C6 dermatome and nerve root

Cervical spinal root

Where is the C6 dermatome?

The C6 dermatome covers the outer forearm, the thumb and the index finger. Its ISNCSCI key sensory point is the back of the thumb’s proximal phalanx. Its key movement is wrist extension (extensor carpi radialis longus and extensor carpi radialis brevis). The C5/C6 disc is the one that usually compresses C6.

C6 at a glance
Type	Cervical spinal root
Key sensory point	The back of the thumb’s proximal phalanx
Key movement	Wrist extension
Tendon reflex	Biceps reflex, brachioradialis reflex and triceps reflex, in part
Usual disc	C5/C6

Try in: Dermatome and Myotome Map Explorer →

C6 myotome: the muscles it supplies

C6 is a major root for 13 of the 20 muscles below and a minor root for the rest.

Muscles C6 supplies, and every root each takes
Muscle	From C6	All its roots
Serratus anterior	Major	C5 to C7
Subscapularis	Major	C5 and C6; C7 in part
Teres major	Major	C5 and C6; C7 in part
Pectoralis major, clavicular part	Major	C5 and C6
Biceps brachii	Major	C5 and C6
Brachialis	Major	C5 and C6
Coracobrachialis	Major	C6 and C7
Brachioradialis	Major	C6; C5 in part
Supinator	Major	C6; C5 and C7 in part
Pronator teres	Major	C6 and C7
Extensor carpi radialis longus	Major, ISNCSCI key muscle	C6; C5 and C7 in part
Extensor carpi radialis brevis	Major, ISNCSCI key muscle	C6 and C7
Flexor carpi radialis	Major	C6 and C7
Deltoid	Minor	C5; C6 in part
Supraspinatus	Minor	C5; C6 in part
Infraspinatus	Minor	C5; C6 in part
Teres minor	Minor	C5; C6 in part
Pectoralis major, sternal part	Minor	C7 and C8; C6 and T1 in part
Latissimus dorsi	Minor	C7; C6 and C8 in part
Triceps brachii	Minor	C7; C6 and C8 in part

Tendon reflexes through C6

Tendon reflexes C6 carries, how each is tested and its roots
Reflex	Role of C6	Tap	Response	Roots
Biceps reflex	Main root	The biceps tendon in the elbow crease, through the examiner’s thumb	The elbow bends	C5 and C6
Brachioradialis reflex	Main root	The thumb side of the forearm a few centimeters above the wrist	The elbow bends and the forearm turns palm up	C5 and C6, mainly C6
Triceps reflex	In part	The triceps tendon just above the point of the elbow	The elbow straightens	C6, C7 and C8, mainly C7

Why a C5/C6 disc compresses C6

Cervical roots leave the spine above the vertebra of the same number, so the C6 root leaves between the C5 and C6 vertebrae, right beside the C5/C6 disc. A disc bulging backwards and to the side presses on it there, which is why a C5/C6 disc gives C6 symptoms.

What a C6 root lesion does

Sensation. Numbness or tingling in the C6 band. Usually a smaller patch than the whole band, because C5 and C7 overlap it: Sherrington found in 1893 that cutting a single root in monkeys left no skin entirely without feeling.
Strength. Wrist extension, the standard’s key movement for C6 (extensor carpi radialis longus and extensor carpi radialis brevis). Also weaker where C6 is a major supply: serratus anterior, subscapularis, teres major, pectoralis major, clavicular part, biceps brachii, brachialis, coracobrachialis, brachioradialis, supinator, pronator teres and flexor carpi radialis.
Reflexes. The biceps reflex is reduced or absent, the brachioradialis reflex is reduced or absent and the triceps reflex may be reduced.

A teaching map. Root territories overlap and vary between people, and a root lesion is diagnosed by examination and imaging, not by a map. Numbness between the legs or around the anus, new bladder or bowel problems, or quickly spreading weakness need emergency care.

A way to remember C6

Make a pistol of the thumb and index finger: a six-shooter for C6.

Neighboring dermatomes

C5: the outer upper arm, over the deltoid, down to the elbow
C7: the middle finger, and a strip down the back of the forearm

Where published maps disagree

Maps disagree whether C7 reaches up the back of the forearm or stays in the hand.
The index finger is C6 in some maps and C7 in others.

Dermatome and Myotome Map Explorer, with C6 lit on a front and back body map
Every dermatome, with the disc levels and key movements side by side
Cervical Spine and Skull Base Explorer, the neck’s vertebrae, which the cervical roots leave between, in 3D
Upper Limb Muscles Explorer, the arm’s muscles in 3D
Reflex Arc Simulator, the loop a tendon reflex runs through the spinal cord
Muscles Worked by Exercise 3D Explorer, a whole body colored by root, in its root mode

Sources. Key sensory points and key movements: International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), American Spinal Injury Association, 2019 revision. Muscles: Aids to the Examination of the Peripheral Nervous System, Medical Research Council and the Guarantors of Brain, 5th ed. (2010), cross-checked with Kendall et al. (2005). Reflex roots: Walker (1990), Clinical Methods, 3rd ed., Table 72.1, and StatPearls, “Physiology, Deep Tendon Reflexes”; the main root as the MSD Manual’s “How to Assess Reflexes” names it. Overlap: Sherrington (1893), Phil Trans R Soc Lond B 184:641-763.