OVERVIEW
The spine is one of the most important parts of your body. Without it, you could not keep yourself upright or even stand up. It gives your body structure and support. It allows you to move about freely and to bend with flexibility. The spine is also designed to protect your spinal cord. This is why keeping your spine healthy is vital if you want to live an active life.
BASIC STRUCTURE
Your spine is made up of 24 small bones (vertebrae) that are stacked on top of eachother to create the spinal column. Between each vertebra is a soft, gel-like cushion called a disc that helps absorb pressure and keeps the bones from rubbing against each other. Each vertebra is held to the others by groups of ligaments. Ligaments connect bones to bones; tendons connect muscles to bones. There are also tendons that fasten muscles to the vertebrae. The spinal column also has real joints (just like the knee or elbow or any other joints) called facet joints. The facet joints link thevertebrae together and give them the flexibility to move against each other.Each vertebra has a hole in the center, so when they stack on top of each other they form ahollow tube that holds and protects the entire spinal cord and its nerve roots. The spinal corditself is a large collection of nerve tissue that carries messages from your brain to the rest ofyour body. In order for your body to function, you need your nerves. The spine branches off into thirty-one pairs of nerve roots. These roots exit the spine on both sides through spaces(neural foramina) between each vertebra.The normal spine has an “S”-like curve when looking at it from the side. This allows for aneven distribution of weight. The “S” curve helps a healthy spine withstand all kinds of stress.The cervical spine curves slightly inward, the thoracic curves outward, and the lumbarcurves inward. Even though the lower portion of your spine holds most of the body’s weight,each segment relies upon the strength of the others to function properly.
VERTEBRAE
Spine anatomy is divided into 4 major sections, typically defined by the number of vertebrae (theround bones that make up the structure of one’s back bone) in each section. Vertebrae are alsosometimes called vertebral bodies.
Cervical spine (neck)
comprised of 7 cervical vertebrae (termed C1 to C7),starting with C1 at the top of the spine and ending with C7 at the bottom of thecervical portion of the spine. Neck problems can cause neck pain and/or pain thatradiates down the arms to the hands and fingers.
Thoracic spine (upper back)
made up of 12 thoracic vertebrae (known as T1to T12), which are attached to the rib bones and sternum (breast bone). Becausethis part of the spine is firmly attached to the ribs and sternum, it is very stable andhas fewer problems associated with motion.
Lumbar spine (lower back)
typically including 5 vertebrae (known as L1 to L5),which have a great deal of motion and flexibility. Because this section of the spinebears most of the body’s weight and allows for the most motion (which stressesthe anatomical structures), this is the area associated with most back problems.Problems in the low back can cause pain that radiates down the legs to the feet.
Sacral region (bottom of the spine)
located below the lumbar spine,the sacrum is a series of 5 bony segments fused together (known as S1 to S5)that create a triangular-shaped bone that serves as the base of the spine andmakes up part of the pelvis.The segment where the lumbar spine meets thesacral region, L5-S1, is an area that is prone to degenerate and create backproblems. Four small bones that extend down from the sacrum make upthe coccyx (the tailbone at the very bottom of the spine).
INTERVERTEBRAL DISC
The intervertebral discs make up one fourth of the spinal column’s length. Discs arenot vascular and therefore depend on the end plates to diffuse needed nutrients. Thecartilaginous layers of the end plates anchor the discs in place..The intervertebraldiscs are cushions serving as the spine’s shock absorbing system, which protect thevertebrae, brain, and other structures (i.e. nerves). The discs allow some vertebralmotion: extension and flexion. Individual disc movement is very limited – howeverconsiderable motion is possible when several discs combine forces.
Annulus Fibrosus and Nucleus Pulposus
Intervertebral discs are composed of an annulus fibrosus and a nucleus pulposus.The annulus fibrosus is a strong radial tire–like structure made up of lamellae;concentric sheets of collagen fibers connected to the vertebral end plates. Thesheets are orientated at various angles. The annulus fibrosus encloses the nucleuspulposus.The nucleus pulposus contains a hydrated gel–like matter that resists compression.The amount of water in the nucleus varies throughout the day depending on activity.
Facet Joint
The facets are the “bony knobs” that meet between each vertebra to form the facetjoints that join your vertebrae together. There are two facet joints between each pairof vertebra, one on each side. They extend and overlap each other to form a jointbetween the neighboring vertebra facet joints. Without the facet joints, you would nothave flexibility in your spine, and you could only move in very straight and stiffmotions.The facet joints are what are known as synovial joints. A synovial joint, such as theknee or elbow, is a structure that allows movement between two bones. In a synovialjoint, the ends of the bones are covered with a material called articular cartilage. Thismaterial is a slick spongy material that allows the bones to glide against one anotherwithout much friction.Surrounding the facet joint is a watertight sack made of soft tissue and ligaments.This sack creates what is called the “joint capsule”. The ligaments are soft tissuestructures that hold the two sides of the facet joint together. The ligaments aroundthe facet joint combine with the synovium to form the joint capsule that is filled withfluid (synovial fluid). This fluid lubricates the joint to decrease the friction, just like oillubricates the moving parts of a machine.
