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Parts of the back

Anatomy of the Spine

The normal anatomy of the spine is usually described by dividing up the spine into three major sections: the cervical, the thoracic, and the lumbar spine. (Below the lumbar spine is a bone called the sacrum, which is part of the pelvis). Each section is made up of individual bones, called vertebrae. There are 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae.

An individual vertebra is made up of several parts. The body of the vertebra is the primary area of weight bearing and provides a resting place for the fibrous discs which separate each of the vertebrae. The lamina covers the spinal canal, which is the large hole in the center of the vertebra through which the spinal nerves pass. The spinous process is the bone you can feel when running your hands down your back. The paired transverse processes are oriented 90 degrees to the spinous process and provide attachment for back muscles.

There are four facet joints associated with each vertebra.

A pair that face upward and another pair that face downward.

These interlock with the adjacent vertebrae and provide stability to the spine.

The vertebrae are separated by intervertebral discs, which act as cushions between the bones.

Each disc is made up of two parts. The hard, tough outer layer, called the annulus, surrounds a mushy, moist center, called the nucleus. When a disc herniates or ruptures, the soft nucleus spurts out through a tear in the annulus and can compress a nerve root. The nucleus can squirt out on either side of the disc, or in some cases, both sides.

The amount of pain associated with a disc rupture often depends upon the amount of nucleus that breaks through the annulus and whether it compresses a nerve. To help alleviate the pain, a laminotomy/microdiscectomy may be performed.

Therapy for Back Pain

Southern California Orthopedic Institute has physical therapy facilities in our Van Nuys, Simi Valley, and Thousand Oaks offices. Our therapists work closely with your physician to return you to full function and pain-free activity as soon as possible.

The majority of cases of back pain occur in the lower back, the region below the bottom of the ribcage. As this is one of the most anatomically diverse regions in the body, with lots of bones, muscles, ligaments, joints, and tendons, there are a lot of potential causes of pain in this area. One of the most common is a lumbar strain, which is when the muscles, ligaments, and/or tendons in the lower back are stretched either suddenly or over time. Lumbar pain is often described as a localised discomfort, which can range from mild to severe pain, and is usually at its worst after physical activity.

Nerve irritation is another common causes, and can be brought on by anything that reduces the amount of free space around the nerve. This could occur because of bony encroachment, where the movement or growth of the vertebrae reduces the amount of space surrounding a nerve, or because an infection causes the nerve to become inflamed, for example. Conditions like these are usually characterised by a dull ache that gets worse with movement, but they can also lead to sciatica. Sciatica is a common condition where pain, numbness, tingling, and weakness can radiate down the sciatic nerve from the lower back all the way to the feet.

Of course, back pain can also originate in the bones, with different issues manifesting very different symptoms. A congenital condition, such as scoliosis, can lead to various types of pain, but will often be diagnosed in the early stages. A fracture on the other hand can come on suddenly, and brings with it a sharp, severe “stabbing” sensation. In cases like these, time is often the best treatment. Then there are conditions such as osteoporosis, where our bones lose density. While they should not be seen as inevitable, these are often conditions a person will have to learn to live with for the rest of their lives, and may require the use of various medications.

The region between the neck and the bottom of the rib cage, often referred to as either the upper or upper-middle back, is far less susceptible to back pain the the lower back. Usually, pain that occurs in this region is due to a long-term problem, such as poor posture. Conditions like fibromyalgia, which causes widespread musculoskeletal pain, can sometimes be to blame, but in most cases you will find that it is lifestyle choices carried out over a number of years that has led to the pain. This can result from an improper sitting posture from someone with a sedentary lifestyle, improper lifting techniques in those who carried out manual labour for most of their lives, or any kind of overuse injury, which could be brought on by years of playing a particular sport.

Since most upper-back pain is a result of long-term issues, long-term solutions are often needed to treat it. This often means making lifestyle changes, such as to your sitting or sleeping position, taking medication such as painkillers, and undergoing a particular physical regime, such as getting regular massages or undergoing physiotherapy.

The back is a complex feature of human anatomy, and arguably one of the most significant areas of our bodies. It’s not surprising, therefore, that we will all experience pain there from time to time. In the majority of cases, this pain is nothing to be overly concerned about, but if you notice a sudden or new type of back pain, it is better to err on the side of caution and get it checked out. If you are not currently experiencing back pain, then plan for the future with our blog on why we should make the effort to sit up straight.

Mark Strozier/istock

Muscles

Lift the sofa to straighten the rug underneath, carry a case of soda from the car…and you may feel a shot of pain so severe you think you’ve broken your back. Far more likely: You have a strain, sprain, or spasm — an extremely common cause of back pain. And while you may be in agony, these uncomplicated muscle aches usually ease within two weeks and disappear in six.

Discs

After years of wear and tear (or, rarely, a sudden trauma), the gelatinous pads that act as cushions between bony vertebrae can become thinner, leaving back bones with less of their natural shock absorbers. The vertebrae crunch closer together and shift from side to side, putting extra strain on the joints and on the muscles and ligaments that support the spine. A disc may also begin to bulge out, or the gel may start to leak out of a rupture — a condition officially known as “herniated,” though often called “slipped” (and, if the disc is pressing on a nerve, sometimes by names that can’t be printed here). If it’s the sciatic nerve that’s hit, you’ll feel it down your leg, as sciatica — which is painful, but rarely permanent. Herniated discs tend to shrink on their own, which reduces the pain-causing pressure. It may feel like three centuries, but within three months, as many as 90 percent of sufferers feel much better.

