C5 dermatome and nerve root

Cervical spinal root

Where is the C5 dermatome?

The C5 dermatome covers the outer upper arm, over the deltoid, down to the elbow. Its ISNCSCI key sensory point is the outer side of the elbow crease, just above it. Its key movement is elbow flexion (biceps brachii and brachialis). The C4/C5 disc is the one that usually compresses C5.

C5 at a glance
Type	Cervical spinal root
Key sensory point	The outer side of the elbow crease, just above it
Key movement	Elbow flexion
Tendon reflex	Biceps reflex and brachioradialis reflex, in part
Usual disc	C4/C5

Try in: Dermatome and Myotome Map Explorer →

C5 myotome: the muscles it supplies

C5 is a major root for 11 of the 16 muscles below and a minor root for the rest.

Muscles C5 supplies, and every root each takes
Muscle	From C5	All its roots
Rhomboids	Major	C5; C4 in part
Serratus anterior	Major	C5 to C7
Deltoid	Major	C5; C6 in part
Supraspinatus	Major	C5; C6 in part
Infraspinatus	Major	C5; C6 in part
Teres minor	Major	C5; C6 in part
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, ISNCSCI key muscle	C5 and C6
Brachialis	Major, ISNCSCI key muscle	C5 and C6
Levator scapulae	Minor	C3 and C4; C5 in part
Diaphragm	Minor	C4; C3 and C5 in part
Brachioradialis	Minor	C6; C5 in part
Supinator	Minor	C6; C5 and C7 in part
Extensor carpi radialis longus	Minor	C6; C5 and C7 in part

Diaphragm: the phrenic nerve.

Tendon reflexes through C5

Tendon reflexes C5 carries, how each is tested and its roots
Reflex	Role of C5	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	In part	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

Why a C4/C5 disc compresses C5

Cervical roots leave the spine above the vertebra of the same number, so the C5 root leaves between the C4 and C5 vertebrae, right beside the C4/C5 disc. A disc bulging backwards and to the side presses on it there, which is why a C4/C5 disc gives C5 symptoms.

What a C5 root lesion does

Sensation. Numbness or tingling in the C5 band. Usually a smaller patch than the whole band, because C4 and C6 overlap it: Sherrington found in 1893 that cutting a single root in monkeys left no skin entirely without feeling.
Strength. Elbow flexion, the standard’s key movement for C5 (biceps brachii and brachialis). Also weaker where C5 is a major supply: rhomboids, serratus anterior, deltoid, supraspinatus, infraspinatus, teres minor, subscapularis, teres major and pectoralis major, clavicular part.
Reflexes. The biceps reflex is reduced or absent and the brachioradialis 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.

Neighboring dermatomes

C4: the tops of the shoulders and a cape across the upper chest and back
C6: the outer forearm, the thumb and the index finger

Dermatome and Myotome Map Explorer, with C5 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.