilage wears away, bone grinds on bone, causing pain and deterioration. Osteoarthritis and rheumatoid arthritis are two common diseases that damage joint cartilage. In the spine, facet joints are covered with cartilage.
Ligaments are strong fibrous bands that connect bone-to-bone. Their main job is to stabilize bones, holding them in place. They do, however, have a little flexibility.
Joint capsules lie between the joints. A fluid, called synovial fluid, is produced in the capsule. Because there is a lot of sliding at these joints, the lubricating fluid is very important in helping prevent grinding. (Cartilage also helps.)
Sacroiliac (SI) Joints
The sacroiliac (SI) joints link your sacrum to your pelvis, specifically to your iliac bones. You can easily feel your iliac bones; they're the bones at the top of your hips. Strong ligaments stabilize and attach your sacrum to your hip bones. Some motion is possible through these joints, but it's very limited. Pregnancy, for example, can loosen these joints, and if they don't return to normal, they can cause instability issues later in life.
The SI joint can be an overlooked source of back pain; it's subject to the same things that can happen to other joints, such as osteoarthritis. Also keep in mind the weight this lowest part of your spine bears. Excessive body weight and lifting injuries can negatively affect these joints. Because lots of muscles attach to the sacrum, muscular weakness or imbalances can misalign joints and be possible sources of pain.
discs sit between each vertebra.
Tough on the outside with a softer, gel-like fluid inside, discs sit between each vertebra. Think of them as car tires on their sides, filled with a thick gel. When your car drives over a bump, the rubber tire 'gives' a little, to absorb the bump. Similarly, each time we move the spine, the discs change shape in relation to the movement. Like so many structures in the body, discs are multifunctional. They are shock absorbers, and they connect and protect vertebral bones. Without discs, bone would touch bone with each movement and eventually grind away.
Discs are made from collagen; technically speaking, they are fibrocartilage, which means they consist of strong fibers with some elasticity.
Also know that the shocks absorbed are usually small and not a problem generally speaking, especially because these discs are quite tough. They do, however, have their limits, just like tires. When the shock is too extreme, something has to give and a tire will blow. In the case of our intervertebral discs, the gel on the inside can burst out (causing a herniated disc) or the outside can protrude (a bulging disc); the discs can also dry out and get thinner (due to disease or sometimes from aging).
The outer layer of the disc
The outer layer of the disc is called the annulus fibrosis. Its main job is to attach to the vertebra above and below, although it also provides some cushion. The fibers are crisscrossed, making the connections super strong. Repetitive stress can sometimes cause this outer layer to bulge. If the bulge pushes on a nerve, the result is pain.
The nucleus pulposus
The nucleus pulposus is the gel-like center of the disc designed to absorb shock and provide lubrication. It's mostly made of water. As we age, it can dry up a bit, making the discs thinner and less shock absorbent. There is some evidence that inversion therapy or lumbar traction can help the discs rehydrate, but the long-term benefits have yet to be demonstrated.
ligaments, tendons, and muscles
Skeletal bones form the framework of our bodies, and in the previous section we talked about the joints and discs that link the bones. But something has to secure all these pieces in place. These are mainly ligaments, tendons, and muscles, all types of connective tissue. Each provides both stability and mobility to a greater or lesser degree.
Connective tissue is a broad term referring to various types of tissue that connect and support structures literally everywhere in the body. Collagen, tendons, and even muscles are types of connective tissue. Fascia, a type connective tissue that lies just under the surface of the skin, can tighten and cause pain in various parts of the body, including the back. Some diseases such as rheumatoid arthritis are considered connective tissue disorders.
Ligaments are like the chief of security, whose job it is to prevent suspicious activity while allowing normal activity. Likewise, spinal ligaments allow some forward, back, and side motion, but they put on the brakes to reduce excessive motion that could cause damage. Ligaments are strong, fibrous bands that have some but not much elasticity. Long ligaments secure the spinal column from the front and back; smaller ligaments attach and secure portions of the vertebra together. Specifically, the anterior longitudinal ligament attaches along the front of the vertebrae and limits how much we can bend backward.
The posterior longitudinal ligament
The posterior longitudinal ligament runs along the back of the vertebrae, and the supraspinous ligament attaches to the tips of the spinous processes. In combination, these two limit how far forward we can bend. Of course, it's possible to overstretch ligaments and—you guessed it—that can be a cause of back pain.
There are two basic types of muscles in the body
There are two basic types of muscles in the body: voluntary (those we move) and involuntary (those that move on their own, such as digestive and heart muscles). Both types can get stronger and more resilient through exercise. We're going to focus on the voluntary muscles that move and support the spine. Lack of muscle strength and flexibility is a common reason for back pain.
Muscles are layered in the body
Muscles are layered in the body. Some are deeper and others more superficial or at the surface. The deeper muscles are more stabilizing—helping to secure bones. Abdominal and back muscles are detailed in the following illustration. Muscles of the hips and legs can also play a part in back problems, but we'll get into their roles in the exercise section of this book.
Your doctor may have already told you that to have a healthy back you need strong abdominal muscles, which help stabilize your whole torso. There are four types of abdominal muscles.
The deepest, transversus abdominis, hugs around your body like a corset. You can feel these muscles contract if you place your hands on your waist and cough. On the sides of your body, you have two sets of "oblique" muscles, the internal obliques are deeper, the external obliques lie closer to surface. Obliques enable you to twist and side bend.