Joints

Your back has small joints, linking the vertebrae, that allow you to bend and twist. If the cartilage in these joints is worn down — a result of injury or simply use over time — the bones underneath rub together, causing pain and swelling: spinal arthritis. This generally occurs in the neck (with pain sometimes felt in the shoulder area) or lower back (pain may be in the buttocks or leg).

Bones
Arthritis, as well as aging or a herniated disc, can cause growths on the vertebrae called bone spurs, which crowd the space through which the spinal cord and nerves run. This narrowing — stenosis — doesn’t always cause problems. But when it does, you might develop chronic back pain, muscle weakness, and, rarely, nerve damage.

Next:

If the Surgeon Says “Operate,” You Say…

Four questions to put to your doctor when the “S” word comes up. Make sure you’re totally satisfied with the answers before you leave.

“What would happen if I waited?”

While there are some rare conditions in which surgery is required quickly (your spine has become unstable, for example, or you have neurological complications), usually there’s time to give other things a chance to work.

“How can I be sure surgery would be best for my condition?”

You want evidence; ask for statistics and studies. At ethicaldoctor.org, you can find reviews of many back procedures, along with a star-rating system that tells you how reliable the studies are.

“What can I try instead?”

A good surgeon should be familiar with other treatments — and comfortable discussing them with you.

“What are the risks?”

If the doctor dismisses possible complications, or doesn’t acknowledge that problems may crop up afterward, run (or hobble) to another practitioner.

Back & Neck

What should I know about the spine, also called the backbone?

The spine, or backbone, runs from the base of the skull to the pelvis, serving as a pillar supporting the body’s weight and as protection for the spinal cord. There are three natural curves in the spine, giving it an “S” shape when viewed from the side. These curves help the spine withstand great amounts of stress by providing an even distribution of body weight.

The spine has three major components: bones, joints, and discs. It is made up of a series of 24 individual bones called vertebrae that are stacked to form the spinal column. The spine is divided into three main sections:

Cervical spine

The cervical spine is the uppermost part of the spine, also called the neck. There are seven vertebrae within the cervical spine. They are numbered C1 to C7, from top to bottom. The first two vertebrae of the cervical spine are specialized to allow for neck movement. C1, also called the atlas, sits between the skull and the rest of the spine. C2, also called the axis, has a bony projection (odontoid process) that fits within a hole in the atlas to allow rotation of the neck. The first spinal curve is located at the cervical spine. It bends slightly forward, resembling a “C.” This forward curve is called a lordotic curve.

Thoracic spine

There are 12 vertebrae (T1 to T12) in the chest section, called the thoracic spine. The ribs attach to the spine on the thoracic vertebrae in back and wrap around to attach to the breastbone called the sternum in the front, except for the last two, T11 and T12. The curve of the thoracic spine bends outward like a reverse “C” and is called a kyphotic curve.

Lumbar spine

The lumbar spine, or lower back, usually consists of five vertebrae numbered L1 to L5. (Some people have six lumbar vertebrae.) The lumbar spine, which connects the thoracic spine and the pelvis, bears the bulk of the body’s weight. For that reason, the lumbar vertebrae are the largest. The curve of the lumbar spine also bends forward (lordotic curve).

Below the lumbar spine is a large bone called the sacrum. The sacrum actually consists of several vertebrae that fuse together during a baby’s development in the womb. The sacrum forms the base of the spine and the center of the pelvis. The coccyx, or tailbone, is another specialized bone created by the fusion of several smaller bones during development.

Vertebrae (bone)

Each vertebra consists of the following parts.

  • Body. The body is the front portion and the main weight-bearing structure of the vertebra.
  • Spinous process is the rear portion of the vertebra. It is the bony ridge you can feel down your back.
  • Laminae are two small plates of bone that join in the back of the vertebra.
  • Pedicles are short, thick bumps that project backward from the upper part of the vertebral body.
  • Transverse processes are the bony projections on either side of the vertebra where the laminae join the pedicles. Muscles and ligaments attach to the spine on the transverse processes.
  • Facet joints are the spinal joints, the areas on the spine where one vertebra comes into contact with another.

In the center of each vertebra is a large opening, called the spinal canal, through which the spinal cord and nerves pass. The vertebrae are held together by groups of ligaments, fibrous tissues that connect bone to bone.

Facet joints

A joint is the area where two or more bones connect. Joints allow for movement, since bones themselves are too hard to bend without being damaged. Facet joints are the specialized joints that connect the vertebrae. The facet joints allow the vertebrae to move against each other, providing stability and flexibility. These joints allow us to twist, to bend forward and backward and from side to side.

Each vertebra has two sets of facet joints. One pair faces upward to connect with the vertebra above and the other pair faces downward to join with the vertebra below.

Intervertebral discs

Intervertebral discs are flat, round cushioning pads that sit between the vertebrae (inter means “between” or “within”) and act as shock absorbers. Each intervertebral disc is made of very strong tissue, with a soft, gel-like center, called the nucleus pulposus, surrounded by a tough outer layer called the annulus. When a disc herniates, some of the soft nucleus pulposus may bulge or even protrude through a tear in the annulus. This bulging of the nucleus pulposus can result in pain when the nucleus pulposus puts pressure on nerves.

Nerves

The spinal cord, the column of nerve fibers responsible for sending and receiving messages from the brain, runs through the spinal canal. It is through the spinal cord and its branching nerves that the brain influences the rest of the body, controlling movement and organ function.

As the spinal cord runs through the spinal canal, it branches off into 31 pairs of nerve roots, which then branch out into nerves that travel to the rest of the body. The nerve roots leave the spinal cord through openings called neural foramen, which are found between the vertebrae on both sides of the spine. The nerves of the cervical spine control the upper chest and arms. The nerves of the thoracic spine control the chest and abdomen, and the nerves of the lumbar spine control the legs, bowel, and bladder.

