Your nervous system is running the show right now. As you read these words, electrical signals are zipping from your eyes to your brain at roughly 268 miles per hour, translating squiggles on a screen into meaning. Every breath you take, every itch you scratch, every memory you recall — all of it is orchestrated by a sprawling network of nerves, fibers, and tissues that stretches into every corner of your body.
The human nervous system contains about 7 trillion nerves and approximately 100 billion neurons in the brain alone. It is, by any measure, one of the most sophisticated communication systems found in nature. And yet, most of us go through life without giving it a second thought — until something goes wrong.
That is exactly why understanding the basic parts of your nervous system matters. Whether you are a student, a fitness enthusiast, or someone dealing with nerve-related discomfort, knowing what is happening inside your body gives you a real edge. Below, you will find a clear breakdown of each major part — what it is, where it sits, and what it does for you every single day.
Nervous System Parts Diagram & Details
The diagram presents a full, front-facing view of the human body with the major components of the nervous system highlighted in blue and red. At the very top sits the brain and cerebellum, colored in pink, with the spinal cord extending downward through the center of the body in a striking red line. From the spinal cord, an intricate web of blue nerve fibers branches outward — reaching into the arms, torso, and legs like the roots of an enormous tree. Each nerve and nerve cluster is labeled clearly, starting from the upper body’s brachial plexus and radiating all the way down to the superficial peroneal nerve near the feet.
What stands out most is just how interconnected everything is. No nerve exists in isolation. The diagram shows a continuous chain of communication, from the command center in your skull to the tips of your toes. With that picture in mind, let’s walk through each labeled part one by one, so you know exactly what role it plays in keeping you alive and functioning.
1. Brain
The brain is the central command hub of your entire nervous system. Sitting inside your skull and weighing about three pounds, it processes every piece of information your body sends and receives. It handles everything from conscious thought and decision-making to regulating your heartbeat and body temperature without you even noticing.
What makes the brain so remarkable is its sheer processing power. It contains roughly 86 billion neurons, each forming thousands of connections with other neurons. That web of connections is what allows you to learn a new language, recall the smell of your grandmother’s kitchen, or pull your hand away from a hot stove in a fraction of a second.
Beyond processing, the brain also initiates action. When you decide to pick up a glass of water, your brain sends electrical signals down through the spinal cord and out to the muscles in your arm and hand. It is both the thinker and the doer — and every other part on this list ultimately reports back to it.
2. Cerebellum
Tucked right beneath the back of the brain, the cerebellum is sometimes called the “little brain.” It makes up only about 10% of the brain’s total volume, but it contains more than half of the brain’s neurons. That density should tell you something about how hard this structure works.
The cerebellum’s primary job is coordination. It fine-tunes your voluntary movements so they are smooth and precise rather than jerky and clumsy. Reaching for your coffee mug without knocking it over, walking in a straight line, typing on a keyboard — the cerebellum is quietly managing all of it behind the scenes.
It also plays a major role in balance and posture. Signals from your inner ear, your eyes, and sensory receptors throughout your body all feed into the cerebellum. It uses this constant stream of data to make real-time adjustments, which is why damage to the cerebellum often shows up as unsteadiness, tremors, or difficulty with precise movements.
3. Spinal Cord
The spinal cord is the main highway between your brain and the rest of your body. It runs from the base of the brain down through the vertebral column, protected by a series of bony vertebrae. In most adults, it is about 18 inches long and roughly as thick as your index finger.
Every motor command heading from your brain to your muscles travels down through the spinal cord. Likewise, every sensory signal heading up from your skin, joints, and organs passes through it on the way to the brain. Cut this highway, and communication below the injury point stops — which is why spinal cord injuries can cause paralysis.
But the spinal cord is more than a passive cable. It also manages certain reflexes on its own. When you accidentally touch something sharp, a reflex arc in your spinal cord can trigger your hand to pull away before the pain signal even reaches your brain. That split-second shortcut can mean the difference between a minor poke and a serious wound.
