Lumbar Spine (Lower Back) Anatomy and Function

The spinal column is made up of 26 bones: 24 unique vertebrae plus the sacrum and coccyx (tail bone) at the end of the backbone. The Vertebrae seem to be chained together). The vertebrae include:
• 7 cervical vertebrae which makes up the neck
• 12 thoracic vertebrae of the chest
• 5 lumbar vertebra or the “lower back”—L1, L2, L3, L4 and L5.

When You Want to Know MoreHere is more information about your nerves, spine and back:

The Spinal Column

Bones and disks of lumbar spine

Bones, disks and facet joints of lumbar spine

The back can move in many different directions, it can stiffen as well as be supple. When looked at from the back, the spine appears to be straight, but looked at from the side you can see 2 curves which cause the back to have an “S” shape—it curves forward at the neck (cervical spine) and lower back (lumbar spine) and slightly backwards at the thoracic spine and sacral region. These curves help support the head and provides strength, flexibility and provides super shock absorbing abilities. Many problems with the back are associated with the normal curvature of the back.

Between each vertebra is a cushion called an intervertebral disk. On the anterior side of each vertebra is an oval shaped disk called the vertebral body. On the posterior side of each vertebra is the vertebral foramen, which is an opening through which the spinal cord passes. A crucial job of the back is to protect and support the vital spinal cord and spinal nerves.

A Spinal Segment

Spinal Segment

Segment is made of two vertebrae, the intervertebral disk, and two spinal nerves

A spinal segment forms a functional unit and is made up of two adjacent vertebrae, the intervertebral disk between them, the two spinal nerves that exit from each side of the spinal cord, ligaments and muscles.

The Sacrum

Side view of the sacrum and tailbone

Side view of the sacrum and tailbone, the body of the sacrum forms a joint with the 5th lumbar vertebra.

The sacrum is the last segment of the spine. At birth, it is made of several vertebrae. By the time you’re an adult these vertebrae have fused together to form the sacrum. The Sacrum is a large, triangular bone, in the lower part of the vertebral column and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones; its upper part or base joins with the 5th lumbar vertebra by intervertebral fibrocartilage and at the bottom it joins with the coccyx or tailbone.

The Lumbar Spine

The Lumbar spine consists of the vertebral body, posterior elements, intervertebral disks, and ligaments. The lumbar spine is made up of the five lumbar vertebrae located between the thoracic spine and the sacrum. This area is commonly called the “lower back”. The lumbar vertebrae are the largest of the vertebrae because of their weight-bearing function supporting the torso and head.

L-5, the 5th lumbar vertebra.

L-5, the 5th lumbar vertebra.














Labeled lumbar vertebra

Labeled lumbar vertebra

The function of the structures of the lumbar spine are to protect and support the spinal cord and spinal nerves. The spinal nerves pass through a large hole (foramen) in the center of each vertebrae, which when lined up is called the spinal canal. The lumbar spinal nerves branch off the spinal cord at each level between the vertebrae. The joints—a joint is where two or more bones meet—between the vertebrae contain a disk (intervertebral disk) that acts as a shock absorber.

The vertebrae of the back are “linked” together by pedicles (lamina, transverse process, and spinous process) to form facet joints.

Ligaments of the Back

The function of ligaments is to attach bones to bones and give strength and stability to the back. Ligaments are strong, tough bands that are not very flexible. The vertebral bodies of the back are connected to each other by multiple ligaments which include:
• posterior longitudinal ligaments
• anterior longitudinal ligaments
• intertransverse ligaments
• interspinous ligaments
• supraspinous ligaments

Tendons of the Back

Tendons are elastic tissues that connect muscles to bones.

Muscles of the Back

Muscles support and move the spine.

Nerves of the Back

Lumbar segment, spine, nerves

Lumbar segment, spine, nerves

Vascular structures of the Back

Arteries supply the vertebrae, ligaments, and muscles with nourishment.

