The sciatic nerve: a plain guide to the body's largest nerve
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- Lumbar support cushion. Best for: Long stretches of sitting at a desk or in the car. See options on Amazon
- Sit-stand desk converter. Best for: Desk workers who sit most of the day. See options on Amazon
- Firm exercise mat. Best for: Core and back exercises at home. See options on Amazon
Where the sciatic nerve starts and runs
StatPearls, the NIH-hosted medical reference, says the sciatic nerve arises from the ventral rami of spinal nerves L4 through S3: two roots from the lower back (lumbar) and three from the sacrum. These join in the pelvis, and the nerve leaves the pelvis through an opening called the greater sciatic foramen, usually passing below the piriformis muscle in the buttock.
From there it runs down the back of the thigh. Just above the back of the knee, it divides into two branches:
- Tibial nerve: continues down the back of the leg into the foot.
- Common fibular (peroneal) nerve: wraps toward the outer and front of the lower leg.
Cleveland Clinic adds that the nerve is narrow at the lower back and gets slightly wider down the leg; at its widest it is about the size of a penny.
What it does
Cleveland Clinic describes two jobs:
| Function | What it covers |
|---|---|
| Motor (movement) | Helps the muscles of the legs and feet move. StatPearls lists the hamstrings at the back of the thigh, the calf muscles through the tibial branch, and the muscles that lift the foot and toes through the fibular branch. |
| Sensory (feeling) | Lets you feel touch, pain and temperature. StatPearls says it supplies the skin of most of the lower leg and foot, except the inner side of the leg. |
Cleveland Clinic notes that although the nerve passes through the buttock, it does not control the buttock muscles.
What can go wrong
Sciatica. Most problems start at the nerve roots in the spine. StatPearls says most sciatica has a spinal cause, such as a disc herniation affecting the L5 or S1 root. The NHS lists a slipped disc as the most common cause, along with spinal stenosis, spondylolisthesis and back injury. The result is pain, tingling, numbness or weakness down the back of one leg.
Piriformis problems. StatPearls says that in about 10% of people the nerve passes through or above the piriformis muscle rather than below it, and describes piriformis syndrome, in which the muscle compresses the nerve, with hip and buttock pain that worsens with sitting and driving.
Other causes. Mayo Clinic notes diabetes raises the risk of nerve damage, and StatPearls notes a poorly placed injection in the buttock can injure the nerve.
For what nerve pain actually feels like, see what sciatica feels like.
Looking after it
Prevention is not always possible, Mayo Clinic says, and sciatica can come back. The habits the sources agree on:
- Regular exercise that strengthens the core and lower back (Mayo Clinic)
- Good posture when sitting, with lower back support (Mayo Clinic), and limiting long periods of sitting (Cleveland Clinic)
- Lifting heavy things safely, with good technique (Mayo Clinic, NHS)
- A healthy weight and not smoking (NHS, Cleveland Clinic)
- Supportive shoes and clear, well-lit walkways to prevent falls (Cleveland Clinic)
When sciatic nerve symptoms are an emergency
StatPearls says cauda equina syndrome, a serious compression of the nerve roots at the base of the spine, is suspected when there is urinary retention or altered sensation around the anus, and it needs prompt surgery. The NHS lists the signs to act on immediately: sciatica in both legs, severe or worsening weakness or numbness in both legs, numbness around or under the genitals or around the bottom, and new bladder or bowel problems. Full details are in sciatica warning signs.
What to look for when you buy
Lumbar support cushion
Best for: Long stretches of sitting at a desk or in the car
Mayo Clinic suggests good sitting posture with lower back support as one way to lower the risk of sciatica.
Watch out: Support is not a license to sit longer; get up regularly.
See options on AmazonSit-stand desk converter
Best for: Desk workers who sit most of the day
Cleveland Clinic says sitting too much and not moving enough may affect spine health, and Mayo Clinic lists prolonged sitting as a sciatica risk factor.
Watch out: Standing still all day is not the answer either; alternate and walk.
See options on AmazonFirm exercise mat
Best for: Core and back exercises at home
Mayo Clinic points to regular exercise that strengthens the core and lower back as a prevention habit.
Watch out: If you already have sciatica, start gently and stop moves that send pain down the leg.
See options on AmazonQuestions people ask
- Where is the sciatic nerve located?
- It starts from nerve roots in the lower spine, passes through the buttock, and runs down the back of each thigh before splitting near the knee into branches for the lower leg and foot.
- What nerve roots form the sciatic nerve?
- StatPearls says it arises from spinal nerves L4 through S3.
- How big is the sciatic nerve?
- It is the largest nerve in the body. Cleveland Clinic says at its widest it is about the size of a penny.
- What does the sciatic nerve control?
- Movement in much of the leg and foot, including the hamstrings, calf and the muscles that lift the foot, plus feeling in most of the lower leg and foot.
- Is sciatica a problem with the sciatic nerve itself?
- Usually the trouble is at the nerve roots in the spine, often from a slipped disc. Cleveland Clinic also describes sciatica-like conditions involving nearby nerves that feel the same.
Sources
- Anatomy, Sciatic Nerve (StatPearls) (ncbi.nlm.nih.gov), NIH National Library of Medicine, NCBI Bookshelf
- Sciatica: What It Is, Causes, Symptoms, Treatment and Pain Relief (my.clevelandclinic.org), Cleveland Clinic
- Sciatica (nhs.uk), NHS
- Sciatica: Symptoms and causes (mayoclinic.org), Mayo Clinic