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When most people mention their back, what they are actually referring to is their spine. The spine runs from the base of your skull down the length of your back, going all the way down to your pelvis. It is composed of 33 spool-shaped bones called vertebrae, each about an inch thick and stacked one upon another.

Each vertebra consists of the following parts:

The body is the largest part of the vertebrae and the part that bears the most weight.

The lamina is the lining of the hole (spinal canal) through which the spinal cord runs.

The spinous process is the bony protrusions you feel when you run your hand down your back.

The transverse processes are the pairs of protrusions on either side the vertebrae to which the back muscles attach.

The facets are two pairs of protrusions where the vertebrae connect to one another, including:

  • The superior articular facets, which face upward.
  • The inferior articular facets, which face downward.

The connection points between the vertebrae are referred to as the facet joints, which keep the spine aligned as it moves. Similar to other joints in the body, the facet joints are lined with a smooth membrane called the synovium, which produces a viscous fluid to lubricate the joints.

Located between the individual vertebrae, discs serve as cushions or shock absorbers between the bones. Each disc is about the size and shape of a flattened doughnut hole and consists of two parts:

  • The annulus fibrosis – a strong outer cover
  • The nucleus pulposis – a “jelly-like” filling.

Running through the center of the spinal column is the spinal cord, a bundle of nerve cells and fibers that transmit electrical signals back and forth between the brain and the rest of the body via 31 pairs of nerve bundles that branch off the spinal cord and exit the column between the vertebrae.

Supporting the spine, while providing it flexibility, are ligaments (tough bands of connective tissue that attach bone to bone) and muscles. Two main ligaments are:

  • anterior longitudinal ligament
  • posterior longitudinal ligament.

Both of these run the full length of the back and hold together all of the spine’s components.

The two main muscle groups involved in back function are:

  • The extensors, which include the many muscles that attach to the spine and work together to hold your back straight while enabling you to extend it.
  • The flexors, which attach at your lumbar spine (lower back), and enable you to bend forward. Located at the front of your body, the flexors include your abdominal and hip muscles.

Although the spine is a continuous structure, it is often described as if it were five separate units. These units are the five different sections of the spine:

  1. The cervical spine – the neck and upper back, composed of the seven vertebrae closest to the skull. The cervical spine supports the weight and movement of your head and protects the nerves exiting your brain.
  2. The lumbar spine – the lower back, composed of five vertebrae, provides support for the majority of your body’s weight.
  3. The thoracic spine – the middle back, made up of the 12 vertebrae in between the cervical and lumbar spine.
  4. The sacrum – the base of the spine that is composed of five vertebrae fused (joined together) as one solid unit. The sacrum attaches to ilium of the pelvis, forming the sacroiliac joints.
  5. The coccyx – the “tailbone” located below the sacrum, composed of four fused vertebrae.

X-rays of the Spine, Neck or Back

Risks of the procedure

You may want to ask your health care provider about the amount of radiation used during the procedure and the risks related to your particular situation. It is a good idea to keep a record of your past history of radiation exposure, like previous scans and other types of X-rays, so that you can inform your health care provider. Risks associated with radiation exposure may be related to the cumulative number of X-ray exams and/or treatments over a long period of time.

If you are pregnant or suspect that you may be pregnant, you should notify your health care provider. Radiation exposure during pregnancy may lead to birth defects. If it is necessary for you to have a spinal X-ray, special precautions will be made to minimize the radiation exposure to the fetus.

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your health care provider prior to the procedure.

Before the procedure

  • Your health care provider will explain the procedure to you and offer you the opportunity to ask questions that you might have about the procedure.

  • Generally, no prior preparation, like fasting or sedation, is required.

  • Notify the radiologic technologist if you are pregnant or suspect you may be pregnant.

  • Notify the radiologic technologist if you have had a recent barium X-ray procedure, as this may interfere with obtaining an optimal X-ray exposure of the lower back area.

  • Based on your medical condition, your health care provider may request other specific preparation.

During the procedure

An X-ray may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your health care provider’s practices.

Generally, an X-ray procedure of the spine, neck, or back follows this process:

  1. You will be asked to remove any clothing, jewelry, hairpins, eyeglasses, hearing aids, or other metal objects that may interfere with the procedure.

  2. If you are asked to remove any clothing, you will be given a gown to wear.

  3. You will be positioned on an X-ray table that carefully places the part of the spine that is to be X-rayed between the X-ray machine and a cassette containing the X-ray film or digital media. Your health care provider may also request X-ray views to be taken from a standing position.

  4. Body parts not being imaged may be covered with a lead apron (shield) to avoid exposure to the X-rays.

  5. The radiologic technologist will ask you to hold still in a certain position for a few moments while the X-ray exposure is made.

  6. If the X-ray is being performed to determine an injury, special care will be taken to prevent further injury. For example, a neck brace may be applied if a cervical spine fracture is suspected.

  7. Some spinal X-ray studies may require several different positions. Unless the technologist instructs you otherwise, it is extremely important to remain completely still while the exposure is made. Any movement may distort the image and even require another study to be done to obtain a clear image of the body part in question. You may be asked to breathe in and out during a thoracic spine X-ray.

  8. The X-ray beam will be focused on the area to be photographed.

  9. The radiologic technologist will step behind a protective window while the image is taken.

While the X-ray procedure itself causes no pain, the manipulation of the body part being examined may cause some discomfort or pain. This is particularly true in the case of a recent injury or invasive procedure like surgery. The radiologic technologist will use all possible comfort measures and complete the procedure as quickly as possible to reduce any discomfort or pain.

