Spinal nerves are the cables that link the spinal cord to the rest of the body. There are 31 pairs of them. They carry signals out to the muscles, and they carry signals back in from the skin and the joints.
Every spinal nerve is a mixed nerve. It carries both sensory and motor fibers at the same time. So one nerve can report what a part of the body feels and also drive a movement in that same part.
What Are Spinal Nerves?
A spinal nerve begins at the spinal cord and leaves through a gap between two vertebrae. That gap is the intervertebral foramen. Once outside, the nerve travels to a target that may be far from the spine.
The nerves are named by the region they leave from and are numbered in order from top to bottom. Eight pairs leave the neck. Twelve leave the chest. Five leave the lower back. Five leave the pelvis. One pair leaves at the very base of the spine.
| Region | Pairs | Levels |
| Cervical (neck) | 8 | C1 to C8 |
| Thoracic (chest) | 12 | T1 to T12 |
| Lumbar (lower back) | 5 | L1 to L5 |
| Sacral (pelvis) | 5 | S1 to S5 |
| Coccygeal (base) | 1 | Co1 |
| Total | 31 |
The 31 pairs of spinal nerves, grouped by the region they leave from. The numbering runs from the neck down to the base of the spine.
How the 31 Pairs Are Numbered
The numbering is not just a label. It is a map the body follows. A nerve at a known level serves a known stretch of skin and a known set of muscles.
That is why the level matters in medicine. If a nerve is pinched, the symptoms appear in the area that nerve serves. The pattern of symptoms points a doctor to the level involved.
One detail is worth knowing. The spinal cord itself stops around the first or second lumbar vertebra, well above the base of the spine. The nerves below that point still leave the column, but they travel down inside it first. That bundle of descending nerves is the cauda equina.
How a Spinal Nerve Forms
Two roots join to make one spinal nerve. One root is sensory. The other is motor. They meet inside the intervertebral foramen and travel onward as a single bundle.
The Dorsal Root Carries Sensation
The dorsal root sits at the back of the cord. Its fibers carry sensory information toward the spinal cord. They bring news of touch, temperature, pain and the position of the limbs.
The cell bodies of those sensory neurons do not sit inside the cord. They sit in a swelling on the dorsal root called the dorsal root ganglion.
The Ventral Root Carries Movement
The ventral root sits at the front of the cord. Its fibers carry motor commands away from the spinal cord to skeletal muscle. The cell bodies of these motor neurons sit inside the gray matter of the cord itself.
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| A segment of the spinal cord seen from its right side, with the dura opened to show the nerve roots leaving the cord. Image: Henry Vandyke Carter, public domain, via Wikimedia Commons |
Because the two roots join, the finished spinal nerve carries both kinds of fiber. This is what makes it a mixed nerve. The diagram below shows how the fibers are arranged once they have merged.
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| A scheme showing the structure of a typical spinal nerve, with its sensory, motor and autonomic fibers labelled. Image: Henry Vandyke Carter, public domain, via Wikimedia Commons |
The Rami and the Nerve Plexuses
The mixed nerve does not stay as one bundle for long. Just after it forms, it splits into two branches. Each branch is called a ramus.
Here is the part that is easy to get wrong. Both rami carry mixed fibers. Both carry sensory and motor signals. They differ in where they go, not in what they carry.
The Dorsal Ramus
The dorsal ramus is the smaller of the two. It curves toward the back. It supplies the deep muscles that run beside the spine and a strip of skin over the back.
The Ventral Ramus
The ventral ramus is the larger branch. It serves the front and the sides of the trunk, and it serves the limbs. Most of the body's deliberate movement and most of its conscious feeling travels this way.
The Four Main Plexuses
In the limbs, a single spinal nerve is not enough. Fibers from several levels mix and re-sort themselves into networks called plexuses. A plexus is a place where fibers swap partners. The nerve that leaves it carries fibers from more than one spinal level.
The cervical plexus serves the neck and part of the head. It also sends the phrenic nerve down to the diaphragm, the muscle that does most of the work of breathing.
The brachial plexus serves the shoulder and the whole upper limb. The lumbar plexus serves the lower abdomen and the front of the leg.
The sacral plexus serves the pelvis, the buttocks and the back of the leg. It gives rise to the sciatic nerve, the largest nerve in the body.
Sources do not all draw the exact root ranges of these plexuses the same way. The brachial plexus, for instance, is listed as C4 to T1 in some texts and C5 to T1 in others. The boundaries are a matter of definition, not a sharp line in the body.
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| The four main nerve plexuses, showing how spinal nerves re-sort into the networks that serve the limbs. Image: OpenStax, CC BY 4.0, via Wikimedia Commons |
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| The brachial plexus, with the spinal nerves that feed into it shown in color. Image: Selket and Marshall Strother, CC BY-SA 3.0, via Wikimedia Commons |
Dermatomes: A Map of Sensation
Each spinal nerve supplies a strip of skin. That strip is called a dermatome. Taken together, the dermatomes form a map of the body's surface.
Doctors use that map to work out which spinal level is causing trouble. If a patch of skin has lost feeling, the dermatome it belongs to points to the nerve root that has failed.
The map is a guide rather than a set of exact tiles. Neighboring dermatomes overlap. A single patch of skin usually draws signals from more than one spinal nerve at once.
Dermatomes cover the whole body except the face. The face is served by cranial nerves, which do not travel through the spinal cord.
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| The dermatomes of the body in an anterior view, each labelled with the spinal nerve that supplies it. Image: Mikael Häggström, public domain, via Wikimedia Commons |
Reflexes and Nerve Damage
A reflex is a fast, automatic response to a stimulus. Some reflexes are wired to run through the spinal cord alone, without waiting for the brain.
