One reflex. One way the arm moves. One numb finger. The complaint is "pain down the arm." Your job is not to name the symptom. Your job is to localize the root.
A 45-year-old woman has neck pain and tingling that runs down the right forearm into the thumb. She cannot cock the wrist back against resistance, the brachioradialis reflex is reduced, and the biceps and triceps reflexes are normal.
Which single nerve root is this?
Brachioradialis reflex plus weak wrist extension plus a numb thumb equals C6. Most students slide to C5 or C7 because those are the reflexes they actually test. The brachioradialis is the rung in between, and it is the one they forget. Number the hand from the thumb: the thumb is 6. Carpal tunnel never touches a deep tendon reflex, so a reduced brachioradialis jerk rules it out.
Start here
Why This Confuses Everyone
Three questions students ask out loud, answered by mechanism so the discrimination sticks instead of the label.
1Why does everyone miss C6?
Because of the reflex they skip. The arm has three deep tendon reflexes in a ladder: biceps, brachioradialis, triceps. Students test the biceps and the triceps and forget the brachioradialis in the middle. So a C6 root, which drops the brachioradialis reflex, weakens wrist extension, and numbs the thumb, gets mislabeled C5 or C7. Check the brachioradialis every time and C6 stops hiding.
2How can the hand tell me the level?
Count the fingers from the thumb. Thumb is 6, middle finger is 7, little finger is 8. That single trick localizes most cervical sensory complaints. C5 sits higher, over the lateral shoulder cap, and T1 runs up the medial arm. So numb thumb is C6, numb middle finger is C7, numb pinky is C8. The hand is the map.
3Why do C8 and T1 break the pattern?
Because they have no reflex. The reflex ladder only runs C5 → C6 → C7. Below that, normal reflexes do not rule out a root. You localize C8 and T1 by the small hand muscles and the medial sensory strip instead: C8 is grip and the little finger, T1 is the interossei and the medial arm. No reflex means look at the hand.
📷 Dermatome map, anterior · tap to expand
📷 Intrinsic hand muscles · tap to expand
From the Attending
Stop asking "is this a pinched nerve." Of course it is. Ask the only question that scores points: which root. Reflex first, then how the arm moves, then which finger is numb. Three findings that name the same level. And test the brachioradialis. The root you skip is the root you miss. Every time.
Interactive
The Localizer
Tap a root. Watch its dermatome light up on the arm and hand, watch the movement that root drives actually play, and watch its reflex on the ladder turn red where the jerk is lost. Then run the Spurling toggle to see how closing the foramen reproduces the symptoms.
C6 nerve root
disc usually C5 to C6
Dermatome
Myotome
Reflex
The tell
Spurling toggle: the foramen test
A root is pinched where it exits, in the intervertebral foramen. Flip the neck position and watch the foramen close onto the exiting root.
📷 C6 to C7 disc herniation · tap to expand
📷 Foraminal narrowing (Spurling target) · tap to expand
From the Attending
Watch the reflex, not the pain. A patient can point pain anywhere down the arm. But the jerk does not lie. Biceps down is C5. Brachioradialis down is C6, and that is the one you forget to tap. Triceps down is C7. Find the dead reflex first. That distinction drives everything.
Side by side
The Five Roots
They all radiate down the arm. Tap each one to see the exact dermatome, myotome, and reflex so you can tell them apart in three seconds.
C5 radiculopathy
single root · disc usually C4 to C5
DermatomeLateral shoulder and upper arm, the deltoid cap.
MyotomeWeak shoulder abduction (deltoid) and elbow flexion (biceps). Cannot lift the arm out to the side.
ReflexBiceps jerk diminished.
SidesUsually one side.
C5 = Shoulder abduction, Biceps reflex, Shoulder cap. Top of the arm, top of the ladder.
📷 Dermatome map · tap to expand
C6 radiculopathy
single root · disc usually C5 to C6 · the commonly missed root
DermatomeLateral forearm and the thumb (and index).
MyotomeWeak wrist extension (cock the wrist back) and elbow flexion.
ReflexBrachioradialis jerk reduced. The rung between biceps and triceps.
SidesUsually one side.
C6 = Brachioradialis reflex, Wrist extension, Thumb. Number the hand from the thumb: thumb is 6.
📷 Cervical disc herniation on MRI · tap to expand
C7 radiculopathy
single root · disc usually C6 to C7 · the most common cervical level
DermatomeThe middle finger.
MyotomeWeak elbow extension (triceps), wrist flexion, and finger extension. The push fails.
ReflexTriceps jerk diminished.
SidesUsually one side.
C7 = Triceps reflex, Elbow extension, Middle finger. Middle of the hand, bottom of the ladder.
📷 C6 to C7 disc herniation · tap to expand
C8 radiculopathy
single root · disc usually C7 to T1 · no reflex
DermatomeMedial forearm and the little finger (and ring).
MyotomeWeak finger flexion (grip) and most of the small hand muscles.
ReflexNone. C8 has no deep tendon reflex.
SidesUsually one side.
C8 = Grip, Little finger, Medial forearm, no reflex. Pinky is 8.
📷 Intrinsic hand muscles · tap to expand
T1 radiculopathy
single root · no reflex · watch the lung apex
DermatomeMedial upper arm and the axilla.
MyotomeWeak finger spreading and pinching, the interossei. Fine hand control fails.
ReflexNone. T1 has no deep tendon reflex.
WatchA Pancoast apical tumor can take T1 plus the sympathetic chain, adding a Horner syndrome.
T1 = Interossei, Medial arm, no reflex. Painless and progressive with a droopy lid means look at the lung.
📷 Brachial plexus · tap to expand
📷 Brachial plexus plate, the C5 to T1 roots · tap to expand
Decision tool
The Discriminator
Do not match the term. Walk the findings. Start with the reflex ladder, drop to the hand when the reflexes are normal, and the tree lands on the root.
Which deep tendon reflex is reduced on that arm?
Reflexes are intact, so this is a low root. Where is the numbness and what fails in the hand?
The reflex ladder, blurred for self-testing
Say the answer out loud, then tap any cell to check. C8 and T1 sit below the ladder with no reflex.
Feature
C5
C6
C7
Reflex
Biceps
Brachioradialis
Triceps
Weak motion
Shoulder abduction
Wrist extension
Elbow extension
Numb skin
Lateral shoulder cap
Thumb
Middle finger
Hand number
Above the hand
Thumb is 6
Middle is 7
Disc level
C4 to C5
C5 to C6
C6 to C7
📷 Cutaneous nerves of the arm · tap to expand
From the Attending
A real MRI shows you the crowded foramen, but it does not localize the symptom. Two patients with the same scan can have different roots firing. The exam localizes, the image confirms. Never let a picture talk you out of the reflex.
Walkthrough
Board-Style Walkthrough
Five board-style vignettes, shuffled and never repeated until the set is exhausted. Right click or long press a choice to cross it out, double tap to highlight. Every choice gets explained.
VIGNETTE 1 OF 5
Tools: right click or long press to cross out a choice · double tap to highlight · tools lock once you answer.
References: Gray's Anatomy of the Human Body · Netter, Atlas of Human Anatomy · Hoppenfeld, Physical Examination of the Spine and Extremities. Images: Wikimedia Commons (public domain and Creative Commons).
Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last reviewed June 2026
Bone Wizardry is an independent educational resource for visual learning in the medical sciences. It is not affiliated with, endorsed by, or sponsored by any licensing or examination board, contains no real or recalled examination questions, and does not guarantee any educational or examination outcome.