After the procedure

Generally, there is no special type of care following an X-ray of the spine, back, or neck. However, your health care provider may give you additional or alternate instructions after the procedure, depending on your particular situation.

Understanding Lower Back Anatomy

Your lower back is a superb feat of engineering—it’s strong, weight-bearing, and sturdy, yet highly flexible with a range of motion in all directions.

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The lumbar region of the spine, more commonly known as the lower back, is situated between the thoracic, or chest, region of the spine, and the sacrum. Watch: Lumbar Spine Anatomy Video

Understanding the anatomy of your lower spine can help you communicate more effectively with the medical professionals who treat your lower back pain.

Here is a description of useful anatomical landmarks.

The lordotic curve

Your lower back (lumbar spine) is the anatomic region between your lowest rib and the upper part of the buttock.1 Your spine in this region has a natural inward curve. This curve, called lordosis, helps to:

  • Balance the weight of your head on top of your spine
  • Evenly distribute weights from your upper body into the lower extremities
  • Reduce the concentration of stresses in the lower spine

A problem in your lower back may cause an increase or decrease in this lordosis and may contribute to lower back pain.2

See Lumbar Spine Anatomy and Pain

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Bones, discs, and joints in your lower back

Your lower back contains 5 vertebral bones stacked above each other with intervertebral discs in between. These bones are connected at the back with specialized joints. The lumbar spine connects to the thoracic spine above and the hips below.

Individual anatomical structures include2:

  • Vertebrae. Your lumbar vertebrae are labeled L1 to L5, which progressively increase in size, allowing them to bear the body’s weight more effectively. Your vertebrae protect important nervous tissues, such as your spinal cord and the cauda equina.

    See Vertebrae in the Vertebral Column

  • Discs. A total of 5 intervertebral discs are situated between your vertebral bodies. The discs typically provide cushioning and shock-absorbing functions to protect your vertebrae during spinal movements.

    See Spinal Discs

  • Facet joints. Your vertebrae are connected in the back of the spine with paired facet joints. These joints provide stability and allow your spine to move in different directions. The joint surfaces are lined by cartilage for smooth movements.
    • The facets of the upper lumbar vertebrae are similar to the thoracic facet joints and allow more back and forth spinal movements.
    • The facets of the lower lumbar spine are more flexible and facilitate side-to-side movements.

See Facet Joint Disorders and Back Pain

Large muscles and an intricate network of ligaments in your lower back support serve to stabilize your spine and power your twisting and bending movements.

See Back Muscles and Low Back Pain

Nerves in your lower back

Five pairs of lumbar spinal nerves labeled L1 to L5 branch off your spinal cord and exit through small holes between the vertebrae. The part of the nerve that emerges out of the spine is called the nerve root.

Your lumbar spinal nerves travel down each leg and are formed by 2 types of fibers—sensory fibers that send messages to the brain (when you feel pain after hitting your knee or toe) and motor fibers that receive messages from the brain (when you need to lift your leg to get out of a car or into a bus).

Your lumbar nerves progressively increase in size and contribute to the following functions4:

  • L1 spinal nerve provides sensation to your groin and genital regions and may contribute to the movement of your hip muscles.
  • L2, L3, and L4 spinal nerves provide sensation to the front part of your thigh and along the inner side of your lower leg. These nerves also control movements of your hip and knee muscles.
  • L5 spinal nerve provides sensation to the outer side of your lower leg, the upper part of your foot, and the web-space between your first and second toes. Your L5 nerve also controls your hip, knee, foot, and toe movements.

The L4 and L5 nerves (along with other nerves) contribute to the formation of the largest nerve in your body, the sciatic nerve, which runs down from your rear pelvis, into the back of your leg, and terminates in your foot.5,6

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Spinal cord and cauda equina in your lower back

Your spinal cord originates in your brain, travels through your spine, and terminates in the upper region of your lower back. This point of termination is called the conus medullaris,7 from where the spinal nerves descend down. These descending spinal nerves resemble a horse’s tail and are called the cauda equina.8

See Spinal Cord and Spinal Nerve Roots

Your spinal cord, conus medullaris, and cauda equina are vital tissues and if they get compressed or damaged, immediate medical attention must be sought.

See Cauda Equina Syndrome

A basic understanding of the anatomy of your lower back can help you identify and differentiate a problem that commonly affects this region, such as localized muscle pain or sciatica. Knowledge of the structures in your lumbar spine can also help you communicate with your doctor about lower back problems.

Learn More:

Causes of Lower Back Pain

Early Treatments for Lower Back Pain

Anatomy of the Spine and Peripheral Nervous System

Glossary of Terms

Annulus fibrosus – The fibrous, ring-like outer portion of an intervertebral disc.

Anterior – Referring to the front of the body or given structure.

Anterolateral – Situated or occurring in front of and to the side.

Arachnoiditis – Inflammation of the arachnoid membrane (the middle of the three protective layers called the meninges); most commonly seen around the spinal cord and cauda equina.

Arthritis – Inflammation of a joint, usually accompanied by swelling, pain and restriction of motion.

Bone spur – Bony growth or rough edge of bone.

Cauda equina – The collection of nerves at the end of the spinal cord that resembles a horse’s tail.

Cervical spine – The neck region of the spine consisting of the first seven vertebrae.

Coccyx – More commonly known as the tailbone, this is a bony structure in the region of the spine below the sacrum.

Conus medullaris – The cone-shaped bottom of the spinal cord, usually at the level of L1.

Disc (Intervertebral) – A tough, elastic cushion located between the vertebrae in the spinal column; acts as a shock absorber for the vertebrae.

Disc degeneration – The deterioration of a disc. A disc in the spine may wear out over time. A deteriorated disc may or may not cause pain.

Distal – Located downstream.