Spinal Reflexes
The withdrawal reflex is the classic example. Touching something hot triggers sensory fibers in the dorsal root. Inside the cord, the signal passes to motor neurons. Those motor neurons fire through the ventral root and pull the hand back.
The brain is told what happened, but it is not needed to make the movement happen. That is why the hand is already moving before the pain is felt.
When a Spinal Nerve Is Compressed
A spinal nerve can be squeezed or irritated somewhere along its path. The medical word for this is radiculopathy.
A herniated disc is a common cause. The soft center of a disc pushes out and presses on a nearby nerve root. Spinal stenosis is another cause. Here the canal that carries the cord and the nerves becomes narrow.
The symptoms follow the nerve. Pain, tingling, numbness and weakness can appear in the area that nerve serves. That pattern is what points to the level involved.
Not every compressed nerve causes symptoms. Some people have clear pressure on a nerve and feel nothing at all.
Key Terms in Plain English
These are the words in this article that would send you to a dictionary. Each one is given here the way it is actually used above.
| Term | What it means |
| Spinal nerve | A mixed nerve that leaves the spinal cord and carries sensory and motor fibers between the cord and the body. |
| Dorsal root | The rear root of a spinal nerve, carrying sensory information toward the spinal cord. |
| Ventral root | The front root of a spinal nerve, carrying motor commands away from the spinal cord to muscle. |
| Dorsal root ganglion | A swelling on the dorsal root that holds the cell bodies of the sensory neurons. |
| Ramus | One of the two branches a spinal nerve splits into after it forms: a dorsal ramus and a ventral ramus. |
| Mixed nerve | A nerve that carries both sensory and motor fibers. Every spinal nerve is a mixed nerve. |
| Intervertebral foramen | The gap between two vertebrae that a spinal nerve passes through as it leaves the spine. |
| Plexus | A network where fibers from several spinal levels mix and re-sort into new nerves, such as the brachial plexus in the arm. |
| Dermatome | The strip of skin supplied by a single spinal nerve. Dermatomes overlap their neighbors. |
| Myotome | The group of muscles supplied by a single spinal nerve. |
| Reflex arc | The route a reflex follows: a sensory fiber carries a signal in, and a motor fiber carries the response straight back out. |
| Cauda equina | The bundle of spinal nerves that descends inside the spine below the point where the spinal cord itself ends. |
| Radiculopathy | The medical term for symptoms caused by a spinal nerve root being compressed or irritated. |
| Herniated disc | A disc whose soft center pushes out and presses on a nearby nerve root. |
| Spinal stenosis | Narrowing of the canal that carries the spinal cord and the spinal nerves, which can compress them. |
| Phrenic nerve | The nerve from the cervical plexus that drives the diaphragm, the main muscle of breathing. |
Key terms used in this article, defined for quick reference.
Key Takeaways
- There are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal pair.
- Each spinal nerve is a mixed nerve, carrying sensory fibers toward the cord and motor fibers out to the muscles.
- The dorsal root is sensory and the ventral root is motor, but once the roots merge, both rami carry mixed fibers.
- The smaller dorsal ramus serves the back, while the larger ventral ramus serves the trunk, the limbs and the plexuses.
- In the limbs, fibers from several levels mix in plexuses, so the nerve that leaves carries fibers from more than one level.
- A dermatome is the strip of skin supplied by one spinal nerve, and neighboring dermatomes overlap.
- Some reflexes run through the spinal cord alone, which is why a hand can pull back from heat before the pain is felt.
Frequently Asked Questions
How many spinal nerves are there?
There are 31 pairs. They are grouped as 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal pair, and each pair is numbered by the level it leaves from.
What is the difference between a dorsal root and a dorsal ramus?
The dorsal root is one of the two roots that join to form the spinal nerve, and it carries sensory fibers only. The dorsal ramus is a branch of the finished nerve, and it carries mixed fibers that serve the muscles and skin of the back.
Why do the roots and the rami carry different kinds of fiber?
The roots are the two inputs that come together, so each one carries a single kind of fiber: sensory in the dorsal root, motor in the ventral root. Once they merge into one nerve and then split into rami, both branches carry the same mix.
What is a nerve plexus?
A plexus is a network where fibers from several spinal levels mix and re-sort themselves. The brachial plexus, which serves the arm, is one example.
Why does a pinched nerve cause numbness in one area?
Each spinal nerve supplies a known strip of skin, called a dermatome, and a known set of muscles. When that nerve is compressed, symptoms appear in the area it serves, which is what lets a doctor work out the level involved.
Key references
• StatPearls: Neuroanatomy, Spinal Nerves (NCBI Bookshelf)
• StatPearls: Anatomy, Skin, Dermatomes (NCBI Bookshelf)
• Cleveland Clinic: Dermatomes
• Cleveland Clinic: Herniated Disk
• Cleveland Clinic: Spinal Stenosis
• Cleveland Clinic: Radiculopathy
• OpenStax Anatomy and Physiology: The Peripheral Nervous System
Sources: StatPearls "Neuroanatomy, Spinal Nerves" and "Anatomy, Skin, Dermatomes" on the NCBI Bookshelf, the Cleveland Clinic pages on dermatomes, herniated disk, spinal stenosis and radiculopathy, and the OpenStax Anatomy and Physiology chapter on the peripheral nervous system. Each was opened and read on 16 October 2026. The count of 31 pairs and its breakdown by region, the sensory role of the dorsal root and the dorsal root ganglion, the motor role of the ventral root, the fact that both rami carry mixed fibers, the supply of the four main plexuses, the overlap between dermatomes, and the pattern of symptoms caused by a compressed nerve root all follow those sources. Where the sources differ on the exact root range of a plexus, the article says so rather than choosing one. Figures are from Wikimedia Commons under the license named in each caption. This article is for education and is not medical advice.