Paraspinal Muscles
The paraspinal muscles refer to the muscles next to the spine. They support thespine and are the motor for movement of the spine. Your joints allow flexibility andyour muscles allow mobility. There are many small muscles in the back – eachcontrolling some part of the total movement between all the vertebrae and the rest ofthe skeleton. These muscles can be injured directly, such as when you have a pulledmuscle or muscle strain of the back muscles. The muscles can also cause problemsindirectly, such as when the muscles are in spasm after injury to other parts of thespine.When you experience a muscle spasm, it is because your muscle tightens up andwill not relax. These spasms usually occur as a reflex – meaning that you cannotcontrol the contraction of these muscles. When any part of the spine is injuredincluding: a disc, ligaments, bones, or muscles, the muscles automatically go intospasm to reduce the motion around the area. This protective mechanism is designedto protect the injured area.When muscles are in spasm they produce too much of the chemical, lactic acid.Lactic acid is a waste product produced by the chemical reaction inside muscle cellsthat must occur to allow the muscle to contract. If the muscle cell cannot relax, toomuch lactic acid builds up inside the muscles. The buildup of lactic acid causes apainful burning sensation.The main reason that lactic acid builds up inside the muscle cells is that when themuscles contract, the small blood vessels traveling through the muscles are pinchedoff (just like a tube pinched between your thumb and finger). When the musclerelaxes, the lactic acid is eventually washed away by fresh blood flowing into themuscle as the blood vessels open up.
Spinal Cord and Nerve Roots
The spinal cord is a column of millions of nerve fibers that run through your spinalcanal. It extends from the brain to the area between the end of your first lumbarvertebra and top of your second lumbar vertebra. At the second lumbar vertebra, thespinal cord divides into several different groups of fibers that form the nerves that willgo to the lower half of the body. For a small distance, the nerves actually travelthrough the spinal canal before exiting out the neural foramen. This collection ofnerves is called the cauda equina while it is still inside the spinal canal.A protective membrane called the dura mater covers the spinal cord. The dura materforms a watertight sack around the spinal cord and the spinal nerves. Inside thissack, the spinal cord is surrounded by spinal fluid.The nerve fibers in your spinal cord branch off to form pairs of nerve roots that travelthrough the small openings (foramina) between your vertebrae. The nerves in eacharea of the spinal cord connect to specific parts of your body. This is why damage tothe spinal cord can cause paralysis in certain areas and not others — it depends onwhich spinal nerves are affected. The nerves of the cervical spine go to the upperchest and arms. The nerves in your thoracic spine go to your chest and abdomen.The nerves of the lumbar spine then reach to your legs, bowel, and bladder. Thesenerves coordinate and control all the body’s organs and parts, and let you controlyour muscles.The nerves also carry electrical signals back to the brain that allow you to feelsensations. If your body is being hurt in some way, your nerves signal the brain thatyou have been hurt. Damage to the nerves themselves can cause pain, tingling, ornumbness in the area where the nerve travels.
Spinal curves
Curves are a normal part of the spine’s structure. Looking at the spine from the side(lateral), several curves can be seen. From this angle, the spine almost resembles asoft ‘S’ shape. When viewing the spinal column from the rear (posterior), the spineappears vertically straight — from the neck to the tailbone. The normal curves aretermed lordosis and kyphosis. However, the natural curves should not be mistakenfor spinal disorders also called Lordosis and Kyphosis. We will talk about abnormalcurves later in this article.Normal lordosis is the two forward curves seen in the neck (cervical spine) and lowback (lumbar spine). Normal kyphosis is the two backward curves seen in the chest(thoracic spine) and hip areas (sacral spine). Each of the naturally occurring andnormal soft curves serves to distribute mechanical stress incurred as the body is atrest and during movement.
Abnormal Curves
As mentioned earlier, Lordosis and Kyphosis are terms that are used to refer tospecific spinal disorders. Scoliosis is another type of disorder identified by abnormalcurvature of the spine. Each of these disorders is defined below.
- Lordosis is defined by an excessive inward curve of the spine. Although it primary affects the lumbar spine, it does occur in the neck too. Patients with excessive lumbar lordosis may appear swayback, the buttocks more prominent, and in general their posture appears exaggerated. Lordosis affects people of all ages and when it affects the low back, it can cause back pain making movement difficult and painful. Spondylolisthesis, osteoporosis, and even obesity may lead to abnormal lordosis.
- Kyphosis is defined by an excessive outward curve of the spine and may cause a deformity such as a humpback or hunchback. Abnormal kyphosis is more commonly found in the thoracic or thoracolumbar (chest area/low back), but can affect the neck too. Patients with excessive kyphosis may appear with a pitched-forward appearance. There are two types of abnormal kyphosis; that caused by poor posture and structural kyphosis.
- Scoliosis is the abnormal curving of the spine to the left or right side. Scoliosis most often affects the thoracic spine and children, although it is found in adults too.