Facet – A joint formed when a posterior structure of a vertebra that joins with a facet of an adjacent vertebra; this joint allows for motion in the spinal column. Each vertebra has a right and left superior (upper) facet and a right and left inferior (lower) facet.

Foramen – An opening in the vertebrae of the spine through which the spinal nerve roots travel.

Herniated disc – Condition in which the jelly-like core material of a disc bulges or ruptures out of its normal position; a herniated disc may exert pressure on the surrounding nerve root and/or the spinal cord.

Joint – The junction of two or more bones that permits varying degrees of motion between the bones.

Lamina – The flattened or arched part of the vertebral arch that forms the roof or back part of the spinal canal.

Lateral – Situated on the side or away from the midline of the body.

Ligament – Fibrous connective tissue that links bones together at joints or that passes between bones of the spine.

Lumbar spine – The lower back region of the spine; consists of the five vertebrae between the ribs and the pelvis.

Nerves – Neural tissue that conducts electrical impulses (messages) from the brain and spinal cord to all other parts of the body; also conveys sensory information from the body to the central nervous system.

Nerve root – The initial portion of a spinal nerve as it originates from the spinal cord.

Neural arch – The bony arch of the back part of a vertebra that surrounds the spinal cord; also referred to as the vertebral arch, it consists of the spinous process and lamina.

Pedicle – The bony part of each side of the neural arch of a vertebra that connects the lamina (back part) with the vertebral body (front part).

Posterior – The back or rear side of the body or a given structure.

Proximal – Located upstream.

Rotation – Twisting movement of one vertebra on another as a patient turns from one side to the other.

Sacrum – Part of the pelvis just above the coccyx (tailbone) and below the lumbar spine (lower back).

Sacrum – Part of the pelvis just above the coccyx (tailbone) and below the lumbar spine (lower back).

Sciatica – A lay term indicating pain along the course of the sciatic nerve; typically noted in the back of the buttocks and running down the back of the leg and thigh to below the knee.

Scoliosis – An abnormal sideways curvature of the spine.

Spinal canal – A bony channel located in the vertebral column that protects the spinal cord and nerve roots.

Spinal cord – The longitudinal cord of nerve tissue enclosed in the spinal canal. It serves not only as a pathway for nerve impulses to and from the brain, but also as a center for operating and coordinating reflex actions independent of the brain.

Spinal stenosis – Abnormal narrowing of the vertebral column that may result in pressure on the spinal cord, spinal sac or nerve roots stemming from the spinal cord.

Spine – The flexible bone column extending from the base of the skull to the tailbone. It is made of 33 bones known as vertebrae, and also is referred to as the vertebral column, spinal column or backbone.

Spondylitis – Inflammation of vertebrae.

Spondylolisthesis – The forward displacement or “slippage” of one vertebra onto another.

Spondylosis – Degenerative bony changes in the spine, usually most marked at the vertebral joints and intervertebral discs.

Superior – Situated above or directed upward toward the head of an individual.

Thoracic spine – The region of the spine attached to the ribcage; located between the cervical and lumbar areas, it consists of 12 vertebrae.

Vertebrae – The 33 bones that make up the spine, individually referred to as a vertebra. They are divided into the cervical spine (neck), the thoracic spine (upper back or rib cage), the lumbar spine (lower back) and the sacral spine (pelvis or base of the spine).

Disclaimer

The AANS does not endorse any treatments, procedures, products or physicians referenced in these patient fact sheets. This information is provided as an educational service and is not intended to serve as medical advice. Anyone seeking specific neurosurgical advice or assistance should consult his or her neurosurgeon, or locate one in your area through the AANS’ “Find a Board-certified Neurosurgeon” online tool.

Anatomy and Function

The spinal segment allows us to focus on the repeating parts of the spinal column to better understand what can go wrong with the various parts of the spine. Sometimes problems in the spine involve only one spinal segment, while other times the problems involve multiple segments.

Each spinal segment is like a well-tuned part of a machine. All of the parts should work together to allow weight bearing, movement, and support. When all the parts are functioning properly, all spinal segments join to make up a remarkably strong structure called the spinal column. When one segment deteriorates to the point of instability, it can lead to problems at that segment causing pain and other difficulties.

Now that you know the parts of the spine, let us look at the spine itself, which has three main segments – the lumbar, thoracic, and cervical spines.

Lumbar Spine

The lowest part of the spine is called the lumbar spine. This area has five vertebrae. However, sometimes people are born with a sixth vertebra in the lumbar region. The base of your spine (sacrum) is a fusion of many bones, and when one of them forms as a vertebra rather than part of the sacrum, it is called a transitional (or sixth) vertebra. This occurrence is not dangerous and does not appear to have any serious side effects.

The lumbar spine’s shape has what is called a lordotic curve. The lordotic shape is like a backwards “C”. If you think of the spine as having an “S”-like shape, the lumbar region would be the bottom of the “S”. The vertebrae in the lumbar spine area are the largest of the entire spine, so the lumbar spinal canal is larger than in the cervical or thoracic parts of the spine. Because of its size, the lumbar spine has more space for the nerves to move about.

Low back pain is a very common complaint for a simple reason. Since the lumbar spine is connected to your pelvis, this is where most of your weight bearing and body movement takes place. Typically, this is where people tend to place too much pressure, such as: lifting up a heavy box, twisting to move a heavy load, or carrying a heavy object. Such repetitive injuries can lead to damage to the parts of the lumbar spine.