4. Brachial Plexus
The brachial plexus is a dense network of nerves located near your neck and shoulder. It forms from the spinal nerves of the lower neck (C5 through T1), and these nerves weave together before branching out to supply your shoulder, arm, forearm, and hand.
Think of it as a distribution hub. Signals coming from the spinal cord get sorted and routed through the brachial plexus to reach the correct destination in your upper limb. Every time you lift your arm, grip a doorknob, or wave hello, the brachial plexus is directing the electrical traffic that makes those actions possible.
Because of its exposed position between the neck and shoulder, the brachial plexus is vulnerable to injury. A hard fall, a motorcycle accident, or even a difficult birth can stretch or tear these nerves, leading to weakness, numbness, or complete loss of function in the arm. Recovery depends heavily on the severity and location of the damage.
5. Musculocutaneous Nerve
Branching off from the brachial plexus, the musculocutaneous nerve runs down the front of your upper arm. Its name gives away its dual role: it serves both muscles (“musculo”) and skin (“cutaneous”).
On the motor side, this nerve powers the muscles responsible for bending your elbow — primarily the biceps brachii and the brachialis. Every time you curl a dumbbell or lift a grocery bag toward your chest, the musculocutaneous nerve is firing to make that flexion happen.
Once it has done its work in the upper arm, the nerve continues as the lateral cutaneous nerve of the forearm. In this role, it provides sensation to the outer side of your forearm. So if someone lightly brushes the outside of your forearm and you feel it, you have this nerve to thank.
6. Radial Nerve
The radial nerve is one of the major nerves of the upper limb, and it takes a winding path from the brachial plexus down the back of the arm, around the humerus bone, and into the forearm and hand. It is the largest nerve in the upper extremity.
Its main motor function is extension — straightening your elbow, wrist, and fingers. Without a functioning radial nerve, you would struggle to extend your wrist or open your hand, a condition sometimes called “wrist drop.” This is why the radial nerve is so critical for actions like pushing a door open or placing your palm flat on a table.
The nerve also carries sensory information from the back of your hand and the outer part of your forearm. Because the radial nerve wraps closely around the humerus bone, it is particularly susceptible to injury from fractures of the upper arm. Even prolonged pressure — like falling asleep with your arm draped over a chair — can temporarily compress it, leading to that tingling, numb sensation people sometimes call “Saturday night palsy.”
7. Intercostal Nerves
Running between your ribs, the intercostal nerves are a set of nerves that emerge from the thoracic region of the spinal cord. There are typically eleven pairs, each following the curve of a rib from the back of the body to the front.
These nerves have a straightforward but essential job: they control the muscles between your ribs (the intercostal muscles) that expand and contract your ribcage during breathing. Every inhale and exhale you take depends on these nerves firing properly. They also supply the muscles and skin of the chest and abdominal wall.
On the sensory side, intercostal nerves carry signals from the skin over your ribs and trunk. This is why conditions like shingles, which can inflame these nerves, produce that distinctive band of pain wrapping around one side of the torso. The pain follows the path of the affected intercostal nerve almost perfectly.
8. Median Nerve
The median nerve travels down the center of your arm and into the hand, and it is one of the most important nerves for hand function. Originating from the brachial plexus, it runs through the forearm and enters the hand via the carpal tunnel — a narrow passage at the wrist.
In the forearm, the median nerve controls muscles that flex your wrist and fingers. In the hand itself, it powers the small muscles at the base of your thumb that allow you to perform the “pinch” motion — picking up a coin, threading a needle, buttoning a shirt. These precision movements are what set human hands apart, and the median nerve is central to all of them.
Most people have heard of carpal tunnel syndrome, and the median nerve is the star of that story. When the carpal tunnel narrows due to swelling, repetitive strain, or other causes, it compresses the median nerve. The result is tingling, numbness, and pain in the thumb, index, and middle fingers — a sensation that millions of people who work with their hands know all too well.
9. Iliohypogastric Nerve
The iliohypogastric nerve originates from the first lumbar spinal nerve (L1) and runs through the muscles of the abdominal wall. It is a relatively small nerve, but it covers a specific and important territory.