Problems, Treatments and Surgery for the Lumbar Spine

• Osteoporosis
• Osteomalacia
• Arthritis
• Ankylosing Spondylitis
• Sacroiliitis
• Lumbosacral sprain and strain
• Acute Cauda Equina Syndrome
• Intervertebral Disk Disease
• Scoliosis
• Spinal Instability
Herniated Disk
Spinal Stenosis

More About the Back

Back Injury
Lumbar Spinal Fusion Surgery


  1. Luana Guzman says:

    I was told I have l3/4 disk compressing my nerve roots “mildly” but my feet are burning really bad and numb from arch to toes on bottom. But I had a cervical fusion posterior, as soon I I woke up from surgery my feet was on fire. I’m confused it the burning and numbness come from my cervical or lumbar?

  2. I find going to the doc for a back problem is similar to taking my car to the garage, it’s trial and error. You get the doctor they choose for you and you will probably get the assistant that is not a real doctor but could luck up and make the correct diagnosis. When you get older, expect problems. I have had spinal surgery for scoliosis with rods and fusion. No problems until I had an accident. Take care of your back and don’t do stupid stuff, like lifting heavy objects. Know your limits and don’t let anyone talk you into doing anything you know is going to be a risk. You will suffer for it.

  3. There is a back pain along with a line like pain along the left leg that gets increase on walking. This is becoming difficult for me even to sleep. How could i overcome this problem by doing what kind of excersices. Please suggest me.

  4. We are asking questions, but we are really supposed to make comments.
    Hamisi Nuhu, you need to have an X-ray or scan of some sort. You need a diagnosis. No good doctor should give you medication and send you on your way without trying to discover what your problem is.

  5. what causes the spinous process to move over to the left or right?

  6. June Tomlinson says:

    What part(S) of of the body is served from the nerves coming out of L3,4 & 5. Thank you

  7. Laurie spicer says:

    Hi there, could you please tell me which nerves coming our at L1 serve which parts of the body?
    Many thanks
    Kindest regards

    Laurie spicer

  8. Patricia a Lynch says:

    I would like to know if you can get drop foot from the spinal surgery in the LS 5 area.

  9. Cindy Schmidler says:

    I am so sorry for your pain. Please, immediately see your doctor and get a second opinion or recommendation for a specialist. There are many other things this could be and finding out quickly from a qualified back specialist or neurologist is important.

  10. GIllian Snyders says:

    I would like to know my husband was at the doctor they said it is Arthrirtis in the spine he has severe lower back pain and even now at the moment pins and needles in his leg and the leg is lame from the hip and cannot feel anything in that area if you pinch it. what can it be. he do not sleep his whole body shakes because of the pain, Help what do we do. tabletts prescribed do not help. what next.

  11. i have a lower back for about two months,i have been given medication but there is NO remarkable change,please help.

  12. Media Partners says:

    Joann, There are many fibrous tissues around muscles, and nerves. It could just be a “sleeve” around the muscle, etc. It’s hard to say exactly which fibrous tissue was involved.

  13. I had a desectomy at L5, S1. After the surgery the doctor talked to my husband (very quickly and breifly) and said the piece of bone causing the pain had origined higher up the spine, dropped down perforated a “fibrous tissue” surroundding the neve and was pressing hard directly onto the nerve. He also said this tissue was very inflated but went down once the bone was removed. What is the firbous tissue called?

  14. Media Partners says:

    I think you are describing a herniated disk that is causing pressure on the nerve and pain down the leg. We do not offer medical advice. We just try to help you learn about health problems so you can better talk with your doctor or health care team about your own problem.

  15. i think the doctor told,my father problem is loss of the fiber protection of the ligament,the liquid is out and pressure to the nerve. what type surgery is better to this time. father occuring leg pain and very difficult to move

  16. thomas mullen says:

    im looking for a picture from the back view showing the lower lumbar region of the back can you help ?

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