Trace the signal. Brain to muscle.
You don’t need a medical degree to play. Your nerves carry every step, every touch and every breath, and a few minutes a day is enough to understand them better. Start with Everyday Nerves for friendly questions about pins and needles, posture, sleep, stress and when to get help. When you want more, switch to Advanced and trace the routes clinicians use, from brain to muscle.
What are nerves, really?
Nerves are your body's wiring. Your brain and spinal cord are the control center, and nerves are the cables running out to every muscle, organ and patch of skin. Signals race along them as tiny electrical pulses, the fastest at more than 200 miles per hour. When a nerve is squeezed, irritated or under-fueled, you feel it as tingling, numbness, weakness or pain, and the pattern tells a clinician where to look.
- Signals outMovement: walking, smiling, gripping (motor)
- Signals inFeeling: touch, heat, pain, where your body is (sensory)
- AutomaticHeartbeat, digestion, breathing, sweat (autonomic)
Studying anatomy or working in healthcare? for 7 more modes and 12 brain-to-muscle pathways.
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GLOSSARY Nerve words in plain English
- Nerve
- A bundle of fibers that carries signals between your body and your brain or spinal cord.
- Neuron
- A single nerve cell, the basic unit that sends a signal.
- Spinal cord
- The main message cable inside your spine, linking your brain and body.
- Nerve root
- The start of a nerve, where it leaves the spinal cord between two spine bones.
- Peripheral nerve
- Any nerve outside the brain and spinal cord, like the ulnar or sciatic nerve.
- Cranial nerves
- Twelve pairs of nerves that come straight from the brain to serve the head and face.
- Plexus
- A junction where several nerve roots mix and regroup, like the brachial plexus for the arm.
- Dermatome
- The strip of skin that one nerve root supplies with feeling.
- Myotome
- The group of muscles that one nerve root powers.
- Reflex
- An automatic response wired through the spinal cord, like the knee-jerk.
- Radiculopathy
- An irritated or pinched nerve root; symptoms follow that root's skin and muscle map.
- Neuropathy
- Damage to nerves outside the spine, often felt first as tingling or numbness in the feet.
- Paresthesia
- Pins and needles: tingling, prickling or buzzing from a nerve.
- Sciatica
- Pain, tingling or numbness traveling down the back of the leg along the sciatic nerve.
- Myelin
- The insulating coat around many nerve fibers that speeds up signals.
- Autonomic nervous system
- The automatic system that runs heart rate, digestion, breathing and sweat.
- Sympathetic
- The fight-or-flight side of the autonomic system.
- Parasympathetic
- The rest-and-digest side, carried largely by the vagus nerve.
- Vagus nerve
- Cranial nerve X, the ‘wandering’ nerve to the heart, lungs and gut.
- Upper motor neuron
- Nerve cells in the brain and spinal cord that send movement commands down.
- Lower motor neuron
- The final nerve cell in the chain, running from the cord out to the muscle.
- Cauda equina
- The bundle of nerve roots at the bottom of the spine; squeezing it is an emergency.
- Referred pain
- Pain felt somewhere other than where it starts, like heart pain felt in the arm.
- Proprioception
- Your sense of where your body parts are without looking.
When nerve symptoms can't wait
CALL 911 NOW
- Face drooping, arm or leg weakness, or slurred or confused speech, especially on one side
- Sudden loss of balance, sudden vision loss or new double vision
- A sudden, severe “worst ever” headache
- Chest pressure with arm, jaw or back pain
- Numbness or weakness after a fall, crash, or head or neck injury
GO TO THE ER TODAY
- Numbness between the legs or inner thighs (the saddle area)
- New loss of bladder or bowel control, or being unable to pee
- Leg weakness that is quickly getting worse, or weakness in both legs
- Back or neck pain with a fever
BOOK A PROMPT EXAM
- Numbness or tingling that is spreading, or lasts more than a few days
- A foot that drags or slaps, or a hand that keeps dropping things
- Symptoms that regularly wake you at night
- Tingling in both feet that is slowly creeping upward
- Back pain with unexplained weight loss or a history of cancer: see your medical doctor soon
Stroke signs follow BE FAST: Balance, Eyes, Face, Arm, Speech, Time to call 911. Even if symptoms fade, call. For non-urgent symptoms, book a visit with a neurological exam.
Tap any nerve. See exactly what stops working.
Each one lists what you lose in motion, what you lose in sensation, which reflex changes, what usually causes it, and when it needs urgent attention.
The map, if you want to study first.
These are the patterns the game tests. Clinicians use them daily to decide which level a problem is coming from.
Dermatomes — where you feel it
| C5 | Lateral shoulder, over the deltoid |
| C6 | Thumb and lateral forearm |
| C7 | Middle finger |
| C8 | Little finger, medial forearm |
| T4 | Nipple line |
| T10 | Umbilicus |
| L3 | Medial knee |
| L4 | Medial leg and medial malleolus |
| L5 | Dorsum of foot, web of great toe |
| S1 | Lateral foot, little toe, heel |
Myotomes — what it moves
| C5 | Shoulder abduction |
| C6 | Elbow flexion, wrist extension |
| C7 | Elbow extension, wrist flexion |
| C8 | Finger flexion |
| T1 | Finger abduction and adduction |
| L2 | Hip flexion |
| L3 | Knee extension |
| L4 | Ankle dorsiflexion |
| L5 | Great toe extension |
| S1 | Ankle plantarflexion and eversion |
Reflexes — the level they test
| Biceps | C5 (with C6) |
| Brachiorad. | C6 |
| Triceps | C7 |
| Patellar | L4 (L2–L4) |
| Achilles | S1 |
| Babinski | Upper motor neuron sign when present in adults |
| Hoffmann | Suggests cervical cord involvement |
The long tracts
| Cortico- spinal | Voluntary movement. Crosses in the medulla, so one side of the brain drives the opposite side of the body. |
| Dorsal column | Fine touch, vibration, joint position. Ascends on the same side, crosses in the medulla. |
| Spino- thalamic | Pain and temperature. Crosses within a segment or two of entering the cord. |
| Spino- cerebellar | Unconscious position sense to the cerebellum for coordination. |
This is the map we read on every patient.
When numbness follows a dermatome, when one reflex is missing, when a single muscle is weak — the pattern tells us the level. That is what a proper neurological exam is for, and it is where every care plan here begins.
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