Each level of your spine gives rise to a pair of spinal nerves that control specific muscles, skin areas, and organ functions. You have 33 vertebrae and 31 pairs of spinal nerves, divided into cervical (neck), thoracic (mid-back), lumbar (lower back), sacral, and coccygeal regions. Here’s what each level is responsible for, from top to bottom.
How Spinal Nerves Relate to Vertebrae
Before diving into the map, one important detail: the nerve that exits at a given vertebral level doesn’t always match the number you’d expect. In the neck, cervical nerves C1 through C7 exit above their same-numbered vertebra. C8 exits between the last cervical vertebra (C7) and the first thoracic vertebra (T1). From T1 downward, every nerve exits below its matching vertebra.
The spinal cord itself ends at around the first or second lumbar vertebra in adults, tapering to a point called the conus medullaris. Below that, a bundle of nerve roots called the cauda equina (Latin for “horse’s tail”) fans out through the lower spinal canal to reach the lumbar, sacral, and coccygeal exit points. This means that injuries to the lower spine compress nerve roots rather than the spinal cord itself, which changes the pattern of symptoms.
Cervical Spine: C1 Through C8
The cervical region is the command center for your head, neck, shoulders, arms, and hands. The spinal cord is actually wider here than in other regions because so many nerve fibers are packed together to serve the upper limbs.
C1 and C2 mostly serve the head and upper neck. C1 helps control small muscles involved in swallowing. C2 provides sensation to the scalp behind and above the ear, and to the skin over the side of the neck. Together, C1 and C2 allow you to nod and rotate your head.
C3 and C4 are critical for breathing. Both contribute to the phrenic nerve, which powers the diaphragm. C3 provides sensation to the front of the neck, while C4 covers the skin over the collarbone and top of the shoulder. C4 also helps supply the trapezius, the large muscle across your upper back and neck. Injuries at C3 or above can compromise the ability to breathe without mechanical assistance.
C5 also feeds into the phrenic nerve and is the main driver of shoulder movement. It powers the deltoid (the muscle that lifts your arm out to the side), contributes to the muscles that stabilize the shoulder blade, and provides sensation to the outer shoulder and upper arm.
C6 controls forearm muscles that rotate the wrist and extend it upward. It supplies the rotator cuff muscles (supraspinatus and infraspinatus) that stabilize the shoulder joint. Sensation from C6 typically covers the thumb side of the forearm and hand.
C7 is the primary nerve root for extending the elbow and wrist. It contributes to the radial nerve, which controls all the extensor muscles running along the back of the forearm. It also helps power the latissimus dorsi, the broad muscle of the back used in pulling motions.
C8 controls grip strength and fine finger movements. It dominantly supplies the small muscles of the hand on the pinky side, and provides sensation to the little finger. C8 also contributes to the ulnar nerve, which is the nerve you feel when you hit your “funny bone.”
Thoracic Spine: T1 Through T12
The thoracic region is unique for two reasons: it supports the rib cage, and it houses the origin of the sympathetic nervous system, the network responsible for your body’s “fight or flight” responses. Sympathetic nerve fibers exit the spinal cord from T1 all the way down to L2, influencing heart rate, blood pressure, sweating, and digestion.
T1 bridges the gap between your arms and trunk. It’s part of the brachial plexus, the nerve network that serves the arms and hands, and it dominantly controls the small muscles at the base of the thumb and the flexor muscles of the fingers. If you can spread your fingers apart or pinch with precision, T1 is involved.
T2 sends nerves into the upper chest and inner arm. Together with T1, these nerves serve the top of the chest wall.
T3 through T5 supply the chest wall muscles and work with the diaphragm to control breathing. The intercostal muscles between your ribs, which expand and contract the rib cage with every breath, are powered by these levels.
T6 through T12 control the abdominal and lower back muscles. These nerves are essential for posture, balance, and forceful actions like coughing or bearing down. Two useful landmarks help doctors locate the level of a thoracic nerve problem: the T4 nerve supplies sensation at the level of the nipples, and T10 corresponds to the navel.
Because the thoracic spine also relays signals to major organs, damage here can affect the lungs, heart, and digestive organs. The lower thoracic nerves (T6 through T12) help regulate abdominal organ function, including parts of the liver and intestines.
Lumbar Spine: L1 Through L5
The lumbar region carries the heaviest loads and is the most common site of disc herniations and nerve compression. These five vertebral levels control your hips, thighs, and much of your lower legs.