Thoracic Spine

The thoracic spine is made up of the middle 12 vertebra of the spine. These vertebrae connect to your ribs and form part of the back wall of the thorax (the ribcage area between the neck and the diaphragm). This part of the spine has very narrow, thin intervertebral discs, so there is much less movement allowed between vertebrae than in the lumbar or cervical parts of the spine. It also has less space in the spinal canal for the nerves. The thoracic spine’s curve is called kyphotic because of its shape, which is a regular “C”-shaped curve with the opening of the “C” in the front.

Cervical Spine

The cervical spine is made up of the first seven vertebrae in the spine. It starts just below the skull and ends just above the thoracic spine. The cervical spine has a lordotic curve (a backward “C”-shape) – just like the lumbar spine. The cervical spine is much more mobile than both of the other spinal regions – think about all the directions and angles you can turn your neck.

Unlike the rest of the spine, there are special openings in each vertebra in the cervical spine for the arteries (blood vessels that carry blood away from the heart), as well as the spinal canal that carries the spinal cord. The arteries that run through these openings bring blood to the brain.

Two vertebrae in the cervical spine, the atlas and the axis, differ from the other vertebrae because they are designed specifically for rotation. These two vertebrae are what allow your neck to rotate in so many directions, including looking to the side.

The atlas is the first cervical vertebra – the one that sits between the skull and the rest of spine. The atlas does not have a vertebral body, but does have a thick forward (anterior) arch and a thin back (posterior) arch, with two prominent sideways masses.

The atlas sits on top of the second cervical vertebra – the axis. The axis has a bony knob called the odontoid process that sticks up through the hole in the atlas. It is this special arrangement that allows the head to turn from side to side as far as it can. Special ligaments between these two vertebrae allow a great deal of rotation to occur between the two bones.

Though the cervical spine is very flexible, it is also very much at risk for injury from strong, sudden movements, such as whiplash-type injuries. This high risk of harm is due to: the limited muscle support that exists in the cervical area, and because this part of the spine has to support the weight of the head. This is a lot of weight for a small, thin set of bones and soft tissues to bear. Therefore, sudden, strong head movement can cause damage.

Copyright © 2003 DePuy Acromed.

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Spinal Anatomy and Back Pain

Spinal anatomy is a remarkable combination of strong bones, flexible ligaments and tendons, large muscles and highly sensitive nerves. It is designed to be incredibly strong, protecting the highly sensitive nerve roots, yet highly flexible, providing for mobility on many different planes.

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The spine is divided into four regions: the cervical spine, thoracic spine, lumbar spine, and sacral region. Watch: Spine Anatomy Overview Video

Most of us take this juxtaposition of strength, structure and flexibility for granted in our everyday lives—until something goes wrong. Once we have back pain, we’re driven to know what’s wrong and what it will take to relieve the pain and prevent a recurrence.

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Typical Anatomical Problems that Cause Back Pain

Many of the intricate structures in the spine can lead to pain, and pain can be concentrated the neck or back, and/or radiate to the extremities or be referred to other parts of the body. For example:

  • The large nerve roots that go to the legs and arms may become irritated or pinched
  • The smaller nerves that innervate the spine may be irritated due to inflammation or degeneration
  • The large paired back muscles (erector spinae) may be strained due to overuse or an injury
  • The bones, ligaments or joints themselves may be injured
  • The disc space in between the vertebrae may become painful
  • Any of the various joint complexes in the spine may degenerate and lead to pain

See Common Causes of Back Pain and Neck Pain

For anyone with a spine condition, understanding spinal anatomy is a good way to better inform and evaluate diagnostic and treatment options.

In This Article:

  • Spinal Anatomy and Back Pain
  • Vertebrae in the Vertebral Column
  • Spinal Discs
  • Spinal Cord and Spinal Nerve Roots
  • Back Muscles and Low Back Pain
  • Sacrum (Sacral Region)
  • Spine Anatomy Overview Video

Cervical, Thoracic, Lumbar and Sacral Spinal Anatomy

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The cervical region is the most flexible region of the spine, followed by the lumbar region and the thoracic region.

There are four major regions of the spine:

  1. The cervical spine (neck)

    The neck supports the weight of the head and protects the nerves that run from the brain to the rest of the body. This section of the spine has seven vertebral bodies (bones) that get smaller as they get closer to the base of the skull.

    See Cervical Spine Anatomy

    Most neck pain is caused by a muscle, ligament or tendon strain or sprain, and will usually heal with time and non-surgical treatments, such as ice and/or heat, medications, physical therapy, and more.

    See Neck Strain: Causes and Remedies

    With neck pain that lasts longer than two weeks to three months, or with mainly arm pain, numbness or tingling, there is often a specific anatomic problem. For example, pain that radiates down the arm, and possibly into the hands and fingers, is usually caused by a cervical herniated disc or foraminal stenosis pinching a nerve in the neck.

  2. See Understanding Hand Pain and Numbness

  3. The thoracic spine (upper back)
    The 12 vertebral bodies in the upper back make up the thoracic spine. The firm attachment of the rib cage at each level of the thoracic spine provides stability and structural support to the upper back and allows very little motion. The thoracic spine is basically a strong cage and it is designed to protect the vital organs of the heart and lungs.

    See Thoracic Spine Anatomy and Upper Back Pain

    The upper back is not designed for motion, so there is not much wear and tear or injury in this region of the spine. However, irritation of the large back and shoulder muscles or joint dysfunction in the upper back can produce very noticeable back pain. While less common, other issues such as a thoracic herniated disc are also possible.

  4. See All About Upper Back Pain

  5. The lumbar spine (lower back)
    The lower back has a lot more motion than the thoracic spine and carries the weight of the torso, which makes it more prone to injury.

    See Lumbar Spine Anatomy and Pain

    The motion in the lumbar spine is divided between five motion segments.