Finally, there's rectus abdominis, better known as the "six pack." Although you can sculpt these into those desirable washboard abs (with a whole lot of work), they're not particularly helpful in stabilizing your back. Their main job is to pull you forward (think sit-ups and crunches). They do help you compress the deeper ab muscles, but when it comes to stabilizing the spine, you want to strengthen the deepest ab muscles, transversus and internal obliques, along with the back muscles. Among the most effective ab and back workouts are Pilates exercises, which target all abdominal and spine muscles quite well.
Deep within the body are two muscles, one on either side of the body, called the iliopsoas muscles, or the psoas (pronounced so-as). These are hip and thigh flexors, meaning they lift the thighs, as in going upstairs, walking. When your legs are stationary, the psoas enable you to bend forward or flex in the hips. When sitting, the psoas help stabilize you in an upright position. One of the largest and thickest muscles in the body, the psoas extend from your lumbar vertebrae, cross in front of each hip, and attach on the inside-top of the thigh bone. Sitting for long periods can constrict or shorten psoas, which can cause pain upon standing.
Like your abs, spinal muscles are layered. The deepest are small and attach one vertebra to one another. At the deepest level, interspinalis muscles connect to your spinous processes; thank them for helping you stretch backward. The transversospinalis group forms a chevronlike pattern along the back of your spine and helps you side bend and twist, and it also assists in back bending. The next layer up is the erector spinae. The main job of this group is also back bending, although they also assist with side bending. Often when we get muscle spasms in the back, it's in the erector spinae muscles.
The next level consists of the rhomboids, between your shoulder blades, which through exercise or physical therapy can help realign your vertebrae. The very large, wing-like muscles on either side of your back are called latissmius dorsi. In addition to stabilizing the back, these muscles help you do all kinds of things, including pull-ups. Finally, the trapezius muscles extend from your neck and midback to your shoulders. These muscles help you move your neck and lift your shoulder blades. When we get tense, we tend to lift our shoulders, which can make these muscles quite tight and sore.
Muscles connect to bones through tendons. When a muscle contracts,the signal is concentrated through the tendon, which moves the bone. Tendons are firmly attached to bones. Although it isn't common, tendonitis, or inflammation of tendons, can occur even in the spine.
The spinal cord is a tube-like structure filled with a bundle of nerves and cerebrospinal fluid, which protects and nourishes the cord. Other protectors of the spinal cord include linings called meninges and vertebral bones. The spinal cord is about an inch across at its widest point and about 18 inches long.
The three types of membranes that surround the spinal cord are referred to as meninges. From the outer layer to the innermost layer, they are dura mater, arachnoid mater, and pia mater. These membranes can sometimes be damaged by disease or trauma. Arachnoiditis is a caused by an inflammation of the arachnoid lining resulting in severe stinging and burning pain. It can occur after surgery and can cause scarring of nerves.
Each area of the body is controlled by specific spinal nerves.
Nerves exit the spinal column in pairs and branch out like a delicate web throughout the rest of the body. Each area of the body is controlled by specific spinal nerves. The placement is fairly logical. For example, nerves in the cervical spine (neck area) branch out into your arms, which is why sometimes a neck issue can lead to pain radiating down your arms. Nerves in the thoracic govern the middle of the body, those in lumbar spine extend into the outer legs, and the sacral nerves control the middle of legs and organ functions of the pelvis.
All nerves ultimately connect to the brain.
All nerves ultimately connect to the brain. There are basically two major types of nerves: sensory and motor.
Sensory nerves send information such as touch, temperature, and pain to the brain and spinal cord.
Motor nerves send signals from the brain back into the muscles, causing them to contract either voluntarily or reflexively.
The nerves of the peripheral nervous system (PNS) extend down the spinal canal and branch out in 31 pairs at openings in the vertebrae called foraminae. They are messengers to and from your brain(or central nervous system), sending pain signals and initiating movement—like, 'Hey, take your hand off the stove, it's hot!' These nerves reflexively cause your spine to twist and turn when you walk to keep you in balance. And they keep you glued to your car seat as you turn a corner at high speeds!
peripheral nervous system
The peripheral nervous system (PNS) is the collective of the millions of nerves throughout your torso and limbs. The PNS nerves convey messages to your central nervous system (CNS), which is the brain and spinal cord.
In case you're wondering, cranial nerves (the ones in your head) supply the sense organs and muscles in your head.
The Back and Beyond
When the problem is in one part of your body yet pain is felt elsewhere, health professionals call it referred pain.
As we mentioned, the nerves that exit the spinal cord do so in pairs: one is a sensory nerve; the other is a motor nerve. It's probably no surprise to learn that motor nerves drive movement and bodily function. If you damage a motor nerve, you might have a weakness in a muscle or loss of function—for example, loss of bladder control. If, however, you can't feel the prick of a pin in your foot, you've lost some sensation, which indicates a problem with your sensory nerves, which govern pressure, pain, temperature, and other such sensations. This is why a doctor might gently poke you with a pin and ask about your bowel movements. If you can't feel the pin or have had a problem with bowel movements, it's a symptom of nerve damage.
A problem with a sensory nerve can sometimes feel like a sharp, electrical pain, which is why good athletic instructors will tell their students to stop if they ever feel this kind of pain. It's not a good idea to persist in any activities that result in this sensation because it could cause further nerve damage.