When you are feeling pain or odd sensations in the distribution of the sciatic nerve you will be feeling it in your buttock and down the back and outer side of your leg. To fully understand what is causing this pain we need to understand where the sciatic nerve originates and what it is that could potentially be harming your sciatic nerve.
Where is the Sciatic Nerve Coming From?
Your sciatic nerve is a collection of nerve roots that branch off from the main spinal cord and the point at which it branches off is marked in relation to what vertebrae it exits under. For example, the L4 nerve root exits under the L4 vertebrae and the L5 nerve root exits under the L5 vertebrae. The letter “L” stands for lumbar region of the back.
The Sciatic nerve is the largest nerve in the body and it is a nerve formed by the coming together of nerve roots L4, L5, S1, S2 and S3. The sciatic nerve comes together outside the spine within the pelvis and then exits the pelvis by passing under the piriformis muscle (a muscle that can potentially pinch the sciatic nerve). When the sciatic nerve continues to travel down the leg it branches off at different points giving “nerve power” to different areas of the foot and leg. So just where is the sciatic nerve? it is basically in the back of your upper leg under layers of muscle.
If you have a tingling sensation say on the outside of your foot your doctor or physiotherapist will use this information to diagnose you with having symptoms of sciatica but knowing where exactly the sciatic nerve is being irritated requires more testing. The nerve can be injured anywhere along its length but the most common place is within the spine around L4, L5. This can happen when the nerve root gets pinched by either abnormal bone growth in the area, the spine is being compressed causing the exit points for the nerve root to narrow, or the softer disc tissue between the vertebrae is bulging out onto the nerve root. This type of injury can be visualized on an MRI or CT scan of the lower back.
The Skeletal Framework
Now where is the sciatic nerve in relation to your spine? The spine consists mainly of bony vertebrae that stack on top of one another with padding in between them call intervertebral discs. There are exit points at each level where nerve roots exit from the spinal cord and then these meet up with other nerve roots outside the spine to form the sciatic nerve. The long spinal column of bones is all interconnected via muscles, tendons and other connective tissue with the skull, ribs and pelvis bones.
As seen in the picture above as a blue padding between the vertebrae (bones) is the intervertebral disc and it is anchored to the vertebrae by a layer of hyaline cartilage and it is composed of strong outer rings called the Anulus Fibrosus and a gel like center (the lemon filling in your donut, if you will) called the Nucleus Pulposus. What these structures are called are not as important as what they do and what goes wrong that it can cause nerve pain.
Where is the Sciatic Nerve in Relation to the Intervertebral Disc?
The intervertebral disc is there to act as a shock absorber and to give a wide range of motion to the spine. This padding is between the vertebral bodies (bones) and over time due to poor posture, long sitting, frequent bending, or lifting improperly we can wear out the disc quickly and cause it to bulge out into what is called the intervertebral foramen where the nerve root exits; or in rare cases into the spinal canal where the major spinal cord is.
As seen in the picture above the nerve root and its intervertebral foramen that it passes through is adjacent to the disc so with such close proximity even a slight bulge in the disc could cause radiating symptoms down the leg. Also pictured above is how the bulge can be on either side of the nerve root. There are many nerve roots exiting from the spine at each level and there are five nerve roots in the lower back that come together after they exit the spine to form the sciatic nerve.
How and Where is the Sciatic Nerve Protected?
The spine is not straight up and down when viewed from the side but has a cervical (neck) curve, a Thoracic (upper back) curve, a Lumbar (lower back) curve, and a sacral/coccygeal curve. All these curves work to balance out the weight of the body evenly, if this is out of balance due to lost curvature or excessive curvature then stress will be placed on an area of the spine and cause back pain or injury over time.
The spinal cord that is basically a continuation of the central nervous system from the brain travels down a pathway through the spine. Then at each level of the spine’s vertebrae nerve roots exit and enter the body to send and receive information. The spinal cord is protected extensively by the bones, connective tissues, and muscles of the spine as they act as protective layers and work together to hold normal balanced posture.