    • Most of the motion in the lumbar spine is at L3-L4 and L4-L5, so these segments are the most likely to breakdown from wear and tear—such as osteoarthritis or degenerative disc disease.
    • The two lowest discs (L4-L5 and L5-S1) take the most strain and are the most likely to herniate. This can cause lower back pain and possibly numbness that radiates through the leg and down to the foot (sciatica).

    See Lower Back Pain Symptoms, Diagnosis, and Treatment

    The vast majority of episodes of lower back pain are caused by muscle strain. While a muscle strain doesn’t sound like a serious injury, it can lead to issues in the lower back can cause severe pain. The good news is that soft tissues have a good blood supply, which brings nutrients to the injured area, facilitates the healing process and often provides effective relief of the back pain.

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  1. The sacral region (bottom of the spine)
    Below the lumbar spine is a bone called the sacrum, which makes up the back part of the pelvis. This bone is shaped like a triangle that fits between the two halves of the pelvis, connecting the spine to the lower half of the body.

    See Sacrum (Sacral Region)

    The sacrum is connected to part of the pelvis (the iliac bones) by the sacroiliac joints. Pain in the sacrum is often called sacroiliac joint dysfunction, and is more common in women than men.

    The coccyx—or the tailbone—is in the sacral region at the very bottom of the spine. Tailbone pain is called coccydynia, which is more common in women than men.

The Back

  • The Basics
    • Terminology
      • Anatomical Position
      • Body Planes
      • Terms of Movement
      • Terms of Location
      • Embryology Terms
    • Joints
      • Classification
      • Synovial Joint
      • Joint Stability
    • Histology
      • Bone
      • Skeletal Muscle
      • Blood Vessels
      • Nerves
      • Lymphatics
      • Skin
    • Embryology
      • Weeks 1-3
      • Dermatomes
      • Myotomes
      • The Limbs
      • Head and Neck
      • Cardiovascular System
      • Respiratory System
      • Urinary System
      • Reproductive System
      • Central Nervous System
    • Imaging
      • X-Ray
      • CT
      • MRI
  • Head
    • Areas
      • Scalp
      • Pterygopalatine Fossa
      • Infratemporal Fossa
      • Cranial Fossae
    • Bones
      • Skull
      • Bony Orbit
      • Sphenoid Bone
      • Ethmoid Bone
      • Temporal Bone
      • Mandible
      • Nasal Skeleton
      • Cranial Foramina
    • Muscles
      • The Tongue
      • Facial Expression
      • Extraocular
      • Mastication
    • Nerves
      • Sympathetic Innervation
      • Parasympathetic Innervation
      • Ophthalmic Nerve
      • Mandibular Nerve
      • Maxillary Nerve
    • Organs
      • The Ear
      • The Eye
      • Nose and Sinuses
      • Salivary Glands
      • Oral Cavity
    • Joints
      • TMJ
    • Vessels
      • Arterial Supply
      • Venous Drainage
      • Lymphatics
    • Other
      • Lacrimal Gland
      • Eyelids
      • Teeth
      • Palate
  • Neuroanatomy
    • Structures
      • Basal Ganglia
      • Cerebrum
      • Cerebellum
      • Meninges
      • Pineal Gland
      • Pituitary Gland
      • Spinal Cord (Grey Matter)
    • Brainstem
      • Midbrain
      • Pons
      • Medulla Oblongata
    • Pathways
      • Ascending Tracts
      • Descending Tracts
      • Visual Pathway
      • Auditory Pathway
    • Cranial Nerves
      • Summary
      • Olfactory Nerve (CN I)
      • Optic Nerve (CN II)
      • Oculomotor Nerve (CN III)
      • Trochlear Nerve (CN IV)
      • Trigeminal Nerve (CN V)
      • Abducens Nerve (CN VI)
      • Facial Nerve (CN VII)
      • Vestibulocochlear Nerve (CN VIII)
      • Glossopharyngeal Nerve (CN IX)
      • Vagus Nerve (CN X)
      • Accessory Nerve (CN XI)
      • Hypoglossal Nerve (CN XII)
    • Blood Vessels & CSF
      • Arterial Supply
      • Venous Drainage
      • Cavernous Sinus
      • Ventricles
  • Neck
    • Areas
      • Anterior Triangle
      • Posterior Triangle
    • Bones
      • Cervical Spine
      • Hyoid Bone
    • Organs
      • Pharynx
      • Larynx
      • Oesophagus
      • Thyroid Gland
      • Parathyroid Glands
    • Muscles
      • Suboccipital
      • Suprahyoids
      • Infrahyoids
      • Scalenes
    • Nerves
      • Phrenic Nerve
      • Cervical Plexus
    • Vessels
      • Arterial Supply
      • Venous Drainage
      • Lymphatics
    • Other
      • Fascial Layers
      • Tonsils (Waldeyer’s Ring)
  • Thorax
    • Areas
      • Superior Mediastinum
      • Anterior Mediastinum
      • Middle Mediastinum
      • Posterior Mediastinum
    • Bones
      • Ribs
      • Sternum
      • Thoracic Spine
    • Muscles
      • Thoracic Cage
      • Diaphragm
    • Organs
      • Thymus Gland
      • Mammary Glands
      • Heart
      • Lungs
      • Tracheobronchial Tree
      • Pleurae
    • Vasculature
      • Aorta
      • Superior Vena Cava
    • Bones
      • Vertebral Column
    • Muscles
      • Superficial
      • Intermediate
      • Deep
    • Nerves
      • Spinal Cord
  • Upper Limb
    • Areas
      • Axilla
      • Cubital Fossa
      • Carpal Tunnel
      • Extensor Tendon Compartments
      • Anatomical Snuffbox
    • Bones
      • Scapula
      • Clavicle
      • Humerus
      • Ulna
      • Radius
      • The Hand
    • Muscles
      • Pectoral Region
      • Shoulder Region
      • Upper Arm
      • Anterior Forearm
      • Posterior Forearm
      • Hand
    • Nerves
      • Brachial Plexus
      • Axillary Nerve
      • Musculocutaneous Nerve
      • Median Nerve
      • Radial Nerve
      • Ulnar Nerve
    • Joints
      • Acromioclavicular Joint
      • Sternoclavicular Joint
      • Shoulder Joint
      • Elbow Joint
      • Radioulnar Joints
      • Wrist Joint
    • Blood Vessels & Lymphatics
      • Arterial Supply
      • Venous Drainage
      • Lymphatics
  • Lower Limb
    • Areas
      • Femoral Triangle
      • Femoral Canal
      • Adductor Canal
      • Popliteal Fossa
    • Bones
      • Femur
      • Patella
      • Tibia
      • Fibula
      • The Foot
    • Muscles
      • Fascia Lata
      • Gluteal Region
      • Thigh
      • Leg
      • Foot
    • Nerves
      • Lumbar Plexus
      • Sacral Plexus
      • Femoral Nerve
      • Obturator Nerve
      • Sciatic Nerve
      • Tibial Nerve
      • Common Fibular Nerve
      • Superficial Fibular Nerve
      • Deep Fibular Nerve
    • Joints
      • Hip Joint
      • Knee Joint
      • Tibiofibular Joints
      • Ankle Joint
      • Subtalar Joint
    • Blood Vessels & Lymphatics
      • Arterial Supply
      • Venous Drainage
      • Lymphatics
    • Other
      • Foot Arches
      • Walking and Gaits
  • Abdomen
    • Areas
      • Abdominal Cavity
      • Calot’s Triangle
      • The Peritoneum
      • Inguinal Canal
      • Hesselbach’s Triangle
    • Bones
      • Lumbar Spine
    • Muscles
      • Anterolateral Abdominal Wall
      • Posterior Abdominal Wall
    • GI Tract
      • Oesophagus
      • Stomach
      • Small Intestine
      • Appendix
      • Cecum
      • Colon
      • Rectum
      • Anal Canal
    • Accessory Organs
      • Liver
      • Gallbladder
      • Pancreas
      • Spleen
      • Adrenal Glands
      • Kidneys
      • Mesentery
    • Vasculature
      • Arterial Supply
      • Venous Drainage
  • Pelvis
    • Areas
      • The Perineum
    • Bones
      • Hip Bone
      • Pelvic Girdle
      • Sacrum
      • Coccyx
    • Muscles
      • Pelvic Floor
    • Organs
      • Ureters
      • Urinary Bladder
      • Urethra
    • Male Repro
      • Penis
      • Testes and Epididymis
      • Scrotum
      • Spermatic Cord
      • Prostate Gland
      • Bulbourethral Glands
      • Seminal Vesicles
    • Female Repro
      • Vulva
      • Vagina
      • Cervix
      • Uterus
      • Fallopian (Uterine) Tubes
      • Ovaries
      • Supporting Ligaments
    • Vasculature
      • Arterial Supply
      • Venous Drainage
    • Other
      • Sacral Plexus
      • Pudendal Nerve
  • 3D Body
    • By Sex
      • Male Body
      • Female Body
    • By Area
      • Head and Neck
      • Thorax, Abdomen and Pelvis
      • Upper Limb
      • Lower Limb
    • By System
      • Skeletal
      • Muscular
      • Cardiovascular
      • Nervous
      • Lymphatic