Its motor fibers help activate the internal oblique and transversus abdominis muscles — the deep core muscles that stabilize your trunk. When you brace your abdomen before lifting something heavy, these muscles contract, and the iliohypogastric nerve is part of the circuit making that happen.
Sensory-wise, this nerve supplies feeling to the skin over your lower abdomen and the upper part of your hip region. Surgeons pay close attention to the iliohypogastric nerve during procedures like appendectomies and hernia repairs, because accidentally cutting or stretching it can leave patients with chronic pain or numbness in the groin area.
10. Subcostal Nerve
Sitting just below the last rib, the subcostal nerve is the ventral ramus of the twelfth thoracic spinal nerve (T12). Despite its somewhat overlooked status, it performs the same kind of work as the intercostal nerves above it.
It provides motor control to muscles of the abdominal wall, including portions of the external oblique and the transversus abdominis. These muscles are involved in trunk rotation, flexion, and the forceful exhalation you use when coughing or sneezing.
On the sensory front, the subcostal nerve supplies skin over the lower part of your abdomen and the area near the top of your hip. Because it sits right at the boundary between the thoracic and lumbar regions, it can sometimes be affected during lower rib fractures or surgical procedures in the flank area.
11. Lumbar Plexus
The lumbar plexus is a network of nerves formed by the ventral rami of the first four lumbar spinal nerves (L1 through L4), with a small contribution from the twelfth thoracic nerve. It sits deep within the psoas major muscle on either side of the lumbar spine.
From this plexus, several major nerves branch out to supply the lower abdomen, hip, and front of the thigh. The femoral nerve, obturator nerve, genitofemoral nerve, and iliohypogastric nerve all emerge from this network. So when you take a step forward, climb a stair, or straighten your knee, you are relying on nerves that originated in the lumbar plexus.
Conditions that compress or irritate the lumbar plexus — such as tumors, abscesses, or bleeding in the psoas muscle — can cause a range of symptoms including thigh pain, weakness in the leg, and difficulty walking. Because the plexus is buried deep in the body, these issues can be tricky to diagnose without imaging.
12. Sacral Plexus
Just below the lumbar plexus, the sacral plexus forms from spinal nerves L4 through S3. It sits against the back wall of the pelvis, in front of the piriformis muscle. Together with the lumbar plexus, it is sometimes referred to as the lumbosacral plexus.
The sacral plexus gives rise to the largest nerve in the body — the sciatic nerve — along with several other important nerves that control the buttocks, back of the thigh, leg, and foot. It also supplies nerves to the pelvic organs, including the bladder and reproductive structures.
Because the piriformis muscle runs directly over the sacral plexus, tightness or spasm in that muscle can compress nerves emerging from the plexus. This is the basis of piriformis syndrome, which mimics sciatica and can cause deep, aching pain in the buttock that radiates down the leg.
13. Genitofemoral Nerve
The genitofemoral nerve arises from the lumbar plexus (L1 and L2) and splits into two branches as it descends: the genital branch and the femoral branch.
The genital branch travels through the inguinal canal — the same passageway where hernias often develop. In males, it supplies the cremaster muscle (which raises and lowers the testicle in response to temperature or touch) and the skin of the scrotum. In females, it supplies the skin of the mons pubis and labia majora.
Meanwhile, the femoral branch supplies a small patch of skin on the upper front of the thigh. Though small in scope, this nerve matters clinically because it can be injured during inguinal hernia repair surgery, leading to chronic groin pain that is notoriously difficult to treat. Surgeons often identify and protect it carefully during these procedures.
14. Obturator Nerve
The obturator nerve originates from the lumbar plexus (L2 through L4) and passes through the obturator foramen — a large opening in the pelvic bone — before entering the inner thigh.
Its primary motor role is supplying the adductor muscles of the thigh. These are the muscles on the inner side of your upper leg that pull your legs together. Crossing your legs, squeezing a horse with your knees while riding, or kicking a soccer ball with the inside of your foot — all of these movements depend on the obturator nerve.