L1 supplies the muscles of the lower abdomen (internal oblique and transverse abdominal muscles) and provides sensation to the upper front of the thigh and the lateral buttock area. It also contributes to sensation in the groin.
L2 and L3 power hip flexion, the motion of lifting your knee toward your chest. They feed into the femoral nerve, the largest nerve from the lumbar plexus, which controls the quadriceps (the big muscles on the front of your thigh). L2 and L3 also supply sensation to the outer and front portions of the thigh.
L4 continues to contribute to knee extension through the quadriceps and provides sensation to the inner lower leg down to the area around the kneecap via the saphenous nerve. L4 is also associated with the ankle, though whether it or L5 is the dominant nerve for lifting the foot upward (dorsiflexion) remains a point of debate in neurology.
L5 is the workhorse for foot and toe movement. It primarily controls the ability to lift your foot and extend your big toe. Compression of the L5 nerve root is one of the most common causes of foot drop, where the foot slaps the ground during walking. L5 sensation covers the top of the foot and the outer shin.
Together, L2 through L4 also form the obturator nerve, which powers the adductor muscles on the inner thigh, the ones you use to squeeze your legs together.
Sacral and Coccygeal Nerves: S1 Through S5
The five sacral vertebrae are fused into a single bone in adults, but five pairs of nerve roots still exit through small openings on each side. These nerves control the lower legs, feet, and pelvic organs.
S1 powers the calf muscles used for pushing off the ground when walking, and it controls the ankle jerk reflex that doctors test by tapping your Achilles tendon. S1 also supplies the short head of the biceps femoris, one of the hamstring muscles. Sensation from S1 covers the outer edge and sole of the foot.
S2 through S4 are the origin of the sacral parasympathetic nervous system, which handles “rest and digest” functions below the waist. These nerves control the bladder, bowel, and sexual organs. The parasympathetic fibers from S2 to S4 specifically supply the descending colon, sigmoid colon, and rectum. Surgical data makes the importance of S3 especially clear: when both S3 nerve roots are preserved during sacral surgery, 100% of patients retain normal bowel function and 69% retain normal bladder function. When S3 is lost on both sides, those numbers drop sharply, with only 25% retaining bladder control.
S4 and S5, along with the single coccygeal nerve, supply the pelvic floor muscles and provide sensation to the skin around the tailbone and perineum, an area sometimes called the “saddle region.”
What Nerve Compression Feels Like by Region
When a herniated disc, bone spur, or other structure presses on a spinal nerve, the symptoms follow predictable patterns based on the level involved. In the cervical spine, compression often causes pain, tingling, or weakness radiating into a specific part of the arm or hand. C6 compression, for example, typically causes thumb-side weakness and numbness, while C8 compression affects grip strength and the pinky finger.
Cervical spinal cord compression (myelopathy) can produce a broader set of problems: clumsiness in the hands, stiff or weak legs, difficulty walking, and sometimes an “electric shock” sensation down the spine when bending the neck forward. This sensation, called Lhermitte sign, is a hallmark of cervical myelopathy.
In the thoracic spine, nerve compression is less common because this region is stabilized by the rib cage, but when it happens, it produces a band-like pain or numbness wrapping around the chest or abdomen at the affected level.
Lumbar nerve compression is the most frequent culprit behind sciatica, the shooting pain that travels from the lower back down one leg. An L5 problem sends pain along the outer leg to the top of the foot. An S1 problem sends it down the back of the leg to the sole.
Compression of multiple nerve roots below the end of the spinal cord produces a condition called cauda equina syndrome. Its hallmark symptoms include urinary retention (the bladder fills but you don’t feel the urge to go), loss of bowel or bladder control, numbness in the groin and buttocks, and weakness in both legs. This is a surgical emergency because permanent damage to bladder and bowel function can result if the pressure isn’t relieved quickly.
The Autonomic Layer
Beyond the muscles and skin you can consciously feel, your spine also houses the wiring for automatic body functions. The sympathetic system, originating from T1 through L2, speeds up your heart, widens your airways, slows digestion, and triggers sweating. The parasympathetic system has two sources: four cranial nerves in the brainstem (including the vagus nerve, which influences heart rate, digestion, and more) and the sacral nerves S2 through S4, which manage bladder emptying, bowel motility, and sexual arousal.
This is why spinal cord injuries don’t just affect movement and sensation. Depending on the level, they can alter blood pressure regulation, temperature control, digestion, and bladder function in ways that aren’t always obvious at first.