The 30 Dermatomes Explained and Located

Each of your dermatomes is supplied by a single spinal nerve. Let’s take a closer look at both of these components of the body.

Your spinal nerves

Spinal nerves are part of your peripheral nervous system (PNS). Your PNS works to connect the rest of your body with your CNS, which is made up of your brain and spinal cord.

You have 31 pairs of spinal nerves. They form from nerve roots that branch from your spinal cord. Spinal nerves are named and grouped by the region of the spine that they’re associated with.

The five groups of spinal nerves are:

  • Cervical nerves. There are eight pairs of these cervical nerves, numbered C1 through C8. They originate from your neck.
  • Thoracic nerves. You have 12 pairs of thoracic nerves that are numbered T1 through T12. They originate in the part of your spine that makes up your torso.
  • Lumbar nerves. There are five pairs of lumbar spinal nerves, designated L1 through L5. They come from the part of your spine that makes up your lower back.
  • Sacral nerves. Like the lumbar spinal nerves, you also have five pairs of sacral spinal nerves. They’re associated with your sacrum, which is one of the bones found in your pelvis.
  • Coccygeal nerves. You only have a single pair of coccygeal spinal nerves. This pair of nerves originates from the area of your coccyx, or tailbone.

Your dermatomes

Each of your dermatomes is associated with a single spinal nerve. These nerves transmit sensations, such as pain, from a specific area of your skin to your CNS.

Your body has 30 dermatomes. You may have noticed that this is one less than the number of spinal nerves. This is because the C1 spinal nerve typically doesn’t have a sensory root. As a result, dermatomes begin with spinal nerve C2.

Dermatomes have a segmented distribution throughout your body. The exact dermatome pattern can actually vary from person to person. Some overlap between neighboring dermatomes may also occur.

Because your spinal nerves exit your spine laterally, dermatomes associated with your torso and core are distributed horizontally. When viewed on a body map, they appear very much like stacked discs.

The dermatome pattern in the limbs is slightly different. This is due to the shape of the limbs as compared with the rest of the body. In general, dermatomes associated with your limbs run vertically along the long axis of the limbs, such as down your leg.

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