On the sensory side, this nerve provides feeling to a patch of skin on the inner thigh. Obturator nerve entrapment, while uncommon, can occur in athletes who perform repetitive thigh adduction, causing inner thigh pain and weakness. It is sometimes confused with a groin strain, which makes accurate diagnosis essential for proper treatment.
15. Femoral Nerve
The femoral nerve is one of the largest nerves emerging from the lumbar plexus, and it enters the thigh by passing beneath the inguinal ligament. Once in the thigh, it fans out to supply the quadriceps muscles — the powerful group on the front of your thigh that straightens your knee.
Every time you stand up from a chair, walk up stairs, or kick a ball, your femoral nerve is driving those quadriceps contractions. Without it, extending the knee becomes nearly impossible, and walking on flat ground becomes a challenge, let alone climbing.
The femoral nerve also carries sensory fibers. It provides feeling to the front of the thigh and, through its continuation as the saphenous nerve, to the inner side of the leg all the way down to the foot. Femoral nerve damage — from pelvic surgery, hip fractures, or even prolonged positioning during surgery — can lead to significant difficulty with mobility and a noticeable area of numbness over the thigh.
16. Ulnar Nerve
You have almost certainly met the ulnar nerve without knowing its name. It runs along the inner edge of your arm, passing behind the bony bump on the inside of your elbow — a spot commonly known as the “funny bone.” That jolt of tingling and pain you feel when you bump your elbow is the ulnar nerve being compressed against the bone.
This nerve controls many of the small muscles in your hand that allow for fine motor skills. Spreading your fingers apart, bringing them together, and gripping objects tightly all require the ulnar nerve to be working properly. It also powers the muscles that allow your ring and little fingers to bend fully.
Sensory coverage from the ulnar nerve includes the little finger and the inner half of the ring finger, as well as a strip of skin along the inner edge of the hand. Chronic compression at the elbow, known as cubital tunnel syndrome, can gradually weaken the hand and cause a claw-like deformity of the ring and little fingers if left untreated.
17. Pudendal Nerve
The pudendal nerve arises from the sacral plexus (S2 through S4) and is the primary nerve of the perineum — the area between the legs. It travels a complex path, exiting the pelvis, looping around a ligament, and re-entering the pelvis to reach its target tissues.
This nerve has both motor and sensory functions that are essential to daily life. On the motor side, it controls the external anal sphincter and the external urethral sphincter, which means it plays a direct role in bowel and bladder control. It also innervates muscles of the pelvic floor.
Sensory-wise, the pudendal nerve supplies feeling to the external genitalia and the perianal skin. Pudendal neuralgia — chronic irritation or compression of this nerve — can cause severe, burning pain in the pelvic region that worsens with sitting. It is more common than many people realize and can significantly affect quality of life.
18. Sciatic Nerve
The sciatic nerve is the longest and thickest nerve in the human body. It originates from the sacral plexus, exits the pelvis through the greater sciatic foramen, and runs down the back of the thigh before splitting into two branches near the knee.
At its thickest point, near the hip, the sciatic nerve is about as wide as your thumb. It carries both motor and sensory signals to nearly the entire lower leg and foot. The muscles that bend your knee, point your toes, and lift your foot all receive their commands through branches of the sciatic nerve.
Sciatica — pain radiating along the path of the sciatic nerve — is one of the most common reasons people visit a doctor for back and leg pain. A herniated disc in the lumbar spine pressing on the nerve root is the most frequent cause, producing sharp, shooting pain from the lower back down through the buttock and leg. The good news is that most cases improve with conservative treatment within a few weeks.
19. Muscular Branches of Femoral Nerve
These are the motor branches that split off from the main femoral nerve trunk specifically to supply the quadriceps muscles. While the femoral nerve also has sensory duties, these particular branches are dedicated to making your muscles move.
Each muscular branch targets a specific part of the quadriceps group — the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. Working together, these four muscles produce the knee extension force you rely on for walking, running, jumping, and standing. The vastus medialis, in particular, is crucial for stabilizing the kneecap during movement.
Selective injury to one of these branches is rare but can happen during hip or knee surgery. When it does, patients may notice weakness in a specific portion of the quadriceps, which can cause the knee to buckle or feel unstable, especially when going downstairs.
20. Saphenous Nerve
The saphenous nerve is the longest purely sensory branch of the femoral nerve. It does not control any muscles at all — its entire job is to carry sensation from the inner side of your leg and foot back to the brain.
Starting in the thigh, the saphenous nerve travels alongside the femoral artery before descending along the inner side of the knee and down the leg. It provides feeling to the skin on the inner calf, the inner ankle, and part of the arch of the foot. That sensitivity you feel when you accidentally bang your shin against a coffee table is partially carried by the saphenous nerve.
Because of its long, superficial path, the saphenous nerve can be injured during varicose vein surgery, knee surgery, or even from tight-fitting boots or leg braces. Saphenous nerve damage typically causes numbness or a burning sensation along the inner leg, which, while not disabling, can be persistently uncomfortable.
21. Common Peroneal Nerve
The common peroneal nerve (also called the common fibular nerve) is one of the two terminal branches of the sciatic nerve. It splits off near the back of the knee and wraps around the head of the fibula — the thin bone on the outer side of your lower leg.
This nerve is responsible for movements that lift your foot upward (dorsiflexion) and turn it outward (eversion). These motions are critical for walking, because dorsiflexion keeps your toes from dragging on the ground as you swing your leg forward with each step.
The spot where the common peroneal nerve wraps around the fibula head is one of the most vulnerable nerve locations in the entire body. Crossing your legs for too long, a tight cast, or even significant weight loss that reduces the padding around the knee can compress this nerve. The result is “foot drop” — an inability to lift the front of the foot, which causes a characteristic slapping gait when walking.
22. Tibial Nerve
The tibial nerve is the other terminal branch of the sciatic nerve, and it is the larger of the two. After the sciatic nerve divides near the knee, the tibial nerve continues straight down the back of the calf, running deep between the muscles.
Motor-wise, this nerve powers the muscles that point your foot downward (plantarflexion) and curl your toes. Pushing off the ground with each step, standing on your tiptoes, and pressing the gas pedal in your car are all actions driven by the tibial nerve.
At the ankle, the tibial nerve passes through a channel called the tarsal tunnel before entering the sole of the foot. Compression here leads to tarsal tunnel syndrome — the foot’s equivalent of carpal tunnel syndrome in the wrist. Symptoms include burning, tingling, and numbness on the bottom of the foot, often worse at night or after prolonged standing.
23. Deep Peroneal Nerve
The deep peroneal nerve is a branch of the common peroneal nerve, and it runs along the front of the lower leg between the tibia and fibula, right next to the anterior tibial artery.
This nerve controls the muscles that dorsiflex the foot and extend the toes. In simpler terms, it is what allows you to pull your foot upward and lift your toes off the ground. Without this nerve functioning properly, clearing your foot during the swing phase of walking becomes extremely difficult.
The deep peroneal nerve also provides sensory input from a very small but specific area — the web space between your big toe and second toe. If that tiny patch of skin feels numb while the rest of your foot has normal sensation, a deep peroneal nerve issue is very likely. Tight shoes, especially those that press hard on the top of the foot, are a surprisingly common cause of irritation to this nerve.
24. Superficial Peroneal Nerve
The superficial peroneal nerve is the second branch of the common peroneal nerve. While its deeper counterpart handles dorsiflexion, the superficial peroneal nerve focuses on eversion — turning the sole of your foot outward.
It innervates the peroneus longus and peroneus brevis muscles on the outer side of the lower leg. These muscles are essential for ankle stability, particularly on uneven ground. If you have ever walked along a rocky trail without rolling your ankle, you can thank these muscles and the nerve that drives them for keeping you upright.
As the superficial peroneal nerve descends, it becomes primarily sensory, supplying feeling to most of the top of the foot and the front of the lower leg. Ankle sprains — especially inversion sprains where the foot rolls inward — can stretch or damage this nerve, which is why some people experience lingering numbness on the top of the foot long after the swelling from a sprain has gone down.
